ISRO successfully conducted the Reusable Launch Vehicle
Autonomous Landing Mission (RLV LEX). The test was conducted at the
Aeronautical Test Range (ATR), Chitradurga, Karnataka in the early hours on 2 April
2023.
The RLV took off at 7:10 am IST by a Chinook Helicopter of
the Indian Air Force as an underslung load and flew to a height of 4.5 km
(above MSL). Once the predetermined pillbox parameters were attained, based on
the RLV's Mission Management Computer command, the RLV was released in mid-air,
at a down range of 4.6 km. Release conditions included 10 parameters covering
position, velocity, altitude and body rates, etc. The release of RLV was
autonomous. RLV then performed approach and landing maneuvers using the
Integrated Navigation, Guidance and control system and completed an autonomous
landing on the ATR air strip at 7:40 AM IST. With that, ISRO successfully
achieved the autonomous landing of a space vehicle.
The autonomous landing was carried out under the exact
conditions of a Space Re-entry vehicle's landing —high speed, unmanned, precise
landing from the same return path— as if the vehicle arrives from space.
Landing parameters such as Ground relative velocity, the sink rate of Landing
Gears, and precise body rates, as might be experienced by an orbital re-entry
space vehicle in its return path, were achieved. The RLV LEX demanded several
state-of-the-art technologies including accurate navigation hardware and
software, Pseudolite system, Ka-band Radar Altimeter, NavIC receiver,
indigenous Landing Gear, Aerofoil honey-comb fins and brake parachute system.
In a first in the world, a winged body has been carried to
an altitude of 4.5 km by a helicopter and released for carrying out an
autonomous landing on a runway. RLV is essentially a space plane with a low
lift to drag ratio requiring an approach at high glide angles that necessitated
a landing at high velocities of 350 kmph. LEX utilised several indigenous
systems. Localised navigation systems based on pseudolite systems,
instrumentation, and sensor systems, etc. were developed by ISRO. Digital
Elevation Model (DEM) of the landing site with a Ka-band Radar Altimeter
provided accurate altitude information. Extensive wind tunnel tests and CFD
simulations enabled aerodynamic characterisation of RLV prior to the flight.
Adaptation of contemporary technologies developed for RLV LEX turns other
operational launch vehicles of ISRO more cost-effective.
ISRO had demonstrated the re-entry of its winged vehicle
RLV-TD in the HEX mission in May 2016. The re-entry of a hypersonic sub-orbital
vehicle marked a major accomplishment in developing Reusable Launch Vehicles.
In HEX, the vehicle landed on a hypothetical runway over the Bay of Bengal.
Precise landing on a runway was an aspect not included in the HEX mission. 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. The
LEX began with an Integrated Navigation test in 2019 and followed multiple
Engineering Model Trials and Captive Phase tests in subsequent years.
Along with ISRO, IAF, CEMILAC, ADE and ADRDE contributed
to this test. The IAF team hand in hand with the Project team and multiple
sorties were conducted to perfect the achievement of release conditions. Dr. S
Unnikrishnan Nair, Director, VSSC, and Mr. Shyam Mohan N, Programme Director,
ATSP guided the teams. Dr. Jayakumar M, Project Director, RLV was the Mission
Director, and Mr. Muthupandian J, Associate Project Director, RLV was the
Vehicle Director for the mission. Mr. Ramakrishna, Director, ISTRAC was present
on the occasion. Chairman, ISRO/Secretary, DOS Mr. S Somanath witnessed the
test and congratulated the team.
With LEX, the dream of an Indian Reusable Launch Vehicle
arrives one step closer to reality.
