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svidale t1_j2dhjfq wrote

Reply to comment by Full_Temperature_920 in eli5: back then, before astronouts goes to space, how do we know about thing like nonexistent of oxygen & zero gravity? by zetasstra

Yes, calculated to get just the right angle and speed to be missing. I don't think thats endless though. As in, most satellites will eventually crash down anyway. Even the international space station has to fire up its boosters sometimes to stay in the right orbit angle.

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Scuka1 t1_j2e3ktu wrote

>I don't think thats endless though

It is endless in theory, if you're high enough.

ISS has to boost because, even though it's technically outside the atmosphere, there are still some air particles floating around up there, producing a tiny amount of drag which needs to be compensated every so often.

For a body to stay in orbit, it needs to have a certain speed. Drag is slowly taking that speed away. Boosting is adding that speed back.

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Full_Temperature_920 t1_j2e7j76 wrote

I'm assuming planets and other celestial bodies don't experience drag in space, so those definitely will keep orbiting their star until it expands and swallow them then? Assuming nothing flying through space impacts them with enough momentum to shift the course

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Scuka1 t1_j2e9lzb wrote

Well, in theory, if conditions don't change, an orbit remains unchanged forever.

However, in practice, in our Solar system for example, you've got planets orbiting the Sun, each at their own pace, and every planet is exerting some gravitational force on other planets as they pass each other by, making tiny changes in their orbits.

So, orbits do change over HUGE periods of time (but we're talking slight changes over millions of years), but they don't really decay.

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