Over the weekend Indian Space Research Organisation (ISRO) has successfully completed the Reusable Launch Vehicle Autonomous Landing Mission (RLV LEX), when it landed in Autonomous mode at the Aeronautical Test Range (ATR) located in Chitradurga, Karnataka which was the site of a test that took place during the early hours on April 2, 2023.
The RLV was lifted by an Indian Air Force (IAF) CH-47 Chinook helicopter as an underslung load and ascended to a height of 4.5 km (above MSL). When the RLV’s Mission Management Computer command met the predetermined Pillbox Parameters, it was released in the air, 4.6 km away from the target.
The RLV was released autonomously, following 10 release conditions that included position, velocity, altitude, and body rates. The Integrated Navigation, Guidance & control system was used to perform approach and landing maneuvers, and the RLV achieved an autonomous landing on the ATR air strip at 7:40 AM IST.
This successful landing marked a significant achievement for ISRO in the autonomous landing of a space vehicle. This autonomous landing was executed in conditions similar to that of a Space Re-entry vehicle’s landing, which involves a high-speed, unmanned and precise landing on the same return path.
The landing parameters were also achieved, simulating the velocity of the ground relative to the vehicle, the sink rate of the landing gears, and precise body rates similar to those experienced by an orbital re-entry space vehicle during its return path.
The RLV LEX utilized advanced technologies such as accurate navigation hardware and software, a Pseudolite system, a Ka-band Radar Altimeter, a NavIC receiver, an indigenous Landing Gear, Aerofoil honey-comb fins, and a brake parachute system.
A historic event has taken place where a helicopter carried a winged body to a height of 4.5 km and then released it to autonomously land on a runway. The winged structure is a type of space plane that has a low lift to drag ratio, which means that it needs to approach at a high glide angle and land at a velocity of 350 kmph.
To achieve this, ISRO developed several indigenous systems such as navigation, instrumentation, and sensor systems, based on pseudolite systems.
They also used a Digital Elevation Model to provide accurate altitude information. Extensive wind tunnel tests and CFD simulations were conducted to characterize the aerodynamics of the space plane prior to flight.
Other launch vehicles of ISRO become more economical with the utilization of advanced technologies designed for the space plane.
During the HEX mission in May 2016, ISRO successfully showcased the re-entry of its winged vehicle RLV-TD, thereby achieving a significant milestone in the development of Reusable Launch Vehicles.
The vehicle was able to land on a hypothetical runway located over the Bay of Bengal, which was not a part of the original mission objectives. However, the subsequent LEX mission achieved a precise landing on a runway, with an autonomous and high-speed (350 kmph) approach. In 2019, the LEX mission conducted an Integrated Navigation test, and in the subsequent years, it carried out various Engineering Model Trials and Captive Phase tests.
The possibility of an Indian Reusable Launch Vehicle becoming a reality has moved a step closer with the introduction of LEX.