Could someone jump from the international space station and live? | Hacker News Reader

Could someone jump from the international space station and live?

physics.stackexchange.com

61 pointsalykhalid41 comments

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 ;=)

The space shuttle descent was basically unpowered (it made an initial burn in orbit to put it on a path into the atmosphere, then after that it was just using thrusters to control orientation), so it's very much possible.

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.

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?

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.

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?

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).

I did a little digging, and this question is not easy to answer. There is much material regarding atmospheric drag on satellites, but those calculations require the assumption of hypervelocity. I wonder whether a simple calculation based on particle density and momentum transfer, with the balloon essentially sweeping out a vertical column of atoms as it fell, would yield a good order-of-magnitude estimate on the drag force available.

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.

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...

Incidentally, the "unobtanium" comment is quite clueless. (...) If you allow a "suit" to get bulky enough

I think that's what the comment is saying. He said it would be unobtanium or a lot, by which I assumed he meant the bulk.

I think the real problem is stability, i.e. how do you keep aerodynamic forces from spinning the (unguided) capsule too fast during reentry? If you look at video of Baumgarter's free-fall he is spinning very fast -- a couple RPM I'd estimate -- when he begins his deceleration after the near-vacuum free fall.

Orbital reentry would last for minutes and at much higher velocities. The centrifugal forces generated by unchecked rotation could cause blackout or even death. You'd also need to figure out what happens if your heat shield is not heated evenly due to rotation.

Guided reentry is a solution, but then we're talking RCS thrusters, fuel tanks, guidance equipment -- maybe something you can strap onto a spacesuit, but approaching a spaceship. And then you need one for each astronaut, increasing weight and complexity.

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

I think the question was asking if survival would be at all possible, rather than whether it's a reasonable course of action in the event of an evacuation.

It looks like, for now at least, the answer is no.

   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.

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.

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

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?

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.

> Have things slipped so far?

Yes. :(

In the US, 15-year-olds are typically going to be in High School, not grammar school, and have a choice of classes. Not everyone takes physics.

You do realize that knowledge of these things is an attribute of a tiny minority?

They have lifeboats on ferries crossing the English Channel. That's not because it's physically impossible to swim the channel (it's quite clearly possible, and is done on a fairly regular basis), but because most people couldn't do it, and even if they could the lifeboat is a safer way of managing an evacuation from a sinking ship.

I'm not saying that it is possible to jump from the ISS, just that the presence of a lifeboat doesn't demonstrate that any other evacuation route is impossible.

> Rolls eyes

In the real world knowledge of this stuff is vanishingly thin actually. Real world - the thing out there, with people and trees and stuff.

Can't believe nobody's mentioned MOOSE yet!

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

That thing is both amazing and scary.

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.

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

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).

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

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.

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.

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

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?

Relevant calculations: http://blog.wolfram.com/2012/10/24/falling-faster-than-the-s...

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.

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...

" " "fun" " "indeed" "

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...

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.

People are working on it: https://www.facebook.com/pages/FreeFly-Astronaut-Project/249...

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

(sorry)

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