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Astronaut Parachute

A parachute to allow low speed reentry from low earth orbit.
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Feel free to bake or bone this one. Either way, tell me why this wouldn't work.

The shuttle orbits at about 300km. At 100 kilometers air is about 2 millionths of the density as it was at sea level. Nitrogen dominates to 200 kilometers, but then up to 600 kilometers it's atomic oxygen and then helium. Still higher, the main component is hydrogen, even lighter than helium.

My idea was to have a parachute that can be deployed in low earth orbit in the event of an emergency evacuation on a station like the ISS or Mir and would use the minimal drag at very high altitude to slow the astronauts down as they orbited. If they wore suits they could use the thrusters on the suits to make them head down towards earth. Once they were heading in the right direction they could deploy the parachute(s?) aand the tiny amount of drag at that height would start to slow them down. As their speed dropped, so would they until they began to move into the thicker atmosphere below. By using a parachute, they would slow down gradually and avoid burning up at high speed. Joe Kittenger jumped from 30km up where there was only something like 1% of the atmosphere and he was fine so I reckon the theory is sound at low speed but would it work at higher heights and speeds?

I realise that this is half baked in every way but tell me what the problems are and how they could be solved.

Bigwill, Sep 17 2007

atmosphere! http://en.wikipedia.../Earth's_atmosphere
[the dog's breakfast, Sep 17 2007]

Reentry suit http://www.popsci.c...004eecbccdrcrd.html
[ldischler, Sep 17 2007]

Discussion about the same topic http://www.thenaked...ions/question/1801/
[create, Feb 17 2015]

[link]






       Unless you have some form of free-flight, it is going to make predicting the impact point of the spacecraft difficult.
In 1959, a USMC pilot ejected at just over 14000 metres, and took 45 minutes to come to Earth, having been caught in a thunderstorm.
coprocephalous, Sep 17 2007
  

       //but tell me what the problems are and how they could be solved.// The whole point of the bakery is that you do this bit by proposing some mad scheme that "might" just work, and make it as plausible as possible.
xenzag, Sep 17 2007
  

       //No parachute could ever withstand those forces//
It's not the forces, it's the heat. The parachute would be glowing like the sun.
ldischler, Sep 17 2007
  

       When a shuttle re-enters it uses the atmosphere as a brake which it skips along to slow the rotational speed around the Earth, not the falling speed towards the Earth, it does not go through pointing straight down. Basically, your problem is the horizontal speed not the vertical speed.   

       Edit: deleted half-arsed calculation attempt.   

       // It's not the forces, it's the heat. // The heat is produced by the frictional force. Anyway, it would be nice to have a glowing parachute made of the stuff the mantle of a gas latern is made of (some kind of ceramic)
marklar, Sep 17 2007
  

       Note linky. "An altitude of 120 km (~75 miles or 400,000 ft) marks the boundary where atmospheric effects become noticeable during re-entry" so you have a couple of hundred km where you chute does effectively nothing - results in freefall - during which you accellerate to silly speeds.   

       <edit>oh yeah youare already doing silly speed going round and round, anything that you washed off here would only be added as a vertical component. Oh, anyone want to grab   

       "Ceramic re-entry eggs with space putty"   

       Two hemispheres - so they stack neatly -joined with clay. May have insulating lining. Your little buddy jumps in & seals up with clay putty at re entry. Haven't worked out how you know when to get out and open a chute, or if anyone would pay the freight charge to get them up there, but......<edit again> and add one of those nice hilsch vortex tube jiggers for your a/c.
the dog's breakfast, Sep 17 2007
  

       //made of the stuff the mantle of a gas latern is made of (some kind of ceramic// Bad idea - gas mantles are radioactive.
coprocephalous, Sep 17 2007
  

       //The heat is produced by the frictional force// - I don't think this is right. The heat is produced by the compression of the air in the shockwave just in front of the falling object - not friction.
hippo, Sep 17 2007
  

       The particles of gas impacting on the parachute at orbital speed have an equivalent temperature of some 40,000 C. The parachute won't get that hot, but hot enough to vaporize it.
ldischler, Sep 17 2007
  

       Getting boned harder than Annabel Chong. Ah well, off we go...
Bigwill, Sep 17 2007
  

       Heh. You're about 250 short.
ldischler, Sep 17 2007
  

       This could only work if you were to slow the astronauts down from 30,000 km/h to 2000 km/h while they were still in space.   

       Then they would drop in a straight line more or less. They would still need a HUGE parachute in the beginning to avoid speeding up too much. As they drop, they would need to deploy progressively smaller parachutes.   

       The breaking maneuver would require extra propellant and fuel weighing several tons. Which would need to be sent into orbit, consuming an extra several hundred tons of fuel.
kinemojo, Sep 17 2007
  

       The truth is, leaving the earth is inherently unsafe. The slightest equipment failure has an excellent probability of causing fatality. Astronauts choose to go anyway.   

       Really, all you can provide the astronauts is the illusion of safety... and they know too much to be fooled. I think the real purpose of trying to make manned spaceflight look safe has more to do with public opinion.
GutPunchLullabies, Sep 17 2007
  

       Energy. Numbers.   

       Suppose the astronaut weighs 100kg (OK, an underestimate with all the gear, but.) Suppose they start out in a low earth orbit, say 300km above the surface, travelling at 8km/s. They have a gravitational potential energy of 300MJ (relative to the earth's surface; mass x height x G), and a kinetic energy of 3200MJ (0.5 x mass x square of velocity), or 3500MJ total.   

       When they land, they must have zero gravitational potential energy. Their velocity when they are standing on the earth's surface is about 460m/s, so the kinetic energy of someone standing still is 10MJ (if they're at the equator - zero at the poles). Hence, their energy by the time they've landed is negligible.   

       So, they've got to dissipate the best part of 3500MJ of energy in their descent. If the body is mainly made of water, this would be enough to raise it from freezing to 100°C 350 times over.   

       I have no idea what this proves, unfortunately.   

       <edit> OK. Ice. 1kg of ice takes about 2.6MJ of energy to melt, heat, and turn into steam. So, if they take 1,346kg of ice with them, they'll be OK.   

       Except that the ice will have its own kinetic and gravitational energy to dissipate, which is a problem.
MaxwellBuchanan, Sep 17 2007
  

       3500MJ. All this heat doesn't go into the astronaut; it goes into heating air, and then the air heats the astronaut unless he has a heat shield.
ldischler, Sep 17 2007
  

       Well, Heinlein pretty much preheated this in "Starship Troopers" (the book, not the dismal farce of a movie). But I think you lot have brought more maths to the table than he did.
normzone, Sep 17 2007
  

       //t doesn't go into the astronaut; it goes into heating air// You are absolutely right - I calculated instead of thinking. However, the heat generated by friction should apportion its elf in some ratio between the air and the astronaut; I'm guessing a substantial fraction goes into the astronaught.
MaxwellBuchanan, Sep 18 2007
  

       If you put the astronaut inside a protective heatshield with cylindrical walls and with parachutes that floats on water, then you'd have an old-school Apollo style space capsule.... that would be sensible to have as an escape pod on the ISS. Or perhaps a mummy shaped heatshield spacesuit with a skydiver's ballute pack on it might work just fine.
quantum_flux, Sep 19 2007
  

       The problem with a parachute is that it's behind the astronaut, so however much heat it can take is irrelevent as the human gets the same in the feet.   

       How about a shiny self-inflating life raft of unnecessarily large diameter. It could be inflated to a low pressure, which would be ample to expand it in a near vacuum. Then as atmospheric pressure increases it forms a slight shuttlecock shape before finally floating in the ocean (probably, or sliding down a mountain).   

       [edit]Or you could make a surfboard of solid oxygen, which can also be defrosted if the station is running a little low. The astronaut rides the surfboard through the atmosphere and as the oxygen boils off he is able to breathe. (yes I do know this would actually result in a firey ball of death)
marklar, Sep 19 2007
  

       I think the mummy shaped heat shield and the unfeasibly large shiny inflatable life-raft cum parachute combo might just work.   

       I'd like to try it - what a way to go!
Karnuvap, Sep 19 2007
  

       I suppose, if there was some way of using the first traces of gas to slow down the argonaut, without falling much, then velocity could be reduced without generating too high a temperature. Needs a glider that can work in near vacuum?
Ling, Sep 19 2007
  

       /No parachute could ever withstand those forces./   

       The forces will initially be small, because the atmosphere is rarified. The frictional force exerted by the atmosphere will gradually increase as the astronaut descends. The parachute could be huge to maximize slowing in the fringes of the atmosphere. Possibly edges could break away during descent.   

       The shuttle is aiming for a spot. The astronaut would land in any old place. The shuttle is in a hurry. The astronaut would not be.   

       Regarding heating, the main friction would be with the parachute, not the astronaut - that is how a parachute works.   

       I would use the thrusters on the suit/pod to help slow down.
bungston, Sep 19 2007
  

       As an unpowered lander, the shuttle practically is a parachute, yes? So just build little shuttles.
GutPunchLullabies, Sep 19 2007
  

       //Possibly edges could break away during descent.//
That's particularly bad news for parachutes!
ldischler, Sep 19 2007
  

       Interestingly enough in 2007 there were other discussions open in this topic and still visible on the web! See link: "Discussion about the same topic" Some comments are hitting the topic hard!   

       But this is also about "quick" jumping. I think people did not really got the idea that you wanted to jump slowly. Yes, week-long jumps (sails) would be fun. I mean fun because cheap. Perfect for sending back stuff from ISS.
create, Feb 16 2015
  

       Welcome, [create]. You might like to turn that URL into a proper link, using the "link" link near the top of the page.
pertinax, Feb 17 2015
  
      
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