How will Gaganyaan’s thermal shield protect the crew?, Pg12

Key Highlights:

• The Gaganyaan crew module will face extreme temperatures of up to 1,800° C during atmospheric re-entry.
• It will re-enter the Earth's atmosphere at a speed of 7,500-8,000 m/s, dissipating over 99% of its kinetic energy as heat.
• A robust Thermal Protection System (TPS), only 30-35 mm thick, is essential to keep the module's internal temperature below 150° C.
• The Gaganyaan mission will utilize an ablative TPS for its crew module.
• This choice leverages ISRO's proven expertise from missions like Space Capsule Recovery Experiment (SRE) and Crew Module Atmospheric Re-entry Experiment (CARE).

Detailed Insights:

• Atmospheric re-entry is a critical phase for space capsules, characterized by rapid deceleration and intense heat generation.
• Unlike rocket ascent, re-entry offers limited scope for crew intervention due to its speed and constantly changing deceleration forces.
• An ablative TPS functions by chemically decomposing and sacrificing its outer layers, forming a protective char and releasing cooling gases.
• These escaping gases create a cooler boundary layer, acting as a buffer against the intense external heat.
• ISRO's LVM-3/CARE mission in 2014 successfully demonstrated the re-entry of a crew module using ablative TPS technology.
• Radiative TPS systems absorb heat and then release it back into space as electromagnetic radiation, ideal for reusable vehicles.
• Heat sink TPS absorbs thermal energy by raising its own temperature without melting or changing its physical state.
• The ablative TPS was chosen for Gaganyaan due to its proven robustness, cost-effectiveness, and suitability for a single-use design.

Scientific/Technical Concepts Involved:

• Thermal Protection System (TPS): A critical shield designed to protect spacecraft from extreme heat generated during atmospheric re-entry.
• Ablative TPS: A single-use system that dissipates heat by burning off its outer layers, forming a protective char and releasing cooling gases.
• Radiative TPS: A system that absorbs re-entry heat and radiates it back into space, typically used for reusable spacecraft.
• Heat Sink TPS: A system that absorbs thermal energy by increasing its own temperature without undergoing a phase change.