India’s Gaganyaan mission represents a major milestone in human spaceflight. During atmospheric re-entry, the crew module will experience extreme heating, and ISRO’s ablative Thermal Protection System (TPS) will protect astronauts by reducing heat transfer and maintaining safe internal conditions.
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Why Re entry is Challenging
- High Velocity: Capsule re‑enters at 7,500–8,000 m/s, converting kinetic energy into heat.
- Extreme Temperatures: Outer surface faces ~1,800°C, risking structural failure.
- No Abort Option: Once descent begins, crew cannot intervene; systems must be fully reliable.
- Rapid Deceleration: Constantly changing forces make manual correction impossible.
How the Thermal Protection System Works
- Ablative Shield:
- Absorbs heat and decomposes into char + vapours, carrying heat away.
- Creates a cooler boundary layer to block heat transfer.
- Thickness: 30–35 mm, keeps module interior below 150°C.
- Materials: Carbon phenolic and silica phenolic used; similar to SpaceX Crew Dragon’s PICA shield.
- ISRO Heritage: Demonstrated in SRE (2007) and CARE (2014) missions.
- Other TPS Types:
- Radiative: Re‑emits absorbed heat as infrared radiation (used in reusable vehicles).
- Heat Sink: Absorbs heat without phase change (e.g., copper/aluminium).
Challenges
- Material Testing: DRDO reports that ablative materials must withstand >1,800°C without structural cracks.
- Reliability: NASA data shows ~20% of spacecraft failures occur during re‑entry phase.
- Single‑Use Limitation: Ablative shields cannot be reused, increasing mission costs.
- Integration: Ensuring TPS bonds with module structure under high stress is critical.
Way Forward
- Advanced Materials: Invest in lightweight composites; ISRO exploring ceramic matrix composites.
- Reusable TPS: Long‑term goal to develop radiative/reusable shields for cost efficiency.
- Simulation & Testing: Expand hypersonic wind tunnel facilities; NITI Aayog (2025) recommended more test centres for aerospace.
- International Collaboration: Learn from NASA, ESA, and JAXA on reusable TPS technologies.
Conclusion
The ablative heat shield is ISRO’s proven choice to ensure astronaut safety, combining simplicity and robustness to withstand the fiery re‑entry of Gaganyaan.
