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Relevance: GS-III (Science & Technology, ISRO Missions, Space Tech) Source: ISRO Space Mission Updates, 2026

1 · What is the scientific challenge?

When ISRO’s Gaganyaan spacecraft returns to Earth, it will plunge into our atmosphere at a blistering speed of 8,000 meters per second. This extreme friction will create a massive fireball around the capsule, with outside temperatures reaching a deadly 1,800°C.

The terrifying part? Once the capsule starts falling, there is absolutely no “abort” button. To ensure the astronauts survive this fiery descent, ISRO relies on a miraculous, 35-millimeter thick barrier called the Thermal Protection System (TPS). Understanding how this specific heat shield works is crucial, as it represents the peak of India’s indigenous space engineering and materials science.

2 · How the Heat Shield Works

Step 1: The Re-entry Fireball
The capsule hits the Earth’s thick atmosphere at hyper-speeds, converting kinetic energy into extreme heat (up to 1,800°C) on its outer surface.
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Step 2: The Sacrificial Burn
Instead of reflecting heat, Gaganyaan’s special “Ablative” shield intentionally absorbs the heat and slowly begins to burn, melt, and char away.
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Step 3: The Gas Buffer
As the shield burns, it releases gases. These escaping gases create a cool protective layer (a buffer) around the capsule, pushing the extreme heat away.
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Step 4: Safe Cabin Temperatures
Thanks to this brilliant chemical burning process, the inside of the cabin stays at a very safe and comfortable temperature below 150°C for the astronauts.

3 · Types of Space Heat Shields

Ablative TPS
The Sacrificial Shield
A single-use shield that chemically burns and chars away to carry the heat off. This is the exact robust technology being used for India’s Gaganyaan.
Radiative TPS
The Reusable Reflector
This shield absorbs heat and bounces it back into space without melting. It is reusable (like the US Space Shuttle) but very fragile and expensive to maintain.
Heat Sink TPS
The Thermal Sponge
Made of heavy metals like copper, it works like a sponge to simply soak up the heat without melting. Rarely used today because it is too heavy for rockets.
Why ISRO Chose Ablative
Compact & Safe
Since Gaganyaan is a single-use capsule, an ablative shield is much safer, highly reliable, and incredibly thin (just 30-35 mm), saving precious weight.

Prelims Quick Facts: Gaganyaan Mission Profile
The Core Mandate Gaganyaan aims to send a crew of three members to a Low Earth Orbit of 400 km for a 3-day mission, followed by a safe sea splashdown.
The Launch Vehicle The mission will use a specially modified, highly reliable rocket called the Human Rated LVM3 (HLVM3).
Past Testing (CARE) ISRO isn’t doing this blindly. They successfully tested this exact heat shield technology back in 2014 during the Crew Module Atmospheric Re-entry Experiment (CARE).
The Material Used ISRO uses specialized carbon phenolic tiles for the front of the shield, which bravely take the maximum brunt of the 1,800°C heat.

MCQ Practice Question
Q. With reference to ISRO’s Gaganyaan mission and its Thermal Protection System (TPS), consider the following statements:

  1. The crew module utilizes a Radiative Thermal Protection System because the capsule is designed to be reusable for future missions.
  2. An ablative heat shield protects the spacecraft by chemically decomposing and burning its outer layers to carry heat away.
  3. The Gaganyaan mission is designed to carry a crew of three members to a 400 km orbit.

Which of the statements given above is/are correct?
(a) 1 and 2 only    (b) 2 and 3 only    (c) 1 and 3 only    (d) 1, 2 and 3

Answer: (b) 2 and 3 only

  • Statement 1 — Incorrect (the trap): Gaganyaan uses an Ablative (single-use) TPS, not a Radiative one. The Gaganyaan crew module is specifically designed for a single-use mission.
  • Statement 2 — Correct: Ablative shields work like a sacrificial barrier, intentionally burning and releasing cooling gases to protect the inside of the cabin.
  • Statement 3 — Correct: The core mandate of the mission is indeed a 3-member crew, 3-day mission, in a 400 km Low Earth Orbit.
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