The first technology demonstrator (TD) launch of the Indian Space Research Organisation’s Reusable Launch Vehicle (RLV), or the spaceplane in popular parlance, will take place on May 23 at 9.30 a.m. from the Satish Dhawan Space Centre (SDSC), Sriharikota, according to ISRO officials.
Visually, the RLV-TD is a rocket-aircraft combination measuring about 17 m, whose first stage is a solid propellant booster rocket and the second stage is a 6.5 m long aircraft-like winged structure sitting atop the rocket.
However, the popular perception of the technology as a marriage between rocket and aircraft is a misnomer.
In RLV-TD that is awaiting launch at SHAR, the first stage, weighing about 9 tonnes, is merely the Satellite Launch Vehicle (SLV-3) flown in the 1980s.
The vehicle will take off like a rocket and the RLV will be taken to a height of 70 km and where the booster will release the vehicle to carry out its manoeuvres.
Hypersonic Experiment 1
According to Dr. K. Sivan, director of the Vikram Sarabhai Space Centre (VSSC), Thiruvanathapuram, where the RLV was designed, assembled and where it underwent basic electrical, hydraulic and “sign check” tests, the objective is to achieve hypersonic speeds to basically test the hypersonic aero-thermodynamic characterisation of the winged body’s re-entry, its control and guidance systems, autonomous mission management to land at a specific location at sea and testing of “hot structures” that make up the structure of the RLV.
The test is, therefore, termed as Hypersonic Experiment 1 (HEX-1).
A conventional launch vehicle (LV), says Dr. Sivan, spends the lowest time of its flight in the atmosphere, whereas the RLV system spends all the time in the atmosphere. Also, while an LV experiences limited flight regime of say Mach 0 to Mach 2 or so, the RLV experiences a much wider range of flight regimes.
Hence the technology of an RLV is much more complex basically arising from the design of the control and guidance systems, he pointed out.
In HEX1, the winged RLV is otherwise a dummy with no powered flight of its own. At the end of the HEX1 mission, the aircraft will land in sea. However, the ultimate objective of the RLV programme of ISRO is to enable the vehicle traverse a very wide range of flight regimes from Mach 0 to Mach 25 based on air-breathing propulsion for achieving two-stage-to-orbit (TSTO) launch capability.
The integrated test system (booster plus the RLV-TD) is already at the SDSC (SDSC), Sriharikota. Prior to being moved to Sriharikota, the RLV subsystem underwent acoustic tests at the National Aerospace Laboratories of the CSIR (CSIR-NAL) and the booster went as a separate subsystem directly from VSSC. At SDSC the two were mated together.
Dr. A.S. Kiran Kumar, ISRO Chairman, called the first test launch HEX1 “a very preliminary step” and stressed that “we have to go a long way” before it could be called a re-usable launch system. “But these are very essential steps we have to take,” he said.
Asked whether the Indian reusable launch system was aimed at bringing down the launch cost, the ISRO Chairman said, “It will bring down the cost. Towards that, we will have to work and go through these initial steps,” the Chairman said.
Flying test bed
The present design is basically “a flying test bed to evaluate various technologies, namely hypersonic flight, autonomous landing, powered cruise flight and hypersonic flight using air-breathing propulsion using a scramjet engine”, according to ISRO website.
The HEX series of experiments will be followed by the landing experiment (LEX), return flight experiment and scramjet propulsion experiment (SPEX).
The basic design of a scramjet has already been evolved.
A test launch of the engine aboard a sounding rocket, which will achieve a flight regime of up to Mach 8, will take place some place in June at SHAR, Dr. Sivan said.