Context: The Gaganyaan crew module will use a multi-stage parachute system to safely decelerate astronauts during atmospheric re-entry and landing.
- Atmospheric drag removes much of the spacecraft's velocity, but parachutes are required for controlled deceleration and soft landing.
- Crew-rated parachutes require redundancy, multi-stage deployment, high-strength materials and reliable packing mechanisms because failure can directly threaten astronaut safety.
How Are the Parachutes Deployed?
The Gaganyaan recovery system uses three types of parachutes:
- Pilot parachute: A small chute that is ejected first and helps pull out the larger drogue or main parachutes.
- Drogue parachute: Deployed earlier during descent to stabilise the crew module and reduce its velocity.
- Main parachute: Has a much larger canopy and provides the final deceleration required for a safe soft landing.
Overcoming the Turbulent Wake
- The crew module's blunt-body shape generates a turbulent wake behind it during atmospheric descent.
- Parachutes must be ejected through this wake and reach the far-wake region before deployment.
- The ejection mechanism must therefore provide sufficient energy to move the parachute through the turbulent flow rapidly and reliably.
- Parachutes are generally deployed after the module has slowed to below the speed of sound, reducing aerodynamic loads during opening.
Why Are Parachutes Deployed in Stages?
- In the lower atmosphere, the Gaganyaan crew module may still travel at around 170 m/s.
- Deploying a full-sized main parachute at such velocity could generate a severe opening shock, potentially damaging the canopy or subjecting astronauts to dangerous deceleration.
- Multi-stage deployment progressively increases parachute size while keeping dynamic pressure within acceptable limits.
Controlled Canopy Inflation
- A cord can initially restrict the expansion of a parachute canopy, preventing it from opening too rapidly.
- After a predetermined delay, a timed cutter severs the restraining cord.
- As the cord loosens, the canopy progressively expands or blooms fully after the vehicle has slowed sufficiently.
How Are Gaganyaan Parachutes Tested?
- Rail Track Rocket Sled
- A Rocket-Propelled Rail Track System (RTRS) accelerates a sled along rails using small solid rocket motors before deploying the parachute at the required velocity.
- The Terminal Ballistics Research Laboratory (TBRL), Chandigarh, has an advanced RTRS facility.
- Aerial and Rocket Tests
- Test articles can be dropped from helicopters or aircraft to simulate required deployment conditions.
- Small rocket-powered test vehicles can also carry a crew-module test article to a specified altitude before releasing it for parachute deployment tests.
- Post-Landing Parachute Release
- After landing or sea splashdown, an attached parachute could become hazardous because wind may drag the module across land or capsize it in water.
- The system therefore incorporates rapid parachute-release mechanisms.
- Pyrotechnic cutters or mechanical quick-release devices can detach the parachutes after touchdown.
Materials Used in Aerospace Parachutes
Parachute materials must balance tensile strength, thermal resistance, elasticity, compressibility and low mass.
- Kevlar: Used in high-load suspension lines, risers and reinforcement tapes because of its high tensile strength and heat resistance.
- Nomex: Used in areas exposed to high temperatures, including regions subjected to hot gas discharge and aerothermal heating.
- Nylon: Widely used for canopy fabric because its elasticity helps absorb initial inflation shocks; its compressibility also allows compact packing.
Gaganyaan’s Parachute Configuration
- The crew module uses redundant clusters of pilot, drogue and main parachutes to provide multiple layers of safety.
- Two drogue parachutes are deployed using mortars.
- Three main parachutes are deployed through mortar-ejected pilot parachutes.
- If one main parachute develops an anomaly, the two remaining independent parachute chains are designed to provide sufficient capability for safe touchdown.
- The Aerial Delivery Research and Development Establishment (ADRDE), Agra, a Defence Research and Development Organisation (DRDO) laboratory, is responsible for developing the parachute system.
Relevant Concept: Dynamic Pressure
- Dynamic pressure is the aerodynamic pressure generated by moving through the atmosphere and is proportional to air density and the square of velocity.
- It rises significantly with increasing velocity, making premature deployment of a large parachute potentially dangerous.
- Staged deployment allows the spacecraft to reduce velocity progressively before exposing the main canopy to high aerodynamic loads.
