Why do astronauts wear spacesuits during launch?

Question

I have noticed that astronauts in every launch I've found wear a spacesuit during launch, like this example from the shuttle.

I don't understand this. What kind of problem could cause loss of cabin pressure without compromising the whole vehicle? It seems like anything serious enough to depressurize a spacecraft would just blow the whole thing up.

Are there failure modes that cause loss of pressure but not rapid, unplanned disassembly? Or is there some other reason for the spacesuits?

I am interested in the topic in general, not just the shuttle.

Answer 1

Are there failure modes that cause loss of pressure but not rapid, unplanned disassembly?

Yes.

The 3-man crew of Soyuz 11 died when a valve was jolted open, venting out all the cabin air supply. Soyuz was redesigned after that accident to carry two crew in pressure suits instead of 3 crew in shirtsleeves. (I believe they now carry three in pressure suits.)

More generally there are any number of failure modes that could depressurize the cabin of any crewed spacecraft without destroying the vehicle. It's common, for example, for crewed capsules to have hatches which can be opened via explosive bolts; on Gus Grissom's Mercury-Redstone 4 flight, the hatch blew open unexpectedly after splashdown. If a failure like that occurred at high altitude or in orbit, the cabin would quickly vent to space without any significant airframe damage.

In such a case, it would be unlikely that the spacecraft could reenter safely, since there would be thermal, drag, and center-of-gravity issues. A micrometeoroid puncture could likewise depressurize a spacecraft, and if small enough, it could be repaired and reentry would probably still be possible, depending on the location.

Answer 2

@Russell hit the most important point (cabin decompression), but there are some others:

1. Protection from small fires or chemical fumes. These are irritants to the eyes and respiratory tract, and can hinder an astronaut's ability to function, if not injure or kill. The suits are fire retardant, so they will not burn like some clothing will. They provide some heat resistance that is useful for handling a small fire, although a large fire like Apollo 1 may still result in injury or death.

2. G-force control. Shuttle suits were able to provide compression to the legs during high G-forces (particularly landing), helping to move blood to the brain instead of pooling in the legs. Fighter jet pilots sometimes call these "G-suits".

3. Protection when ejection seats are used, particularly for the Gemini and first 4 Shuttle flights.

4. Parachute. This was the normal landing method for Vostok flights, part of the emergency bailout procedure with Shuttle ACES suits, and also needed for the above-mentioned ejection seats.

5. Water survival. Many suits have had flotation collars which keep the head above water, and neck dams which keep water out of the body of the suit. Some have also had an inflatable 1-person life raft built in.

6. Survival gear. Knives, guns, survival food, and water rations have all been parts of spacesuits.

7. Rescue. A person in a bright orange suit is easier to spot than other colors (the blue uniforms of the suitless Shuttle era were especially bad). Spacesuits also often carry radios, radio beacons, mirrors, flashlights, and glow sticks.

Answer 3

The most recent Crew Dragon mission had a near miss with a piece of space debris on its way to the ISS

The 4 astronauts on board were instructed to put their suits back on in case of a collision

"For awareness, we have identified a late breaking possible conjunction with a fairly close miss distance to Dragon," SpaceX's Sarah Gilles told the astronauts about 20 minutes before the conjunction on Friday. "As such, we do need you to immediately proceed with suit donning and securing yourselves in seats."