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.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.
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.
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?
Simpo Two said:
Plan C: Fire your retros until you're stopped completely (geostationary), then drop straight down by chute...
taking the most direct route like that would cause problems. You dont have time to slow down before hitting the ground going that quick will tear off any parachute you deploy. Travelling that quick through the atmosphere will generate tremendous heat.
Do you remember this:
Meteor over russia coming in as a ball of fire? thats a rock. and its not even coming straight down, maybe 40° above horizon. and even that is too much for that rock.(its entry speed was much higher due to not entering from a LEO, but thats more in depth physics)
So yes, you could drop straight down, but not for long.
Simpo Two said:
Plan C: Fire your retros until you're stopped completely (geostationary), then drop straight down by chute...
Problem with that is you would need to boost into orbit a mahoosive booster and all its fuel - requiring an even more mahoosive booster to lift all that stuff off the ground in the first place.The current system is still the most effective and easiest.
callmedave said:
Simpo Two said:
Plan C: Fire your retros until you're stopped completely (geostationary), then drop straight down by chute...
taking the most direct route like that would cause problems. You dont have time to slow down before hitting the ground going that quick will tear off any parachute you deploy.But Eric is right, the current version is the simplest.
So much misunderstanding of orbital mechanics in this threads its amusing.
To try and explain it simply, at a set speed you orbit at a set altitude (to be geo stationary you need to be at an altitude of 35,786 kilometres), to de orbit you need to reduce your velocity (burn retrograde) to the point where you are entering the upper atmosphere, as you speed decreases so will your altitude, you cant fall straight down you need to come down in an arc, obvious once you hit the upper atmosphere you will start to slow from air friction.
So anyway a parachute, errrrr not sure, not sure why you'd want to open a parachute that high up the atmosphere is thin so it would have to be massive, and made out of some very complex material, perhaps a ram-air style parachute could have some uses to land on a runway due to the additional control it would give.
To try and explain it simply, at a set speed you orbit at a set altitude (to be geo stationary you need to be at an altitude of 35,786 kilometres), to de orbit you need to reduce your velocity (burn retrograde) to the point where you are entering the upper atmosphere, as you speed decreases so will your altitude, you cant fall straight down you need to come down in an arc, obvious once you hit the upper atmosphere you will start to slow from air friction.
So anyway a parachute, errrrr not sure, not sure why you'd want to open a parachute that high up the atmosphere is thin so it would have to be massive, and made out of some very complex material, perhaps a ram-air style parachute could have some uses to land on a runway due to the additional control it would give.
Eric Mc said:
I thought my explanation was reasonable.
Parachutes CAN be deployed at high speed but at speeds not so high that they will cause the parachute to burn. This type of system is being trialled for landing heavy craft onto the surface of mars, with mixed results so far.
Eric your explanations always are Parachutes CAN be deployed at high speed but at speeds not so high that they will cause the parachute to burn. This type of system is being trialled for landing heavy craft onto the surface of mars, with mixed results so far.
I just wanted to add some points ie that speed and altitude are related and that when you fall to earth you do so in an arc. we need different entry solutions for different planets, we've found the one for earth with current technology so we'll stick with it.
And you can use a chute because you're falling straight down not going sideways at 17,000mph
Foliage said:
to de orbit you need to reduce your velocity (burn retrograde) to the point where you are entering the upper atmosphere, as you speed decreases so will your altitude, you cant fall straight down you need to come down in an arc...
Fire the retros for longer until you've lost all forwards speed...Simpo Two said:
And you can use a chute because you're falling straight down not going sideways at 17,000mph
That will require a rocket the same size as the one that accelerated the spacecraft to that speed in the first place - and you'd then need an even bigger rocket to launch the one to slow you down againFoliage said:
to de orbit you need to reduce your velocity (burn retrograde) to the point where you are entering the upper atmosphere, as you speed decreases so will your altitude, you cant fall straight down you need to come down in an arc...
Fire the retros for longer until you've lost all forwards speed...MartG said:
That will require a rocket the same size as the one that accelerated the spacecraft to that speed in the first place
I suspect that decelerating in a weightless vacuum would use much less power than accelerating upwards against gravity, but yes, it would of course use fuel that you'd have to carry up.Simpo Two said:
I suspect that decelerating in a weightless vacuum would use much less power than accelerating upwards against gravity, but yes, it would of course use fuel that you'd have to carry up.
Not a lot of difference really. The reality is that the lifting rocket would need to be DOUBLE the size, if not more, of a "normal" rocket. Why go to all that trouble when you can get the braking effect of the atmosphere for more or less nothing.Indeed, some space probes to other planets have done just that because it means that they need to carry less fuel all the way to their target planet. All they need to do is graze the atmosphere at just the right angle and they will kill off the necessary speed to enter orbit. The technique is known as "Aerobraking".
You should only need to use rockets for slowing when the planet or moon you are trying to orbit or land on has no atmosphere.
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