ISRO Tests Reusable Launch Vehicle For Sustainable Space Exploration

March 29, 2024

The Indian Space Research Organisation (ISRO) successfully carried out its second Reusable Launch Vehicle (RLV) Landing Experiment, named RLV-LEX-02, at the Aeronautical Test Range (ATR) in Chitradurga, Karnataka on March 22, 2024. This follows the trailblazing success of the first landing test, RLV-LEX-01, on April 2, 2023. The vehicle showcased in these tests is expected to be pivotal in a ground-breaking reusable two-stage orbital launch system by 2030. The advancement underscores ISRO's innovative prowess and sets the stage for future sustainable and cost-effective space missions, heralding a new era in space exploration.

As per ISRO, RLV is essentially a spaceplane with a low lift-to-drag ratio requiring an approach at high glide angles that necessitated a landing at high velocities of 350 km. During the recent test, the RLV was put as an underslung to a Chinook Helicopter of the Indian Air Force (IAF). After take-off, the helicopter reached an altitude of 4.5 km, and subsequently, the RLD was released in mid-air. After release 4 km from the runway, the craft autonomously approached the runway along with cross-range corrections. It landed precisely on the runway and came to a halt using its brake parachute, landing gear brakes and nose wheel steering system.

A spaceplane is a combination of aircraft and spacecraft. It can fly as an aircraft close to Earth and as a spacecraft in space. Scientists have been working on the idea of spaceplanes since the 1960s. The US and China are the leading players in this field; however, states like Russia, the UK, Japan, and France are also known to be working on these technologies.

The spaceplane used during the RLV-LEX-02 mission was a 6.5-meter prototype spaceplane. This craft is known by the name Pushpak, and the test was similar to the first test. However, during the second test, the craft undertook more complicated manoeuvres. This included employing cross-range and downrange corrections and landing on the runway in a fully autonomous mode. Also, the test is known to have validated various indigenous technologies critical for a high-speed autonomous landing of a space-returning vehicle. As per ISRO, during this test, they have re-validated multiple technologies they developed in navigation, control systems, landing gear, and deceleration systems essential for performing a high-speed autonomous landing of a space-returning vehicle. A critical takeaway from this mission was that it reused the winged body and all flight systems from the first test, proving their reusability.

ISRO has been working on the RLV program for more than a decade. This program was announced in January 2012 as a technology demonstrator (RLV-TD) program. ISRO is known to have started some initial work on this project in 2006. In January 2007, ISRO successfully undertook a Space Capsule Recovery Experiment (SRE–1) mission. By launching and recovering back (on Earth) this 550 kg capsule, ISRO had demonstrated de-orbiting and recovery capabilities. During this process, ISRO validated various new technologies; from the spaceplane perspective, the technologies validated then, like the reusable thermal protection system, are essential. By 2016, ISRO had successfully tested the scramjet engine, which is significant for this project. During the recent RLV-LEX-02, ISRO's vehicle successfully simulated RLV's approach and high-speed landing conditions, similar to the craft returning from space.

Interestingly, India’s Defence Research and Development Organisation (DRDO) started developing a spaceplane project called AVATAR (Aerobic Vehicle for Hypersonic Aerospace Transportation) in 2001. The design focused on creating a reusable system capable of undertaking at least one hundred launches and atmospheric re-entries. Nothing much is known about this project; it could have been shelved by now. This was an unconnected project to the ISRO’s RLV program. However, DRDO's interest in such a project demonstrates the dual-use nature of the spaceplane. The most apparent use of such systems is to launch small satellites and swarm satellites in space. Such crafts, as fully operational systems, can stay in space for hundreds of days. Perceptibly, spaceplanes could provide militaries with an option of launching on demand.

The US has made major strides in the field of spaceplanes. Boeing built a craft called the X-37B from them. The first mission of this spaceplane took off on April 22, 2010, and the craft was in space for 224 days. This craft's sixth mission (May 17-November 12, 2020) lasted 908 days in orbit. The seventh mission is in progress and has taken off on December 29, 2023. It is important to note that the US Space Force steers these missions under the military's National Security Space Launch program. For all these years, the Pentagon has yet to respond about the nature of this program. Most of these missions were possibly operating at an altitude of 2000 km (in low earth orbit). However, the seventh mission could be operating in new orbital regimes. There are even speculations that this spaceplane could move towards the Moon to drop off a payload. What is known is that the X-37B is carrying out a NASA experiment to study how plant seeds are affected by prolonged exposure to radiation in space.

On December 19, 2023, China embarked into space with the launch of its third spaceplane mission, Shenlong. This latest endeavour builds on a pioneering legacy that began with Shenlong's first voyage in September 2020—a brief, yet possibly experimental, mission that spanned just two days. The second mission dramatically extended its reach, remaining operational for 276 days.

The United States and China are keenly advancing their spaceplane technology, a venture that undeniably harbors strategic implications. These state-of-the-art spacecraft, envisioned as uncrewed space platforms, are poised to undertake many military functions. Beyond their conventional capabilities, they could be adapted for counter-space missions, directly challenging the security dynamics in outer space. Against this backdrop, it becomes imperative for India to adapt and innovate. The development of India's Reusable Launch Vehicle (RLV) program as a dual-use initiative is not just strategic but essential. It ensures that India remains at the vanguard of space technology, capable of leveraging its advancements for both civilian and defense purposes, thereby safeguarding its interests in the rapidly evolving arena of space exploration and security.

Author Note
Group Captain (Retd.) Dr. Ajey Lele, Deputy Director General, The Manohar Parrikar Institute for Defence Studies and Analyses (MP-IDSA), New Delhi. Views are personal.