Spacewalks: How do astronauts survive outside of a spacecraft?
Spacewalks – which are technically referred to as extravehicular activities (EVAs) – are characterised as any activity performed by an astronaut outside the protected environment of a spacecraft’s cabin.
Each EVA is conducted by an astronaut in a specialised spacesuit called an extravehicular mobility unit (EMU), which unlike the spacecraft’s cabins use 100 per cent pure oxygen instead of air. The use of pure oxygen is necessary as the EMU suit is pressurised to one-third of atmospheric pressure, and at that level the quantity of oxygen in air is insufficient. The oxygen in each
EMU suit comes courtesy of two tanks located on its back.
Due to the duration of a typical modern EVA ranging from four to eight hours, the EMU is also equipped with an internal 0.9-kilogram (32-ounce) drink bag and valved drink tube. The valve is automatically opened when the astronaut sucks on the tube, allowing hands-free access to water. For particularly lengthy spacewalks, the EMU can also be equipped with a nutrient food bar, accessible on a suit-mounted strut.
In addition to an EMU suit, most EVAs today are also undertaken with a simplified aid for EVA rescue (SAFER) exoskeleton unit. This piece of cutting-edge equipment is secured to the EMU’s backpack via a waist-mounted connector and acts as an emergency propulsion system should the astronaut become separated from the spacecraft or robotic arm platform during a spacewalk. The system works, when activated, by directing nitrogen gas through a series of nozzles into the surrounding void of space, generating small, adjustable jets of the gas that can be used to propel the astronaut in a range of directions.
Each EVA begins in the spacecraft’s airlock, which is directly vented of its atmosphere once the astronaut is suited and acclimatised. This process reduces the airlock’s pounds per square inch absolute (psia) pressure from 14.7 psia down to around 1-2 psia. Once this is achieved, the external airlock door is released.
The vast majority of spacewalks are performed to carry out spacecraft repair or maintenance and, as such, involve the astronaut taking along a selection of tools with them. These tools, which include drills, ratchet wrenches, nitrogen guns and adapted power tools to name just a few, are tethered to the EMU via twin-release action cords. These ensure that the tools stay secured at all times during the operation and also allow the astronaut’s hands to remain free for manoeuvring around the spacecraft.
Astronaut Bruce McCandless II participates in a historical spacewalk.
Spacewalk kit
Helmet
This protects against harmful light rays and contains a set of headlights and television cameras. Due to the long periods of time astronauts spend on EVAs these days, there’s also an internal water hose so that the astronaut can drink.
Gloves
EVA spacesuit gloves have thumb and fingertips moulded from silicone rubber for sensitivity and enhanced grip. Internal heaters in the fingertips prevent the astronaut’s digits from getting cold and turning numb.
Utility belt
For each EVA an astronaut is equipped with a selection of tools, including drills, ratchet wrenches, nitrogen guns and glass-filled Lexan power tools. These allow them to perform a range of repairs and essential maintenance to the external spacecraft.

Suit
An EVA spacesuit has 14 layers of differing materials with sewn channels for protecting and regulating in-suit temperature. It comes in two pieces, with leg and torso segments slotting together at the waist.
Backpack
For modern EVAs, astronauts are equipped with a SAFER backpack system. This is an exoskeleton that allows propulsion through space via a series of nitrogen gas- firing nozzles. It acts as a backup system if the astronaut should ever become separated.
Notepad
Externally mounted to one of the astronaut’s arms is a simple notepad and space-pen. This enables astronauts to jot things down while on an EVA without having to worry about losing either while performing manoeuvres.
Harness
The first and most fail-safe system to keep astronauts linked to the spacecraft or robotic arm is a clip harness. This attaches to the astronaut’s utility belt.
Platform
While astronauts do perform detached EVAs, the majority today are undertaken from the end of a robotic arm (such as the Canadarm2). Astronauts hook their feet into a special platform to remain securely attached.
The first spacewalk
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Plus, take a look at:
Danger on the ISS: When spacewalks go wrong
Why do astronauts train underwater?
