A reusable rocket brings its costly parts back to fly again; ISRO is testing this idea with a winged vehicle, the RLV, designed to land on a runway.
Almost every rocket India has flown is used once. Its stages fall into the sea and a new rocket is built for the next launch. A reusable launch vehicle is designed to come back and fly again, so less hardware is thrown away.
ISRO's Reusable Launch Vehicle (RLV) programme is building a winged craft that ISRO describes as a space plane. The idea is that it returns from space, glides through the atmosphere and lands on a runway by itself.
The first big test came in May 2016. The RLV-TD flew the hypersonic experiment HEX and re-entered the atmosphere. That flight ended with a landing on an imaginary runway over the Bay of Bengal; a real runway landing was not part of the test.
Next, ISRO tested the landing itself at the Aeronautical Test Range in Chitradurga, Karnataka. Each time, an Indian Air Force Chinook helicopter carried the vehicle up and released it at 4.5 km.
LEX-03 used NavIC among its navigation sensors.
ISRO says the guidance methods proven in these tests are needed for its future orbital re-entry mission. Landing from a 4.5 km drop is the last few minutes of a real return. Coming back from orbit means first surviving the heat of re-entry.
Look out for RLV test flights alongside the regular PSLV, GSLV and LVM3 launches. See upcoming ISRO launches
The landing tests covered only the very end of a return from space. Compare the energy per kilogram.
Released at 4.5 km. Potential energy = g × h = 9.81 × 4,500 ≈ 44 kJ/kg.
Touchdown at about 350 km/h (LEX-01). v = 350 / 3.6 ≈ 97.2 m/s; kinetic energy = ½v² ≈ 4.7 kJ/kg. Most of the 44 kJ/kg was lost to drag on the way down, which is how a glider controls its descent.
Returning from a 400 km orbit. ½v² at 7.67 km/s ≈ 29.4 MJ/kg — about 670 times the LEX drop energy. That is why a full RLV needs a heat shield, and why HEX in 2016 focused on hypersonic re-entry.
Landing speed. LEX-03's touchdown at over 320 km/h compares with about 260 km/h for a commercial airliner. Kinetic energy grows with v², so (320/260)² ≈ 1.5 — about 50% more energy per kilogram to absorb on the runway. ISRO describes the RLV as a space plane with a low lift-to-drag ratio, so it comes in fast.
Cross-range. Releasing the vehicle 500 m off the runway centreline (against 150 m in LEX-02) tests whether the guidance can correct sideways errors as well as distance errors. A real returning vehicle will never arrive exactly on the centreline.
Reuse. LEX-02 reused the LEX-01 vehicle after certification. LEX-03 reused the LEX-02 vehicle with no changes at all. Reflying the same hardware is the whole point of a reusable rocket, and these tests were its first demonstration in India.
At the Aeronautical Test Range, Chitradurga, Karnataka. An Indian Air Force Chinook helicopter carried it to 4.5 km and released it.
It was released 500 m to the side instead of 150 m, so the vehicle had to correct a larger cross-range error while landing autonomously.
From orbit, a vehicle carries about 29 MJ of energy per kilogram, hundreds of times more than a 4.5 km drop, and must survive re-entry heating before it ever reaches the landing phase.