On Monday morning, the Indian Space Research Organisation successfully flight tested its ‘Reusable Launch Vehicle – Technology Demonstrator’ (RLV-TD) from the Satish Dhawan Space Centre (SDSC) in Sriharikota, Andhra Pradesh. This winged craft, with its distinctive twin tail-fins, is intended as a key step toward the space agency’s goal of creating a reusable launch vehicle that could cut launch costs by as much as nine-tenths.
In the flight test, the RLV-TD was carried aloft by a rocket booster and reached an altitude of about 65 km. It then descended, reaching a peak velocity of five times the speed of sound, before landing in the Bay of Bengal about 13 minutes later. “The vehicle’s navigation, guidance and control system accurately steered the vehicle during this phase for safe descent,” an ISRO release said, and the craft successfully survived the “high temperatures of re-entry with the help of its Thermal Protection System.”
ISRO’s current conception for such a reusable launcher is to have a two-stage-to-orbit configuration. A winged first stage would incorporate an advanced air-breathing propulsion system that takes in air as it flies to burn the fuel carried onboard. This stage would take the second stage and payload high up into the atmosphere and, after separating from the latter, return to land on a runway.
The second stage would accelerate the payload the rest of the way using conventional rocket propulsion. Afterward, this second stage too would be brought back to the ground. However, such an advanced launch vehicle may materialise only “some 20 years from now”, according to K. Sivan, director of the Vikram Sarabhai Space Centre in Thiruvananthapuram, ISRO’s lead centre for launch-vehicle development.
But with SpaceX, the American spaceflight company started by entrepreneur Elon Musk, promising to achieve rocket reuse and bring about lower launch costs with existing technology, ISRO has some plans to ensure it remains competitive in the short-term as well.
SpaceX’s Falcon 9 rocket, with just two stages powered by liquid engines, has carried satellites into orbit and sent its Dragon capsule, loaded with cargo, to dock with the International Space Station. On three such flights, the rocket’s first stage, after separating from the second stage, fired its engines again and successfully made a controlled descent back to earth. On one occasion, it returned and made a vertical touchdown a short distance from the launch pad it had left a short time earlier. Then, in two recent flights, it landed on a drone ship stationed out in the ocean.
SpaceX intends to reuse the first stages that return but has yet to demonstrate this capability. The company’s president, Gwynne Shotwell has indicated that such reuse could lead to a 30% saving in costs.
Sivan made it clear that ISRO’s immediate priorities are to make its own launch vehicles more reliable, increase the payload they are able to carry and reduce the cost of their manufacturing. If the Geosynchronous Satellite Launch Vehicle (GSLV), which can launch a 2.2-tonne communications satellite, is able to carry a 3.5-tonne satellite, “the vehicle becomes more efficient,” he remarked. And with vehicle cost remaining unchanged, the cost per kg for the satellite it launches comes down.
In the case of the next generation GSLV Mk-III rocket, its payload capability could be increased from four tonnes to six tonnes. Then, substituting a semi-cryogenic engine, which is currently being developed, for the two Vikas liquid propellant engines in the rocket’s core booster could further raise its payload to 7.5 tonnes.
Vehicle costs could also be reduced. One measure being considered is to shift from maraging steel used for the big solid boosters that form the first stage of the PSLV and the GSLV to a cheaper steel, Sivan said.
In addition, ISRO was “very seriously” thinking of retrieving and reusing the core boosters of the GSLV and GSLV Mk-III in a SpaceX-like manner, according to him. The next generation Heavy Lift Launch Vehicle could also be designed with such reuse in mind.
The GSLV’s first stage, along with the four liquid-propellant strap-on boosters attached to it, account for almost three-fourths of the launch vehicle’s costs. “If we are able to recover and reuse [it], our reduction in cost will be maximum,” he said.
The GSLV’s payload would be halved if the the rocket’s first stage and strap-ons were manoeuvred back to the SDSC. However, the loss in payload would come to only about 80 kg if the stage soft-landed where it would naturally fall after separation. India could take advantage of the Andaman Islands and get the first stage to land there after equatorial launches from Sriharikota, Sivan remarked.
Gopal Raj is a science journalist based in Thiruvananthapuram. He has written extensively about the Indian space programme, including a book, Reach for the Stars: The Evolution of India’s Rocket Programme.