

Could someone jump from the international space station and live? - alykhalid
http://physics.stackexchange.com/q/40886

======
nagrom
A lot of comments on the SE site make the same point: it's clear that such a
person needs to wear a space suit of some type. And it's clear that it is
possible to do with an elaborate vehicle. So the question really just depends
on how elaborate you allow the suit to be.

If you allow active propulsion systems, then the answer is certainly yes - but
your suit now becomes a vehicle and that's probably not in the spirit of the
question.

If your constraint is "No (active) propulsion system", then you can redefine
the question:

"Is it possible to build a passive wing system to make a (slow, 30ms^-2?)
controlled descent into the upper reaches of the atmosphere for a mass of
approx. 200kg (man+suit) and, if so, what is the minimum temperature that the
exterior of such a construction will reach during its deceleration phase? Are
there man-made materials that can withstand such a temperature?"

My feelings are a) yes, b) way too high and c) no. The precise answer is left
as an exercise to the reader ;=)

~~~
Someone
I do not think it matters, but there is an extra (implicit) constraint: you
would want the descent to be done in some reasonable timeframe (say a week)

Also, I think your _"Is it possible to build a passive wing system"_ is too
restrictive. If I had to design something for this, I would consider wrapping
a huge balloon around the astronaut to limit the rate of descent. It could
start out uninflated as a gigantic air brake, then work from a compressed air
cylinder; at lower altitudes, it might be possible pump in air an/or heat air.
100% safe it would never be, but it might be possible to get something that
works sometimes. Braking without melting/burning this thing probably might be
a stumbling block, though.

~~~
vannevar
I think your balloon idea has some merit. For much of the early fall, very
little gas would be needed to support a very large balloon that would retard
the fall and limit terminal velocity. If your velocity stays low from the
start, you never have to worry about heat building up. As the descent
continued, eventually the atmosphere would thicken to the point that the
balloon provided actual buoyancy, and subsequently a controlled descent could
be made. Perhaps two balloons would be required, one weak, large one for the
initial fall at the edge of the atmosphere and another stronger one for the
final descent through ordinary weather conditions. The question is, how big
would that first balloon need to be at the altitude of the space station?

~~~
rrmm
At the start of the jump you're already going about 27000 km/h (ISS orbital
velocity). The falling part of the problem isn't the hard part.

~~~
vannevar
I'm assuming the orbital velocity has already been scrubbed off, and we're
talking about a simple fall, which is more in the spirit (if not the letter)
of the original question. Could you prevent the velocity from building up with
a large drag device such as a balloon in that case?

~~~
rrmm
To me, the question implied that the design of the suit would have to overcome
that problem; but I can see it either way.

Check out <http://en.wikipedia.org/wiki/Reentry> , there is a section on an
inflatable heat shield launched on a sounding rocket (so sub-orbital, but
lower altitude).

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stcredzero
Summary: If you allow making a man-shaped space capsule with retro rockets,
heat shield, and parachute, then it's possible. If you call that cheating,
then it's not.

Incidentally, the "unobtanium" comment is quite clueless. People have proposed
making ablative heat shields out of wood, for heaven's sake. If you allow a
"suit" to get bulky enough, an ablative heat shield in one is well within the
realm of existing materials science.

~~~
andyjohnson0
The ablative heat shield used by the Spirit and Opportunity rovers was a blend
of cork wood and silica spheres [1].

Also, the reentry vehicles for the Chinese FSW reconnaissance satellites used
heat shields made from Oak.

[1]
[http://marsrover.nasa.gov/mission/spacecraft_edl_aeroshell.h...](http://marsrover.nasa.gov/mission/spacecraft_edl_aeroshell.html)

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cstross
_Rolls eyes_

There is a _reason_ they keep two Soyuz ships docked on the ISS at all times
as lifeboats, in case they need to evacuate in a hurry. Those things are
bloody expensive; if jumping overboard was a reasonable alternative, it'd be
vastly preferable to keeping ten tons of ironmongery and heat shields on hand.

Having said that, see 1963's Project MOOSE:

<http://www.astronautix.com/craft/moose.htm>

~~~
wr1472

       Rolls eyes
    

why do you need to type that? I think it is irrelevant, rude and
condescending. Otherwise your comment was quite informative and I would have
upvoted it.

~~~
stcredzero
There are a number of comments on that site that are eye roll worthy. There
are even a few comments that show cluelessness about the magnitude and
implications of orbital velocity.

~~~
WayneDB
That's no reason to be condescending and rude. Not everybody knows about that
stuff.

~~~
cstross
Really?

It's stuff I was taught about in physics lessons at grammar school, circa age
15, back in the 1970s. Have things slipped so far?

~~~
dkokelley
The way I see it, " _rolls eyes_ " is a violation of

> _When disagreeing, please reply to the argument instead of calling names.
> E.g. "That is an idiotic thing to say; 1 + 1 is 2, not 3" can be shortened
> to "1 + 1 is 2, not 3."_

from the site guidelines. Granted, this was in reply to an article rather than
another commenter, but I think the principle is the same.

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bunderbunder
Can't believe nobody's mentioned MOOSE yet!

<http://en.wikipedia.org/wiki/MOOSE>

~~~
Florin_Andrei
That thing is both amazing and scary.

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sageikosa
Yes. "For how long" is the operative question. While still affected by gravity
(at about 9m/s Earthward) the forward velocity of the ISS's frame of reference
is balanced to maintain orbit. At the 0.5m/s (or so) velocity delta in
whatever direction chosen, it will take some time for orbital decay to alter
the orbit of the jumper.

Things burn up on re-entry because of the tangential speed of the craft
(laterally through the increasingly thickening atmosphere as distance to
ground increases), not because of the plummet composition of the velocity
vector.

If someone could manage a strait jump from that height without forward
velocity (in relation to the Earth's rotating frame), I suspect they'd be in
freefall (without a normal terminal velocity) until they hit the atmosphere,
at which point they'd probably be going pretty fast (9m/s for a few hundred
kilometers adds up) and would have some severe heating issues to deal with.

~~~
pyre
9m/s is velocity. How does this 'add up' over a distance?

~~~
gvb
That is a typo, it should be 9m/s^2
<http://en.wikipedia.org/wiki/Earth%27s_gravity#Altitude> (gravity at the
earth's surface is 9.8m/s^2, the link states it is 90% of that at the ISS).

~~~
sageikosa
Yes, that one: (9m/s)/s. Less a typo on my part and more of a "brain-o".

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dennisgorelik
Is it possible to try to glide at, say, 100km?

Obviously the atmosphere is extremely thin at that height, but on the other
hand astronaut would have extremely high speed at this moment which would help
both gliding and add centrifugal force.

If gliding is possible at such height, then it can help lowering into thicker
atmosphere prematurely, and therefore would prevent extremely fast
deceleration.

Basically the more astronaut slows down - the lower it would glide, always
trying to maintain manageable deceleration.

Obviously gliding idea was discussed by space engineers, but I couldn't find
the reason why it was rejected.

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SeanDav
I would imagine that this would be extremely risky, purely from the risk of
collision with space junk, before looking at all the numerous other risks. To
protect yourself from space junk collisions you pretty much need a small
spaceship around you. Then you still have to face the problem of bleeding
orbital velocity sufficiently that you can enter the atmosphere without
burning to a crisp. Additionally you are accelerating towards the earth at 1g
and that velocity would have to be neutralized as well.

Your "suit" will likely have to be nearly a spaceship and then really you are
arguing on what point a suit becomes a spaceship.

~~~
andyjohnson0
Losing orbital velocity via friction with the atmosphere is the main problem.
The ISS orbits the earth at 7.7km/s [1].

Using some kind of active braking system ("retro rockets") before hitting the
atmosphere might help, but its hard to imagine it being portable. You'd need
fuel, pumps, guidance and control systems to run it. As you say, your suit
becomes a spaceship.

Edit: I'm not sure whether collision with orbiting junk would be a significant
risk. Most of it is very small, and as far as I know the chances of being hit
only really rise if you spend a lot of time in orbit.

[1] <http://www.esa.int/esaHS/ESA7YL0VMOC_iss_0.html>

------
fsiefken
I wondered something like that as well, in the last Star Trek movie the young
Kirk jumps out of a space ship onto a planet. If you could match the orbital
velocity could you jump without heat shield and survive?

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lloeki
Relevant calculations: [http://blog.wolfram.com/2012/10/24/falling-faster-
than-the-s...](http://blog.wolfram.com/2012/10/24/falling-faster-than-the-
speed-of-sound/)

I'm not versed enough in Wolfram Alpha to extend this all the way to ISS
orbital altitudes. That's of course assuming one nullifies the _lateral_
velocity, which is actually the main concern for not turning oneself into
ashes from friction.

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ck2
Didn't they once make a miniature space shuttle glider?

I think that would be a lot more "fun" than jumping with just a super bulky
spacesuit.

added: couldn't find the original one from years ago but here's something new

[http://i.space.com/images/i/18008/original/dream-chaser-
capt...](http://i.space.com/images/i/18008/original/dream-chaser-captive-
carry.jpg)

~~~
ngvrnd
" " "fun" " "indeed" "

------
hammock
Has anyone ever considered using water as heat shielding? I mean that stuff is
already one of the best coolants known to man for myriad applications.

Edit: found at least one idea
[http://www.newscientist.com/article/dn3551-water-could-
repla...](http://www.newscientist.com/article/dn3551-water-could-replace-
spacecraft-heat-shield-tiles.html)

~~~
T-hawk
Water is heavy. For spaceflight, what almost always counts is the performance
of something per unit of weight/mass. It's not so efficient to launch a large
mass of water that contributes nothing to the mission besides boiling off on
reentry. Your article mentions this offhandedly: "But the weight of all that
water on a real mission may well swell launch costs."

Water is a good coolant because it absorbs lots of heat energy in boiling. But
that's not so efficient for its weight/mass, since a water molecule boils only
once and then is gone. A solid material can disperse more heat per weight over
a longer time without being consumed.

------
castles
People are working on it: [https://www.facebook.com/pages/FreeFly-Astronaut-
Project/249...](https://www.facebook.com/pages/FreeFly-Astronaut-
Project/249289161775970)

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ngvrnd
Answer the question as stated: it depends. Can he get back to the space
station by tether or suit rockets?

(sorry)

