A couple of days back the Indian Space Research Organisation (ISRO) announced that it had successfully completed its third reusable launch vehicle (RLV) landing experiment (LEX) at the Aeronautical Test Range (ATR) in Chitradurga, Karnataka. This time, it showed that the launch vehicle could land on its own, even in tougher conditions. This mission tested the approach and landing conditions for a vehicle returning from space at high speeds. It confirmed that ISRO had the necessary skills to develop an RLV. Earlier ISRO’s LEX-01 mission on April 2, 2023, and LEX-02 mission on March 22, 2024, had also been executed flawlessly.

Following these successful missions, ISRO announced that the RLV LEX-03 mission had, once again, demonstrated the vehicle’s ability to land autonomously. This time, it performed under tougher conditions, including a wider release range of 500 metres compared to LEX-02’s 150 metres and more challenging wind conditions. The 21-foot-long winged vehicle, called ‘Pushpak’, was dropped from an Indian Air Force Chinook helicopter at a height of 4.5 km, and a similar distance away from the runway. Pushpak then automatically adjusted its course, approached the runway and made a precise horizontal landing right at the centre of the runway.

“As this vehicle has a low lift-to-drag ratio, it had to land at a speed of over 320 km/h. In comparison, commercial planes usually land at around 260 km/h and fighter jets typically land at about 280 km/h. A low lift-to-drag ratio means an aircraft or object generates a relatively smaller lift compared to the drag it experiences, resulting in less efficient flight performance and increased fuel consumption. Drag is the force that resists an object’s motion through air or fluid, slowing it down and requiring energy to overcome,” explained space expert Girish Linganna.

ISRO noted that this mission tested and confirmed an advanced guidance algorithm that corrects errors in both forward and sideways directions. This system is crucial for future missions where vehicles re-enter Earth’s atmosphere from orbit.

“The RLV-LEX uses a combination of sensors, including an inertial sensor, radar altimeter, flush air data system, pseudolite system and NavIC. The space agency highlighted that the RLV-LEX-03 mission reused the winged body and flight systems from the previous LEX-02 mission without any changes. This shows ISRO’s strong ability to design flight systems that can be reused for multiple missions,” added Linganna.

After the success of the LEX program, ISRO’s ‘Reusable Launch Vehicle-Technology Demonstrator’ (RLV-TD) project is set to advance by testing an unmanned Orbital Re-entry Vehicle (ORV). This new vehicle will be about 1.6 times larger than Pushpak. It will be launched into a 400-km orbit within the next two years using a modified geosynchronous satellite launch vehicle (GSLV).

The ORV mission will carry out several experiments in space. These tests are designed to evaluate a heat shield that protects against high temperatures during re-entry into Earth’s atmosphere, as well as a foldable landing gear system.

Over 50 years ago, the idea of reusable launch vehicles emerged. However, it was SpaceX that transformed this concept into reality. In December 2015, SpaceX achieved a historic milestone by successfully landing the first stage of a Falcon 9 rocket vertically on a landing pad at Cape Canaveral. Since then, the restoration of Falcon 9 boosters has become routine, and SpaceX continues to push the boundaries with innovations like the reusable nose cone and the Starship rocket—a fully reusable space vehicle currently in testing.

“An RLV is a vertical (retrograde) multistage launch system that allows for the reuse of some or all of its component stages. Unlike science fiction depictions, we haven't yet created an all-encompassing reusable launch engine that operates both in the air and space. However, progress is underway, with projects like the Sabre engine in development. Reusing the first stage and nose fairing can slash overall launch costs by 30–40 percent. SpaceX's RLV can compete across multiple payload classes (medium, heavy, and transitional) by adjusting boosters and choosing between reusable and disposable options,” said Srimathy Kesan, founder and CEO of Space Kidz India, which is into design, fabrication and launch of small satellites, spacecraft and ground systems.

“Vehicle-Technol India's space agency, ISRO, has been developing the RLV-TD—a scaled-down prototype to test technologies for future reusable launch vehicles. The RLV-TD has undergone successful hypersonic flight experiments, demonstrating crucial aspects like aerodynamic manoeuvring and autonomous landing,” she added.

This expert says that achieving vertical reusability demands intricate engineering and precise landing capabilities. “Other reusable technologies, such as horizontal (winged) launch systems, exist. These use jet aircraft as accelerators, simplifying launch requirements but sacrificing payload mass. SpaceX's success has inspired other players. As the industry evolves, RLVs will continue to shape the future of space exploration, making access to space more sustainable and economically viable,” said Kesan.

Besides India several countries have pursued, or are pursuing, programs similar to ISRO’s RLV-TD. For instance, in the United States, the Space Shuttle is one of the most famous reusable spacecraft programs, that operated from 1981 to 2011 and X-37B is an unmanned, reusable space plane operated by the US Air Force. Similarly in the US SpaceX Falcon 9 and Falcon Heavy were partially reusable launch vehicles with landing boosters and Blue Origin’s New Shepard a reusable suborbital launch vehicle.

In Russia, too Buran which was similar to the US Space Shuttle, only flew once in 1988 and the Federation spacecraft (in development) is a planned partially reusable crewed spacecraft. Also in Europe Space Rider (in development phase) is an unscrewed, reusable space plane by the European Space Agency. China too has a reusable experimental spacecraft which was tested in 2020 but details are limited.

When one compares ISRO’s RLV-TD with other global peers it is a small-scale technology demonstrator, while some other programs (such as Space Shuttle) were full-scale operational systems. “ RLV-TD is primarily focused on demonstrating technologies for future reusable vehicles, while some other programs are or were operational launch systems. In design terms also RLV-TD uses a winged body design similar to the Space Shuttle and X-37B, but different from vertical landing systems, such as SpaceX’s Falcon 9. RLV-TD is still in the early testing phases, while some other programs are operational, or in advanced stages of development. Also like the X-37B, RLV-TD is designed for autonomous operation, unlike crewed systems, such as the Space Shuttle,” pointed out Linganna.

While ISRO’s RLV-TD program is not as advanced as some other countries’ reusable spacecraft programs, it represents a significant step for India in developing this technology. The program aims to reduce launch costs and increase access to space, which aligns with global trends in the space industry.

(With Reporting by The Week)