How astronauts do spacewalks from the ISS
Spacewalks from the International Space Station are carefully choreographed operations that let astronauts repair hardware, install new equipment, and test systems in microgravity.
The process depends on pressure suits, airlock procedures, mission control coordination, and extensive training to keep crew members safe in the vacuum of space.
Although the term “spacewalk” sounds simple, an extravehicular activity, or EVA, involves complex planning long before an astronaut reaches the station’s hatch.
Every step matters, because outside the ISS there is no breathable air, no atmospheric pressure, and only limited time to work.
What a spacewalk is on the ISS
An ISS spacewalk is an EVA performed by astronauts or cosmonauts outside the station’s pressurized modules.
During an EVA, crew members may inspect solar arrays, replace parts on external experiments, route cables, or install new components such as batteries and antennas.
NASA, Roscosmos, ESA, JAXA, and CSA crews have all contributed to EVA work aboard the station.
These operations are essential for station maintenance because many systems are exposed to harsh conditions such as atomic oxygen, extreme temperature swings, and micrometeoroid impacts.
Why spacewalks are performed
Spacewalks are used when a task cannot be completed by robotic arms or by astronauts working inside the station.
Common EVA objectives include:
- Repairing or replacing external hardware
- Installing scientific experiments and instruments
- Upgrading solar power and communications systems
- Inspecting for damage after debris impacts
- Preparing for assembly of new station modules
The ISS has a long operational history, and many of its systems need periodic servicing.
EVA teams often focus on tasks that must be completed in a single mission because the station’s external environment is too hostile for long-term exposed equipment.
How astronauts prepare before a spacewalk
Preparation starts days or even weeks in advance.
Mission planners define the timeline, tools, spare parts, and exact sequence of actions.
Astronauts rehearse each task in neutral buoyancy training pools, where underwater conditions simulate the body support challenge of microgravity.
They also practice in mockups of the ISS and in virtual reality trainers.
This allows crew members to memorize handholds, tether points, tool locations, and body positions needed to work efficiently in bulky suits.
Before the EVA, astronauts review procedures with flight controllers, study contingency plans, and configure communications links.
They also manage hydration, nutrition, and sleep so their physical condition is optimized for a long and demanding day.
The spacesuit that makes a spacewalk possible
ISS spacewalks require a highly specialized pressure suit.
NASA’s Extravehicular Mobility Unit, often called the EMU, is designed to supply oxygen, maintain pressure, remove carbon dioxide, control temperature, and protect the astronaut from radiation and micrometeoroids to a limited extent.
The suit is not a single garment but a system made of multiple parts, including:
- A hard upper torso and lower torso assembly
- A helmet with visor and lighting
- Gloves engineered for dexterity and thermal protection
- A life support backpack, known as the Primary Life Support System
- Boots, restraints, and layers for insulation
Because the suit is pressurized, it feels stiff compared with normal clothing.
Astronauts must exert significant effort to bend their arms, grip tools, and maneuver through handrails.
How astronauts exit the ISS
Spacewalks begin in the station’s airlock, typically the Quest Airlock on the U.S. segment or, in some cases, an airlock on the Russian segment.
The airlock allows crew members to transition from the station’s normal pressure to the vacuum of space in a controlled way.
Here is the basic sequence:
- Astronauts enter the airlock in their suits and connect life-support umbilicals.
- The airlock is depressurized gradually to reduce pressure-related risks.
- They perform leak checks, communications checks, and final suit inspections.
- Once clearance is given, the hatch opens and the astronauts begin the EVA.
Depressurization is crucial because it helps prevent decompression sickness, also known as “the bends,” which can occur if dissolved gases form bubbles in the body too quickly.
What astronauts do during the walk
Once outside, astronauts move using handrails, foot restraints, and tethers.
They do not “walk” in the normal sense; instead, they float while pulling themselves along the station’s exterior.
Every motion is deliberate because momentum carries farther in microgravity and there is no air resistance to slow movement quickly.
Tasks are usually assigned in pairs.
One astronaut may act as the lead worker while the other manages tools, assists with setup, and monitors safety.
Mission control in Houston, Moscow, or other control centers tracks timeline progress, suit status, oxygen levels, and communication quality throughout the EVA.
Typical EVA work can include:
- Opening thermal covers
- Unbolting and replacing components
- Routing cables and attaching connectors
- Photographing external structures for inspection
- Deploying or retrieving experiment hardware
Robotic systems such as Canadarm2 often support these operations by positioning astronauts, moving equipment, or providing camera views.
How astronauts stay safe in vacuum
Safety is built into every part of the EVA plan.
A spacewalk suit must keep the astronaut alive if they are separated from the station for hours, but multiple layers of redundancy are also used.
Important safety measures include:
- Tethers to prevent drifting away from the station
- Communication headsets for continuous contact
- Oxygen supply and backup reserves
- CO2 removal systems to prevent buildup inside the suit
- Thermal control to manage extreme hot and cold cycles
- Strict time limits for work outside
Flight controllers monitor biomedical data and environmental readings, ready to shorten or abort the EVA if conditions change.
Astronauts also train for emergency return procedures in case a tool issue, suit problem, or weather of orbital debris forces a rapid end to the work.
How long ISS spacewalks usually last?
Most ISS EVAs last around six to seven hours, though exact duration depends on the mission objective and crew workload.
The longest part is often not the exit itself but the actual task execution, because every action outside the station is slowed by suit stiffness, tether management, and communication steps.
Crew members must also return through the airlock, repressurize gradually, and complete post-EVA checks.
Afterward, astronauts often undergo medical monitoring to assess fatigue, hydration, and any effects from the space environment.
What astronauts do after returning inside
Once back inside the ISS, astronauts remove the suits, inspect gloves and tools, and report any issues to mission control.
The crew also debriefs the timeline, verifies that the external repair or installation succeeded, and documents observations for future maintenance planning.
Spacewalk follow-up may include reviewing video, checking station telemetry, and confirming that the hardware is functioning as expected.
If the EVA revealed new damage or unexpected conditions, engineers may adjust later procedures or schedule another spacewalk.
Why ISS spacewalks matter for long-duration missions
Spacewalks are not routine sightseeing trips; they are a core part of operating a habitable laboratory in orbit.
The ISS depends on them for upkeep, scientific deployment, and adaptation to changing mission needs.
As agencies prepare for future missions to the Moon and Mars, the skills developed during ISS EVAs remain highly relevant.
The procedures, suit technologies, and crew training used on the station continue to inform how humans will work outside spacecraft in deep space.
Common misconceptions about ISS spacewalks
- Astronauts do not freely swim through space; they move using tethers and handrails.
- The suit is not just for oxygen; it also controls pressure, temperature, and carbon dioxide.
- Spacewalks are planned far in advance and are rarely spontaneous.
- Robotics reduce risk, but many repairs still require human hands.
Understanding how astronauts do spacewalks from the ISS shows just how much engineering, training, and teamwork are required to work safely beyond the station’s walls.