Gaganyaan module faces extreme heat, must survive re-entry

The Gaganyaan crew module will hit the Earth's atmosphere at a speed of 7,500 to 8,000 metres per second during re-entry. The Hindu reports that more than 99% of this kinetic energy is dissipated into the atmosphere as heat, but the small fraction directed back at the module is intense enough to melt it without a robust thermal protection system (TPS).

The TPS uses two methods: ablation, where material sacrificially chars and erodes to carry heat away, and thermal insulation, which uses low-conductivity materials to block heat from reaching the capsule's structure. The module must hit a precise re-entry corridor: too shallow and it bounces off the atmosphere, too steep and lethal deceleration and heat exceed survival limits. A communication blackout occurs when ionised plasma blocks radio signals, lasting until the capsule slows enough for the plasma to dissipate.

ISRO demonstrated re-entry capability with its 2007 Space Capsule Recovery Experiment. The Gaganyaan mission will use parachutes to slow the module from terminal velocity, still hundreds of kilometres per hour, to a soft landing in the sea. The precise launch date for the crewed mission is awaited.