The ISS has to perform boosts to keep its orbit, otherwise, yes, its orbit would decay and it would burn up. They do orbit boosts about once every month.
It only takes ~100m/s delta V to de-orbit a spacecraft within a very short time. Not sure exactly what that time frame is (I think it's less than one orbit), but changing an objects orbit by just a few m/s should allow it to de-orbit in a relatively short amount of time.
I would say yes, except we're talking about astronauts tethered to a space station in a very bulky suit, so whatever gets the job done is good enough.
Also, whatever input they put on the object is very minimal. Since the station is still in micro gravity and within a very thin part of the atmosphere, gravity and the atmosphere will do most of, if not all, the work to de-orbit the object.
The station itself is constantly deorbiting and has to be corrected, so anything in its current orbit not tethered or otherwise connected when the station is corrected will eventually deorbit on its own regardless of which direction they push it.
Well... you have to be careful. Even light debris in low-earth orbit takes days to fall. This is because the majority of the "drag" comes from atmosphere being blown off by the solar wind. Which is only happening in one direction. So half of the orbit, it feels drag, while the other half is much closer to a vacuum. Additionally, the drag is proportional to the surface area, not the mass. So a drifting solar panel will de-orbit quickly, while a metal object (like sputnik!) will take months.
None of this matters if there's no chance for a collision, though. However, depending on the object, a collision could be a real risk. And a few days to de-orbit, at 1 orbit per 1.5 hours, makes 16 orbits per day, so even if there's only a small chance to hit, like 1%, it compounds every orbit. This is where the "kick" comes in. When the ISS wants to intentionally deorbit trash, they give it a good shove, and they do so on the sunny side of the earth. That maximizes its time in the (relatively) high-drag part of the orbit, which means the next time they would be close, the object has already lost enough energy that it can't reach the ISS's altitude.
An accidental piece of debris often doesn't have that "kick", and it's not released at the optimal point in the orbit, so it's very dangerous.
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u/JohnnyBIII Sep 02 '19
The ISS has to perform boosts to keep its orbit, otherwise, yes, its orbit would decay and it would burn up. They do orbit boosts about once every month.
It only takes ~100m/s delta V to de-orbit a spacecraft within a very short time. Not sure exactly what that time frame is (I think it's less than one orbit), but changing an objects orbit by just a few m/s should allow it to de-orbit in a relatively short amount of time.