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This question was inspired by this other question and one of its answers. Essentially we have a lot of debris flying around in close proximity to Earth, and it is often going quite fast - fast enough to tear into or through somebody. Satellites and other such bodies have a lot of physical shielding, but even given any sort of armoring in a spacesuit, it just wouldn't be the same. So when astronauts go outside a station or a shuttle in a spacesuit, what keeps random debris from flying through their suits and into their bodies? How are they safe?

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Looking at that part in the answer, taking into account the number of hits, the time it has been out there (15 years), the size of the part and an anstronaut, one can probably estimate the "average number of debris hits per day". Its probably a few per month, and my gut says that although (see other answers) the risk can be reduced, it surely has happened, maybe someone comes up with an incident report. Also you can use your space station or whatever as a shield against the most likely debris trajectories. –  PlasmaHH Jun 26 at 15:43
@PlasmaHH There was one incident with a torn glove (IIRC one of the Space Shuttle EVAs) and a bleeding finger that was only detected post ingress and real cause never established. I'm not aware of any other EVA incident that could potentially be attributed to collision with space debris or other types of micrometeorites. And since SAFER, astronauts keep closer to the station and are attached with tethers. So they don't move as independently as during Space Shuttle / MMU days. –  Noordung Jun 26 at 15:49

3 Answers 3

up vote 11 down vote accepted

Safe is a big word, so can we first settle for safe enough that their EVA are worth the risk? OK, another big word in threat mitigation is risk management.

What this means is, that on top of larger debris being tracked by ground radars, their orbits predicted days in advance and assessing risk of these know debris entering the pizza box (imaginary square protected area around the station), EVA are scheduled to take place when and where the risk of collision with smaller (untracked) debris is predicted to be the smallest, and every step taken that they decrease exposure time. Obviously, this goes the same for space weather, for example scheduling during low Solar activity and during station's orbits that don't cross the South Atlantic Anomaly regions. And having backup EVA dates, if they have to be scrubbed for some unexpected reason, e.g. detected Solar flare pointing towards the Earth a day or so before the planned excursion, the station having to do orbital maneuvers to avoid larger debris,...

This risk management might mean taking fewer EVA and doing more tasks during each excursion, keeping the number of EVA astronauts / cosmonauts to the minimum that can still deal with unexpected situations (that would be two in egress and one in the station as support crew, and ground stations tracking their progress and monitoring other sensor readings), determining and prioritizing tasks necessity, placing ingress / egress and work locations in station's wake or otherwise protected by station's own hardware to minimize exposure to highest relative velocity debris, including changing station's own configuration, like rotating solar arrays, and so on.

So while safe is a lot to demand, various risk management procedures work, and make EVAs safer.

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Space is very big and even though there is a lot of junk, astronauts are small targets. Nothing keeps it from happening really.

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We're looking for long answers that provide some explanation and context. Don't just give a one-line answer; explain why your answer is right, ideally with citations. Answers that don't include explanations may be removed.

Yeah I was wondering that myself. If there is a reason I'd like to know. –  Matt M Jun 26 at 15:03
"Space is big, what can happen?" is a dangerous mindset. Collision with tiny and untracked debris is not an imaginary threat, it's very much real, and happens all the time. Station is protected against those, astronauts cannot be as much. –  Noordung Jun 26 at 15:14

IIRC, like the Apollo Lunar EVA suits, the ISS suits are multi-layered to give the best chance of mitigating impact of sub-radar sized flecks etc. Think of it as 'spaced armour' on a vehicle. Outer layer takes the big hit, spalls a bunch of lesser splashes towards next layer. Recurse until non-lethal...

Also, this is why so much emphasis has gone into the Canadarm and tele-operated 'robots'.

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Do you have any citations supporting your assertion that spacesuits are multilayered to shield against micrometeorites? My understanding is they're multilayered mostly because of thermal / environmental containment and to prevent ballooning. I highly doubt anyone would even attempt to design spacesuits to absorb micrometeorite impact force, since you need centimeters thick space between several layers for that at relative velocities that can be over 15 km/s, which would make them terribly bulky and cumbersome, which would only prolong EVA time in turn, and still not shield against all debris. –  Noordung Jun 26 at 23:30

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