Abstract: In the context of the enormous cost of building and operating conventional launch vehicles based on chemical fuels, there is a worldwide quest to develop reusable space vehicle that could render space journey routine and affordable. The only reusable space vehicle, the US space shuttle, was phased out in July 2011 after it was realized that it wasnot only costly and technologically complex but also far from safe to ferry humans. India has now joined the race to build its own reusable space vehicle along with the front ranking space faring nations including USA and Russia.
The current genre of conventional, once-only used launch vehicles based on chemical fuels are costly and technologically complex space transportation systems.As such,there isa worldwide clamour to build and operate reusable space vehicles that are technologically viable, economically efficient and safe. Of course, the era of reusable space transportation system was inaugurated with the successful flight of the US space shuttle way back in 1981. However the space shuttle which was found to be unsafe for human crew—besides being costly and technologically complex to operate—was phased out in July 2011.
As it is,more than one in 25 space shuttle astronauts had lost their lives during the three decades long operations of this US reusable space transportation system. Incidentally, the break-up of the Soviet Union in the early 1990s leading to the emergence of Russia had resulted in the phasing out of the Buran reusable space vehicle development programme. Currently, USA, India, Russia and China are among the space faring nations which have unveiled their own programmes for developing new generation reusable launch vehicles. Incidentally, focus of the global quest for a reusable space vehicle is on safe, affordable and easy to operate reusable space transportation systems for routine orbital journeys.
Space Capsule Recovery Experiment (SRE-1) is an experimental spacecraft launched by ISRO in 2007, Indian Navy recovering the spacecraft
Everything going as planned, in September 2015, the Indian Space Research Organisation (ISRO) will carry out the first ever technology demonstrator flight as a first step towards developing a full-fledged Indian Reusable Launch vehicle (RLV) that would bring down the cost of access to space by a substantial extent. The maiden technology demonstrator flight of RLV will be launched from Satish Dhawan Space Center (SDSC) the Indian space port in Sriharikota island on the eastern coast of the country. Equipped with solid strap-on thrusters like the ones used in the four-stage Indian space vehicle PSLV (Polar Satellite Launch Vehicle), the test vehicle will fly at five times the speed of sound to touch an altitude of 100kms. Afteractivating its fin and wing control, the vehicle will glide a bit before starting its descent and land in theBay of Bengal. “The Sept launch is just the initial one. We need to validate the concept. There are multiple experiments “ said AS Kiran Kumar, Chairman ISRO. Going ahead, he noted, “In Sept, the launch vehicle will make a landing in the Bay of Bengal while the ultimate attempt would be to land it on an airstrip at Sriharikota,” said Kumar.
ISRO has developed heat resistant tiles that would form the outer cover of the vehicle. These would be able to withstand extremes of temperatures of up to 1,200 degrees Celsius that the US space shuttle used to experience while re-entering the earth’s atmosphere. The ultimate objective of the Indian reusable launch vehicle programme is bringing down the cost of launching one kg of payload to US$500 from the current US$5000 per kg.
On its part, ISRO has configured a winged Reusable Launch Vehicle Technology Demonstrator (RLV-TD) to act as a flying test bed to evaluate various technologies, namely- hypersonic flight, autonomous landing, powered cruise flight and hypersonic flight using an air breathing propulsion system towards realizing a Two Stage to Orbit (TSTO) full-fledged reusable launch vehicle.
Air breathing propulsion along with Reusable Launch Vehicle Technology is the key for low cost access to space. Unlike conventional rockets, air breathing propulsion system makes use of atmospheric oxygen for combustion, thus resulting in substantial improvement in payload fraction and reduction in overall cost. As such a reusable space vehicle is required to carry only liquid hydrogen as fuel. In distinct contrast a conventional launch vehicle is required to carry oxygen as an oxidizer along with hydrogen.
The S-9 Solid Rocket Booster (SRB) undergoing tests at Liquid Propulsion Systems Center
Though the developmental activities towards dual mode ramjet engines and its associated technologies have been initiated, the current focus is on the development of scramjet engine and flight testing of the same through a cost effective method using Advanced Technology Vehicle (ATV). The ATV has the unique capability to carry a payload of 200-400kgupto an altitude of 800km.Ascent of ATV in a direct vertical profile is an excellent platform for studies related to upper atmosphere and short duration transient phenomenon in the atmosphere. ATV provides a cost effective platform for the study of microgravity providing a time of ten minutes at levels better than 100 micro-g which can be used for micro gravity experiments in fluid physics, combustion, materials science, biology and also to perform precursor experiment for launch vehicles, satellites and human spaceflight mission. ATV has been identified to carry out scramjet characteristics flights with active scramjet engines.
The Thiruvananthapuram-based Vikram Sarabhai Space Center (VSSC), the largest Indian space establishment, is the lead agency for developing the scramjet system meant for developing the reusable-space vehicle. Since air breathing propulsion has the capability to operate only during the atmospheric phase of the flight, it always needs to be adopted along with the conventional rocket booster stage for meeting the final orbital requirements. According to ISROsources, the development of scramjet (supersonic combustion ramjet) system, involves a number of new and novel technologies including the mixing of the very high speed air; achieving stable ignition and flame holding in addition to enabling combustion within the practical length of the combustor. ISRO sources also say that an air breathing propulsion system based on scramjet will pave for an “easy, efficient and routine” access to space through a reusable space vehicle.
HYPERSONIC TECHNOLOGY DEMONSTRATOR VEHICLE program is to demonstrate a scramjet engine integrated vehicle performance in autonomous mode
The feasibility studies on scramjet propulsion for space transportation and missile systems have been in vogue sincethe late 1950s. The most striking advantage of scramjet is that it helps in the seamless integration of air and space operations.
In the second half of 1990s, Defence Research and Development Organisation (DRDO) had unveiled the design of a 25-tonne class reusable space vehicle named AVATAR meaning reincarnation in the Indian classical language of Sanskrit .The Avatar concept was meant to serve as a workhorse for routinely launching low cost defence and civilian satellites. It was also envisaged that the technology developed for Avatar could be used for building superfast passenger aircraft and hypersonic cruise missile systems. Ideally, Avatar is well suited for hurling satellite payloads into a near earth orbit on a routine basis and in an economically viable manner. Of course Avatar too would operate with air breathing propulsion technology. Dr.R.M.Vasagam, a rocketry expert, says that the technology envisaged for building Avatar is feasible. Of course, building Avatar underpins the need for a massive quantum of funds and technological challenges of huge dimension. Former Indian President and well known space and defence scientist Dr. A.P.J. Abdul Kalam explains, “The Avatar hyper-plane project is a national mission". The programme is bigger than an individual or an institution. We must realize our dream of operationalizing the most efficient, technologically reliable and low cost launch system, even at the cost of challenging the developed countries.”
Towards Developing Indias Reusable Space Vehicle - Centre for Land Warfare Studies (CLAWS)
