ISRO used a 15-tonne rocket with 9-tonne of propellants (solid fuel) as a booster to fly the winged reusable launch vehicle into lower earth orbit for demonstrating the feasibility of the technology. The space agency’s telemetry, tracking and command network (Istrac) in Bangalore will collect data from the vehicle spanning vertical take-off, its release in space by the rocket booster for maneuvers and its plunge into the sea in the Bay of Bengal. RLV-TD made history today because its made-in-India and ISRO’s very own indigenous version of a ‘Space Shuttle’. The efforts of more than 600 scientists over the last five years has finally paid off. This is India’s one of the most extraordinary milestones in space exploration. It is cheered as a baby step towards the historic launch of the advanced RLV by 2020.
What are RLVs
- A new generation of vehicles that can launch satellites into the orbit and then re-enter the atmosphere
- A Reusable Launch Vehicle (RLV) is the space analog of an aircraft.
- It takes off vertically on the back of an expendable rocket and then glides back down like an aircraft
- During landing phase, an RLV can either land on a runway or perform a splashdown.
- The main advantage of an RLV is it can be used multiple times, hopefully with low servicing costs.
Let’s dig a little deeper into the Technology:
A rocket-aircraft combination, the RLV-TD measures about 17 m. In the first stage, it is a solid-propellant booster rocket, while in the second it is a 6.5 m long-winged structure that looks like an aircraft and sits atop the rocket. In the first stage, the RLV-TD is the Satellite Launch Vehicle (SLV-3) flown in the 1980s. Like a rocket, it will first take off. The RLV will be released from the height of 70 km by the booster.
The RLV was designed, assembled at the Vikram Sarabhai Space Centre (VSSC) in Thiruvananthapuram. It also underwent basic electrical, hydraulic and “sign check” tests. According to the director of VSSC, Dr K Sivan, the objective of the experiment is to achieve hypersonic speeds. This will test the hypersonic aero-thermodynamic characterisation of the space shuttle’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 experiment has been named Hypersonic Experiment 1 (HEX-1).
ISRO Chairman Dr AS Kiran Kumar has called the first test launch HEX1 “a very preliminary step”. He 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.
According to Dr. Sivan, a conventional launch vehicle (LV) spends the lowest time of its flight in the atmosphere, whereas the RLV remains all the time there. Talking about the flight regime, an aircraft has a limited one of suppose Mach 0 to Mach 2, the RLV on the other hand, experiences a much wider range (Mach 5). So, RLV’s technology is much more complex because of the design of the control and guidance systems, he said.
The winged RLV in HEX1 has no powered flight of its own and it’s otherwise a dummy. According to Dr Sivan, in this experiment, the RLV experienced a flight regime of Mach 5 and the booster alone assisted it. At the end of the HEX1 experiment, the aircraft landed in the sea. The total flight duration of the space shuttle from launch till landing was about 10 minutes. The objective of ISRO’s RLV program is to allow the vehicle navigate a wide range of flight regimes from Mach 0 to Mach 25. This will be based on air-breathing propulsion for achieving Two-Stage-To-Orbit (TSTO) launch capability.
Mating of Booster and RLV-TD
The RLV subsystem underwent acoustic tests at the National Aerospace Laboratories of the CSIR (CSIR-NAL), then it was moved to Sriharikota while the booster was sent directly from VSSC as a separate subsystem. The booster and the RLV-TD were mated together at SDSC.
Lower Launch Cost
When asked by NewsNation, whether the Indian reusable launch system was aimed at bringing down the cost, the ISRO chairman said, “It will bring down the cost. Towards that, we will have to work and go through these initial steps.” If the RLV mission gets successful, it will save ISRO millions of capital invested in the following missions. The average cost of launching a space shuttle without a reusable spaceship is around 5000 USD per 1 kg. If this mission turns out to be a success, it will bring down the cost to around 2000 USD per kg, which is a reduction of more than half.
Flying Test Bed
According to ISRO Website, “the present design was 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.” After the HEX series of experiments, there will be the landing experiment (LEX), return flight experiment and scramjet propulsion experiment (SPEX).
After a series of tests at the sub-system level such as actuator and flight control tests, followed by integration of the shuttle parts with electronic tests in March this year, RLV-TD was sent to National Aerospace Laboratories (NAL) in Bengaluru for acoustics testing, VSSC director K Sivan said in an interview to TOI.
“RLV-TD is a baby step towards the launch of the advanced RLV with air breathing propulsion system (ABPS) and reusable launch vehicle technology. The purpose of developing advanced RLV with ABPS is to reduce the cost of space launches if engines and structures are recovered and re-used. Current RLV-TD has no recovery plans,” he said.
The Indian government has spent a whopping Rs. 95 crores in the making of the RLV-TD. The advanced RLV with ABPS uses atmospheric air as oxidizer for combustion, with vehicle fuel to propel the rocket, and it can bring down space travel cost by 110th and eventually by 1100th later.
“With the first-of-its-kind delta wings that makes supersonic flights feasible, this space shuttle RLV-TD that weighs about 1.75 tons was propelled into the atmosphere on a special rocket booster, all built indigenously,” said project director of this mission Shyam Mohan.
“A key technology developed by scientists here is the reusable thermal protection system (TPS) to make materials that can withstand extreme temperatures, that the exterior of the space shuttle will have to bear when it returns into the dense atmosphere after its journey through near vacuum in space,” he said.
It involved developing lightweight heat resistant silica tiles, that are plastered on the underbelly of the spacecraft, that can withstand temperatures up to 7,000 degrees celsius. The first of its kind indigenously developed carbon-carbon nose cap can resist high temperatures up to 2,000-degree celsius, when the vehicle reaches hypersonic speed, added Mohan.
ESA back in February 2015, conducted a similar experimental launch of its own reusable launch vehicle. It was named as Intermediate eXperimental Vehicle (IXV). The IXV successfully completed its 100-minute mission on 11 February 2015 being the first ever lifting body to perform full atmospheric reentry from orbital speed. Nasa, however, grounded its space shuttle program in 2011 after using its reusable vehicles like Discovery, Endeavor, Columbia and Challenger as a space transportation system for over three decades since 1981 to launch various missions, including the International Space Station (ISS) and the Hubble telescope. While the Russians flew their space shuttle only once.