Gaganyaan’s Thermal Protection System
Prelims:
Science &
Technology
Mains:
GS Paper III:
Science & Technology, Indigenisation of technology and development of new
technology
Current relevance:
The Gaganyaan crew module will face extreme heat during atmospheric re-entry. To protect the spacecraft and its crew, it will use an ablative Thermal Protection System (TPS) that absorbs and dissipates heat while maintaining the module’s structural integrity and safe internal conditions.
Highlights:
Atmospheric Re-entry Challenges:
1.
The
Gaganyaan crew module will enter Earth's atmosphere at an extremely high
velocity of about 7,500–8,000 m/s.
2.
More
than 99% of its kinetic energy will be dissipated into the atmosphere as
heat, but even the small portion directed back towards the module could
melt it without adequate protection.
3.
Some
exterior regions of the crew module may experience temperatures as high as 1,800°C.
4.
Once
atmospheric descent begins, there is no provision to abort the mission,
while the rapid descent and continuously changing deceleration forces provide
little scope for manual crew intervention.
5.
Therefore,
the spacecraft's systems must be sufficiently robust and reliable to
withstand extreme re-entry conditions.
Ablative Heat Shield Working mechanism:
1.
Gaganyaan uses an ablative Thermal Protection System, which
protects the spacecraft by sacrificing its outer layers through physical
and chemical processes.
2.
The TPS absorbs intense thermal energy and chemically decomposes to form
solid char and outgassing vapours, carrying heat away as the material
burns off.
3.
The escaping gases also create a cooler boundary layer, reducing
the transfer of intense heat into the crew module.
4.
Despite being only around 30–35 mm thick, the TPS is designed to
maintain structural integrity by keeping the module's temperature safely
below 150°C.
5.
Carbon phenolic and silica phenolic are examples of ablative thermal-protection
materials.
Types of Thermal Protection Systems:
A TPS is
predominantly classified into three types depending on how it removes
heat:
1.
Ablative
TPS: Removes heat by
allowing protective material to decompose and shed its outer layers. It
is primarily a single-use system.
2.
Radiative
TPS: Absorbs re-entry
heat and releases it back as electromagnetic radiation, mainly infrared.
Since it remains intact, it is suitable for reusable re-entry vehicles.
3.
Heat
Sink TPS: Protects the
spacecraft by absorbing thermal energy and increasing its own temperature
without melting or undergoing a phase change; copper and aluminium are
examples.
Reasons for the Selection of Ablative TPS
for Gaganyaan:
1.
An ablative TPS is a proven and highly robust solution suited to
Gaganyaan's single-use crew module design.
2.
It can withstand extreme and fluctuating thermal loads without
requiring complex or delicate surface maintenance.
3.
Compared with reusable radiative systems, it avoids expensive
manufacturing, specialised inspection and complex installation processes,
making it a safer and more cost-effective option.
4.
ISRO has prior experience with ablative technology: the Space Capsule
Recovery Experiment (SRE) used carbon phenolic material, while the LVM-3/CARE
mission in 2014 successfully demonstrated crew-module re-entry using an
ablative TPS.
5.
These experiences provide the technological foundation for the
thermal protection system being used in Gaganyaan.
Source: THE HINDU - https://www.thehindu.com/sci-tech/science/how-gaganyaans-thermal-protection-system-will-survive-re-entry-explained/article71369185.ece