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Human spaceflight and space stations
Human spaceflight: India's crewed programme and its test flights, space stations, astronauts on foreign missions, and keeping a crew alive in orbit and bringing it home. Prelims has asked about Gaganyaan and other microgravity missions.
UPSC has asked
- Prelims 2025: Axiom-4, SpaDeX and Gaganyaan as microgravity missions
21 Aug 2026 · Prelims and Mains
Gaganyaan
Gaganyaan is the first human spaceflight programme of the Indian Space Research Organisation (ISRO), and it will carry a crew module to low Earth orbit and bring it back. The programme is being proved in stages, and each test clears one of the things that can kill a crew.
- The first uncrewed flight, carrying the half humanoid Vyommitra, is targeted for the last quarter of 2026, with two more uncrewed flights and the first crewed flight by 2027.
- The crew escape test TV-D1 and two parachute air drop tests are done, and TV-D2 is in progress.
- Every stage of the human-rated LVM3 (Launch Vehicle Mark-3) has been ground tested.
The Hindu, 21 Aug 2026: How Gaganyaan's heat shield will protect the crew (opens in a new tab) · PIB, 5 Aug 2026: Gaganyaan timeline and Bharatiya Antariksh Station (opens in a new tab)
21 Aug 2026 · Prelims and Mains
Re-entry heat shielding
Coming home is the most demanding part of the flight, because the whole energy of orbit has to be shed as heat in a few minutes. The crew module meets the atmosphere at 7,500 to 8,000 metres a second, which takes its outside to about 1,800 °C while the structure beneath has to be held below 150 °C.
Ablative
- The surface chars and burns away, taking the heat with it
- Single use
- Chosen for the Gaganyaan crew module
Radiative
- A hot outer skin radiates the heat back out
- Can be reused
- Needs materials that stay sound at high temperature
Heat sink
- A thick mass of metal soaks up the heat and holds it
- Heavy, so suited to small capsules
- Between the two is a thermal protection system 30 to 35 mm thick.
- The Gaganyaan module uses an ablative shield, which does not resist the heat so much as spend itself on it.
- Its outer layers char, decompose and burn away, carrying the absorbed heat off with them.
- The gases escaping from the surface form a cooler boundary layer that holds the hottest gas away from the wall.
- Because the material is consumed, an ablative shield is used once.
The Hindu, 21 Aug 2026: How Gaganyaan's heat shield will protect the crew (opens in a new tab)
1 Sep 2026 · Prelims and Mains
Radiation shielding for a crew
Away from the shelter of the Earth's magnetic field, a crew takes whatever the Sun sends, and an eruption during a long mission is the case that has to be planned for. Shielding has to stop charged particles without adding weight a rocket cannot lift.
- Weight for weight, hydrogen rich polymers stop protons better than lead, because a hydrogen nucleus is a single proton.
- AstroRad, a vest of such material made by Israel's StemRad, was shown to cut the dose a crew would take in a solar storm.
- It flew uncrewed on Artemis I, a Moon mission of the National Aeronautics and Space Administration (NASA).
- The modelled dose fell by about 60 per cent for the August 1972 storm and about 40 per cent for October 1989.
- Such shielding holds off the charged particles of a solar storm but not galactic cosmic rays.