How much time is needed to an astronaut on ISS to prepare herself for an EVA? Is this time so much different from time needed during Apollo missions?

  • 1
    $\begingroup$ looking at the answer, it's not entirely clear what you mean - the specific time before each and every EVA, or the time needed to fit a suit to the cosmonaut once (and prepare other equipment that I don't know about) $\endgroup$
    – mart
    Oct 7, 2013 at 12:30

2 Answers 2


There is no emergency escape procedure onboard the International Space Station (ISS) that would involve Extravehicular Activity (EVA). If you'd be racing in your space suit, be it the Extravehicular Mobility Units (EMU) or the Russian Orlan-M space suit, it would be from your EVA back towards the ISS's Joint Airlock "Quest", like the Italian ESA (European Space Agency) astronaut Luca Parmitano did during his second EVA when his EMU helmet started filling with cooling water originating from his PLSS (Portable Life Support Unit):

    Joint Airlock "Quest"

      View of the Quest Airlock (left) taken from Space Shuttle Atlantis during docking procedures on 9 April 2002 as part of the
      STS-110 mission to the International Space Station. (Image: NASA)

Which space suits are onboard the ISS was also already covered in this answer, and I'm saying all of this so there won't be any expectation that the procedure of getting into one's space suit would be a timed or a life-saving racing event.

Before the airlock hatch is opened and the EVA gets underway there are lots of preparations that have to take place to make sure that the EVA proceeds seamlessly. We'll be the most interested in the EVA donning procedure, but for the sake of completeness, I'll include shortened versions of the complete Standard EVA Preparations, taken from the ESA's EVA support information brochure (PDF):

  • Airlock Preparation:

    The day before the first EVA starts, the ISS Quest Joint Airlock needs to be configured and activated. The equipment has to be laid out to be easily accessible to the EVA astronauts during the EVA. This includes hardware for installation during the EVA and tools needed to carry out the relevant work, which will also need configuring before the start of the EVA (and during).

  • EVA Suit Checkout:

    The EVA suits are known as Extravehicular Mobility Units or EMUs. These procedures are performed at least 1 day before the EVA. The purpose of EMU checkout is to ensure the integrity of the suits. This can include tasks such as powering up and installing the suits batteries necessary during the EVA, checking the Life Support Systems and Simplified Aid for EVA Rescue (SAFER) units that allow an astronaut to return to the ISS if he comes untethered during the EVA and checking that the suits communication devices are working.

  • Camping Out (Nitrogen Purge):

    Astronauts have to be in very good physical condition in order to undertake an extravehicular activity. One of the potential risks relating to EVA work is decompression sickness. For this reason, prior to the EVA the astronauts go through a regime of breathing pure oxygen in order to purge nitrogen out of their blood systems.

    The day before the EVA, the relevant astronauts will sleep in the airlock, which will be sealed and the pressure reduced from 1 bar to 0.7 bar. 1 bar is normal ISS (and earth sea-level) pressure. This process is known as camping out.

  • Donning EVA suits:

    The EVA suits known as Extravehicular Mobility Units or EMUs are extremely complex, containing many different layers and systems in order to provide the astronaut with an as safe and comfortable environment during EVAs whilst remaining functional for performing the tasks at hand. The EVA astronauts are usually assisted in donning their suits by one or more astronauts, with relevant checks being carried out during this procedure.

    When suiting up the astronaut first puts on the urine collection device and then a Liquid Cooling and Ventilation Garment. This spandex garment has water-cooling tubes running through it and also supports a network of ducting that draws ventilation gas from the suit extremities and routes it back to the primary life support system.

    The astronaut now gets into the Lower Torso Assembly of the space suit and then rises into the Hard Upper Torso section, which is attached to the airlock wall by an adaptor. The Lower Torso Assembly can be seen as the waist, trousers and boots of the EMU and has separation joints above the knee and above the ankle. The flexible waist section and waist bearing afford the astronaut a large degree of movement about the waist, e.g. bending and hip rotation.

    Donning EVA suits
    ISS Expedition 12 Flight Engineer Valery Tokarev being assisted into the Hard Upper Torso section of an EMU by Expedition
    12 Commander Bill McArthur on 23 October 2005. (Image: NASA)

    The Hard Upper Torso is a rigid fibreglass vest onto which the Lower Torso Assembly attaches. It also acts as the attachment point for the helmet and the flexible arm sections, which have an arm bearing to allow for arm rotation. The Life Support System is attached to the back of this assembly with Life Support controls mounted to the front in easy reach of the astronaut. Connections between the two parts must be aligned to enable circulation of water and gas into the Liquid Cooling Ventilation Garment and return. The Life Support System provides the crew member with pure oxygen to breath, removes carbon dioxide exhaled, regulates the temperature in the suit, and keeps the pressure during EVA at 0.3 bar, this is 30% of the air pressure at sea level on Earth and 30% of the normal ISS air pressure. This low pressure is necessary to maintain suit flexibility. If the pressure level was higher the suit would become too stiff to work.

    Once the upper torso section is donned the astronauts put on their communications headset otherwise known as a snoopy cap with headphones and microphones for two-way communications between crew members and to Mission Control. This is followed by the gloves and lastly the extravehicular visor and helmet assembly.

    This provides protection from micrometeoroids and from solar ultraviolet and infrared radiation. This is made of a rugged, impact resistant polycarbonate material. A vent assembly, bonded to the inside rear of the polycarbonate shell, serves to diffuse the incoming gas over the astronaut's face.

    The Extravehicular Visor Assembly is a light-and-heat-attenuating shell which fits over the Helmet Assembly. It is designed to provide protection against micrometeoroid activity and accidental impact damage, plus protect the crewmember from solar radiation. A special coating gives the sun visor optical characteristics similar to those of a two-way mirror; it reflects solar heat and light, yet permits the astronaut to see. Adjustable eyeshades may be pulled down over the visor to provide further protection against sunlight and glare.

    An extra unit that is attached to the EMU once it is donned is the SAFER unit. This is a small, self-contained, propulsive backpack system used to provide a free-flying self-rescue capability for an EVA crewmember if he becomes separated from the ISS during an EVA.

    So as not unnecessarily use up EMU battery power the EMUs will remain plugged into the ISS electrical power supply via an umbilical. The spacesuits will then be ventilated with pure oxygen and the airlock will be re-pressurised to 1 bar. The EVA crew members will continue the prebreathe of pure oxygen inside their spacesuits for 50 minutes. The EVA astronauts will go into the crewlock of the Quest airlock where the hatch will be closed. The depressurisation of the crewlock will now be initiated.

  • Depressurisation:

    The usual pressure inside the ISS is 1 bar, though in the Quest airlock this is 0.7 bar during depressurisation in connection with nitrogen purging. When the astronauts are in the crewlock ready to start their EVA this pressure is reduced first to 0.35 bar when a leak check is performed on the suits. If this is ok the crewlock is reduced in pressure down to 0.2 bar. The final depressurisation to vacuum occurs through venting through a valve in the EVA hatch. The hatch can now be opened and the EVA can begin.

I've somewhat shortened the other points we're not as interested in to answer your questions, but the full description and many more photographs explaining the procedure are available in the linked to brochure. As you can see, these procedures are laborious and time consuming. Donning of the spacesuit might be the shortest of the procedures, but would in reality still take hours, with the soon to EVA astronauts possibly already in the Lower Torso Assembly long before donning the rest of the space suit and all the equipment that attaches to it.

So, to conclude, we could say that all procedures involved take at least one day, and the donning of the spacesuit itself maybe a few hours? Nobody would be racing either, there's way too many things to check and recheck, complete spacesuits are essentially your mini personal spaceships with all the bells and whistles and that means they're complex while trying to be as ergonomic as possible once you're in them. Comfort of getting in and out of them was somewhat sacrificed for that. And you can't just walk out of the station either, once in the suit. Depressurization of the airlock prior to egress will take some time, and so will repressurization and sometimes purging of possible contaminates (like ammonia that is used as external cooling liquid and those systems are often worked on during EVAs, if it couldn't have been baked-off during EVA with exposure to the Sun or airlock sensors still detected some despite attempts to not bring any in) during ingress.

  • $\begingroup$ Chris Hadfield's autobiography gives an excellent description that is very similar. See An Astronaut's Guide to Life on Earth: What Going to Space Taught Me About Ingenuity, Determination, and Being Prepared for Anything (2013). $\endgroup$
    – user8406
    Feb 11, 2015 at 6:49
  • $\begingroup$ Maybe a related question: are there new suit designs in development purposed to be emergency life support, and if so, how quickly could an astronaut suit up in one (what is the target)? $\endgroup$
    – Anthony X
    Mar 4, 2017 at 14:59

Some of it depends on which space suit they will use. There are two sets of suits at the station. The Russian Orlan suits and the US suits.

The US suits require customization to lengthen/shorten bits so it fits properly. Earlier suits were customized per use on Shuttle flights and took hours or days by trained technicians to adjust. The current suits on the station are upgrades that are easier and faster but still take some time to adjust.

So first EVA by an astronaut in a US suit takes longer than the second, due to this issue.

  • $\begingroup$ are we talking minutes or hours? $\endgroup$
    – mart
    Oct 7, 2013 at 9:48
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    $\begingroup$ @mart It used to be days. They got it down to hours. But still many hours, when customizing the size. $\endgroup$
    – geoffc
    Oct 7, 2013 at 11:14

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