Understanding EVA
How an EVA Works
Before an EVA, astronauts spend several hours "pre-breathing" pure oxygen at low pressure to purge nitrogen from their blood and prevent decompression sickness (the bends). They then don their spacesuits — the NASA EMU or newer AxEMU — which provide oxygen, temperature regulation, radiation protection, micrometeoroid shielding, and communications. An airlock is depressurised, the hatch opens, and astronauts tether themselves to the station using safety cables. All tools are also tethered to prevent them becoming orbital debris.
EVA Milestones
| Mission | Year | Milestone |
|---|---|---|
| Voskhod 2 | 1965 | First EVA (Alexei Leonov, 12 min) |
| Gemini 4 | 1965 | First American EVA (Ed White, 23 min) |
| Apollo 11 | 1969 | First lunar surface EVA (Moon walk) |
| STS-61 | 1993 | Hubble Space Telescope repair EVA |
| ISS assembly | 1998–2011 | 160+ EVAs to build the ISS |
| Polaris Dawn | 2024 | First commercial EVA (SpaceX suit) |
Risks and Challenges
EVAs are among the most dangerous activities in spaceflight. Astronauts face exposure to extreme temperature swings (-157°C in shadow to +121°C in sunlight), micrometeoroid impact risk, radiation (outside the station's shielding), and suit malfunction. In 2013, ESA astronaut Luca Parmitano's EVA was aborted when water leaked into his helmet from the cooling system, threatening drowning. Gloves frequently develop small holes from sharp surfaces, and hand fatigue from working against pressurised suit joints limits effective work time.