US Space Program - a thread

[Fenrir]

NASA's Stubby 747 Has A Big Telescope In The Back That Can See Pluto

NASA’s New Horizons spacecraft has recently begun sending back the first color images of Pluto and Charon, and they are spectacular. But prior to the probe making its close approach to Pluto on July 14th, scientists have been scouting Pluto’s atmosphere using a 98-inch telescope mounted inside a highly modified Boeing 747SP.

A combined effort between NASA and the German Aerospace Center (DLR), the aircraft is called SOFIA (registration N747NA, callsign “NASA747”), which stands for Stratospheric Observatory for Infrared Astronomy. SOFIA probably isn’t the best-known 747 belonging to NASA, but it is enabling valuable scientific observations because of its unique capabilities.

And while SOFIA has been flying astronomy missions since 2010, the idea of putting a telescope in an airplane to study the stars is almost 100 years old.

Telescope Planes

In the early 1920’s, Sherman Mills Fairchild developed the then-revolutionary electrically-driven K-3 aerial camera for mapping and reconnaissance missions. While the cameras were originally intended to be pointed towards Earth and not skyward, this ultimately spurred the earliest airborne astronomy flights from biplanes during the 1920’s and 1930’s, which were undertaken primarily for observing solar eclipses.

On September 10th, 1923, the U.S. Navy attempted to measure the centerline of a solar eclipse from the air using K-3 type mapping cameras and hypersensitized film aboard 16 different aircraft flying simultaneously. While precise details about all of the aircraft that were used during the attempt are elusive, one of the aircraft involved was reportedly a Felixstowe F5L “flying boat” biplane.

The convergence of smooth running jet aircraft, improved telescope technology and infrared sensors in the 1950s and 1960s led to the field of airborne astronomy taking on research beyond eclipse observations. In 1968, Gerald Kuiper (yes, that Kuiper) aimed a 12-inch telescope through the window of a NASA Learjet. Today, Kuiper is revered as a pioneer in airborne astronomy and planetary science, his work spurring a series of unique aircraft built to carry telescopes aloft.

One of NASA’s early airborne telescopes was the Galileo Observatory, a converted Convair 990airliner that supported scientists at the Ames Research Center. That aircraft met an untimely demise in a 1973 mid-air collision with a US Navy P-3C Orion while on final approach at Moffett Field. A replacement aircraft called Galileo II was built, but unfortunately it was destroyed in a fire following an aborted takeoff in 1985.

Despite such unfortunate luck with the two Galileo Observatory aircraft, NASA operated theKuiper Airborne Observatory (KAO) from 1974-1995, a Lockheed C-141A Starlifter modified with a 36-inch reflecting telescope. SOFIA is KAO’s follow-on program, offering scientists increased capabilities via a higher performance aircraft with a larger aperture telescope.

The Kuiper Airborne Observatory and SOFIA on the tarmac at NASA’s Ames Research Center.

Meet SOFIA

SOFIA’s donor aircraft is a Boeing 747SP widebody airliner, one of only 13 current airworthy examples. The 747SP (SP stands for “Special Performance”) was originally designed to compete with the Douglas DC-10 and Lockheed L-1011 tri-jets in the early 1970’s. Lacking a competitive product in their lineup at the time, Boeing chose to offer airline customers a scaled-down version of the 747 instead of scaling up a smaller jet.

Boeing introduced the 747SP in 1973 with changes including a fuselage shortened by over 48 feet, lighter wings, solid flaps and the removal of under-wing canoes. All of this added up to an empty 747SP weighing around 45,000 pounds less than an empty 747-200, making the jet ideal for long-range intercontinental flights. Because the shorter, lighter 747SP retained the same four engines and as the original 747, it could also fly faster and higher.

These special characteristics of the Boeing 747SP lend themselves perfectly to SOFIA’s mission, as they enable long loiter times and extended range, all while flying at higher altitudes. At an operating height of 41,000-43,000 feet, SOFIA flies above over 99 percent of the atmosphere’s water vapor, giving SOFIA opportunities to gaze into the heavens with clarity rivaled only by telescopes in orbit.

The specific 747SP aircraft that was selected for modification for the SOFIA program originally entered commercial service with Pan American World Airways in 1977, where it was christenedClipper Lindbergh, a name it still officially retains today. Pan Am sold the aircraft to United Airlines in 1986, for whom it operated in commercial service until 1995, when it was sent to storage.

SOFIA wearing an early livery during a 1998 test flight.

In 1997, it was retrieved from storage and NASA acquired it for conversion into an airborne observatory. Raytheon began the first step of SOFIA’s conversion in 1998 by installing a 13.5 foot wide retractable door behind the wing on the aft side. SOFIA’s door arcs 18 feet upward along the fuselage and can retract in flight, protecting the highly sensitive onboard instruments from the sun until conditions are ideal for data collection.

Beyond the huge door that reveals the enormous telescope onboard, SOFIA was modified with heavy shock absorbers, pressure bulkheads and counterweights to accommodate the telescope instruments. The aircraft’s interior was also retrofitted to provide space for educators to work during missions. Throughout the course of the program, SOFIA will invite thousands of science teachers, planetarium scientists and others to fly onboard. This ensures that the benefits of SOFIA’s science missions will reach as many people on Earth as possible.

SOFIA remained in budgetary and developmental purgatory until late 2009, when the optical systems were finally integrated into the airframe and it was first flown with the door open. Routine scientific flights began in 2010, and full capabilities were set to come online in 2014. Then, NASA abruptly announced that they would drastically cut SOFIA’s funding request for FY 2015, indicating that they planned to place the aircraft into storage and that, “savings from SOFIA can have a larger impact supporting other science missions.”

A 2014 report from NASA’s Inspector General found that SOFIA is one of the most expensive programs in NASA’s science portfolio. With total program life cycle costs estimated at $3 billion, SOFIA costs more than $100,000 per planned research flight hour to operate. After publicly stating that SOFIA’s “contributions to astronomical science will be significantly less than originally envisioned,” the program hung in limbo for about a year, when suddenly NASA changed their minds in early 2015.

For now, the program appears to be on stable budgetary footing, with the aircraft having flown regularly throughout the first half of the year. Even so, NASA’s spastic decision-making and SOFIA’s estimated $1 million per mission costs should illustrate that SOFIA could easily be a sacrificial lamb for future NASA budgets. Pulling the plug on SOFIA as soon as the program finally starts to perform science missions is hasty and ignores the unique capabilities that no other observatory can provide.

Seeing What We Can’t See

SOFIA is currently deployed to Christchurch, New Zealand until July 2015 and is observing parts of the sky that aren’t visible from the Northern Hemisphere with four main instruments, more than ever before. Hopefully the program will be allowed to continue unfettered now that it is finally mature enough to generate substantial scientific observations.

While there is no argument that orbital telescopes are ideally situated to capture images that improve our understanding of the universe, there are a few areas where airborne telescopes have advantages over orbital telescopes. Instruments aboard SOFIA are far easier to maintain and service, whereas missions to repair orbital telescopes (such as STS-125 in 2009) are hugely expensive and risky.

Additionally, SOFIA is not vulnerable to the ever-increasing risk of space junk, whereas the Hubble Repair mission in 2009 had a one-in-221 chance of colliding with orbital debris(although NASA deemed this risk acceptable). During the mission, a four inch piece of debris from a recently-exploded Chinese weather satellite came less than two miles away from the Hubble telescope and Space Shuttle Atlantis.

The ability to place optical instruments in the ideal place and time to observe rare astronomical events is central to appreciating the value of an asset like SOFIA. In 2011, SOFIA was at the right place at the right time to observe Pluto’s occultation in 2011. Notably, NASA says that it was the only observatory capable of doing so in the world at the time.

Ground-based telescopes can only observe a certain tract of the sky, and orbital telescopes aren’t easily repositioned. However, a telescope mounted on an intra-atmospheric aircraft that can produce a snapshot of the sky at precisely where and when desired is a unique capability, and one that is worth preserving in the event that orbital telescopes become incapacitated.

Night after night, SOFIA prowls the skies while making observations about comets, the life cycles of distant stars, the formation of planets and the chemical makeup of interstellar space. Requests from the scientific community for time aboard SOFIA far outpace the number of flight hours available, showing how the aircraft is hugely versatile for studying our celestial neighbors both near and far away.

Throughout the last century of flight, airborne telescopes have clearly proven their worth to the science community, and SOFIA should remain the pinnacle of airborne telescope technology for many years to come, especially seeing as NASA now has two retired 747 Shuttle Carriers to use for spares free of charge. The big flying telescope also sits as yet one more reminder of just how versatile the 747 design remains almost 50 years after its first flight.

 

[jamahir]

These Astronauts Will be the First to Launch With SpaceX and Boeing

NASA Thursday named the first four astronauts who will fly on the first U.S. commercial spaceflights in private crew transportation vehicles being built by Boeing and SpaceX – marking a major milestone towards restoring American human launches to U.S. soil as soon as mid-2017, if all goes well.

The four astronauts chosen are all veterans of flights on NASA’s Space Shuttles and to the International Space Station (ISS); Robert Behnken, Eric Boe, Douglas Hurley and Sunita Williams. They now form the core of NASA’s commercial crew astronaut corps eligible for the maiden test flights on board the Boeing CST-100 and Crew Dragon astronaut capsules.

Behnken, Boe and Hurley have each launched on two shuttle missions and Williams is a veteran of two long-duration flights aboard the ISS after launching on both the shuttle and Soyuz. All four served as military test pilots prior to being selected as NASA astronauts.

The experienced quartet of space flyers will work closely with Boeing andSpaceX as they begin training and prepare to launch aboard the first ever commercial ‘space taxi’ ferry flight missionsto the ISS and back – that will also end our sole source reliance on the Russian Soyuz capsule for crewed missions to low-Earth orbit and further serve to open up space exploration and transportation services to the private sector.

Boeing and SpaceX were awarded contracts by NASA Administrator Charles Bolden in September 2014 worth $6.8 Billion to complete the development and manufacture of the privately developed CST-100 andCrew Dragon astronaut transporters under the agency’s Commercial Crew Transportation Capability (CCtCap) program and NASA’s Launch America initiative.

“I am pleased to announce four American space pioneers have been selected to be the first astronauts to train to fly to space on commercial crew vehicles, all part of our ambitious plan to return space launches to U.S. soil, create good-paying American jobs and advance our goal of sending humans farther into the solar system than ever before,” said NASA Administrator Charles Bolden, in a statement.

“These distinguished, veteran astronauts are blazing a new trail — a trail that will one day land them in the history books and Americans on the surface of Mars.”

NASA Administrator Charles Bolden (left) announces the winners of NASA’s Commercial Crew Program development effort to build America’s next human spaceships launching from Florida to the International Space Station. Speaking from Kennedy’s Press Site, Bolden announced the contract award to Boeing and SpaceX to complete the design of the CST-100 and Crew Dragon spacecraft. Former astronaut Bob Cabana, center, director of NASA’s Kennedy Space Center in Florida, Kathy Lueders, manager of the agency’s Commercial Crew Program, and former International Space Station Commander Mike Fincke also took part in the announcement. Credit: Ken Kremer

The selection of astronauts for rides with NASA’s Commercial Crew Program (CCP) comes almost exactly four years to the day since the last American manned space launch of Space Shuttle Atlantis on the STS-135 mission to the space station on July 8, 2011 from the Kennedy Space Center in Florida.

Hurley was a member of the STS-135 crew and served as shuttle pilot under NASA’s last shuttle commander, Chris Ferguson, who is now Director of Boeing’s CST-100 commercial crew program. Read my earlier exclusive interviews with Ferguson about the CST-100 – here andhere.

Since the retirement of the shuttle orbiters, all American and ISS partner astronauts have been forced to hitch a ride on the Soyuz for flights to the ISS and back, at a current cost of over $70 million per seat.

“Our plans to return launches to American soil make fiscal sense,” Bolden elaborated. “It currently costs $76 million per astronaut to fly on a Russian spacecraft. On an American-owned spacecraft, the average cost will be $58 million per astronaut.

Behnken, Boe, Hurley and Williams are all eager to work with the Boeing and SpaceX teams to “understand their designs and operations as they finalize their Boeing CST-100 and SpaceXCrew Dragon spacecraft and operational strategies in support of their crewed flight tests and certification activities as part of their contracts with NASA.”

Until June 2015, Williams held the record for longest time in space by a woman, accumulating 322 days in orbit. Behnken is currently the chief of the astronaut core and conducted six space walks at the station. Boe has spent over 28 days in space and flew on the final mission of Space Shuttle Discovery in Feb. 2011 on STS-133.

The first commercial crew flights under the CCtCAP contract could take place in 2017 with at least one member of the two person crews being a NASA astronaut – who will be “on board to verify the fully-integrated rocket and spacecraft system can launch, maneuver in orbit, and dock to the space station, as well as validate all systems perform as expected, and land safely,” according to a NASA statement.

The second crew member could be a company test pilot as the details remain to be worked out.

Boeing and SpaceX are building private spaceships to resume launching US astronauts from US soil to the International Space Station in 2017. Credit: NASA

The actual launch date depends on the NASA budget allocation for the Commercial Crew Program approved by the US Congress.

Congress has never approved NASA’s full funding request for the CCP program and has again cut the program significantly in initial votes this year. So the outlook for a 2017 launch is very uncertain.

Were it not for the drastic CCP cuts we would be launching astronauts this year on the space taxis.

“Every dollar we invest in commercial crew is a dollar we invest in ourselves, rather than in the Russian economy,” Bolden emphasizes about the multifaceted benefits of the commercial crew initiative.

Under the CCtCAP contract, NASA recently ordered the agency’s first commercial crew mission from Boeing – as outlined in my story here.SpaceX will receive a similar CCtCAP mission order later this year.

At a later date, NASA will decide whether Boeing or SpaceX will launch the actual first commercial crew test flight mission to low Earth orbit.

Boeing’s commercial CST-100 ‘Space Taxi’ will carry a crew of five astronauts to low Earth orbit and the ISS from US soil. Mockup with astronaut mannequins seated below pilot console and Samsung tablets was unveiled on June 9, 2014 at its planned manufacturing facility at the Kennedy Space Center in Florida. Credit: Ken Kremer

“This is a new and exciting era in the history of U.S. human spaceflight,” said Brian Kelly, director of Flight Operations at NASA’s Johnson Space Center in Houston, in a statement.

“These four individuals, like so many at NASA and the Flight Operations Directorate, have dedicated their careers to becoming experts in the field of aeronautics and furthering human space exploration. The selection of these experienced astronauts who are eligible to fly aboard the test flights for the next generation of U.S. spacecraft to the ISS and low-Earth orbit ensures that the crews will be well-prepared and thoroughly trained for their missions.”

Both the CST-100 and Crew Dragon will typically carry a crew of four NASA or NASA-sponsored crew members, along with some 220 pounds of pressurized cargo. Each will also be capable of carrying up to seven crew members depending on how the capsule is configured.

The spacecraft will be capable to remaining docked at the station for up to 210 days and serve as an emergency lifeboat during that time.

The NASA CCtCAP contracts call for a minimum of two and a maximum potential of six missions from each provider.

The station crew will also be enlarged to seven people that will enable a doubling of research time.

The CST-100 will be carried to low Earth orbit atop a man-rated United Launch Alliance Atlas V rocket launching from Cape Canaveral Air Force Station, Florida. It enjoys a 100% success rate.

Boeing will first conduct a pair of unmanned and manned orbital CST-100 test flights earlier in 2017 in April and July, prior to the operational commercial crew rotation mission to confirm that their capsule is ready and able and met all certification milestone requirements set by NASA.

The Crew Dragon will launch atop a SpaceX Falcon 9 rocket. It enjoyed a 100% success rate until last weeks launch on its 19th flight which ended with an explosion two minutes after liftoff from Cape Canaveral on June 28, 2015.

SpaceX conducted a successful Pad Abort Test of the Crew Dragon on May 6, as I reported here. The goal was to test the spacecrafts abort systems that will save astronauts lives in a split second in the case of a launch emergency such as occurred during the June 28 rocket failure in flight that was bound for the ISS with the initial cargo version of the SpaceX Dragon.

SpaceX plans an unmanned orbital test flight of Crew Dragon perhaps by the end of 2016. The crewed orbital test flight would follow sometime in 2017.

This post by Ken Kremer originally appeared at Universe Today.

@levina @thesolar65

 

[Fenrir]

NASA's incredible 3 billion mile journey to Pluto, explained

Distances like "3 billion miles" are well beyond the scale of anything we experience here on Earth (the circumference of our planet is a mere 25,000 miles). So we made this video to help make sense of the immense journey that the New Horizons spacecraft has traveled over the past 9 years:

In the 1960s and '70s, NASA's Mariner missions showed us Mars, Venus, and Mercury, and in the 1970s and '80s, the Voyager missions showed us Jupiter, Saturn, Neptune, and Uranus. In much the same way, New Horizons will give us a close-up view of Pluto for the first time on July 14.

New Horizons launched from Cape Canaveral in January 2006. At that time, Pluto hadn't yet officially been demoted from planet to dwarf planet, and the mission was initially billed as a visit to the solar system's only unexplored planet. That's not the only thing that has changed here on Earth since the launch. Two of Plutos five known moons (Kerberos and Styx) have also been discovered since then.

New Horizons will pass within 6,200 miles of Pluto on July 14th. Until this mission, Voyager 1 was the spacecraft that flew closest to Pluto, and New Horizons will be 158,000 times closer than that. It will return detailed images of Pluto and its moons, far better than the blurry pictures our telescopes have managed.

The images won't be available immediately though. The data will travel billions of miles over radiowaves and then undergo processing.

 

[Fenrir]

This is the Soundtrack of a Martian Marathon

The first Martian marathon was no easy trek: the Opportunity rover had to struggle through smooth, soft sand and clamber over sharp rocks. This is the sounds of the terrain it covered in its 11-year journey exploring the red planet.

In July 2014, the Mars Opportunity rover broke the off-world driving marathon. In March 2015,it completed the first extraterrestrial marathon. It wasn’t an easy marathon: this was an off-track, all-terrain monster of a race. This is the view from the rover’s hazard-avoidance camera[left frame] and a map tracking progress [right frame] set to a soundtrack where the auditory intensity reflects the roughness of the terrain, condensing 11 years into under 8 minutes.

The video is a compilation of images from NASA’s Mars Exploration Rover Opportunity as it journeyed over 42.2 kilometers (26.2 miles) from its landing location in January 2004 to Marathon Valley in April 2015. The rover has been studying the rim of the 22 kilometer (14 mile) diameter Endeavour Crater since 2011. Almost all the tracks from its journey are now gone, blown away by the frequent dust storms of Mars.

The soundtrack reflects the roughness of the terrain, recorded as vibration measurements. When Opportunity rolled over soft, squishy sands, the soundtrack mellows into a quiet hiss (especially when the poor rover was stuck in a sand dune in May 2005); when it hauled its 185 kilogram mass over rough rocks, the soundtrack climbs to an angry growl.

Traces of Opportunity’s landing rocket blasts and earliest rover tracks were already fading between April 2004 [top] and November 2006 [bottom]. Image credit: NASA/JPL/Malin Space Science Systems/University of Arizona/JGR

After the epic trek, Opportunity took a three-week break of reduced activity as the Martian solar conjunction interrupted communication. Since the rover no longer has the capacity to store data and needs to call home every night with a data downlink, it would’ve been futile for it to blast ahead with full sciencing when it couldn’t report back to Earth. Now it will bask on the sun-facing slopes of Marathon Valley, poking at clay-rich outcrops.

Opportunity completed its first Martian marathon in March 2015, immediately beginning its second by venturing into Marathon Valley. Image credit: NASA/JPL-Caltech/Univ. of Arizona

Opportunity didn’t always rely exclusively on short-term memory. The non-volatile flash memory used to store data during overnight power-downs, but started glitching out. It was temporarily restored by reformatting, but started dying again this spring. Instead of arguing with the aging rover that robots aren’t supposed to develop amnesia, mission control switched to using random-access memory only, which can only retain data when the power is on, and downloading everything daily. As Opportunity Project Manager John Callas explains:

Opportunity can continue to accomplish science goals in this mod. Each day we transmit data that we collect that day. Flash memory is a convenience but not a necessity for the rover. It’s like a refrigerator that way. Without it, you couldn’t save any leftovers. Any food you prepare that day you would have to either eat or throw out. Without using flash memory, Opportunity needs to send home the high-priority data the same day it collects it, and lose any lower-priority data that can’t fit into the transmission.

The durable Mars Opportunity rover basking in sunset on the rim of Endeavour Crater in 2012. Image credit: NASA/JPL-Caltech/Cornell/Arizona State Univ.

The Opportunity rover is working on its second marathon eleven years into its 90-day mission. Its twin Spirit worked for six years before declaring it had enough poking about for evidence of ancient wet environments.

Top image: Opportunity looking back towards the west rim of Endeavour Crater in August 2014. Credit: NASA/JPL-Caltech/Cornell Univ./Arizona State Univ.

 

[Norwegian]

This is the Soundtrack of a Martian Marathon

The first Martian marathon was no easy trek: the Opportunity rover had to struggle through smooth, soft sand and clamber over sharp rocks. This is the sounds of the terrain it covered in its 11-year journey exploring the red planet.

In July 2014, the Mars Opportunity rover broke the off-world driving marathon. In March 2015,it completed the first extraterrestrial marathon. It wasn’t an easy marathon: this was an off-track, all-terrain monster of a race. This is the view from the rover’s hazard-avoidance camera[left frame] and a map tracking progress [right frame] set to a soundtrack where the auditory intensity reflects the roughness of the terrain, condensing 11 years into under 8 minutes.

The video is a compilation of images from NASA’s Mars Exploration Rover Opportunity as it journeyed over 42.2 kilometers (26.2 miles) from its landing location in January 2004 to Marathon Valley in April 2015. The rover has been studying the rim of the 22 kilometer (14 mile) diameter Endeavour Crater since 2011. Almost all the tracks from its journey are now gone, blown away by the frequent dust storms of Mars.

The soundtrack reflects the roughness of the terrain, recorded as vibration measurements. When Opportunity rolled over soft, squishy sands, the soundtrack mellows into a quiet hiss (especially when the poor rover was stuck in a sand dune in May 2005); when it hauled its 185 kilogram mass over rough rocks, the soundtrack climbs to an angry growl.

Traces of Opportunity’s landing rocket blasts and earliest rover tracks were already fading between April 2004 [top] and November 2006 [bottom]. Image credit: NASA/JPL/Malin Space Science Systems/University of Arizona/JGR

After the epic trek, Opportunity took a three-week break of reduced activity as the Martian solar conjunction interrupted communication. Since the rover no longer has the capacity to store data and needs to call home every night with a data downlink, it would’ve been futile for it to blast ahead with full sciencing when it couldn’t report back to Earth. Now it will bask on the sun-facing slopes of Marathon Valley, poking at clay-rich outcrops.

Opportunity completed its first Martian marathon in March 2015, immediately beginning its second by venturing into Marathon Valley. Image credit: NASA/JPL-Caltech/Univ. of Arizona

Opportunity didn’t always rely exclusively on short-term memory. The non-volatile flash memory used to store data during overnight power-downs, but started glitching out. It was temporarily restored by reformatting, but started dying again this spring. Instead of arguing with the aging rover that robots aren’t supposed to develop amnesia, mission control switched to using random-access memory only, which can only retain data when the power is on, and downloading everything daily. As Opportunity Project Manager John Callas explains:

Opportunity can continue to accomplish science goals in this mod. Each day we transmit data that we collect that day. Flash memory is a convenience but not a necessity for the rover. It’s like a refrigerator that way. Without it, you couldn’t save any leftovers. Any food you prepare that day you would have to either eat or throw out. Without using flash memory, Opportunity needs to send home the high-priority data the same day it collects it, and lose any lower-priority data that can’t fit into the transmission.

The durable Mars Opportunity rover basking in sunset on the rim of Endeavour Crater in 2012. Image credit: NASA/JPL-Caltech/Cornell/Arizona State Univ.

The Opportunity rover is working on its second marathon eleven years into its 90-day mission. Its twin Spirit worked for six years before declaring it had enough poking about for evidence of ancient wet environments.

Top image: Opportunity looking back towards the west rim of Endeavour Crater in August 2014. Credit: NASA/JPL-Caltech/Cornell Univ./Arizona State Univ.

Welcome to PDF. Another Norwegian!

 

[Fenrir]

How Did We Get to Pluto So Fast?

On July 14th, the New Horizons spacecraft will make history when it sails past Pluto, formerly known as the ninth planet. Even more incredible is how fast we got there. The spacecraft traveled 3 billion miles in nine and a half years. That’s about a million miles a day for almost ten years. How the heck did we do it?

Size and timing mattered a lot. So did Jupiter. Since the early days of the Space Age, we’ve learned to exploit nature to shave years off our interplanetary journeys. Here’s how humanity’s very first Pluto mission made the long haul at breakneck speed.

The Fastest Launch In History

On the afternoon of January 19th, 2006, a piano-sized spacecraft weighing 1,040 pounds roared into the sky aboard an Atlas V rocket. Separating from its solid fuel-kick motor after just 45 minutes, New Horizons was flung away from the Earth at solar system escape velocity, roughly 36,000 miles per hour. It was the highest speed at which a spacecraft has ever escaped Earth’s gravity well, besting the previous launch speed record (32, 400 mph) set by the Pioneer 10 probe in 1972.

New Horizons Launch aboard an Atlas V rocket. Goodbye forever, Earth. Image credit: NASA/KSC

How did we get New Horizons off the ground so fast? Basically, size. The compact craft was designed to run light on power and fuel, reserving most of its payload for its sevenonboard science instruments. At liftoff, the New Horizons propulsion system included only 170 pounds of hydrazine propellant. That’s a minuscule amount when you consider the craft’s journey, but it was intended to be used only for trajectory corrections and spinup/spindown maneuvers.

In other words, New Horizon’s ten year, 3 billion-plus mile journey would be basically propulsion-free. (Now if that doesn’t sound like the best car sales pitch, ever.)

After liftoff, New Horizons received additional velocity boost from Earth’s orbital motion around the sun, which is approximately 18.6 miles per second tangential to the orbital path. Altogether, then, the spacecraft barreled into the solar system with a heliocentric (sun-relative) speed of nearly 100 thousand miles per hour.

The timing of the launch was critical. Based on the orbital position of the Earth, NASA was looking at a short window, from mid-January through early February 2006, in which the New Horizons spacecraft could be launched in order to make a close pass by Jupiter in 2007. And we needed Jupiter big time.

The fastest route between two points on Earth may be a straight line, but when it comes to outer solar system exploration, nothing beats a little cosmic kick from Jupiter’s massive gravity well.

Jupiter’s Big Gravity Assist

Thanks to its quick start, New Horizons made the 500 million mile journey to Jupiter in just over a year, faster than any of the seven previous Jupiter-bound missions.But the sun’s gravitational pull is relentless, and by the time New Horizons reached Jupiter in early 2007, it had slowed to (a mere!) 43,000 miles per hour. Jupiter would help New Horizons regain what it had lost.

As it neared the gas giant, New Horizons began to speed up once more, reeled in by Jupiter’s prodigious gravity, which also acted to bend the spacecraft’s trajectory. On February 28th, 2007, the tiny probe made its closest approach to the gas giant and then flung itself away, snagging a bit of Jupiter’s momentum in a move that rocket scientists call a ‘gravity assist.’ Essentially, as New Horizons was dragged into Jupiter’s gravitational field, it gained kinetic energy amounting to nearly 9,000 miles per hour worth of speed, increasing its velocity to over 52,000 miles per hour.

To balance the books, Jupiter lost as much kinetic energy as New Horizons gained, causing it to fall a little closer to the sun. A year on Jupiter today is slightly shorter than it was before—all because humans wanted to get a good look at Pluto.

New Horizons’ heliocentric velocity during its mission, via JHU mission design document by Guo & Farquhar

The effect of Jupiter’s gravity assist can be seen on the graph above, which shows us the spacecraft’s heliocentric velocity as a function of distant from the Sun. For comparison, the graph below shows Voyager 2’s trajectory across our solar system from 1977 to 1989. As you can see, Voyager 2 used several gravity assists to keep up a quick pace as it toured the planets in our outer solar system. Both spacecraft continued to lose velocity as they headed into the outer solar system, but at a decreasing rate as the Sun’s gravity field weakened. (The weakening gravitational pull of the Sun also explains why solar system escape velocity decreases as we travel outward.)

Image via Cmglee, Wikipedia

Voyager’s clever route afforded the spacecraft a series of speed boosts while allowing it to collect a trove of planetary science data. Likewise, New Horizon’s Jupiter detour sent back a wealth of fascinating intel on our solar system’s largest planet, revealing lightning near the poles, the internal structure of volcanoes on Io, and the path of charged particles traversing the length of the gas giant’s long magnetic tail.

Oh, and it also shaved three full years off the trip to Pluto.

The Approach and Beyond

For the next seven and a half years, New Horizons sailed quietly across interplanetary space, on the longest leg of its journey. Its last major waypoint before the Pluto approach came on August 25, 2014, when made another record, crossing Neptune’s orbit some 2.75 billion miles away from the Earth in eight years, eight months. (Coincidentally, NASA’s Voyager 2 spacecraft made its much closer Neptune pass 25 years earlier to the day. A cosmic coincidence, perhaps, but one that everybody took as a promising sign of what was to come.)

To put the full trajectory in perspective, here are a few images from NASA:

For the past year, New Horizons has continued to stay the course, losing speed slowly as it approaches Pluto. Still, New Horizons’s historic flyby won’t exactly be a leisurely stroll. At 11:50 UTC on July 14th, the spacecraft will sail past Pluto at a blistering 30,000 miles per hour relative to the dwarf planet’s surface.

After New Horizons spends some time exploring Pluto and its three moons, it’ll hopefully continue on to the Kuiper belt, a vast rim of primordial, icy debris that encircles our solar system. The three promising Kupiter Belt Objects, or KBOs, NASA has ID’d as targets are all roughly a billion miles from Pluto, and it’ll take New Horizons another three to four years to reach any of them. NASA is waiting to get some science back from the primary Pluto mission before making a final decision on the Kuiper Belt extension. In the meanwhile, we’re left with the mind-blowing possibility that by 2020, New Horizons could be beaming home data on a cosmic graveyard four billion miles away.

And after the Kuiper belt? New Horizons is expected to eventually join Voyager 1 and 2 as the third human probe to enter interstellar space. Launched nearly 40 years ago, both of the Voyager probes are still in communication with the Earth as they wander about the cosmic hinterlands. It’s impossible to say just how far from home any of these probes will get.

But if one thing’s clear, it’s that New Horizon’s astounding journey has only just begun.

 

[Fenrir]

New Horizons

Spacecraft Systems and Components

Designed and integrated at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland — with contributions from companies and institutions in the United States and abroad — the New Horizons spacecraft is a robust, lightweight observatory designed to withstand the long, difficult journey from the launch pad on Earth to the solar system's coldest, darkest frontiers.

The New Horizons science payload was developed under direction of the Southwest Research Institute (SwRI), with instrument contributions from SwRI, APL, NASA's Goddard Space Flight Center, the University of Colorado, Stanford University and Ball Aerospace Corporation. Fully fueled, the agile, piano-sized probe weighed 478 kilograms (1,054 pounds) at launch. Designed to operate on a limited power source — a single radioisotope thermoelectric generator — New Horizons needs less power than a pair of 100-watt light bulbs to complete its mission at Pluto.

On average, each of the seven science instruments uses between 2 and 10 watts — about the power of a night light — when turned on. The instruments send data to one of two onboard solid-state memory banks, where data is recorded before later playback to Earth. During normal operations, the spacecraft communicates with Earth through its 2.1-meter (83-inch) wide high-gain antenna. Smaller antennas provide backup communications. And when the spacecraft was in hibernation through long stretches of its voyage, its computer was programmed to monitor its systems and report its status back to Earth with a specially coded, low-energy beacon signal.

New Horizons' "thermos bottle" design retains heat and keeps the spacecraft operating at room temperature without large heaters. Aside from protective covers on five instruments that were opened shortly after launch, and one small protective cover opened after the Jupiter encounter, New Horizons has no deployable mechanisms or scanning platforms. It does have backup devices for all major electronics, its star-tracking navigation cameras and data recorders.

New Horizons has operated mostly in a spin-stabilized mode while cruising between planets, and also in a three-axis “pointing” mode that allows for pointing or scanning instruments during calibrations and planetary encounters (like the Jupiter flyby and, of course, at Pluto). There are no reaction wheels on the spacecraft; small thrusters in the propulsion system handle pointing, spinning and course corrections. The spacecraft navigates using onboard gyros, star trackers and Sun sensors. The spacecraft's high-gain antenna dish is linked to advanced electronics and shaped to receive even the faintest radio signals from home — a necessity when the mission's main target is more than 3 billion miles from Earth and round-trip transmission time is nine hours-plus.

Structure

New Horizons' primary structure includes an aluminum central cylinder that supports the spacecraft body panels, supports the interface between the spacecraft and its radioisotope thermoelectric generator (RTG) power source, and houses the propellant tank. It also served as the payload adapter fitting that connected the spacecraft to the launch vehicle.

Keeping mass down, the panels surrounding the central cylinder feature an aluminum honeycomb core with ultra-thin aluminum face sheets (about as thick as two pieces of paper). To keep it perfectly balanced for spinning operations, the spacecraft was weighed and then balanced with additional weights just before mounting on the launch vehicle.

Command and Data Handling

The command and data handling system – a radiation-hardened 12 megahertz Mongoose V processor guided by intricate flight software – is the spacecraft’s “brain.” The processor distributes operating commands to each subsystem, collects and processes instrument data, and sequences information sent back to Earth. It also runs the advanced “autonomy” algorithms that allow the spacecraft to check the status of each system and, if necessary, correct any problems, switch to backup systems or contact operators on Earth for help.

For data storage, New Horizons carries two low-power solid-state recorders (one backup) that can hold up to 8 gigabytes each. The main processor collects, compresses, reformats, sorts and stores science and housekeeping (telemetry) data on the recorder – similar to a flash memory card for a digital camera – for transmission to Earth through the telecommunications subsystem.

The Command and Data Handling system is housed in an Integrated Electronics Module that also contains a vital guidance computer, the communication system and part of the REX instrument.

Thermal Control

New Horizons is designed to retain heat like a thermos bottle. The spacecraft is covered in lightweight, gold-colored, multilayered thermal insulation – like a survival camping blanket – which holds in heat from operating electronics to keep the spacecraft warm. Heat from the electronics has kept the spacecraft operating at between 10-30 degrees Celsius (about 50-85 degrees Fahrenheit) throughout the journey.

New Horizons’ sophisticated, automated heating system monitors power levels inside the craft to make sure the electronics are running at enough wattage to maintain safe temperatures. Any drop below that operating level (about 150 watts) and it will activate small heaters around the craft to make up the difference. When the spacecraft was closer to Earth and the Sun, louvers (essentially heat vents) on the craft opened when internal temperatures were too high.

The thermal blanketing – 18 layers of Dacron mesh cloth sandwiched between aluminized Mylar and Kapton film – also helps to protect the craft from micrometeorites.

Propulsion

The propulsion system on New Horizons is used for course corrections and for pointing the spacecraft. It is not needed to speed the spacecraft to Pluto; that was done entirely by the launch vehicle, with a boost from Jupiter’s gravity.

The New Horizons propulsion system includes 16 small hydrazine-propellant thrusters mounted across the spacecraft in eight locations, a fuel tank, and associated distribution plumbing. Four thrusters that each provide 4.4 newtons of force (1 pound) are used mostly for course corrections. Operators also employ 12 smaller thrusters – providing 0.8 newtons (about 3 ounces) of thrust each – to point, spin up and spin down the spacecraft. Eight of the 16 thrusters aboard New Horizons are considered the primary set; the other eight comprise the backup (redundant) set.

At launch, the spacecraft carried 77 kilograms (170 pounds) of hydrazine, stored in a lightweight titanium tank. Helium gas pushes fuel through the system to the thrusters. Using a Jupiter gravity assist, along with the fact that New Horizons does not slow down or go into orbit around Pluto, reduced the amount of propellant needed for the mission.

Guidance and Control

New Horizons must be oriented precisely to collect data with its scientific instruments, communicate with Earth, or maneuver through space.

Attitude determination – knowing which direction New Horizons is facing – is performed using star-tracking cameras, Inertial Measurement Units (containing sophisticated gyroscopes and accelerometers that measure rotation and horizontal/vertical motion), and digital Sun sensors. Attitude control for the spacecraft – whether in a steady, three-axis pointing mode or in a spin-stabilized mode – is accomplished using thrusters.

The IMUs and star trackers provide constant positional information to the spacecraft’s Guidance and Control processor, which like the Command and Data Handling processor is a 12-MHz Mongoose V. New Horizons carries two copies of each of these units for redundancy. The star-tracking cameras store a map of about 3,000 stars; 10 times per second one of the cameras snaps a wide-angle picture of space, compares the locations of the stars to its onboard map, and calculates the spacecraft’s orientation. The IMU feeds motion information 100 times a second. If data shows New Horizons is outside a predetermined position, small hydrazine thrusters will fire to re-orient the spacecraft. The Sun sensors back up the star trackers; they would find and point New Horizons toward the Sun (with Earth nearby) if the other sensors couldn’t find home in an emergency.

Operators use thrusters to maneuver the spacecraft, which has no internal reaction wheels. Its smaller thrusters are used for fine pointing; thrusters that are approximately five times more powerful are used during the trajectory course maneuvers that guide New Horizons toward its targets. New Horizons spins – typically at 5 revolutions per minute (RPM) – during trajectory-correction maneuvers and long radio contacts with Earth, and while it “hibernated” during long cruise periods. Operators steady and point the spacecraft during science observations and instrument-system checkouts.

Communications

New Horizons’ X-band communications system is the spacecraft’s link to Earth, returning science data, exchanging commands and status information, and allowing for precise radiometric tracking through NASA’s Deep Space Network of antenna stations.

The system includes two broad-beam, low-gain antennas on opposite sides of the spacecraft, used mostly for near-Earth communications; as well as a 30-centimeter (12-inch) diameter medium-gain dish antenna and a large, 2.1-meter (83-inch) diameter high-gain dish antenna. The antenna assembly on the spacecraft’s top deck consists of the high, medium, and forward low-gain antennas; this stacked design provides a clear field of view for the low-gain antenna and structural support for the high and medium-gain dishes. Operators aim the antennas by turning the spacecraft toward Earth. The high-gain beam is only 0.3 degrees wide, so it must point directly at Earth. The wider medium-gain beam (4 degrees) is used in conditions when the pointing might not be as accurate. All antennas have Right Hand Circular and Left Hand Circular polarization feeds.

Data rates depend on spacecraft distance, the power used to send the data and the size of the antenna on the ground. For most of the mission, New Horizons has used its high-gain antenna to exchange data with the Deep Space Network’s largest antennas, 70 meters across. Even at Pluto, because New Horizons will be more than 3 billion miles from Earth and radio signals will take more than four hours to reach the spacecraft, it can send information at about 1,000 bits per second. It will take 16 months to send the full set of Pluto encounter science data back to Earth.

New Horizons is flying the most advanced digital receiver ever used for deep space communications. Advances include regenerative ranging and low power – the receiver consumes 66% less power than earlier deep-space receivers. The Radio Science Experiment (REX) to examine Pluto’s atmosphere is also integrated into the communications subsystem.

The entire telecom system on New Horizons is redundant, with two of everything except the high gain antenna structure itself.

Power

New Horizons' electrical power comes from a single radioisotope thermoelectric generator (RTG). The RTG provides power through the natural radioactive decay of plutonium dioxide fuel, which creates a huge amount of heat. Unlike fission or fusion nuclear reactions, the RTG simply harnesses the heat produced and turns it into electricity.

The New Horizons RTG, provided by the U.S. Department of Energy, carries approximately 11 kilograms (24 pounds) of plutonium dioxide. Onboard systems manage the spacecraft’s power consumption so it doesn’t exceed the steady output from the RTG, which has decreased by about 3.5 watts per year since launch.

Typical of RTG-based systems, as on past outer-planet missions, New Horizons does not have a battery for storing power.

At the start of the mission, the RTG supplied approximately 245 watts (at 30 volts of direct current) – the spacecraft’s shunt regulator unit maintains a steady input from the RTG and dissipates power the spacecraft cannot use at a given time. By July 2015 (when New Horizons flies past Pluto) that supply will have decreased to about 200 watts at the same voltage, so New Horizons will ease the strain on its limited power source by cycling science instruments during the encounter.

The spacecraft’s fully redundant Power Distribution Unit (PDU) – with 96 connectors and more than 3,200 wires – efficiently moves power through the spacecraft’s vital systems and science instruments.

 

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New Horizons - Instrument Overview

Spacecraft Overview, Mission Section

The New Horizons spacecraft is outfitted with six primary science instruments and one student-operated payload, driven by the power and mass requirements of the mission.

The instruments are installed fixed to the spacecraft structure, requiring the craft itself to change its orientation for pointing of the instruments. New Horizons is equipped with instruments covering optical imaging, spectroscopy in multiple bands, as well as plasma, particle and dust sensing to obtain a detailed picture of Pluto, its composition both on the surface and its atmosphere, its moons and its environment.

These are New Horizons' instruments:

• Alice – Ultraviolet Imaging Spectrometer
• Ralph – Imaging Telescope
• REX – Radio Science Experiment
• LORRI – Long-Range Reconnaissance Imager
• SWAP – Solar Wind at Pluto
• PEPSSI – Pluto Energetic Particle Spectrometer Science Investigation
• VB-SDC – Venetia Burney Student Dust Counter

[Alice and Ralph are also collectively referred to as PERSI – Pluto Exploration Remote Sensing Investigation.]

The fundamental (Group 1) science objectives of the New Horizons mission can be achieved with the core science payload comprised of Alice, REX and Ralph.

The supplemental payload deepens and broadens the mission science, but is not required to achieve the minimum criteria for a mission success. The boresights of the Ralph, LORRI, and Alice airglow channel are aligned with the spacecraft –X axis allowing them to operate simultaneously:

Alice – Ultraviolet Imaging Spectrometer

The ALICE instrument of the New Horizons spacecraft is an imaging spectrometer sensitive for wavelengths in the ultraviolet range. It is an improved version of the ALICE instrument of the Rosetta comet exploration craft, featuring the addition of a second channel and different bandpass characteristics than the system flown on Rosetta. As an imaging spectrometer, ALICE separates the different wavelengths of ultraviolet radiation while simultaneously capturing an image of the target so that the finished data product is an image that, within each of its pixels, contains a full spectrum of that pixel.The primary task of ALICE is studying the atmosphere of Pluto, determining the abundance of different atomic and molecular constituents of the atmosphere, but also delivering information on the atmospheric structure. UV Spectroscopy has become a powerful tool for the investigation of physical and chemical properties in the field of astrophysics as the ultraviolet range of the spectrum can be used to extract a wealth of information on atmospheric constituents and all interplanetary spacecraft making a first journey to a planet carried ultraviolet sensors, highlighting ALICE’s role on New Horizons as one of the core instruments.

ALICE will address the New Horizons mission objective of characterizing the neutral atmosphere of Pluto and its escape rate. Specifically, the instrument will determine the mixing ratios of major atmospheric constituents including nitrogen, carbon monoxide, methane, hydrogen and noble gases. Also, ALICE can study the vertical density and thermal structure of the upper layers of the atmosphere, look at the hydrocarbon and nitrile photochemistry ongoing in the upper reaches of the atmosphere and determine whether hydrodynamic escape occurs on Pluto. The instrument makes its measurements in part by observing a solar occultation, that is, observing the sun through the Plutonian atmosphere and recording the UV spectrum. At wavelengths smaller than 100nm, nitrogen is responsible for the majority of opacity allowing sampling of the uppermost atmosphere while methane dominates between 100 and 150nm providing a look at the middle atmosphere from 300 to around 1200 Kilometers. At higher wavelengths, hydrocarbons with strong Far-UV absorption bands can expected to be optically important as well as hazes which will deliver information about the lowest part of the atmosphere down to about 100 Kilometers. ALICE can also shed light on the thermal structure of the atmosphere that is suspected to be dominated by a steep temperature increase from 10 Kilometers up due to absorption of infrared radiation by methane bands. Further heating by Lyman-Alpha Photodissociation could increase temperatures to 120K at 600km in altitude. At even higher altitudes, absorption of solar extreme UV radiation by Nitrogen may be at work to deliver additional heating, but atmospheric temperature likely decreases above 600km due to cooling associated with hydrodynamic escape.

The ALICE instrument can also look at the mixing ratio profiles and their variation with altitude to examine winds within the atmosphere which is a crucial piece of information when assessing the planet’s escaping wind. Furthermore, studies will be made to determine condensable species within the atmosphere and possible precipitation of these photochemical reaction products to the surface. Another open question is the abundance of Argon within Pluto’s atmosphere which can be easily answered by ALICE.ALICE uses a common UV spectrometer design utilizing a Rowland circle. Overall, the instrument weighs around 4.5 Kilograms and fits within an envelope of 20 by 41 by 12 centimeters with a low power consumption of 4.4 Watts. The instrument covers a spectral range of 46.5 to 188 nanometers, covering the far and extreme UV spectral ranges. ALICE achieves a spectral resolution up to 3.6 Angstroms and a spatial resolution of 0.05 by 0.6 degrees. The ALICE-P instrument differs to the ALICE instrument on Rosetta in a number of characteristics, the most notable being the use of two separate entrance apertures that feed light to the telescope, the main aperture known as the Airglow Channel AGC and the Solar Occultation Channel SOC. Light entering the telescope section of the instrument through the AGC passes through an aperture of 40 by 40 millimeters while the SOC uses a one-millimeter diameter opening perpendicular to the telescope section of the instrument, requiring an additional relay mirror to direct the radiation collected through SOC into the telescope. Light entering either aperture is collected and focused by an off-axis paraboloidal mirror.

The light is focused on the entrance slit of the spectrograph from where it reaches the dispersive element, a toroidal holographic grating, before entering the microchannel plate detector. The slit, grating and detector are arranged on a 0.15-meter rowland circle. Light entering the telescope section of ALICE first passes through the aperture that is equipped with a door that is opened after launch using a limited angle torque motor that allows the door to be closed and opened on command to protect the instrument during thruster operation and lengthy periods of cruising. ALICE uses a variety of baffles and low-scatter materials inside the instrument to reduce stray light within the optics section.

The off-axis parabolic mirror of the telescope section of the instrument has a clear aperture of 41 by 65 millimeters and reflects the incoming radiation to the spectrometer section of ALICE. The mirror and its mounting fixture is made of a monolithic piece of Aluminum that is coated with electroless Nickel and polished using a low-scatter technique. The optical surface of the mirror is coated with Silicon Carbide for optimized reflectivity in the Extreme and Far-UV range. Heaters are installed on the OAP mirror to avoid cold-trapping of contaminants during flight.The focused light from the mirror is passed onto the Spectrograph Entrance Slit that is composed of two sections – one for the Airglow Channel and one for the Solar Occultation Channel. The AGC slit is an actual slit with a field of view of 0.1 by 4.0° while the SOC uses a square with a field of view of 2.0 by 2.0 degrees. This slit design was driven for the Airglow Channel by the combination of spectral resolution and stray light minimization, encompassing the center boresight and providing and extended source spectral resolution of around 9 Angstroms. The choice of a rather large square for the Solar Occultation Channel was driven by the requirement to have the sun within the instrument field of view during the very short measurement window of solar occultations by Pluto and Charon which also occur nearly simultaneously with the occultation observation of the Radio Science Experiment.

ALICE-P is aligned on the spacecraft with a 2° tilt on the instrument’s spatial axis so that the sun is centered within the SOC field of view when the High Gain Antenna is pointing to Earth for radio science. The large SOC field of view will allow misalignments up to +/-0.9 degrees between the SOC FOV and the antenna boresight. From the slit, the light is passed to the toroidal holographic grating that has low-scatter and near-zero line ghost problems. The grating also uses a Silicon Carbide coating and heaters. The ALICE spectrograph uses the first diffraction order throughout the 520 – 1,870-Angstrom passband, although the lower half of the first order wavelength coverage also appears in second order between the first order wavelengths.

ALICE uses a 2D imaging photon-counting detector utilizing a microchannel plate Z-Stack that feeds the readout array which utilizes double-delay readout. The MCP front surface is coated with opaque photocathodes of Potassium Bromide for the 520-1180Å range and Caesium Iodide for the 1250-1870Å range. The detector tube is a lightweight brazed alumina-Kovar structure that is welded to a housing. The entire tube body is enclosed in a vacuum chamber housing using stainless steel and aluminum.

This chamber is used to protect the photocathodes against damage from moisture exposure during ground processing and outgassing once in space. The housing is equipped with a door to be opened early in flight and allow light to enter the detector. This door includes a Magnesium Fluoride window that allows UV radiation of >1200Å to pass for ground testing and in case the window failed to open. Opening the door is accomplished by using a dual-redundant torsion spring.

ALICE Detector Protection Mechanism & Door

The MCP detector has an effective area of 35 by 20 millimeters in the dispersion and spatial dimensions with a pixel format of 1024 by 32 pixels (dispersion direction by spatial dimension) – the 6-degree spatial field of view is imaged onto the central 22 of the detector’s 32 channels to be able to use the remaining channels for dark current measurements. The MCP Z-Stack uses three 80:1 length-to-diameter microchannel plates that are curved with a radius of 75 centimeters to match the Rowland circle geometry to ensure an optimum focus. The MCPs are 46 by 30 millimeters in size with 12-micrometer pores on 15μm centers. A repeller grid located above the MCP is biased at a negative voltage (-900V) to reflect electrons that may be liberated in the interstitial regions of the MCP Z-Stack to improve the efficiency of the detector. The MCP Z-Stack itself requires a high negative voltage bias of –3kV and an additional –600V is needed between the MCP stack and the anode array.

One concern for the instrument is the saturation of the detector at the Lyman-Alpha emission which requires physical attenuation that is achieved by masking the MCP detector where the emission comes to focus. The bare MCP glass exposed in this area has a quantum efficiency around ten times less than that of KBr at 1216 Angstroms. This masking approach has been flown successfully on Rosetta and other Space-based UV instruments.Signals generated by the MCPs are passed to the detector electronics that are located on three 63.5 by 76.2-millimeter circuit boards mounted inside an aluminum housing installed behind the detector vacuum chamber. Using pre-amplifiers, the analog MCP output is amplified and the electronics also convert the output pulses to pixel address locations. To be processed by ALICE, the signal pulses need to have an intensity above a set threshold level. For each event that meets the minimum intensity, a 10-bit x address and 5-bit y address is generated by the electronics for transmission to the data handling electronics. In addition to the address, the digitized amplitude of each event is sent to the command & data system. A pulse simulator can be used to test the pixel location read-out and data transfer path to allow testing of the entire ALICE detector and data system without activating the high-voltage power supply of the detector.
The ALICE support electronics include the Power Controller Electronics, Command & Data Handling Electronics, telemetry and command interface electronics, the decontamination heaters and a High-Voltage Power Supply for the detector. The ALICE instrument is controlled by an Intel 8052 microprocessor that has 32KB of local program RAM and 128KB of acquisition RAM as well as 32KB of SRAM and 128KB of EEPROM.The Power Controller Electronics include DC-to-DC converters that interface with the spacecraft power bus to convert it to a stable 5-Volt ALICE instrument bus that is used by the various electronics of ALICE and the High-Voltage Supply. The PCE also includes the switching circuit that controls the heaters as well as circuitry to command the limited angle torque motor of the front aperture door.

The Command and Data Handling electronics are responsible for the execution of commands sent to ALICE from the spacecraft, data acquisition & handling from the detector, formatting of telemetry and science data, control & monitoring of the high-voltage power supply and control of the aperture door. A 4MHz Intel 8052 microprocessor is used to build the interface with the spacecraft for data transmission and command receipt. Housekeeping telemetry is delivered to the C&DH system of the spacecraft via an RS-422 analog bus.ALICE uses two decontamination heaters – one installed behind the off-axis parabolic mirror and one behind the grating. These heaters are 1 Watt resistive heaters and are accompanied by two redundant thermistors to provide feedback control of the heaters. The heaters can be separately activated by the ALICE command system. The High-Voltage Power Supply for the MCP detector is located in a bay behind the OAP mirror. It conditions the –4.5kV required for the operation of the detector.

The voltage of the Z-Stack is fully commandable over a range of 0 to –6.1kV in 25V steps. The HVPS consumes 0.6W of power during operations.ALICE can be operated in three different modes – image histogram, pixel list and count rate mode. Each mode uses a 32k x 16-bit acquisition memory.In the Image Histogram Mode, the acquisition memory is used as a two-dimensional array in its size corresponding to the spectral and spatial dimensions of the detector array. A read-increment-write sequence is performed for each event as the x and y values are used as an address in a 16-bit cell in the 1024 by 32 element histogram memory. During a programmed integration time, the events are accumulated one at a time to create a 2D image. In the pixel list mode, the acquisition memory is used as a one dimensional array to allow the sequential collection of the x,y event address into the linear pixel list memory. Time-binning of events is accomplished by inserting a time marker in the array at specified intervals. The Count Rate Mode uses the memory as a linear array and periodically collects the total detector array count rate sequentially in the linear memory array. ALICE also includes a feature that allows certain areas of the detector to be excluded in suppression of hot pixels and other defects – this filtering is performed ahead of data processing to avoid large fractions of acquisition memory to be taken up by erroneous data.

Ralph – Imaging Telescope

Ralph is a visible/near infrared multispectral imaging and short wave infrared spectral instrument that delivers the primary imagery of Pluto and Charon for the study of their geology, morphology and composition.

The instrument is basically comprised of two sub-instruments, the Multispectral Visible Imaging Component (MVIC) covering four bands in the visible spectral range and the Linear Etalon Imaging Spectral Array (LEISA) that includes three detectors sensitive for infrared radiation. Ralph is a collaboration between NASA’s Goddard Spaceflight Center, the Southwest Research Institute and Ball Aerospace. The two components of Ralph share a single optical telescope bringing the total instrument weight to 10.5 Kilograms. Ralph requires a peak power of 7.1 Watts.The MVIC part of Ralph is in charge of delivering full-color images of Pluto and Charon at a resolution of up to 1 Kilometer per pixel. Imagery includes stereo images and nighttime acquisitions to provide data for the refinement of Pluto and Charon’s radii and aid the search for clouds and hazes in Pluto’s atmosphere, help in the search for rings and additional moons in orbit around Pluto.

First and foremost, MVIC imagery will deliver the first color photos of a new world, unlocking the mystery of what Pluto – once the ninth planet in our solar system – actually looks like when resolved beyond a few pixels. Geological maps can be generated from MVIC data which is the primary objective of this part of the Ralph instrument.LEISA is responsible for the mapping of water, methane, carbon dioxide, nitrogen ice and other materials on the sunlit face of Pluto and Charon. Infrared imagery can also provide insights into surface temperatures across Pluto and Charon. Visible and infrared imagery of previously unknown bodies can deliver a wealth of critical data such as cratering history, surface structures, spatial variability of the surface, volatile transport and many more. Furthermore, Ralph looks at the distribution of the main species on Pluto/Charon, examines the areas of pure ices and mixed areas, studying seasonal transport, searching for complex species, and it assesses the connection between geology and composition.

The Ralph instrument is comprised of a single optical telescope that feeds the two focal planes of MVIC and LEISA. Ralph’s telescope uses an unobscured, three-mirror anastigmatic design that was chosen as it provides a larger field of view than the conventional Cassegrain or Ritchey-Chrétien systems. Light enters the telescope through a 75-millimeter aperture and falls onto the primary mirror that directs the radiation to the secondary and tertiary mirrors which focus it onto the focal plane. In between the tertiary mirror and the focal plane assembly is a dichroic beam splitter that transmits infrared radiation at a wavelength greater than 1.1 micrometers to the LEISA focal plane and reflects shorter wavelengths to the MVIC focal plane located perpendicular to the LEISA detectors. The overall focal length created by the three-mirror design is 658 millimeters.The entire telescope assembly is manufactured from grain aligned 6061-T6 aluminum and so are the three mirror assemblies. This creates a lightweight, athermal and thermally conductive design ensuring the optical performance of the system is minimally influenced by temperature as thermal gradients are largely eliminated. The telescope entrance is heavily baffled for stray light rejection and additional measures are taken within the telescope in the form of a field baffle at an intermediate focus between the secondary and tertiary mirrors plus a Lyot stop at the exit pupil of the optics after the tertiary mirror. A protective door in front of the instrument aperture protects the instrument from contamination during ground processing and accidental exposure to direct sunlight during the early mission phase. The door has a 20% throughput and is opened in a one-time mission event.

Ralph is a scanning instrument, requiring the New Horizons spacecraft to move the instrument field of view across its target while the detectors are read-out as part of a pushbroom design, forming the image swath as the spacecraft sweeps out the targeted image.

The MVIC Focal Plane Assembly consists of seven independent Charged Coupled Device arrays mounted on a single thermally controlled substrate, each CCD array equipped with its own specific bandpass filter for the generation of multi-band imagery with the filters mounted 700 microns above the detector surface.

Two of the 32 by 5024-pixel arrays are operated in Time-Delay Integration mode to deliver panchromatic imagery in the 400 to 975-nanometer range. Four 32 x 5024-pixel arrays are used for multi-band imaging covering a blue band (400-550nm), a red band (540-780nm) and the near infrared region (780-975nm) as well as a narrow-band methane channel at 860 to 910 nanometers. The Time Delay Integration TDI is accomplished by synchronizing the parallel transfer rate of each of the 32 CCD rows (each 5024 pixels wide) to the relative motion of the image across the detector surface. TDI is suitable for the generation of large-format images acquired as the spacecraft scans across the target. The presence of 32 rows increases the integration time by the same factor and thus allows for high signal-to-noise measurements. Using two detector arrays for the panchromatic imagery yields a double sampled spatial resolution to be used in the processing of data into hemispheric maps of Pluto and Charon. The normal body rates required for MVIC imaging are 1600 microrad/sec for panchromatic and 1000microrad/sec for multispectral imaging which correspond to integration times of 0.4 and 0.6 seconds, respectively. Spacecraft attitude control is sufficient to keep image smear within a quarter of one pixel over a 0.7sec integration, eliminating any smear-related concerns.

Each of the TDI arrays has a static field of view of 5.7 by 0.037°. When acquiring images of Pluto, 4600 pixels will be filled by the object, the rest being margin for pointing errors while 12 pixels on either side are dark pixels used as reference and for injected charge. All pixels used on MVIC are 13 by 13 micrometers in size.The remaining detector elements of MVIC measuring 128 by 5024 pixels are operated in staring mode with a 0.15 by 5.7° field of view. This framing array is to be used in optical navigation of the spacecraft.

The LEISA instrument is a wedged infrared spectral imager capable of generating spectral maps in the short wave infrared spectral region from 1.25 to 2.5 micrometers. It uses a linear variable filter that is placed around 100 micrometers above the detector array. LEISA features a 256 by 256-pixel Mercury Cadmium Telluride array detector (40 by 40 micrometer pixels) operated as a push-broom sensor just like the MVIC instrument.

Employing Time Delay Integration, LEISA reads out its detector at a speed that is synchronized to the rate of the scan and automatically creates a spectral map as the image is swept out due to the use of a linear variable filter. This LVF is manufactured so that the transmit wavelength varies along the in-scan direction only so that the row-to-row image motion builds up a spectrum (analog to TDI increasing the signal over a single spectral interval on MVIC). The LEISA instrument field of view is 0.9 by 0.9 degrees.

LEISA requires spacecraft rotations of 120 microrad/sec for a frame rate of 2Hz, however, frame rate can be varied from 0.25 to 8Hz to accommodate imaging in various spacecraft rotation modes. Read-out is accomplished through two ribbon cables and a multilayer fan-out board fabricated into a single element.The filter is comprised of two segments, the first covers wavelengths from 1.25 to 2.5 microns at an average spectral resolving power of 240. This creates the composition maps to be obtained from LEISA. The second segment of the filter covers a narrow range from 2.1 to 2.25 microns at a spectral resolving power of 560 to gather compositional information, but also collect surface temperature maps by measuring the characteristic spectral shape of frozen Nitrogen.

Both of the focal plane assemblies, in particular LEISA’s, require active cooling to limit dark currents especially in the long wavelength range of the instrument. A radiator on the top of the Ralph instrument is directly exposed to space and thermally coupled to the focal plane and the Telescope Detector Assembly. The entire telescope structure is kept at 220K in order to limit the conductive and radiative load on the focal planes. MVIC is further cooled to around 175K at the CCDs while LEISA is operated at a focal plane temperature under 130K. For calibration of MVIC and LEISA, the Ralph instrument includes a second radiation input whose field of view is offset by 90 degrees to the instrument, aligned with the spacecraft antenna pointing to allow solar radiation to provide diffuse illumination within the telescope assembly. When the spacecraft is in its nominal Earth/Sun-pointing orientation, sunlight can enter the instrument through the Solar Illumination Assembly aperture that is 4 millimeters in diameter.

A small fused silica lens with a focal length of 10mm is part of SIA and images the light onto the input end of a 125-micrometer core fiber, 10cm in length with the end of the fiber illuminating a pair of lenses directly under the Lyot stop behind the tertiary mirror and just 10cm from the two Focal Plane Assemblies.The overall goal of the Solar Illumination Assembly is to create a repeatable pattern that can be used for tracking the stability of the pixel-to-pixel response (flat-fielding) during the long mission duration. SIA illuminates the entire LEISA detector and about 3000 pixels of each MVIC array. Even though the sun will only measure 50 microns in diameter when imaged onto the fiber at Pluto distance, it will still underfill the fiber. A second fiber with a high attenuation can be used for flat-fielding when New Horizons is still close to the sun.Another use of SIA is its alignment with the Solar Occultation Channel of ALICE, so that Ralph could also be used to create an atmospheric spectrum during the occultation when the Plutonian atmosphere is placed between the entrance of the instrument and the sun. Although SIA only delivers diffuse radiation into the instrument’s telescope, a vertical spectral profile can still be acquired by summing the spectra from all rows into a single spectrum.

The Ralph electronics assembly contains three boards – the detector electronics, the command and data handling board and a low voltage power supply. The electronics box of the instrument is installed directly to the spacecraft below the Telescope Detector Assembly to be able to operate at the spacecraft surface temperature. The detector board delivers biases and timing signals to both focal planes, amplifies the signals received from MVIC and LEISA and performs the analog-to-digital conversion of the imaging data. The science data uses 12-bits per pixel. The command and data handling system executes the spacecraft commands, converts low-rate engineering data from the analog to the digital format and delivers the high-speed imaging data interface to the Instrument Card within the Integrated Electronics Assembly and the low-rate engineering feed directly to the spacecraft C&DH processor. The power supply is in charge of converting the 30V spacecraft bus to the various low-voltages required by the Ralph electronics.

The entire electronics assembly of Ralph is fully redundant in architecture with two strings of components that feature abundant cross-strapping to flexibly bypass any failed components and ensure Ralph can fulfill its function as part of the core instrument suite of New Horizons. Redundancy within the MVIC instrument can not be guaranteed but at least some functionality of the instrument could be preserved in case of a failure by grouping the CCD arrays in two segments with two color and one panchromatic CCDs so that at least some data is still available in case of a single-point failure. LEISA has four independent outputs from the 128 by 128 pixel frames so that science can still be completed in case one quadrant stops working.

REX – Radio Science Experiment

The New Horizons Radio Science Experiment makes use of the spacecraft’s high-gain antenna and associated signals processors to obtain temperature and pressure profiles of Pluto’s tenuous atmosphere by measuring radiometric temperature, gravitational moments and ionospheric structure.

The instrument can also look for an ionosphere around Pluto or an atmosphere around Charon and conduct a bistatic surface scattering study on Pluto. REX functions by receiving a 4.2-centimeter wavelength radio signal (7.2GHz) from Earth (transmitted at high power) and recording the signal attenuation (or changes in the signals caused by the radio waves traveling through the atmosphere) as the New Horizons spacecraft passes behind Pluto so that the atmospheric layers are placed in between the signal source and receiver, causing an effect on the structure of the signal that allows the 4.2cm thermal emission to be deduced.

Normally, such measurements are made with the spacecraft sending the signal and a ground station capturing it and recording it, reducing resources needed on the craft in terms of power, memory and mass. However, this was not possible on New Horizons due to the large distance between the Earth and Pluto. A combination of occultation measurements and two-way tracking can be used to determine the total mass of the Pluto system to about 0.01% and also improve the accuracy of the Pluto-Charon mass ratio. The dedicated REX hardware weighs just 160 grams as the only addition to the operational communication system is an additional Uplink Receiver/Decoder card that can process the REX signal into science data. On approach to Pluto, REX measures the radiometric temperature of Pluto and Charon and completes an occultation measurement on Charon to search for a discernible atmosphere. During the close portion of the flyby, REX is in charge of measuring the spacecraft’s velocity vector with high accuracy so that the masses of Pluto and Charon can be separated. After closest approach come the critical occultation measurements on Pluto and Charon to obtain the profile of the refractivity of Pluto’s atmosphere. The precision reached by REX for atmospheric pressure and temperature is 0.1Pa and 3K. It is also possible for REX to be used for the study of the solar wind, the interplanetary plasma and the solar corona when being used during cruise.The requirement to use a ground station to transmit the signal instead of the spacecraft arose from the desired signal to noise ratio of the measurements, the large distance to Pluto and the high flyby speed of the spacecraft. Large transmitter powers are needed to support an accurate measurement of the tenuous atmosphere of Pluto which is hardly possible with the energy constraints of an RTG powered spacecraft. Additionally, the flyby velocity limits the occultation observation to minutes for the upper atmosphere and mere seconds for the lower layers of the atmosphere, increasing the required Signal to Noise Ratio.

New Horizons, within its radio system, incorporates an Ultra-Stable Oscillator USO as an inherent component of the design, both of the REX experiment and the Doppler-Tracking technique employed for navigation. The spacecraft transmitter is always referenced to the USO frequency which is entirely independent of the received uplink signals. Normally, systems use the uplink signal transmitted from the ground to form the frequency of the downlink signal for doppler tracking which creates a direct relationship between the frequency of the received uplink and the transmitted downlink which makes a calculation of the spacecraft radial velocity possible through the comparison of uplink and downlink.New Horizons does not implement the formation of the downlink signal directly from the uplink signal. Instead, it analyzes the uplink and then uses the USO reference frequency to calculate the difference between the number of radio cycles arriving at the spacecraft and the number of USO cycles in the same period.

The observed frequency difference is sent back to the ground as part of telemetry data and makes possible the determination of the Doppler shift and the USO frequency by taking into account the inherent difference in frequency between the ground transmitter and the USO. This brings the advantage of a simpler radio system on the spacecraft, the increased stability of the downlink and the increased flexibility in using the radio link for scientific studies.Within the receiving system of New Horizons, the noise performance has been improved by the placement of the leading Low-Noise Amplifier closer to the antenna to reduce the physical temperature of the X-Band waveguide connecting the amplifier to the high-gain antenna. The REX system follows the 4.5MHz buffer and the anti-phasing filter includes an analog-to-digital converter feeding a triple-redundant Field Programmable Gate Array. Within the FPGA, the two core functions of REX are handled – the calculation of the total power within the 4.5MHz bandwidth from the uplink signal entering the antenna that is being put through a total power integrator, and processing of the 4.5 MHz data in a digital filter to isolate the 1kHz portion of the frequency spectrum that contains the occultation signals relevant for the experiment. These signals are then processed into digital science data and routed to the data recorder to be sent to the ground for further processing and analysis.

LORRI – Long-Range Reconnaissance Imager

LORRI, the Long Range Reconnaissance Imager, is the high-resolution imaging instrument of the New Horizons Spacecraft tasked with the observation of Pluto, its giant satellite Charon and the smaller moons Nix and Hydra as well as other Kuiper Belt objects. The instrument is a narrow-angle telescope that can acquire high-resolution imagery of objects even at great distances.

Its primary purpose is the acquisition of imagery to provide information on Pluto’s geology and surface morphology as well as collisional history, atmosphere-surface interactions and any signs of activity such as plumes or cryovolcanoes, surface layering, atmospheric haze, and other phenomena occurring on the surface or within the atmosphere. Imagery acquired during the flyby will show features as small as 100 meters on the surface of Pluto and 260 meters on the surface of Charon.LORRI is a panchromatic imager sensitive for the visible wavelengths. Imagery from the instrument finds application in optical navigation, the determination of the orbits of Pluto’s satellites before delivering the sharpest images ever obtained of Pluto and its moons. The instrument was developed and manufactured at Johns Hopkins University and SSG Precision Optronics Inc.

The LORRI instrument consists of four principal components, the Optical Telescope Assembly, the Aperture Door, the Associated Support Electronics and the Focal Plane Unit. All components are interconnected by an electrical harness and the instrument includes no moving parts except for the aperture door. All instrument components aside from the door are installed on the Central Deck of the New Horizons spacecraft while the door is mounted to an external spacecraft panel.

Thermal considerations were an important aspect in the development of LORRI since the telescope views cold space while residing within the spacecraft body that is kept well above freezing at all times. To optimize optical performance, a material with high thermal conductivity and low coefficient of thermal expansion was needed for the construction of the optical system.

As a result, the Optical Telescope structure, the primary and secondary mirrors and a metering structure were all manufactured from silicon-impregnated silicon-carbide which offers favorable thermal characteristics. LORRI employs a telescope with a 20.8-centimeter aperture diameter using a Ritchey-Chretien design consisting of a hyperbolic primary mirror and a hyperbolic secondary mirror to eliminate third-order coma and spherical aberration. The telescope has a focal length of 263 centimeters and a narrow field of view of 0.29 by 0.29 degrees.

In total, LORRI has a mass of 8.6 Kilograms, 5.6kg of which are the optical telescope. The instrument requires 5 Watts of electrical power plus up to 10W of heater power. The telescope was designed to have a high light throughput given the low light level at Pluto that is about 1/1000 of that found at Earth. This is also required because LORRI is limited to short exposure times given the stability of the spacecraft that only uses thrusters for attitude control.
The entire telescope structure is monolithic consisting of the primary mirror bulkhead, a short cylindrical section, and the three-blade spider hosting the secondary mirror. A field flattener assembly is installed on the primary mirror mounting plate protruding through the mirror and facilitating fused silica lenses which are the only refractive elements of the LORRI telescope. The telescope structure is mated to the composite baffle tube via three titanium feet that provide vibration isolation. The baffle is attached to the spacecraft structure itself using six glass-epoxy legs that provide thermal isolation.

Multilayer insulation is used to cover the entire Optical Telescope Assembly for thermal protection while thermal gradients are reduced through the choice of materials. The silicon-carbide structures of the Optical Telescope Assembly have a very low expansion with temperature and Invar 36 was chosen for all inserts that allow bolting together of the assembly given its comparable thermal characteristics in the expected temperature range. All Invar inserts and the secondary mirror feet are epoxy-bonded to the Optical Telescope Assembly.

The telescope itself is installed within the telescope baffle tube that consists of highly conductive graphite epoxy and forms a uniform cold sink around the entire structure to help reduce thermal gradients.The interior of the telescope is protected from contamination and solar illumination by a door mechanism that is opened after launch. The door is mounted external to the spacecraft and interfaces with the baffle to build a contamination seal.

The door is machined from a single piece of aluminum and is covered in multilayer insulation for thermal control while the door is closed. In a one-time event, the door is opened using redundant sets of loaded springs and paraffin actuators to guarantee a successful deployment.Baffling within the telescope assembly is accomplished using graphite composite baffle vanes to suppress stray light and reduce image ghosting. A second inner baffle is extending out from the hole in the primary mirror with inner and outer vanes plus threading.

The Focal Plane Assembly of the LORRI instrument features a temperature-controlled Charged Coupled Device detector installed on a bracket that is mounted on the Optical Telescope Assembly via titanium flexures while the bracket itself is attached to a gold-coated beryllium conduction bar that interfaces with a radiator installed on an outside spacecraft panel. Because the radiator is installed separate from the telescope, a highly-conductive aluminum alloy S-link is used to connect the radiator to the Focal Plane Assembly to allow for some motion between the two. The Focal Plane Unit hosts a back-illuminated, high-quantum efficiency CCD detector supplied by E2V Technologies, 1024 by 1028 pixels in size, with four dark columns to create usable imagery of 1024 by 1024, using the standard 13-micrometer pixel size. The instrument has a passband of 350 to 850 nanometers, covering the visible wavelengths. The CCD is highly sensitive and employs anti-blooming technologies. The charge level within each pixel of the CCD is represented by a 12-bit binary word and the entire CCD has a frame transfer time of 13 milliseconds. LORRI supports exposure times from 1 millisecond to 29.9 seconds, however, typical exposures are 50 to 200 milliseconds optimized for the spacecraft pointing capabilities. The Focal Plane Assembly includes a switchable 4x4 on-chip binning option to deliver 256 by 256-pixel images. For calibration, the Optical Telescope Assembly uses two incandescent bulbs that can illuminate the CCD through light scattered throughout the OTA.

Located within the Focal Plane Unit is an AD9807 analog integrated circuit that is in charge of double sampling of the CCD, amplification of the read-out signals and analog to digital conversion to the digitized 12-bit data format. This conversion occurs at a maximum rate of 6MHz, well above the pixel read out speed at 1.5Mhz.

A dedicated latch-up protection circuit is in place to avoid radiation-related latch-up of the analog device. The signal delivered to the double sampler is already amplified using a low-noise, wide-band amplifier located between the CCD and sampler to avoid having to run the analog amplifier within the sampler at high gain. Clocking signals for the CCD are provided by dedicated MIC4427 drivers delivering phase, image zone and memory zone clocking.

The digitized signals are delivered from the Focal Plane Unit to the Associated Support Electronics that are comprised of three components – a Low-Voltage Power Supply, an Event Processor Unit and an Input/Output slice.

The Event Processing Unit communicates with the spacecraft via an RS-422 link to receive commands and transmit engineering data. EPU hosts a RTX2010RH Field Programmable Gate Array as Central Processor.

The main function of the Input/Output board is the reception of serial image data from the Focal Plane Unit and and transmission of that data to one of the Instrument Interface cards of the two Integrated Electronics Modules of the spacecraft for storage within the onboard memory. Data transmission is possible on an RS-422 bus and an LVDS link, both links exist separately to either of the IEMs.

Further tasks of the Input/Output slice are to store/transmit the image header, to receive commands from the RTX processor, command the Focal Plane Unit mode and set exposure times based on inputs from RTX. The Input/Output board contains two Field Programmable Gate Arrays(FPGA) – an imager-interface and and RTX-bus interface. The first reads the images from the FPU and transmits them to the IEM, but it also generates test pattern images for transmission to the IEM. The imager-interface can also receive data from the RTX to be sent to the Focal Plane Unit setting the FPU mode and exposure time and to write the 408-bit image header that is written over the first 34 image pixels. The header information is used to match engineering data with image data. The RTX-bus calculates the 32-bin histogram of the FPU image currently being transmitted to then calculate future exposure times in a dynamic scheme to avoid overexposed images. It also gathers FPU status and temperature parameters that are made available to RTX.

The Low-Voltage Power Supply of the instrument is comprised of a redundant set of DC-to-DC converters and delivers 2.5, 6, and 15V power as required by the other electronics within LORRI.

Also, LVPS actuates the instrument heaters and delivers power bus health data back to the Power Distribution Unit.

LORRI begins Pluto observations 90 days prior to the encounter with Pluto and Charon already resolved as separate objects. These initial observations are used to refine the orbits of Pluto and Charon and the smaller moons, Nix and Hydra. Single frames and 2x1 mosaics are acquired to cover ten full orbits until about 14 days before encounter. Imagery provided in the week leading up to encounter are used for the search for librations of Pluto and Charon. The last full frame of Pluto comes ten hours prior to closest approach and two 3x3 global mosaics are taken during closest approach showing the illuminated disk of the dwarf planet. Additional images taken around the time of closest approach show a smaller area but at a great resolution for morphological studies of the surface and atmosphere. The full disk of Charon is imaged with 3x3 mosaics.

 

[Fenrir]

New Horizons - Instrument Overview

SWAP – Solar Wind at Pluto

All major interplanetary missions carry a Solar Wind Analyzer and New Horizons is no exception as it offers the first opportunity to study the interaction of Pluto with the solar wind. SWAP, the Solar Wind at Pluto instrument, is the largest-aperture instrument ever built to measure solar wind particles given the large distance of Pluto to the sun and the low intensity of the solar wind.

Despite its distance to the sun, Pluto is not safe from solar wind interaction. In fact, scientists believe that, due to its minute gravity, Pluto is losing a significant amount of material through escape processes driven by the solar wind as atmospheric gas molecules or atoms are stripped away by interactions with the solar wind. The SWAP instrument sets out to quantify the loss encountered by Pluto and also look at the underlying loss mechanisms to compare them with other planets. Learning about atmospheric loss also provides valuable information on the structure of the atmosphere itself.

The SWAP instrument combines a Retarding Potential Analyzer (RPA) with an Electrostatic Analyzer (ESA) to make extremely fine and accurate energy measurements of the solar wind, capable of detecting even minute changes in solar wind speed. SAP was developed by the Southwest Research Institute like many other electrostatic instruments flown to all kinds of places throughout the solar system. The instrument weighs 3.4 Kilograms and draws 2.8 Watts of power.

The electro-optics of SWAP are comprised of the RPA, a deflector and the ESA which work together to select the angles and energies of the solar wind to be measured. Energetic ions selected by the electro optics based on the voltage settings are then registered with a coincidence detector system ahead of signal digitization and storage. The RPA rejects an ions with energy per charge values that are under the voltage setpoint of the system. Ions arriving at angles can be deflected into the subsequent electro-optics by applying a voltage to the deflector ring. The final selection of ions occurs within the ESA that rejects ions outside its set Energy/charge range and also eliminates UV light and neutrals. The ion passband can be solely determined by ESA in case the RPA is turned off, but high-resolution differential measurements of the incident ion beam can only be made by differentiating adjacent RPA/ESA combinations.
The ions that are selected by the analyzers then enter the detector section which features an ultra-thin carbon foil to create secondary ions and two channel electron multipliers (CEMs) to generate a measurable electron signal. Both, the primary particle and the secondary electrons are measured as part of the coincidence measurement by Charge Amplifiers that service the CEMs.

Overall, SWAP has a field of view of 276 by 10 degrees that is deflectable by over 15 degrees. Ion energies of 35 electron-volt to 7.5 kilo-electron-volt are supported by the instrument. The instrument can acquire either full energy and detailed peak measurements or deliver additional full energy sweep data when stepping through 128 discrete voltage steps with 0.39-second step lengths to deliver full energy spectra. SWAP is installed on the –Z corner of the spacecraft where its field of view is free of any structure. This location also allows the spacecraft to point its imaging instruments on the +Z axis and still permit SWAP to acquire measurements.

To account for the low density of the solar wind at Pluto distance, the SWAP instrument had to utilize a unique design with a very large aperture. Nevertheless, the SWAP instrument is similar in its overall architecture to various top-hat electrostatic analyzers that have flown before. To be able to detect fine-changes in solar wind speed, ESA was coupled with RPA.

The RPA consists of four concentric aluminum cylinders/screens with 90,000 close-packed holes to create a grid structure that is self-supported and has a 65% transmission rate. The grid is 0.25 millimeters thick and the holes 0.34mm in diameter drilled into 0.38mm thick nickel. The four cylinders have diameters of 17.44, 16.96, 16.64 and 16.16 centimeters. The outside and innermost cylinder are not biased and are kept at ground potential while the two central cylinders are biased between 0 and –2000 Volts in 0.49V steps. Ceramic insulators are used to isolate these cylinders from the rest of the system.

The RPA provides a low-pass filter with a sharp energy cutoff, allowing SWAP to make fine sweeps across the solar wind beam once it is located with a coarse ESA scan. Ions need to have sufficient energy to pass the grids. In the process of passing, the ions are decelerated which requires SWAP to re-accelerate the ions to their original energy which is completed in the path from the inner RPA grids to the final grounded grid.

The deflector used by SWAP is used to deflect particles from further out in –Z direction into the central plane of the instrument. It is located just inboard of the RPA and operates at a voltage of 0 to +4000 Volts applied to a metal ring. It can deflect ions of up to 7000eV/q to an angle of up to 15 degrees. Deflections for lower energies are higher.

The Electrostatic Analyzer provides a coarse energy selection and protects the detectors from UV radiation. The outer sphere of the top hat is blackened with an Ebanol coating to reduce scattering of light and particles while the inner surface is blackened but not serrated. A grounded cone completes the ESA design by providing a field-free region through which particles enter the detector area. The ESA can be operated at voltages of 0 to –4000V.

After passing through the field free region, the selected particles are accelerated towards a Focus Ring which holds the ultra-thin carbon foil with a thickness of 1 micrometer. The foil is held in place by a grid with 66% transmission. When striking the grid, the particle generates secondary electrons which, along with the primary particle, continue onward to the Primary Channel Electron Multiplier, accelerated in a 100V potential on the PCEM strip. Electrons scattered backwards are directed to a Secondary Channel Electron Multiplier to be collected.

Counts from the two CEMs are registered by the CHAMP (Charge Amplifier) and the associated electronics. A pulse from one of the CEMs starts a 100-nanosecond anti-coincidence counter during which the other CEM has to provide a pulse as well for the signal to be taken into account to rule out dark counts, UV noise and other erroneous measurements.

There are two detectors within SWAP to provide redundancy over the course of the long mission duration. A second focus ring was added to the SCEM to draw back scattered electrons for measurements without PCEM. SWAP features a two-segment door that is opened once in flight using a tensioned spring assembly. The doors are coated with back nickel and have grounding wires to keep them at spacecraft potential.

The SWAP instrument contains within it all electronics needed for the operation of the instrument, specifically, the High-Voltage Power Supply (a HVPS Driver and High Voltage Boards) and Control Board, located in an electronics volume below the SWAP instrument. Separately, the CHAMP boards are located closer to the sensor to prevent excessive noise.
The Charge Amplifiers convert a charge pulse from the CEMs to a TTL pulse that can be accepted by the Control Board for subsequent processing. The CHAMPs are located in enclosures to the top of the instrument Strong Back to keep them close to the detectors. The pulses from the CEMs are delivered to the CHAMPs through short coaxial cables. A threshold voltage for the CHAMPS can be set by a Digital to Analog Converter on the Control Board through commanding. A resistor sets the output pulse width to 70 nanoseconds and also controls the 100ns amplifier dead time. The output pulses are buffered by two Schmitt trigger buffers before being transmitted through a back-terminated series resistor to the interface cable leading to the Control Board.

The High Voltage Power Supply sets the voltage on all optical surfaces, the RPA, the deflector, the ESA and the Focus Rings. It also supplies power to the CEMs requiring six different voltage to be generated and adjusted based on the instrument mode of operation or external commands. HVPS delivers a 0 to –4500 Voltage to PCEM, 0 to +4500 to SCEM, 0 to 100 to the focus ring, 0 to +2000 to RPA, 0 to +4000 to the deflector, and 0 to –4000 to ESA. Accuracy for the deflector and ESA are 4V, the CEMs 5V and the RPA just 0.5V. The HVPS system is fully redundant to ensure reliable generation of bias voltages.

The Control Board provides the data interface between the SWAP instrument and the New Horizons spacecraft, receiving and executing commands from the spacecraft by using an 8051 microprocessor that responds to commands, controls the operation of the instrument, sets the power sequences and collects the data, also formatting the housekeeping data stream. The Control Board is connected to the two Integrated Electronics Modules of the spacecraft via an RS-422 data bus. DC-to-DC converters on the Control Board deliver the 5-Volt instrument power bus.

The instrument microcontroller runs at 4.9 MHz and 0.4 MIPS (Million Instructions Per Second). The instrument boot code is stored in 32KB PROM, with two 128KB EEPROMs providing redundant storage, 64KB bit storage for the program code and 64KB of Look-Up Tables. A 128KB SRAM memory provides code and data memory space. All instrument memory allocations are controlled by a dedicated Field Programmable Gate Array.

The Control Board receives all CHAMP pulses once a data acquisition window is opened which only occurs when all voltages have been set and initial settling is complete. From that point on, all pulses are registered and those with signals from both CEMs within a 100ns interval are converted to digital science data. Commanding the HVPS board via an interboard connection, the Control Board sets all voltages and receives feedback on current and voltage that is input into housekeeping telemetry.

CEM health monitoring is also performed by the Control Board which can take action to keep the instrument safe in case count rates or any health parameters exceed specified limits.

SWAP can operate in different modes – a simple BOOT mode in which the instrument is booted from the PROM image enabling the upload of new code, a LVENG (Low Voltage Engineering Mode) running from an EEPROM image considered the instrument safe mode, a LVSCI (Low Voltage Science Mode) used to verify instrument performance through CHAMP test pulses, a HVENG Mode when high voltage is set through commands for calibration and checkout, and HVSCI, the main science mode of the instrument running ESA/RPA/DFL voltages according to science run tables.

In its nominal mode of operation, SWAP completes 64-second runs to acquire data, starting with a 32-second coarse sweep across the complete instrument range in 32 steps taking 0.5 seconds each. Then, the Control Board calculates the peak that is then set as the center of the fine sweep which covers a narrow energy range and again employs 32 energy steps to 0.5 seconds each.

PEPSSI – Pluto Energetic Particle Spectrometer Science Investigation

PEPSSI is the most compact directional energetic particle spectrometer flown on a space mission and complements the SWAP instrument by covering electrons and ions at high energies to deliver additional data on solar wind interactions of the Plutonian atmosphere. Built at Johns Hopkins University’s Applied Physics Laboratory, the instrument studies the density, composition, and nature of energetic particles and plasmas that are the result of escape processes ongoing at Pluto. As a spectrometer, the instrument can identify species escaping from the atmosphere which also provides valuable information on the structure of the atmosphere itself.

PEPSSI weighs 1.5 Kilograms and requires 2.3 Watts of power. It is a classic time of flight particle spectrometer and measures electrons from 25 kilo-electronvolt to 500keV, ions from 700eV to 1MeV, CNO ions from 15 keV to 1.2MeV, and protons from 40keV to 1MeV. PEPSSI has a field of view of 160 by 12 degrees and measures 19.7 by 14.7 by 21.6 centimeters in size in its launch configuration.

The instrument is mounted on a bracket that provides the proper angular offset of the fan-shaped field of view from any of the spacecraft decks. The viewing geometry was optimized for the study of freshly ionized pick-up ions in the vicinity of Pluto caused by charge exchange from Pluto’s atmosphere. The bracket allows the spacecraft to be mounted on the spacecraft deck while looking past the large High Gain Antenna and not being obscured by the dish structure.

Alignment control for PEPSSI was kept within 1.5 degrees. The installation of PEPSSI allows the instrument to detect solar ions when the spacecraft is in its nominal communications attitude while not directly looking into the sun.

The instrument is installed on the top deck of New Horizons with four stainless steel bolts while thermal isolation from the bracket is provided by thermal washers between the bracket and PEPSSI’s base plate.

The instrument consists of a collimator and sensor assembly known as the Sensor Module sitting atop an Electronics Board Stack facilitating six electronics boards within a box. Contained within the Sensor Head is the time of flight section about 6 centimeters in length feeding an array of Silicon Solid State Detectors that measures energy and delivers timing signals for the calculation of the time of of flight of the particles. Event energy and time of flight (velocity) can be combined to calculate the particle mass (E=0.5mv²) to determine the particle species.

The PEPSSI instrument was launched with the deployable door mechanism, consisting of two door segments that provided protection from contamination during ground operations as well as acoustic environments occurring during launch that could have damaged the ultra-thin foils within the Sensor Module.

Each half of the door covers half of the 160° aperture and swings outward on deployment that is driven by torsion springs initiated by firing an actuator that retracts a retaining pin. Tension of the springs keeps the doors open for the remainder of the mission.

For the examination of ions, PEPSSI uses an approach known as Time-of-Flight (TOF) by Energy and TOF by Microchannel Plate Pulse Height to determine the energy and velocity of ions which allow their mass to be calculated, allowing an identification of the ion species. Electrons are detected by solid state detectors that sense energy and directional distribution.

The Sensor Module consists of an aperture opening, electron deflectors, start foils and anodes, a microchannel plate detector, stop anodes and foils, solid state detectors and pre-amplifiers as well as supporting electronics. The PEPSSI Sensor Module includes TOF sections 6 centimeters across that feed the silicon solid-state detectors. The SSD array and the individual pre-amplifiers are connected to an Event Board that determines particle energies.

The direction of an incoming particle is determined as a function of the solid state detector that is struck by the particle, with six different viewing directions along the 160° fan represented by six physical Solid State Detector Elements covering 25° with 2° of spacing in between individual elements providing an accuracy sufficient to estimate the overall direction of particle inflow. Sectors 1, 3, 6 consist of two SSD detectors, one for ions and one for electrons. The electron detectors are covered with a 1-micron Aluminum layer to reject low-energy protons and heavy ions. Sections 2, 4, 5 are pure ion detectors. For ions, the directionality is determined by the detection of the entrance position on the microchannel plate time-delay anode nearest to the start foil.

As an ion enters the instrument, it first passes through a thin foil in the collimator before reaching the start foil (aluminum-polyamide-aluminum) and generating secondary electrons. These electrons are then directed from the primary particle path to the microchannel plate detector where the Start Signal is generated for the Time of Flight measurement.
A 500-Volt potential between the foil and the MCP directs the secondary electrons to the TOF detector with high accuracy (0.4ns dispersion in transit time). The segmented MCP anodes with one start anode for each of the six angular segments provide data on the direction of travel of the ion.

Secondary electrons that are created as a result of the ion passing through the stop foil (palladium-polyimide-palladium) are again directed to the MCP and cause a Stop Signal. The time-difference between the two signals represents the time it took the ion to pass through the 6-centimeter TOF instrument. Both foils, start and stop, are installed to a high-transmittance stainless steel grid for structural support.

After the stop foil, ions impact the Solid State Detectors that either consist of electron and ion pixels or are pure ion pixels. The SSD determines ion energy which coupled with the TOF measurement delivers ion mass and particle species data.

Electrons entering the instrument are first decelerated by a 2.6kV potential which is part of the TOF system for ion measurements. After passing the stop foil, the electrons are again accelerated by a 2.6kV potential. Reaching the SSD detectors, the electrons are detected in the electron pixels that can measure electrons at energies of 25 keV to 0.5 MeV.

The electron detectors are covered with 1-micrometer aluminum metal flashing that rejects protons with energies under 100keV. Light ions are blocked as well, but for heavy ions with energies over 100keV coincident TOF measurements are needed to discriminate between ions and electrons to only register electrons.

Particle energy can be measured for protons starting at 40keV and heavy ions (such as the CNO group) starting at 150keV up to over 1MeV. Lower-energy ion fluxes are measured via TOF only while the MCP pulse height can only point to a coarse indication of low-energy particles.

Housed within the electronics box below the Sensor Module are six electronics boards that provide all functionality to the PEPSSI instrument and build the interface between instrument and spacecraft. The Energy Board accepts the SSD event signals on 12 channels with amplitudes proportional to particle energy.
These analog signals are converted to 10-bit digital numbers by processing through a charge sensitive amplifier and peak shaping algorithm before being put through an Analog to Digital Converter. A dedicated TOF board processes the time of flight data – amplifying the start and stop signals, computing the time of flight duration between the two signals and converting the measurement into a digital format.

The High Voltage Power Supply generates the voltage bias on the entry/exit foils (-2600V), the microchannel plates (-2100 and –100V), the deflector plates (-2900V) and the SSD bias of –100V. A Digital Interface Board is in charge of running the event validation logic monitoring energy and TOF event counters and running interface functions. The Events Processor board receives energy and TOF data from the other boards that is processed into science data transmitted to the spacecraft via RS-422. It also delivers instrument status telemetry and accepts spacecraft commands that are then executed by the instrument. Finally, the Low Voltage Power Supply delivers the 15 and 5-Volt instrument buses to the electronics boards, generated from the 30V main spacecraft bus.

Operational modes supported by PEPSSI are a TOF-plus-Energy mode, TOF-Only and Energy-Only. All of them are made concurrently based on the data that is available. TOF-Plus-Energy is determined using TOF and SSD data from the same particle. TOF-Only occurs when TOF data can be gathered from secondary electron pulses but no SSD response is registered which is the case for light particles such as protons, although heavy ions at low energies can also lack an SSD signal when below the given energy threshold. Energy-Only measurements occur when ions fail to generate secondary electrons and when the TOF time is sufficiently close to zero.

VB-SDC – Venetia Burney Student Dust Counter

SDC is a student-developed instrument designed at the Laboratory for Atmospheric and Space Physics, University of Colorado at Boulder. Its purpose is to detect microscopic dust grains in the solar system from 1AU to at least 30 Astronomical Units. Dust particles can be released by asteroids, comets, and Kuiper Belt objects, for example as the result of collisions. Obtaining an accurate count and size distribution of dust particles can provide insight into the collision rate of such bodies in the outer solar system. SDC can also search for dust in the Pluto system to look at the impact rate of tiny impactors on Pluto’s moons.

The measurement of the spatial and size distribution of interplanetary dust particles is needed to verify the existence of predicted structures within the Zodiacal cloud. Five previous deep space missions have carried dust sensors into deep space – Pioneers 10 and 11, Ulysses, Galileo and Cassini. None of these missions was able to conduct dust measurements beyond 18 AU which means SDC, despite being a student-built instrument, will deliver a truly unique data set. The instrument is expected to continue working after the Pluto flyby to examine the dust environment within the Kuiper Belt which has not yet been explored what so ever. These measurements can advance the current understanding of the formation and evolution of the solar system and deliver new data for models of planet formation out of dust disks in other planetary systems.

The SDC instrument is comprised of two major pieces – a detector assembly with an active dust-sensing system that is exposed to the space environment, and an electronics box residing within the spacecraft. Overall, the instrument weighs 1.9 Kilograms and requires up to five Watts of electrical power. It is the first student-built payload to fly on a NASA planetary mission.

The SDC instrument features a set of polyvinylidene fluoride PVDF film impact sensors that are mounted on a detector support panel that is installed on the exterior of the New Horizons spacecraft and facing the ram direction when the spacecraft is in is nominal Earth-pointing attitude to maximize the probability of dust impacts. Signals from the sensors are relayed via an intra-harness to the instrument Electronics Box facilitated within the warm spacecraft body.

The instrument was designed to provide a spatial resolution of 0.1 Astronomical Units to be able to resolve expected resonance structures.

SDC is capable of detecting the mass of particles between one picogram and one nanogram which corresponds to grain sizes of one to 10 micrometers in radius. Heavier particles can still be detected, though their masses can not be determined.

The dust impact detector has an active area of around 0.1 square meter and uses permanently polarized PVDF films. When a particle hits, a depolarization change is caused as it impacts the film which can be measured by relatively inexpensive sensors that are stable even in extreme thermal, mechanical, electrical and radiation environments.

The magnitude of the depolarization change within the PVDF depends on the momentum of the particle and whether it fully penetrates the film. SDC uses a film 28 micrometers in thickness which is known to stop particles with a mass of 10 nanograms at a speed of 20 Kilometers per second.

The SDC sensor element consists of 12 sensor patches each 14.2 by 6.5 centimeters in size plus two detector patches on the backside of the detector assembly used as a reference to monitor the background noise level caused by mechanical vibration or cosmic ray hits to the electronics. The detector elements are installed atop a one-centimeter thick aluminum honeycomb panel which itself is attached to the exterior of the spacecraft via a three-point compliant mount consisting of titanium flexures for thermal expansion flexibility.

To protect the PVDF film from overheating, the honeycomb panel is directly attached to a high-emissivity polyimide tape that is radiatively coupled to the support panel below to spread out the heat from below the detectors. The top surface is covered with Teflon tape capable of reflecting 90% of incident solar energy.

The PVDF film on the sensors features a thin (1000 Angstroms) Aluminum-Nickel electrode material on the top and bottom surfaces. The detecting element is bonded between a pair of fiberglass frames that have built-in electrical contact wires to the two electrode surfaces bonded to the electrodes with conductive silver filled epoxy. The small signal wires run to the connection tabs where they interface with a coaxial cable. The wire is harnessed so that is can withstand dust impacts.

The electronics of the SDC instrument are facilitated on two printed wiring assemblies housed inside the electronics board. Signals from the detector are delivered through the harness to the analog Printed Wiring Assembly where amplification occurs followed by signal conditioning and conversion to the 16-bit digital regime. The digitized data is collected by registers of the Field Programmable Gate Array of the digital Printed Wiring Assembly and then directed to the microprocessor of the instrument that adds time-stamps and stores the data frames in a long-term non-volatile memory. The digital PWA also hosts the instrument power supply, health monitoring system and the interface between the instrument and the spacecraft.

The SDC Digital Board hosts an Actel RT54SX72S FPGA that completes address decoding functions, conditions the housekeeping data stream, facilitates an interrupt controller and watchdog timer for instrument safety functions and it collects the science data from the analog board.
It is also in charge of delivering housekeeping and science data one of the two Integrated Electronics Modules of New Horizons and accepts commands from the spacecraft. It watches over the performance of the instrument microcontroller and has the authority to reset it. The FGPA has access to 32KB of PROM holding the boot code, 32KB of SRAM and 4MB of Flash RAM to hold science data.

The Amtel 80C32E Microcontroller handles the communications with the spacecraft, executes commands, manages the flash memory and handles the science data, all through the FPGA.

The SDC instrument has been designed for stand alone operations to be able to keep recording dust events even when the New Horizons spacecraft is in hibernation mode. It can manage itself for up to 500 days without the need to communicate with the spacecraft or the ground. A number of autonomy rules are stored within the instrument to provide adequate response for any number of anomalies that could be encountered during the cruise to Pluto. Daily checks of the memory health are part of the instrument’s routine and the number of interrupts on each channel are measured to allow the system to take action by switching channels for lower sensitivities or block them altogether to keep the instrument in a good configuration for actual science collection.

 

[Fenrir]

New Horizons flew by Pluto this morning — and we just got the signal confirming it!!!

It's official: NASA's New Horizons became the first spacecraft ever to fly by Pluto today, passing within 7,750 miles of the dwarf planet at 7:49 am ET.

This fact was widely celebrated this morning, but in reality no one knew whether the probe successfully made it until scientists received a signal this evening. That's because New Horizons was busy collecting data during the flyby — not transmitting it — and once it did send a signal, the transmission took 4.5 hours to reach Earth.

Now, after receiving the signal this evening, mission scientists have confirmed that the probe made it through as planned (there was roughly a 1-in-10,000 chance it could have been hit by a piece of errant space debris). The first photos of the encounter should arrive sometime tomorrow, and over the next weeks and months, we'll see gorgeous, high-resolution photos of Pluto — 10 times sharper than anything taken so far.

 

[Fenrir]

New Horizons; from Pluto's perspective

I still love you Pluto, you'll always be a planet to me.

 

[Fenrir]

Fly Through the Largest Ever Map of Our Galaxy's Cosmic Dust

A team of astronomers has created the largest ever three-dimensional map of our galaxy’s cosmic dust—and you can fly right through it.

The researchers, from Harvard University, have mapped out the distribution of space dust across three quarters of the night sky. They did that using data about 800 million stars taken with the Pan-STARRS telescope in Hawaii. They calculated exactly where dust existed by measuring the red hue that it lends to stars in the data acquired by the telescope—in much the same way that particles around Earth cause sunsets to look reddish orange.

The results, soon to be published in the Astrophysical Journal, have been turned into a series of fly-through videos by the researchers. The one above, for instance, takes you on a spin around our very own Sun, labelled Sol. Elsewhere, though, you can explore the team’s 3D Dust Mapping site which contains even bigger tours of the galaxy.

Aside from looking amazing, the resulting maps should help astronomers understand the Milky Way in more detail than ever.

 

[Fenrir]

Charon, You are a Glorious, Beautiful Moon

This is Pluto’s largest moon, Charon, in the most beautiful, detailed, highest-resolution single frame image we’ll be downlinking from the flyby this month. And it is amazing.

This image was taken just 466,000 kilometers (290,000 miles) from Charon within hours of New Horizon’s closest approach early on July 14, 2015. The image was taken with the spacecraft’s high-resolution high-resolution, monochromatic LORRI camera at 02:41:49 UTC, just over nine hours before the critical mission flyby. The approximately 2.3 kilometers per pixel resolution makes this the most detailed single-frame image of the moon we’ll be getting during these initial failsafe downlinks. We’ll eventually see mosaics of Charon in more detail, but not until after the primary science-gathering phase is past and the probe switches over into downloading all of its data to Earth. This image was included in the first data downlink early this morning after the New Horizons probe reestablished contact late last night.

The Massive Moon of Pluto

Charon is by far the largest of Pluto’s five known moons. At 1,200 kilometers diameter, it’s nearly half the diameter of Pluto, making it the largest moon in the solar system compared to its parent. The entire moon has a surface area of just 4.6 million square kilometers. That’s only a whisper larger than India (3.2 million km2), and half the size of Australia (7.7 million km2).

At just over 10% the mass of Pluto, tidally-locked Charon has enough heft to pull the dwarf planet into a distinctive orbital wobble about their mutual center of mass (barycenter). This makes it not only the largest moon in the solar system compared to its parent, but makes a solid argument for declaring that Pluto-Charon is the first binary dwarf planetary system.

Charon is small enough that its gravity isn’t even 3% that on Earth: the escape velocity to launch from the moon is just 0.58 kilometers per second, or roughly twice the current land speed record at 2,088 kilometers per hour (1297 mph).

Charon, Pluto’s Partner in the Cosmic Underworld

As many astronomical bodies are, Charon was discovered by accident. In 1978, US Naval observatory astronomer James Christy was studying photographic plates of Pluto taken at the 1.55 meter Flagstaff telescope when he noticed a slight, periodic bulge. Later observations would show that the bulge was due to a smaller accompanying body, whose periodicity corresponded to Pluto’s rotational period. This finding—strong evidence that the bulge was due to another close by body in a synchronous orbit—led astronomers to reassess Pluto’s size, mass, and other physical characteristics.

Charon’s discovery at the Naval Observatory Flagstaff Station as a time-varying bulge on the image of Pluto (seen near the top at left, but absent on the right)

But Charon’s existence wouldn’t be confirmed until 1985, when the two planetary bodies entered a five-year period of mutual transits, crossing each others’ path in Earth’s line of sight. This is an event that only occurs twice in Pluto’s 248 year rotation around the sun, when the Pluto-Charon plane is edge on as seen from the Earth. And we’re damn lucky it happened when it did, or we might have spent many additional years doubting Charon’s existence.

Christy first suggested the moon be called ‘Charon’ after his wife Charlene, nicknamed ‘Char.’ Only later did he realize what a coincidence the name actually was: Those versed in Greek mythology will know that Charon is the mythological ferryman of the dead, closely associated with Hades, the god of the underworld. And it just so happens the Roman underworld god, Pluto is a direct derivation of Hades. It’s incredible that these two planetary bodies, dancing around each other in an endless gravitational embrace in the cold, dark hinterlands of the solar system, get their names from two mythological figures who shared very much the same relationship.

Official adoption of the name Charon announced by the International Astronomical Union on January 3, 1986. Notable features on Charon are going to follow an exploration theme. It’s still to be announced if that theme is exploration destinations, exploration vessels (“New Horizons” would make a lovely name for a plateau), or the explorers themselves.

Coming Into Focus

Until the New Horizons flyby, we had very, very few images that resolve Charon as anything more than a bulge off Pluto’s backside. Here’s the best image of the 1990s, taken by the Hubble Space Telescope. Pluto and Charon appear as small, enigmatic worlds, barely visible through one of the most powerful telescopes of the time.

Pluto and Charon seen by the Hubble Space Telescope on February 21, 1994. Image credit: ESA/NASA

Hubble swung around for another look in 2006, getting another shot at the moon that was just as squint-inducing but captured a few pixels of the smaller moons Nix and Hydra. In a bit of historical symmetry, part of the imaging team this time included Alan Stern, Principal Investigator for the New Horizons Mission.

The Pluto-Charon seen by the Hubble Space Telescope on June 22, 2006. Image credit: ESA/NASA

Grainy and low-res though they may be, this fascinating image helped convince NASA that the Pluto system was worth an exploratory trip.

After New Horizons woke up for its Pluto approach, Charon started zooming into focus. In February, the spacecraft beamed back this time-lapse video showing an entire ‘Pluto day’ (roughly 6.5 Earth days) in the Pluto-Charon system, captured from a distance of 203 million kilometers (126 million miles). The composite of shots, taken from January 25-31, shows the gravitational wobble around the system’s mutual center of mass.

Fuzzy, pixelated Charon has continued to grow, sharpen, and develop geologic surface features before our eyes. A batch of images downlinked in mid-June revealed a prominent dark splotch on one of the moon’s poles, taken by New Horizons’ high-definition, monochromatic LORRI camera at a distance of 50.7 million kilometers (31.5 million miles). The dark spot was totally unexpected, sending the science team into a flurry of still-ongoing speculation.

We got our first-ever detailed look at Charon’s surface one week ago on July 8, 2015. From 6 million kilometers (3.7 million miles) away from the Pluto-Charon system, the still-unexplained dark cap on its northern pole started coming into focus. We also got our first hints of the moon’s cratering, an idea that filled Geology, Geophysics and Imaging team leader Jeff Moore with glee as he revelled in the possibility of impact-generated windows below the surface.

Days later, we saw the moon in enough detail to start our first geological interpretation. The possibility of craters was upgraded to specific probable locations, and new linear features joined the list as potential chasms. The speculation about that odd northern pole increased — could it be the same dark material we were seeing on Pluto, evidence of a shared atmosphere or at least the capture of Pluto’s sublimating ices clinging to the moon?

The view of Charon by New Horizons on July 11, 2015 reveals potential craters and chasms. Image credit: NASA/JHUAPL/SWRI

As part of the final failsafe data downlink before the New Horizon probe’s closest approach to the Pluto-Charon system, we got our first colour look at the moon yesterday. The colours are real as in the red filter is displayed as red, but enhanced and saturated to over-exaggerate changes so isn’t what we’d see with our own eyes.

Mission scientists offered the interpretation of the red polar cap as hydrocarbons, tholins formed when methane and nitrogen are exposed to ultraviolet radiation. Those elements have already been confirmed in Pluto’s polar ice cap and tholins are molecules small enough to aerosolize, so it’s theoretically possible that Charon’s cap is formed by capturing sublimated ice escaping form the dwarf planet. If New Horizons finds an atmosphere on the moon, and if that atmosphere is uncannily similar to Pluto’s, it gets downright probable the dark cap is a consequence of the two objects are swapping gas.

Alternately, instead of material transported from the dwarf planet, the patch could be coming from Charon’s interior. To confirm that, we’ll need to take a look at that mottled surfaces covering the rest of the moon, checking if any crater interiors reveal matching material.

Charon in enhanced real colour on July 13, 2015. Note the distinct red cap, and the diverse mottling in the southern hemisphere. Image credit: NASA/APL/SwRI

One of the other mysteries that we might solve in the next few days is why Charon’s surface is so much more cratered than Pluto’s. Both objects should be roughly the same age and subject to the same history of bombardment, so something is happening on Pluto to smooth out its surface that isn’t also happening on Charon. If it’s an internal process on Pluto, we’re left confused by how something so small could still be warm enough to be active. If it’s ice-related, we’ve got a new mystery into how the cryogenic processes are different than on Charon.

In that final pre-flyby package of data, New Horizons also sent home one last image of Charon taken with its high-resolution camera. Taken on July 13, 2014 from just under 1.5 million kilometers away from the moon, the 7.2 kilometer per pixel resolution image was impressive but no where near as glorious as the photograph we’d see the very next day.

As we’re learning right now based on the the latest image, Charon has far fewer craters than we expected. This raises the fascinating possibility that the moon is geologically active! But, to be fair, we don’t know exactly how many craters are on this image, and we’ll get additional data tomorrow. The fascinating gash across Charon’s surface is also revealed in the highest resolution to date—this feature is way, way bigger than the Grand Canyon, perhaps up to 3 miles deep and 600 miles long.

So, it looks like there’s some process that’s keeping heat and geologic activity going on Charon. It can’t be tidal energy—Pluto and Charon are in tidal equilibrium, meaning there’s no significant exchange of tidal energy between the two bodies. One possibility is that the decay of radioactive material inside Charon is powering a lot of the geologic activity on the surface. It’s also possible that Charon has managed to store heat from its formation for a long, long time. But the New Horizons team doesn’t want to speculate too much—yet.

The New Horizons probe has safely completed its closest approach to the Pluto-Charon system, but the mission is far from over. The probe is continuing to collect additional observations on its way out of the system, including more photographs of Charon as a crescent moon and lit by reflected light of Pluto-shine. Because the probe can only make observations or send data home, not both, we won’t be getting any higher-resolution full-disk images of the moon this month. When the probe does switch to data-transmission mode, it’ll take over a year to send all the data back to Earth. After that, it will continue to explore deep space, hopefully with extended mission funding to fly past a second Kuiper Belt Object.

 

[Fenrir]

Earth, Meet Hydra

Hydra is the outermost of Pluto’s known moons, and until now, we’d only ever seen it as a faint pixel of light. Today, planet Earth gets its first real glimpse of this tiny, enigmatic satellite.

This never-before-seen view of Hydra’s surface was captured yesterday at a distance of 645,000 km, within hours of New Horizons closest approach on the morning of July 14th, 2015. Captured with the spacecraft’s high-resolution, monochromatic LORRI camera at approximately 3.2 kilometers per pixel, we’re literally watching a point of light transform into a bonafide moon. That is a big fucking deal.

For the first time, we know the size of Hydra. It’s about 48 kilometers by 30 (28 miles by 19 miles), a decidedly elongated, lopsided lump of rock and ice. It has an intermediate albedo, a brightness about halfway between Pluto and Charon. That means the surface must be almost entirely icy.

We think that Hydra is either the second or third-largest moon of Pluto, but we won’t know for certain until tomorrow when we get our first high-resolution at the other contender, Nix.

The image above is also the most detailed single-frame image we’ll be getting during the initial series of failsafe downlinks. Hydra was included in the first data downlink early this morningafter the New Horizons probe reestablished contact late last night.

Recent Additions to the Pluto Family

Charon might have been the first moon spotted in the Pluto system, but within the past decade, we’ve added four additional satellites to the flock— Nix, Styx, Kerberos, and Hydra. We were already preparing to launch the New Horizons probe to Pluto when Hydra and Nix were discovered in June of 2005 by the Hubble Space Telescope’s ‘Pluto Companion Search Team.’ Kerberos was detected later, in 2011 during a Hubble survey searching for rings around Pluto, while teeny tiny little Styx wasn’t spotted until July of 2012, when the New Horizons team was conducting a search for potential hazards to the reconnaissance mission.

On June 21st, 2006, the name ‘Hydra’ was assigned by the International Astronomical Union. Hydra, a nine-headed serpent from Greek mythology, pays double homage to Pluto’s then-tenure as the ninth planet in our solar system (Pluto was reclassified as a dwarf planet in August 2006), with the ‘H’ also indicating its discovery by Hubble.

An Enigma of a Moon...Until Now!

Hydra orbits Pluto at roughly 64,800 kilometers (40,264 miles) from the gravitational center (barycenter) of the system. Its nearly circular, prograde orbit is in the same plane as the moon Charon. Hydra is sometimes brighter than the other oblong moon, Nix, suggesting that it is either larger or that the surface of the moon varies in brightness.

Until the New Horizons flyby, astronomers had no direct measurements of Hydra’s size. We had worked out some very rough size estimates based on the assumption that Hydra is the same brightness as Charon. That assumption, however, would imply Hydra is compositionally very similar to Charon (roughly a 50 / 50 mix of ice and rock), and we really had no good reason to expect that it is. There could be any number of processes—collisions between planetary bodies, different ices or gases siphoned off Pluto—that might make Pluto’s system compositionally diverse, similarly to the moons surrounding Jupiter, Saturn, and Neptune.

That Charon, Hydra and Nix are all relatively the same brightness is simply the best guess we were able to make based on incredibly limited information. But with our first real image of Hydra, we can start to make some more sophisticated observations and hypotheses about what this enigma of a moon is actually made of.

Despite the fact that we were really just guessing at Hydra’s size before today, we were correct in supposing the moon isn’t massive enough to form a spheroid under its own gravity. Like Mars’ moon Phobos, Hydra (and Nix) are rather oblong little things:

Zooming in On Hydra

During the New Horizons mission to fly through the Pluto-Charon system, our previous best look at the smaller moons Nix and Hydra was way back in February.

Pluto, Charon, Nix, and Hydra seen by the Hubble Space Telescope in 2006. Image credit:NASA/ESA/H. Weaver/A. Stern

Nix and Hydra each orbit Pluto about once a month. Image credits: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

Heavy processing brings out Nix and Hydra more clearly

while losing pesky details like background stars

. Image credits: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute​

And her she is again, as revealed moments ago:

Fascinated by Hydra? Hold onto your keyboards, nerds! This is only the beginning. We’ll be getting back even higher resolution images of Hydra in the coming days, and learning much, much more about Pluto’s outermost known moon in the weeks and months ahead. We’ll get our first downlink of Pluto’s other oblong moon, Nix, later tonight.​

 

[Chanakya's_Chant]