Scientific Innovations

[The SC]

'Microthrusters' Could Propel Small Satellites

http://images.sciencedaily.com/2012/08/120817135544-large.jpg?1345229507
http://web.mit.edu/newsoffice/images/mini-thrusters.jpg

The device, designed by Paulo Lozano, an associate professor of aeronautics and astronautics at MIT, bears little resemblance to today's bulky satellite engines, which are laden with valves, pipes and heavy propellant tanks.

Instead, Lozano's design is a flat, compact square -- much like a computer chip -- covered with 500 microscopic tips that, when stimulated with voltage, emit tiny beams of ions. Together, the array of spiky tips creates a small puff of charged particles that can help propel a shoebox-sized satellite forward.

"They're so small that you can put several [thrusters] on a vehicle," Lozano says. He adds that a small satellite outfitted with several microthrusters could "not only move to change its orbit, but do other interesting things -- like turn and roll."

Lozano and his group in MIT's Space Propulsion Laboratory and Microsystems Technology Laboratory presented their new thruster array at the American Institute of Aeronautics and Astronautics' recent Joint Propulsion Conference.

Cleaning up CubeSat clutter

Today, more than two dozen small satellites, called CubeSats, orbit Earth. Each is slightly bigger than a Rubik's cube, and weighs less than three pounds. Their diminutive size classifies them as "nanosatellites," in contrast with traditional Earth-monitoring behemoths. These petite satellites are cheap to assemble, and can be launched into space relatively easily: Since they weigh very little, a rocket can carry several CubeSats as secondary payload without needing extra fuel.

But these small satellites lack propulsion systems, and once in space, are usually left to passively spin in orbits close to Earth. After a mission concludes, the satellites burn up in the lower atmosphere.

Lozano says if CubeSats were deployed at higher orbits, they would take much longer to degrade, potentially creating space clutter. As more CubeSats are launched farther from Earth in the future, the resulting debris could become a costly problem.

"These satellites could stay in space forever as trash," says Lozano, who is associate director of the Space Propulsion Laboratory. "This trash could collide with other satellites. … You could basically stop the Space Age with just a handful of collisions."
Engineering propulsion systems for small satellites could solve the problem of space junk: CubeSats could propel down to lower orbits to burn up, or even act as galactic garbage collectors, pulling retired satellites down to degrade in Earth's atmosphere.

However, traditional propulsion systems have proved too bulky for nanosatellites, leaving little space on the vessels for electronics and communication equipment.

Bioinspired propulsion

In contrast, Lozano's microthruster design adds little to a satellite's overall weight. The microchip is composed of several layers of porous metal, the top layer of which is textured with 500 evenly spaced metallic tips. The bottom of the chip contains a small reservoir of liquid -- a "liquid plasma" of free-floating ions that is key to the operation of the device.

To explain how the thruster works, Lozano invokes the analogy of a tree: Water from the ground is pulled up a tree through a succession of smaller and smaller pores, first in the roots, then up the trunk, and finally through the leaves, where sunshine evaporates the water as gas. Lozano's microthruster works by a similar capillary action: Each layer of metal contains smaller and smaller pores, which passively suck the ionic liquid up through the chip, to the tops of the metallic tips.

The group engineered a gold-coated plate over the chip, then applied a voltage, generating an electric field between the plate and the thruster's tips. In response, beams of ions escaped the tips, creating a thrust. The researchers found that an array of 500 tips produces 50 micronewtons of force -- an amount of thrust that, on Earth, could only support a small shred of paper. But in zero-gravity space, this tiny force would be enough to propel a two-pound satellite.

Lozano and co-author Dan Courtney also found that very small increases in voltage generated a big increase in force among the thruster's 500 tips, a promising result in terms of energy efficiency.

"It means you have a lot of control with your voltage," Lozano says. "You don't have to increase a lot of voltage to attain higher current. It's a very small, modest increase."
Timothy Graves, manager of electric propulsion and plasma science at Aerospace Corp. in El Segundo, Calif., says the microthruster design stands out among satellite propellant systems for its size and low power consumption.

"Normally, propulsion systems have significant infrastructure associated with propellant feed lines, valves [and] complex power conditioning systems," says Graves, who was not involved in the research. "Additionally, the postage-stamp size of this thruster makes it easy to implement in comparison to other, larger propulsion systems."
The researchers envision a small satellite with several microthrusters, possibly oriented in different directions. When the satellite needs to propel out of orbit, onboard solar panels would temporarily activate the thrusters. In the future, Lozano predicts, microthrusters may even be used to power much larger satellites: Flat panels lined with multiple thrusters could propel a satellite through space, switching directions much like a rudder, or the tail of a fish.

"Just like solar panels you can aim at the sun, you can point the thrusters in any direction you want, and then thrust," Lozano says. "That gives you a lot of flexibility. That's pretty cool."


http://www.laboratoryequipment.com/news/2012/08/penny-sized-microthrusters-can-power-satellites-space

 

[The SC]

Novel Nano-Structures to Realize Hydrogen's Energy Potential

Engineers demonstrated that hydrogen can be released and reabsorbed from a promising storage material, overcoming a major hurdle to its use as an alternative fuel source.

Researchers from the Materials Energy Research Laboratory at the University of New South Wales in nanoscale (MERLin) at UNSW have synthesized nanoparticles of a commonly overlooked chemical compound called sodium borohydride and encased these inside nickel shells.

Their unique "core-shell" nanostructure has demonstrated remarkable hydrogen storage properties, including the release of energy at much lower temperatures than previously observed.

"No one has ever tried to synthesise these particles at the nanoscale because they thought it was too difficult, and couldn't be done. We're the first to do so, and demonstrate that energy in the form of hydrogen can be stored with sodium borohydride at practical temperatures and pressures," said Dr Kondo-Francois Aguey-Zinsou from the School of Chemical Engineering at UNSW.

Considered a major a fuel of the future, hydrogen could be used to power buildings, portable electronics and vehicles -- but this application hinges on practical storage technology.

Lightweight compounds known as borohydrides (including lithium and sodium compounds) are known to be effective storage materials but it was believed that once the energy was released it could not be reabsorbed -- a critical limitation. This perceived "irreversibility" means there has been little focus on sodium borohydride.

However, the result, published last week in the journal ACS Nano, demonstrates for the first time that reversibility is indeed possible using a borohydride material by itself and could herald significant advances in the design of novel hydrogen storage materials.

"By controlling the size and architecture of these structures we can tune theirproperties and make them reversible -- this means they can release and reabsorb hydrogen," said Aguey-Zinsou, lead author on the paper. "We now have a way to tap into all these borohydride materials, which are particularly exciting for application on vehicles because of their highhydrogen storage capacity."

The researchers observed remarkable improvements in the thermodynamic and kinetic properties of their material. This means the chemical reactions needed to absorb and release hydrogen occurred faster than previously studied materials, and at significantly reduced temperatures -- making possible application far more practical.

In its bulk form, sodium borohydride requires temperatures above 550 degrees Celsius just to release hydrogen. Even on the nano-scale the improvements were minimal. However, with their core-shell nanostructure, the researchers saw initial energy release happening at just 50 °C, and significant release at 350 °C.

"The new materials that could be generated by this exciting strategy could provide practical solutions to meet many of the energy targets set by the US Department of Energy," said Aguey-Zinsou. "The key thing here is that we've opened the doorway."


Novel Nano-structures to Realize Hydrogen's Energy Potential

 

[The SC]

Liquid Crystals: Actively Controlled Materials

Contributing geometric and topological analyses of micro-materials, University of Massachusetts Amherst mathematician Robert Kusner aided experimental physicists at the University of Colorado (UC) by successfully explaining the observed "beautiful and complex patterns revealed" in three-dimensional liquid crystal experiments.

The work is expected to lead to creation of new materials that can be actively controlled.

Kusner is a geometer, an expert in the analysis of variational problems in low-dimensional geometry and topology, which concerns properties preserved under continuous deformation such as stretching and bending. His work over 3 decades has focused on the geometry and topology of curves, surfaces and other spaces that arise in nature, such as soap films, knots and the shapes of fluid droplets. Kusner agrees with physicist and lead author Ivan Smalyukh of UC Boulder that their collaboration is the first to show in experiments that some of the most fundamental topological theorems hold up in real materials. Their findings appear in the current early online issue of Nature.

UMass Amherst's Kusner explains, "There are two important aspects of this work. First, the experimental work by the Colorado team, who fabricated topologically complex micro-materials allowing controlled experiments of three-dimensional liquid crystals. Second, the theoretical work performed by us mathematicians and theoretical physicists while visiting the University of California Santa Barbara's Kavli Institute for Theoretical Physics (KITP). We provided the geometric and topological analysis of these experiments, to explain the observed patterns and predict what patterns should be seen when experimental conditions are changed."

Kusner was the lone mathematician among four organizers of last summer's workshop on "Knotted Fields" at KITP, which led to this work. The workshop engaged about a dozen other mathematicians and about twice as many theoretical and experimental physicists in a month-long investigation of the interplay between low-dimensional topology and what physicists call "soft matter."

In their experiments, the physicists at UC Boulder showed that tiny topological particles injected into a liquid crystal medium behave in a manner consistent with established theorems in geometry and topology, Kusner says. The researchers say they have thus identified approaches for building new materials using topology.

UC Boulder's Smalyukh and colleagues set up the experiment by first creating colloids, solutions in which tiny particles are dispersed but not dissolved in a host medium, such as milk, paint and shaving cream. Specifically, they injected tiny, different-shaped particles into a liquid crystal, which behaves something like a liquid and a solid. Once injected into a liquid crystal, the particles behaved as predicted by topology.
Smalyukh says, "Our study shows that interaction between particles and molecular alignment in liquid crystals follows the predictions of topological theorems, making it possible to use these theorems in designing new composite materials with unique properties that cannot be encountered in nature or synthesized by chemists. These findings lay the groundwork for new applications in experimental studies of low-dimensional topology, with important potential ramifications for many branches of science and technology."

For example, he adds, these topological liquid crystal colloids could be used to upgrade current liquid crystal displays like those used in laptops and television screens, to allow them to interact with light in new, more energy efficient ways.

Fars News Agency :: Liquid Crystals: Actively Controlled Materials