Human Spaceflight and Microgravity Research

This note covers the science of human spaceflight and microgravity, and Gaganyaan's crewed programme structure. India's other recent named missions, Chandrayaan-3, Aditya-L1, NISAR, SpaDeX and Axiom-4, are covered in ISRO's Recent Missions You Should Know.

Microgravity is free fall, not the absence of gravity

The single most commonly misunderstood fact about spaceflight is what causes the floating sensation astronauts experience. It is not that gravity is absent in orbit; at the altitude of the International Space Station, Earth's gravity is still roughly 90% as strong as it is at the surface. Rather, an orbiting spacecraft and everything inside it are in a continuous state of free fall, falling toward Earth under gravity's pull while also moving forward fast enough that the curve of that fall matches the curvature of the Earth itself, so the spacecraft perpetually falls around the planet rather than into it. Because the spacecraft, the astronauts, and everything loose inside are all falling at exactly the same rate simultaneously, objects appear weightless relative to each other, even though gravity itself has not gone away. This state is more precisely called microgravity rather than zero gravity, since gravity's effect has not been eliminated, only its relative effect on objects moving together has.

Why microgravity research cannot be done on the ground

Microgravity conditions let scientists study physical, chemical and biological processes with gravity's usual confounding effect on convection, sedimentation and buoyancy essentially removed, which is impossible to replicate reliably or for any meaningful duration on Earth's surface. This is why crewed and robotic microgravity platforms are treated as genuinely distinct scientific infrastructure rather than a more expensive, less convenient version of a ground laboratory: certain classes of experiment, in fluid behaviour, crystal growth, combustion, and human physiology under sustained weightlessness, simply have no ground-based equivalent at all.

Gaganyaan: India's crewed spaceflight programme

Gaganyaan is ISRO's programme to launch India's first crewed human spaceflight, carrying Indian astronauts to orbit aboard an Indian rocket launched from Indian soil. The programme follows a deliberately staged testing sequence before any crew is placed on board: uncrewed Test Vehicle (TV) flights validate the crew escape system specifically, the mechanism designed to pull the crew module safely away from the launch vehicle in the event of a failure during ascent, and these are followed by fully uncrewed orbital flights of the actual crew module before a crewed mission is attempted.

Vyommitra, a humanoid robot astronaut whose name combines the Sanskrit words for "space" and "friend," is planned to fly on one of these uncrewed missions ahead of the crewed flight, equipped to monitor the crew module's onboard systems, issue alerts, and carry out life-support operations, effectively rehearsing the mission's systems under real flight conditions before a human crew is exposed to them. The crew module itself is the capsule that will carry India's astronauts into orbit and back, with recovery planned in the Bay of Bengal after splashdown.

Quick revision points

• Microgravity is free fall, not the absence of gravity. At orbital altitude, Earth's gravity is still nearly as strong as at the surface; astronauts float because the spacecraft and everything in it are falling together at the same rate. This is the correction a question testing "weightlessness" is built around.
• Microgravity research studies processes (fluid behaviour, crystal growth, combustion, human physiology) with gravity's usual confounding effects removed, which cannot be reliably replicated on the ground, making it genuinely distinct infrastructure rather than a costlier ground lab.
• Gaganyaan: India's crewed spaceflight programme. Staged testing: uncrewed Test Vehicle (TV) flights validate the crew escape system first, followed by uncrewed orbital flights of the crew module, before any crewed mission.
• Vyommitra: a humanoid robot astronaut flying ahead of the crewed mission to monitor systems, issue alerts and rehearse life-support operations under real conditions.
• India's other recent named missions (Chandrayaan-3, Aditya-L1, NISAR, SpaDeX, Axiom-4) are covered in ISRO's Recent Missions You Should Know.