ISRO conducted the Reusable Launch Vehicle Autonomous Landing Mission (RLV-LEX) successfully on April 2, 2023 at the Aeronautical Test Range (ATR) in Chitradurga, Karnataka. This was the first successful test of its kind conducted by ISRO and marks a major milestone in the development of reusable launch vehicles. The RLV-LEX mission involved launching a model of the RLV, which was then brought back to Earth under autonomous guidance. The mission was successful and will pave the way for future launches and development of reusable launch vehicles which will significantly reduce the cost associated with space exploration.
ISRO’s RLV mission took off at 7:10 am IST on a Chinook Helicopter of the Indian Air Force as an underslung load and flew to a height of 4.5 km (above MSL). The predetermined pillbox parameters were attained, based on the RLV’s Mission Management Computer command, and the RLV was released in mid-air, at a down range of 4.6 km. All ten parameters covering position, velocity, altitude and body rates had to be satisfied for the release of the RLV to be successful and autonomous. After its release, the RLV used its Integrated Navigation, Guidance & Control System to perform approach and landing maneuvers and successfully completed an autonomous landing on the ATR air strip at 7:40 AM IST.
The autonomous landing of a Space Re-entry vehicle was an incredible feat, accomplished with exact precision and accuracy. Parameters such as Ground relative velocity, sink rate of Landing Gears, as well as exact body rates that a space vehicle would experience on its return path, were all achieved. This was made possible through the use of state-of-the-art technologies such as accurate Navigation hardware and software, Pseudolite system, Ka-band Radar Altimeter, NavIC receiver, indigenous Landing Gear, Aerofoil honey-comb fins and a brake parachute system.
In a world-first, a winged body was carried to an altitude of 4.5 km by a helicopter and released for an autonomous landing on a runway. The RLV, essentially a space plane with a low lift to drag ratio, required an approach at high glide angles and as such necessitated a landing at high velocities of 350 kmph. In order to make this possible, ISRO developed various indigenous systems such as localized navigation systems based on pseudolite systems, instrumentation and sensor systems. A Digital Elevation Model (DEM) of the landing site with a Ka-band Radar Altimeter provided accurate altitude information as well. Furthermore, extensive wind tunnel tests and CFD simulations were conducted in order to aerodynamically characterize the RLV prior to the flight. The adaptation of contemporary technologies developed for RLV LEX has made other operational launch vehicles of ISRO more cost-effective.
In May 2016, ISRO had demonstrated a major accomplishment in developing Reusable Launch Vehicles (RLV) with the re-entry of its winged vehicle RLV-TD in the HEX mission. During the mission, the vehicle landed on a hypothetical runway over the Bay of Bengal, however precise landing on a runway was an aspect not included. In 2019, the LEX mission achieved the final approach phase that coincided with the re-entry return flight path exhibiting an autonomous, high speed (350 kmph) landing,and this mission has been successful.
The successful test of Reusable Launch Vehicle-Technology Demonstrator (RLV-TD) was made possible due to a great team effort from several major organisations. Along with the Indian Space Research Organization (ISRO), the Indian Air Force (IAF), the Centre for Military Airworthiness and Certification (CEMILAC), the Aerospace Development Establishment (ADE) and the Armament Research and Development Establishment (ADRDE) all contributed to this historic event. The IAF team worked hand in hand with the Project team and multiple sorties were conducted to perfect the achievement of release conditions. Dr. S Unnikrishnan Nair, Director at VSSC, and Shri Shyam Mohan N, Programme Director at ATSP, guided the teams. Dr. Jayakumar M, Project Director at RLV, was the Mission Director for this mission, and Shri Muthupandian J, Associate Project Director at RLV, was the Vehicle Director. Shri Ramakrishna, Director of ISTRAC, was also present during the test. Chairman of ISRO/Secretary of DOS Shri S Somanath witnessed the test and congratulated the entire team on their success.