Parachutes. From space.
Discussion
So say you are in a low earth orbit and need to return to earth.
Could you hypothetically use a parachute opened in space to slow your descent? Or would it be comparable to jumping off high bridge into water, (as in very rapid change in density hitting the atmosphere proper).
Or would the parachute burn up no matter how large it was due to the difference in speed between the fabric and the gas molecules?
Lastly if you were stationary above the earth rather than orbiting, say 200 miles out and dropped would that still work, or would you approach orbital type speed due to acceleration from gravity?
Could you hypothetically use a parachute opened in space to slow your descent? Or would it be comparable to jumping off high bridge into water, (as in very rapid change in density hitting the atmosphere proper).
Or would the parachute burn up no matter how large it was due to the difference in speed between the fabric and the gas molecules?
Lastly if you were stationary above the earth rather than orbiting, say 200 miles out and dropped would that still work, or would you approach orbital type speed due to acceleration from gravity?
marshalla said:
I mean the fact he got there in a lighter-than-air ballon is indicative that there is still a lot of atmosphere at only 25 miles high, but I'm really asking about coming in from LEO (the ISS for example is at 250miles), and travelling at like 5 miles a second.Eric Mc said:
If you are in low earth orbit, it means you are travelling at 17,500 mph. You can only come back to earth if you knock off some of that speed. You cannot use a parachute to do this because you are outside the atmosphere so deploying a parachute, which needs air to work, is pointless.
The trick is to fire a set of retro rockets to kill off some of that speed - say, reduce the speed from 17,500 mph to about 17,300 mph. That will change the angle of the orbit causing it it dip towards the earth slightly. The craft will then start ploughing through the thin upper atmosphere. That will be enough to start causing the craft to slow down even more. However, this braking effect comes at the expense of massive heating. Any parachute deployed at this point in the re-entry would be instantly vapourised.
The trick is to allow the craft to keep slowing all the time being protected by some sort of heat shield. Eventually, atmospheric drag acting on the spacecraft alone will have dropped its speed to a more manageable 400 to 500 mph. At this point, parachutes can be used.
This is exactly how traditional manned space capsules such as Mercury, Gemini, Apollo, Vostok, Voshkod, Soyuz and Chenzhou have operated for decades.
I mean that's my point, the ISS in a LEO and is frequently being boosted due to the (small) residual effects of atmospheric drag even at that altitude right? So I'm talking about A hypothetical enormous/impractical parachute, vs 'we can't wait 5 weeks for the capsule/system to decelerate gradually' I mean the ISS isn't slowly being eaten away/vaporized by being in an LEO is it (or is it)?The trick is to fire a set of retro rockets to kill off some of that speed - say, reduce the speed from 17,500 mph to about 17,300 mph. That will change the angle of the orbit causing it it dip towards the earth slightly. The craft will then start ploughing through the thin upper atmosphere. That will be enough to start causing the craft to slow down even more. However, this braking effect comes at the expense of massive heating. Any parachute deployed at this point in the re-entry would be instantly vapourised.
The trick is to allow the craft to keep slowing all the time being protected by some sort of heat shield. Eventually, atmospheric drag acting on the spacecraft alone will have dropped its speed to a more manageable 400 to 500 mph. At this point, parachutes can be used.
This is exactly how traditional manned space capsules such as Mercury, Gemini, Apollo, Vostok, Voshkod, Soyuz and Chenzhou have operated for decades.
In my head I would think if you had a system with a giant parachute say ballistically deployed in a LEO it would (eventually) be slowed down by resistance of the (sparse) atmosphere on it, potentially taking days/weeks to re-enter the atmosphere?
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