h a l f b a k e r y"This may be bollocks, but it's lovely bollocks."
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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.
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]
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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. |
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//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. |
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//No parachute could ever withstand those forces//
It's not the forces, it's the heat. The parachute would be glowing like the sun. |
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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. |
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Edit: deleted half-arsed calculation attempt. |
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// 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) |
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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. |
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<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 |
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"Ceramic re-entry eggs with space putty" |
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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. |
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//made of the stuff the mantle of a gas latern is made of (some kind of ceramic// Bad idea - gas mantles are radioactive. |
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//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. |
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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. |
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Getting boned harder than Annabel Chong. Ah well, off we go... |
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Heh. You're about 250 short. |
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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. |
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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. |
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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. |
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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. |
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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. |
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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. |
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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. |
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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. |
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I have no idea what this proves,
unfortunately. |
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<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. |
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Except that the ice will have its own
kinetic and gravitational energy to
dissipate, which is a problem. |
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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. |
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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. |
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//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. |
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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. |
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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. |
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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). |
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[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) |
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I think the mummy shaped heat shield and the unfeasibly large shiny inflatable life-raft cum parachute combo might just work. |
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I'd like to try it - what a way to go! |
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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? |
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/No parachute could ever withstand those forces./ |
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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. |
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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. |
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Regarding heating, the main friction would be with the parachute, not the astronaut - that is how a parachute works. |
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I would use the thrusters on the suit/pod to help slow down. |
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As an unpowered lander, the shuttle practically is a parachute, yes? So just build little shuttles. |
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//Possibly edges could break away during descent.//
That's particularly bad news for parachutes! |
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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! |
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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. |
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Welcome, [create]. You might like to turn that URL into a proper link, using the "link" link near the top of the page. |
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