The Gaganyaan crew module, which houses the astronauts, orbits the Earth at a velocity of about 7,800 metres per second. On its return, the module must shed this immense kinetic energy during re-entry.

Atmospheric drag acts as the primary brake, dissipating most of the energy through aerobraking. Once the module descends below 12 kilometres altitude, a multi-stage parachute system is deployed, initiated by pyro-actuated mortars, to further reduce velocity for a controlled landing.

A recovery system is essential to ensure a safe touchdown, whether at sea or on land. It includes parachutes, locating devices to identify the splashdown site, and an up-righting system to maintain the correct orientation in case of a sea landing.

Crew modules such as SpaceX Dragon, NASA Orion, and India’s Gaganyaan are designed for sea landings. For land-based recovery, additional braking motors or inflated airbags are used to reduce impact velocity. Russian Soyuz and Chinese Shenzhou modules employ retro-rockets to achieve controlled terrestrial landings.

Parachutes alone are insufficient for land landings because the ground is unforgiving. A safe terrestrial touchdown requires velocities as low as 1 to 2 metres per second, whereas sea landings can tolerate higher speeds of 7 to 9 metres per second thanks to water’s natural energy absorption.

Reducing velocity to below 2 metres per second using parachutes alone is impractical due to the inverse-square relationship between speed and drag area. To slow a module from 7 metres per second to 1 metre per second would require a parachute nearly 49 times larger, which is both unmanageable and prone to deployment issues.

The landing zone is elliptical rather than pinpoint. This is because the module’s kinetic energy is concentrated along its flight path. At hypersonic speeds, small variations in atmospheric density or re-entry conditions can cause overshooting or undershooting by hundreds of kilometres. Lateral deviations are minimal, resulting in an elongated landing footprint along the trajectory.

Selecting sea or land as a landing site involves balancing geography, safety, and logistics. Land landings demand vast, uninhabited areas to avoid populated zones, but they allow easier crew recovery and faster refurbishment of the module.

Sea landings are favoured by nations without large deserts or plains, though they require extensive logistics such as recovery ships, flotation bags, and specialised equipment to ensure crew safety in rough waters.

Crew training covers both nominal landings and emergency aborts. Astronauts are prepared to exit the module under stressful conditions such as fire or leaks. Training includes removing pressure suits, donning waterproof gear, and deploying life rafts.

Off-course landings in remote areas are mitigated by a 48-hour survival kit containing rations, medical supplies, and signalling tools like satellite phones, flares, flashlights, mirrors, and whistles. In extreme cases, parachutes can be repurposed as tents. Some missions, such as Soyuz, even provide firearms for protection against wildlife.

The up-righting system ensures the module floats correctly after splashdown. Ideally, modules are monostable, naturally flipping upright due to a low centre of gravity. However, many are multi-stable and risk floating upside down. To counter this, up-righting floats are inflated at the top of the module, pushing it into the correct orientation.

Locating a floating module in the ocean is challenging due to waves and currents. Recovery teams rely on predictive tracking, electronic signalling, and visual aids. The module transmits GPS coordinates and homing signals via radio beacons, while releasing bright green fluorescent dye for aerial spotting.

At night or in poor visibility, high-intensity strobe lights are used. To enhance visibility against the sea, the module and flotation bags are painted international orange.

The Gaganyaan recovery operation will be led by the Indian Navy with other stakeholders. After parachute-assisted descent, the module will splash down in the Bay of Bengal. Parachutes will be released immediately to prevent entanglement, and flotation bags will inflate automatically to keep the module upright.

The module will transmit GPS and beacon signals while releasing sea marker dye for aerial spotting. Naval divers will then secure the module with a flotation collar and towing gear, enabling it to be winched onto a ship’s deck for safe crew extraction in a nominal mission.

This comprehensive system of aerobraking, parachutes, flotation devices, signalling aids, and naval recovery ensures that Gaganyaan astronauts can return safely to Earth.

Agencies