Sen—India is preparing for the maiden flight of a reusable launch vehicle (RLV), slated for July or August this year.
The unmanned mission, designated RLV-TD (Reusable Launch Vehicle Technology Demonstration) will be launched from the Satish Dhawan Space Centre in Sriharikota. The test is a first-of-its-kind space mission for India, opening a new chapter in India’s nearly 50-year-old space history.
Though the vehicle is considered by many as the Indian version of the space shuttle, the comparison is inappropriate since the RLV is not designed to carry humans, but only for ferrying satellites.
It is a USD $15.7 million mission which is likely to attract global interest.
The main objective of the RLV is to provide low cost access to space. An ISRO official estimated that once RLV becomes operational the cost of placing a kilogram into orbit could come down to as little as USD $500.
The mission profile of the first flight, which will evaluate the hypersonic flight regime, envisages the 1.5 tonne spaceplane, which won't carry any payload, being launched by a single solid rocket booster with nine tonnes of propellant. After lift off the spaceplane will separate and fly to an altitude of between 70 to 100 km before beginning its re-entry at five times the speed of sound. It will end its flight with a soft landing in the Bay of Bengal.
The RLV is largely made of aluminium but is covered with 600 heat-resistent silica tiles. During the critical re-entry phase, the spaceplane will experience a lot of heat and the silica tiles have been tested to withstand temperatures up to 1,500°C. To survive the searing re-entry heat the nose of the vehicle is protected by a carbon-carbon shield.
The total mission time is expected to be around fifteen minutes.
An ISRO document about this project says that the first mission will also prove the autonomous navigation, guidance and control for the ascent, re-entry and descent flight.
The big question is whether after touchdown the vehicle will be recovered for post-flight analysis. An ISRO official told Sen that in all probability the vehicle will not be recovered: "We have done amazing measurements and simulated every type of possible post-flight scenario which eliminates the need to recover the vehicle. However, if in the next few weeks there is a change of plan we will seek the help of the coast guard and the Indian Navy to recover the spaceplane from the ocean," he said.
A series of four test flights have been planned to study various aspects of the technology.
The second flight will focus on the vehicle's autonomous landing capabilities. "In this we plan to drop the spaceplane from a helicopter and observe how it lands on runway," an ISRO official told Sen.
The third test flight will be a powered cruise flight and involve installing a jet engine to the vehicle.
The fourth test will use scramjet propulsion.
A high-level ISRO official told Sen that the remaining three tests will be carried out in reasonably quick succession, but a precise timeline cannot be fixed. Asked when the programme will become operational, he said that since it was currently at a preliminary level the process may take years. "It is one of the most technologically challenging projects of ISRO and we have to evaluate a lot of data. To fix any time line therefore would not be correct," he said.
The project has already undergone ground-based tests for example at the balloon facility of the Tata Institute of Fundemental Research at Hyderabad where the radar altimeter of the spaceplane was evaluated.
All the structural elements needed at the launch pad at Sriharikota have been assembled.
Though the RLV project received the green light from the government several years ago, it has remained on the back burner as other programmes including the GSLV Mark 3, the human space flight programme and the development of the indigenous cryogenic engine took priority over the RLV. As a result, the project which is now taking shape at the Vikram Sarabhai Space Centre in Thiruvanathanapuram never fully took off and testing, originally scheduled for 2011, was delayed. The RLV programme is now been fast tracked, though there have been delays this year from the original target date of a March test flight.
If everything now progesses on schedule, the spaceplane, now receiving its final touches at the Vikram Sarabhai Space Centre, will be moved to Sriharikota in the second or third week of June for launch preparations. The booster has already been positioned on the first launch pad at Sriharikota.
This will be ISRO’s third effort to recover a spacecraft after launch and evaluate the re-entry characterestics. The first was the unmanned 555 kg Space Capsule Recovery Experiment (SRE-1) which was launched on Jan. 10, 2007 by a PSLV and recovered on January 22.
The second was the Crew Module Atmospheric Re-entry Experiment (CARE) launched on board the maiden flight of the GSLV Mark 3 on Dec. 18, 2014. After a 19-minute flight the unmanned module splashed down in the Bay of Bengal and was recovered by the coast guard and handed over to ISRO.
The experience and knowledge gained by the SRE-1 and CARE missions will be used for the human space flight programme.
The third one will be the RLV-TD flight which ISRO officials reiterated has nothing to do with manned missions.
ISRO is rocketing into the challenging domain of designing and developing reusable launch vehicles against the background of similar efforts not being too successful in other countries.
For example, the Hermes spaceplane, a collaborative effort of the French space agency, CNES and the European Space Agency, was approved in November 1987, but cancelled in 1992 as it suffered numerous delays and funding problems.
The HOPE-X of the Japanese Space Agency was launched in 1980, but was scrapped in 2003 for a variety of reasons, mainly financial. The trial missions of sub-scale test bed had, however, flown successfully.
The Russian Buran spaceplane was started in 1974 in response to Nasa’s Space Shuttle programme. It completed one unmanned orbital spaceflight in 1988 before it was cancelled in 1993.
Nasa’s Space Shuttle flew from 1981 to 2011 covering a total of 135 missions. Despite its numerous achievements like launching satellites and repair of the Hubble Space Telescope, the feeling among NASA officials and space experts was that the shuttle failed to achieve its promised cost and utility goals. Another major criticism was that it failed to lower the cost of access to space. An analysis showed that the incremental per pound launch costs turned to be higher than those of regular expendable rockets.
Against this grim scenario, where is the guarantee that ISRO’s RLV will be successful and achieve its goals? To this the high-level ISRO replied in a single sentence: "We will make use of the knowledge obtained from these missions while making any possible design changes to our spaceplane. We are hopeful that the mission will accomplish its goals."