Gaganyaan Thermal Protection System (TPS), Need, Types, Working

The Gaganyaan mission’s Thermal Protection System (TPS) is in focus for its critical role in protecting the Crew Module during atmospheric re-entry

About Gaganyaan Thermal Protection System (TPS)

The Gaganyaan Thermal Protection System (TPS) is a critical safety system that protects the Crew Module and astronauts from the extreme heat generated during atmospheric re-entry, ensuring their safe return to Earth.

Gaganyaan Thermal Protection System (TPS) Need 

The need for the Gaganyaan Thermal Protection System (TPS) arises from the extreme conditions faced by the Crew Module during its return to Earth.

• The Crew Module will re-enter the atmosphere at around 7,500-8,000 m/s, carrying enormous kinetic energy. More than 99% of this kinetic energy will be dissipated into the atmosphere as heat, creating extremely high thermal loads around the spacecraft.
• Even the small portion of heat directed back towards the Crew Module can be intense enough to melt its outer structure without adequate protection. As a result, some regions of the Crew Module may experience temperatures of up to 1,800°C during re-entry.
• The situation is more challenging because re-entry is extremely fast and the deceleration forces continuously change. This leaves astronauts very little time to manually identify and correct a sudden system abnormality. Moreover, once atmospheric descent begins, there is no provision to abort the mission.

Therefore, the Crew Module must be capable of withstanding these extreme conditions through reliable onboard systems. The TPS plays the crucial role of managing the intense re-entry heat and protecting the spacecraft’s structure, keeping its temperature below about 150°C despite the extreme conditions outside.

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Gaganyaan Thermal Protection System (TPS) Types and Working 

The TPS protects the Crew Module by absorbing, removing or managing the heat generated during re-entry. It is broadly classified into three types based on how it deals with this heat.

• Ablative TPS: It absorbs extreme heat and gradually sacrifices its outer material through chemical and physical decomposition. The material forms a protective char layer, while escaping gases carry heat away and create a cooler boundary layer that reduces further heat transfer to the Crew Module.
• Radiative TPS: It absorbs the intense heat and releases it back into space as electromagnetic radiation, mainly infrared radiation. Unlike an ablative system, it remains largely intact without melting or degrading, making it suitable for reusable re-entry vehicles.
• Heat-Sink TPS: It absorbs and stores the heat, raising its own temperature without melting or changing its physical state. Copper and aluminium are examples of heat-sink materials.

Why Does Gaganyaan Use an Ablative TPS?

The Gaganyaan Crew Module uses an ablative TPS because it is a proven and robust technology suited to the single-use design of the Crew Module.

• Handles extreme heat: It can withstand extreme and fluctuating heat loads during re-entry.
• Protects the structure: It gradually sacrifices its outer material, carrying heat away while protecting the structure underneath.
• Requires less maintenance: Unlike reusable thermal protection systems, it does not require complex maintenance and specialised inspection after use.
• Greater tolerance: Radiative systems are less forgiving of design errors, as localised overheating can quickly cause dangerous heat transfer.
• Safe and cost-effective: The ablative approach provides a suitable combination of safety, reliability and cost-effectiveness for Gaganyaan.

The choice also builds on India’s earlier re-entry experience. The Space Capsule Recovery Experiment (SRE) used carbon-phenolic ablative material on its nose cap, where heat flux was highest. This experience was further strengthened by the LVM-3/CARE mission in 2014, which successfully demonstrated Crew Module re-entry using an ablative TPS. Globally, the same approach is also used in SpaceX’s Crew Dragon, which employs Phenolic Impregnated Carbon Ablator (PICA).