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Why do astronauts wear pressurised suits? | Explained
Why do astronauts wear pressurised suits? | Explained
Space is the vast area beyond the earth's atmosphere, filled with stars, planets, and galaxies. In this airless environment, one of the most critical differences from life here is the absence of atmospheric pressure.
The atmosphere is a thick layer of gases held around the earth by its gravity. It protects us from harmful solar radiation, keeps temperatures stable, and provides gases to respirate. The atmospheric pressure presses down on our bodies with about 20 tonnes of force, but we don't feel it because our bodies have evolved to push back with equal force, balancing it out. As we go higher, the atmosphere gets thinner and its pressure drops.
When a human body is suddenly exposed to vacuum, a sequence of sudden lethal effects occur, including ebullism (boiling of bodily fluids at low pressure), decompression (rapid loss of atmospheric pressure in a spacecraft), and lack of oxygen (hypoxia). The absence of atmospheric pressure causes gases to expand rapidly in the lungs and tissues, leading to loss of consciousness in seconds and death in a few minutes.
Astronauts wear special suits during space travel for their safety. Extra-vehicular activity (EVA) suits or spacesuits are for walks and work outside the spacecraft, like fixing external components and conducting maintenance. They have 12-14 layers and serve as a personal spacecraft, protecting its wearer against the vacuum of space, extreme temperatures, radiation, and space debris. Each EVA suit weighs 100-130 kg. Likewise, intra-vehicular activity (IVA) suits are worn inside the spacecraft and include a flight suit and a pressure suit. A flight suit is a general-purpose garment worn by pilots and astronauts, primarily for fire resistance, and protection against environmental conditions like temperature extremes or low pressure at high altitudes. Astronauts wear flight suits as their daily uniform while working in training facilities or onboard the International Space Station.
A pressure suit is a specialised garment designed to protect against the extremely low pressure environment of high altitudes or space. It provides full-body pressurisation, oxygen supply, and thermal regulation, making it more robust than a standard flight suit. During high-risk space missions such as launch and reentry, astronauts wear pressure suits to protect against potential cabin depressurisation and emergencies. The pressure suit weighs about 8-10 kg and has two or three major layers, depending on the model. It provides basic pressurisation, oxygen for breathing, ventilation, and communication controls. The suit's pressure bladder is pressurised with pure oxygen to approximately 40% of standard atmospheric pressure to maintain body pressure in the event of cabin pressure failure. The outer layer is a tough, bright shell for durability and visibility, making it easier to find the crew after landing.
In 1961, Yuri Gagarin, the first human to go to space, wore a specialised IVA suit called SK-1. The U.S. and Russia have developed eight to 10 IVA suit designs.
In the tragic Soyuz 11 mission in 1971, three cosmonauts died when returning to the earth. When the crew's descent module separated from the orbiting module, a vent valve meant to balance cabin pressure opened too early at about 168 km altitude. It didn't close properly, causing the air to rush out quickly, suffocating the cosmonauts. The disaster led to major safety changes in the Soviet space program, including bringing in a mandate to wear IVA suits during ascent and descent. These phases are dynamic and under exigency may involve high G-forces, sudden loss of cabin pressure, extreme heat, and vibrations, all of which pose serious risks.
In 2018, a booster separation failure during the Soyuz rocket's ascent to the International space station triggered violent spinning, forcing an emergency abort. Wearing Sokol KV-2 suits, NASA astronaut Nick Hague and Roscosmos cosmonaut Aleksey Ovchinin endured high G-forces and landed safely in the Kazakh steppe, with the suits playing a critical role in their survival.
In Gaganyaan, India's first human spaceflight mission, the ‘gaganyatris' will be using the Russian Sokol KV2 suit manufactured by Zvezda. The suit consists of two layers: an inner pressure bladder made of rubberised polycaprolactam to remain airtight, and an outer restraint layer of white nylon canvas for structural support and protection. Many astronauts have worn the Sokol suit and it has been involved in more than 128 Soyuz crewed missions. Unlike some IVA suits that use bright colours, like international orange, for high visibility, the Sokol suit uses a more neutral colour scheme, with reflective or contrasting elements to render its wearer more visible during emergencies, such as post-landing recovery in diverse environments like water or land.The gaganyatris were trained with the Sokol suit, including putting it on and taking it off (i.e. donning and doffing) quickly in the simulated microgravity conditions of space. This weightless environment was created by flying an aircraft in a parabolic trajectory. This flight path creates short periods of free fall during which passengers feel weightless for 20-30 seconds per parabola. While the Sokol suit provides vital assurance, it also underscores a key phase in India's space journey: leveraging global expertise while pursuing the goal of indigenous human spaceflight capability.
Unnikrishnan Nair S. is Former Director, VSSC; Founding Director, HSFC.
Published - November 12, 2025 08:30 am IST
Text and Context / The Hindu Explains / astronomy / space programme / space programme
Source: The Hindu
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