How Will Gaganyaan’s Thermal Shield Protect the Crew?

Gaganyaan’s crew module will face temperatures of up to 1,800°C during atmospheric re-entry, making its Thermal Protection System (TPS) crucial for keeping the spacecraft and astronauts safe.

Why Does Gaganyaan Need a Thermal Protection System?

• During re-entry, the crew module enters Earth’s atmosphere at about 7,500–8,000 m/s, generating enormous aerodynamic heating.
• More than 99% of the spacecraft’s kinetic energy is dissipated into the atmosphere as heat energy during re-entry.
• The exterior of the crew module may experience temperatures of nearly 1,800°C in some regions.
• Gaganyaan’s TPS, although only about 30–35 mm thick, is designed to keep the module’s structural temperature below about 150°C.
• Re-entry is particularly critical because the crew has very limited time to intervene manually if any system fails.

How Does TPS Protect the Crew Module?

• Thermal Protection Systems are broadly classified as ablative, radiative and heat-sink systems depending on how they manage heat.
• An ablative TPS sacrifices its outer layers, absorbing heat and chemically decomposing into protective char and vapours.
• Escaping gases from the ablative material create an insulating boundary layer that reduces heat transfer into the spacecraft.
• A radiative TPS absorbs heat and then releases it into space as electromagnetic radiation, while remaining structurally intact.
• A heat-sink TPS absorbs and stores thermal energy within the material without melting or changing phase.

Why Does Gaganyaan Use an Ablative TPS?

• Ablative TPS is a proven and highly robust technology suited to Gaganyaan’s single-use crew-module design.
• It can withstand extreme and fluctuating thermal loads without requiring complex or delicate surface maintenance.
• Ablative shielding provides greater tolerance to design variations and reduces the risk of rapid overheating during re-entry.
• Compared with reusable radiative systems, an ablative TPS avoids expensive manufacturing, specialised inspections and complex installation procedures.
• ISRO therefore considers ablative protection a safer and more cost-effective option for human spaceflight re-entry.

Technology Heritage

• ISRO’s Space Capsule Recovery Experiment (SRE) used a carbon-phenolic ablative material to protect the capsule during re-entry.
• The LVM3/CARE mission in 2014 successfully demonstrated crew-module re-entry using an ablative TPS.
• SpaceX’s Crew Dragon also uses an ablative material known as PICA (Phenolic-Impregnated Carbon Ablator).
• Experience from SRE and CARE forms the technological foundation for Gaganyaan’s present thermal protection system.