How Gaganyaan’s thermal protection system will survive re-entry | Explained
Details have emerged on the design of the Thermal Protection System (TPS) that will shield Gaganyaan's Crew Module during atmospheric re-entry.
The Crew Module — India's first human-rated spacecraft, built to carry a three-member crew — uses an ablative heat shield that chars and erodes to dissipate the extreme heat of re-entry.
Three candidate ablative materials — Carbon Phenolic (CP), Silica Phenolic (SP), and Medium Density Silica Phenolic (MDSP) — were tested in ISRO's Plasma Wind Tunnel facility under simulated re-entry heat flux conditions to select the final configuration.
The Crew Module uses a sphere-cone shape: the blunt base creates a detached shockwave that deflects intense heat away from the vehicle, while the conical section helps manage lift and reduce g-forces on astronauts during descent.
Ablative Thermal Protection Systems (TPS)
An ablative heat shield protects a re-entry vehicle by intentionally burning away (ablating) a sacrificial outer layer. As the material chars, melts, and erodes, it carries heat energy away from the vehicle instead of conducting it inward, keeping the crew cabin at survivable temperatures during hypersonic re-entry (speeds can exceed Mach 20, with surface temperatures rising to several thousand degrees Celsius).
Key Details
- Ablative composites tested for Gaganyaan include Carbon Phenolic (CP), Silica Phenolic (SP), and Medium Density Silica Phenolic (MDSP); CP showed the lowest surface erosion in wind-tunnel tests among the three.
- Lighter medium-density silica phenolic tiles are used on the leeward (lower-heating) side of the capsule to save weight, while heavier, more heat-resistant material covers the windward (high-heating) side.
- This ablative approach mirrors the heritage of India's earlier Space Capsule Recovery Experiment (SRE-1, 2007), which validated re-entry and recovery technology, and is analogous internationally to NASA's Apollo-era ablative shields and PICA (Phenolic Impregnated Carbon Ablator) used on modern capsules like SpaceX's Dragon.
The TPS is the single most safety-critical subsystem for Gaganyaan because it is the only barrier between the astronauts and re-entry heating; the choice of ablative material and its testing regime directly determines crew survivability during descent.
Gaganyaan Mission Architecture
Gaganyaan is ISRO's Human Spaceflight Programme, designed to independently demonstrate India's capability to send a crew of astronauts to Low Earth Orbit (LEO) and return them safely to Earth. The Crew Module is a double-walled, human-rated capsule that serves as the habitable module for astronauts during flight.
Key Details
- The mission targets sending a three-member crew to roughly a 400 km LEO for a short-duration mission before a safe splashdown.
- The programme has progressed through uncrewed test flights, including the Crew Module Atmospheric Re-entry Experiment and Test Vehicle abort missions, to validate the crew escape system and re-entry systems ahead of the crewed flight.
- The Crew Module's sphere-cone aerodynamic configuration (used by most crewed capsules globally) creates a detached bow shockwave at the blunt end that deflects the bulk of re-entry heat away from the vehicle surface.
The current milestone — TPS material finalisation and testing — is a precursor validation step in the sequence of uncrewed test flights that must be completed before ISRO commits to launching a crewed Gaganyaan mission.
- Gaganyaan aims to place a three-member crew in an approximately 400 km Low Earth Orbit.
- Three ablative TPS candidate materials were tested: Carbon Phenolic (CP), Silica Phenolic (SP), and Medium Density Silica Phenolic (MDSP).
- Wind-tunnel tests were conducted at a simulated heat flux of 150 W/cm² for a duration of 180 seconds; CP recorded the lowest surface recession (1.8 mm) among the three materials tested.
- The Crew Module uses a sphere-cone configuration, the same basic aerodynamic shape used by crewed capsules internationally (e.g., Apollo, Soyuz, Dragon).