Spacewalks explained — what, why, and how often
What an EVA actually involves, why astronauts go outside, what they wear, how long it takes, and how many spacewalks the Station has needed so far.
A spacewalk — officially an extravehicular activity, or EVA — is exactly what it sounds like: a crew member leaves the pressurised interior of the Station and works outside, in the vacuum. It is one of the most dangerous things an astronaut does, and one of the most routine.
Why they go outside
The Station cannot be fully maintained from the inside. Solar arrays need replacing. Ammonia coolant lines need mending. New equipment has to be bolted on. Old experiments have to be swapped out. If something on the exterior breaks, someone has to go out and fix it. Robotic arms handle some tasks, but many still require human hands and human judgment.
Some spacewalks are planned months in advance — a new solar array installation, for example. Others are unscheduled: an ammonia leak, a failed pump module. The most dramatic EVAs in Station history have been emergency repairs.
What they wear
The suit used on the American side is the EMU (Extravehicular Mobility Unit). It is essentially a one-person spacecraft: pressurised, temperature-controlled, with its own oxygen supply, carbon-dioxide scrubber, water cooling, communications, and a battery. Russian spacewalks use the Orlan suit, which works on similar principles but with a rear-entry hatch.
Both suits are bulky and stiff under pressure. Working in one is physically exhausting — astronauts compare it to squeezing a balloon with every hand movement, for six or seven hours straight.
How a spacewalk unfolds
The day starts hours before the hatch opens:
- Pre-breathe protocol. Crew members breathe pure oxygen to flush nitrogen from their blood and avoid decompression sickness — the same risk divers face.
- Suit checks. Every seal, valve, and joint is tested.
- Airlock depressurisation. The crew lock is slowly pumped down to vacuum.
- The work. Typical EVAs last six to seven hours. Astronauts are tethered to the Station at all times, moving hand-over-hand along handrails.
- Repressurisation. Back inside, the airlock fills with air, the suits come off, and the crew debriefs with mission control.
How many have there been
By mid-2026 the Station has hosted over 270 spacewalks since assembly began in 1998. The total EVA time adds up to more than sixty-eight days. That is sixty-eight days of cumulative human presence in hard vacuum — held alive by nothing but those suits.
Can you watch one
Spacewalks are broadcast live on NASA TV, and you can usually catch them on the Station’s live cameras. They are scheduled in advance and announced on the NASA Spot The Station feed. If you want to know who is aboard right now, see our crew page; to understand the broader context, read what the ISS is.
Frequently asked
What is an EVA or spacewalk?
An EVA, or extravehicular activity, is when a crew member leaves the pressurised interior of the Station and works outside in the vacuum. It is one of the most dangerous things an astronaut does, and also one of the most routine.
How long does a spacewalk last?
Typical spacewalks last six to seven hours, during which astronauts are tethered to the Station at all times and move hand-over-hand along handrails.
Why do astronauts breathe pure oxygen before a spacewalk?
To flush nitrogen from their blood and avoid decompression sickness, the same risk that divers face. This pre-breathe protocol happens before the suit goes on and the airlock is depressurised.
How many spacewalks has the ISS had?
By mid-2026 the Station has hosted over 270 spacewalks since assembly began in 1998, adding up to more than sixty-eight days of cumulative time in hard vacuum. The American side uses the EMU suit and the Russian side the Orlan.
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