Spacewalks are one of the most dangerous pursuits performed by astronauts, with each one requiring technical skill, advanced technology and nerves of steel.
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 acclimatized. 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.
To date, over 200 spacewalks have been performed, with most occurring during the construction of the International Space Station (ISS). The most recent spacewalk was conducted by American astronaut Sunita Williams and Japanese astronaut Akihiko Hoshide on 1 November 2012. This EVA was undertaken to isolate a leak in the ISS’s power channel ammonia cooling system. The team successfully fixed the leak, spending a total of six hours 38 minutes walking in space.
1. Not for everyone – While more than 500 astronauts have been in space over the past 50 years, only just over 200 of them have actually performed a spacewalk or moonwalk.
2. The waiting game – Once an astronaut is securely in their EVA suit, they can’t immediately go out into space, but instead must spend an hour acclimatizing to the pressure in the airlock.
3. Loaded – As of 2012 seven space tourists have paid GBP 15.5 million ($25 million) each to be transported to the ISS, spend a week on board and perform a spacewalk.
4. Cutting the cord – For untethered spacewalks a special EVA suit is used, known as a manned manoeuvring unit (MMU). These use a variety of gaseous nitrogen nozzles to propel the wearer about.
5. Elite – To date the only space agencies that have successfully demonstrated an ability to conduct spacewalks are NASA (USA), CNSA (China) and the FKA (Russia).