RLVs are the buzzword in space missions

India’s space scientists must be proud of the remarkable progress they have made towards building a reusable space launch system. Its successful development will cut the price tag on space missions substantially and
give the Indian Space Research Organisation (ISRO) a leg-up in the space launch domain.

On June 23, ISRO’s winged spaceplane — the Reusable Launch Vehicle (RLV) — made a picture-perfect landing autonomously at the Chitradurga Aeronautical Test Range in Karnataka. Christened ‘Pushpak’, the RLV was released from an Indian Air Force helicopter at an altitude of 4.5 km. Pushpak carried out several cross-range correction manoeuvres before making a greased-on landing on the centreline of the runway.

This was ISRO’s third and final RLV landing experiment (RLV-LEX), and it reportedly validated all flight parameters such as the high glide angles and searing speeds needed by the craft to land safely. It was earlier flight-tested in April 2023 and again in March this year. In 2016, its scaled-down version, the RLV-Technology Demonstrator, was released at an altitude of 65 km, short of the 100 km barrier between the atmosphere and outer space. After evaluating its hypersonic (above five times the speed of sound) flight potential, the craft re-entered the atmosphere and glided back to land in the Bay of Bengal from where it was retrieved.

ISRO engineers use data from these flights to improve the RLV test-bed’s capabilities such as powered cruise flight, navigation systems, hypersonic flight, atmospheric re-entry, and autonomous landing. The goal is to develop an RLV with an air-breathing scram jet engine which uses the craft’s forward motion and shock wave effect to compress the incoming air, doing away with the need for fins. Although this is still a long way off, once developed, it would be the perfect first stage for India’s planned two-stage-to-orbit (TSTO) reusable vehicle, the RLV-ORV. The RLV-ORV will launch atop a rocket into a 400 km orbit around the Earth, deploy its payload, and return to land on a runway.

While ISRO has impeccable credentials in the global launch market, offering reliable and low-cost satellite launch services, it is still susceptible to the economic vagaries of the launch business. The most advanced space rockets can hardly lift 2% of their launch weight into low Earth orbit (LEO): a ratio which remains constant after 63 years of spaceflight! Even the use of cheaper air-breathing engines to penetrate the atmosphere has not changed the equation, and getting into space is still very expensive.

During the Apollo Moonshots era of the 1960s, space scientists realised that low-cost access to space would remain a pipedream as long as the focus was on optimising conventional rocket technology. Since chemical rockets had limitations, American and Russian space engineers toyed with the idea of RLVs which, in those days, seemed utopian. In fact, NASA originally planned to have a reusable spacecraft for putting the first men on the Moon in 1969. But it dropped the idea because of prohibitive costs, and instead opted for a liquid fuel launcher like the mighty Saturn rocket.

It was not until the mid-1970s that the world’s first true RLV — NASA’s crewed space shuttle — took off. Launched like a rocket using giant boosters, the shuttle reached LEO, and after completing its mission used its wings to glide back to the Earth like an aircraft, landing on a runway. The space shuttle and the erstwhile Soviet Union’s spaceplane, Buran, which was test-flown only once before being mothballed, were the only RLVs in those days to fly successfully. As it happened, however, safety concerns and cost overruns eventually grounded the shuttle fleet in 2011, putting paid to the expectations of space scientists of making big strides in reusability technology.

It took the emergence of private industry and space entrepreneurs to rekindle interest in RLV technologies, and players like Space X, Virgin Galactic, and Blue Origin in the US, LandSpace in China, and Arianespace in France ensured significant advances in reusability. Today, several space-faring countries have RLV programmes and have developed reusable launch systems to put reusable spacecraft into orbit. The China National Space Administration is building reusable rockets for manned space missions; France’s Centre National d’Etudes Spatiales has completed testing Themis (a reusable rocket first stage) and Prometheus (a low-cost reusable engine powered by liquid oxygen and methane), and Japan’s JAXA operates a reusable liquid propulsion system for its launchers. Australia is developing a small RLV with scramjet propulsion.

As competition in the space domain hots up, reusability has become the watchword for making satellite launches and space exploration more economical and sustainable. ISRO’s active collaboration with industry partners and research institutions to accelerate India’s RLV programme is an acknowledgement of this. As frontier technologies such as 3D printing and self-monitoring systems driven by artificial intelligence (AI) cut costs dramatically, it will be easier for ISRO’s RLV-ORV to come off the drawing board.

Interestingly, private players in India are keen to fly their own RLVs. The Hyderabad-based ABVYOM, for instance, is ISRO’s first Registered Space Tutor. It plans to test its TSTO Small Reusable Launch Vehicle, India’s first commercialised RLV, with a LEO payload capacity of 1,500 kg by 2027. In 2028, the company aims to fly a TSTO RLV with a booster capable of launching cargo and crew into LEO and landing vertically to facilitate reuse. This expendable heavy lift launcher can also put satellites into a 36,000 km Geostationary Earth Orbit where the satellite appears motionless at a ‘fixed’ position in the sky to observers on the ground.

With ISRO’s support, such initiatives will help establish a vibrant space ecosystem in the subcontinent.

(The writer is former editor of the Indian Defence Review. He writes on aerospace and strategic affairs)