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Say you're in a space capsule. The space capsule has mostly survived re-entry, but the capsule's parachutes fell off. If you had a regular skydiving parachute with you, is there any way you could skydive and survive? Would you even be able to open the door? When should you jump?

Stéphane Gourichon
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Fax
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    You may be interested in how Yuri Gagarin landed from Vostok 1. Admittedly, that was planned. – notovny Mar 06 '20 at 20:48
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    You may be interested in how Jebediah Kerman landed safely from an orbital EVA. https://www.youtube.com/watch?v=oKh3Z8Uf5aU Apparently the trick is to land on your head. What? It worked in KSP! – Criggie Mar 08 '20 at 08:25

3 Answers3

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Would you even be able to open the door?

It would depend on the capsule, but since the Apollo 1 fire, one expects crewed American capsules to have explosively-jettisoned hatches that can be activated by the crew.

If you had a regular skydiving parachute with you, is there any way you could skydive and survive?

Yes. Terminal velocity for falling capsules isn't particularly high, so in general it should be possible to blow the hatch, jump free, and skydive to safety. As @notovny notes, this was how the first couple of Soviet Vostok flights ended, although they had the benefit of a rocket powered ejection seat to clear the capsule.

When should you jump?

High enough to ensure that your parachute has time to fully deploy, but otherwise as low as is practical -- the capsule will be moving slower due to resistance from denser air, and you'll be less likely to get hurt on your way out the hatchway. The Apollo capsule's drogue chutes were supposed to automatically deploy at around 7km altitude, and the main chutes somewhere below 3km, which is low for recreational skydiving, so you probably want to get out as soon as you realize the mains have failed.

Note that capsule parachute failure is rare. The 1967 Soyuz 1 accident is, as far as I know, the only fatal parachute failure in spaceflight thus far. One of the Apollos had one of its 3 main chutes fail to deploy correctly, resulting in a hard landing but no serious injury.

Russell Borogove
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    Excellent answer. Parachute failures may be rare in the real world, but not so much in Kerbal Space Program. It's good to know that the Kerbal way of dealing with poor parachute planning is not too far-fetched. – Fax Mar 06 '20 at 23:10
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    @Fax Which is the Kerbal method, bailing out or unplanned lithobraking? – chrylis -cautiouslyoptimistic- Mar 07 '20 at 08:16
  • I'm not an expert, but it sounds to me that 3000m is not low at all for recreational skydiving, if we are talking about the opening. – Martin Argerami Mar 07 '20 at 12:04
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    It’s low for the departure from the aircraft. – Russell Borogove Mar 07 '20 at 15:26
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    @RussellBorogove: I think most recreational skydivers want to have some time to enjoy free fall before they have to open their chute; they could safely jump from lower altitudes, but it wouldn't be as must fun. – supercat Mar 07 '20 at 21:52
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    In recent KSP, all kerbals have parachutes in EVA, so the player frantically bails out each Kerbal, opens their parachute, and switches to the next. – ikrase Mar 07 '20 at 22:52
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    In recreational skydiving, it's common to jump from 4000 m to enjoy the free fall but many divers jump from ~1500m or lower, open immediately and focus on parachute maneuvers so 3000m is not necessarily low. – Relaxed Mar 08 '20 at 00:02
  • It's also worth noting that remaining orbital velocity is a big factor in survivability here. When your capsule is in orbit, it's traveling very fast, parallel to the earth's surface (else it wouldn't be in orbit). In reentry, this speed is bled off. So, early in reentry, the winds might be too high and rip off the parachute. You want to jump after you've decelerated most of the way. – John Walthour Mar 09 '20 at 13:54
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    People have free-jumped from the top of radio towers with parachutes, it's not safe by any means with very little time to fix problems if they arise... but it can be done. – Magic Octopus Urn Mar 09 '20 at 15:30
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    A "standard" solo skydive will exit between 3000m and 4500m and deploy their main parachute around 1000m while travelling at 120mph. Most will have a safety device that will automatically deploy the reserve parachute at 225m if the skydiver is still in freefall. That's about as low as you can confidently open a parachute while travelling at 120mph (standard terminal velocity). When jumping from fixed objects velocity is slower, so less altitude is required to open the parachute. – thelem Mar 09 '20 at 16:24
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The Red Bull Stratos jump was done from about 39km up (high altitude balloon). It was fairly straightforward, in that he jumped and opened a parachute. His max speed was just above mach 1 (800mph/1300kpm roughly) and when he moved himself from the freefall to a more traditional skydive position, he was at a more tolerable 500mph/700kph. By the time he reaches 10,000ft he's just barely at 125mph/200kph. Parachute opens at 9000ft. BBC video linked, but the Red Bull site above has one with mission data in-lined (like SpaceX does)

The catch here is assuming the capsule isn't tumbling out of control. If so, good luck trying to get the door open (even with explosive bolts, you have to reach the switch), let alone getting yourself out. If it's just free-falling, you should be able to do what Stratos did and merely jump with an appropriate parachute.

The other catch is making sure you orient yourself to open the chute. If you start tumbling, it could be game over.

Machavity
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  • Good point about tumbling. Are space capsule parachutes designed in such a way that they work regardless of whether the capsule is spinning uncontrollably, or would the cords twist up like on skydiving parachutes? – Fax Mar 06 '20 at 23:02
  • I'm not sure if you could grab a capsule chute and use it like that, but you do need some stability to open it, or the cords will tangle – Machavity Mar 06 '20 at 23:06
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    Just to say it, the jumper's name is Felix Baumgartner, from Austria. – Greg Mar 07 '20 at 00:25
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    @Fax The drogue chutes will damp spin significantly even if they get tangled. – Russell Borogove Mar 07 '20 at 00:52
  • Isn't mach 1 much slower in the less dense air at high altitudes? – d-b Mar 07 '20 at 12:47
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    @d-b yes, red bull took that into account. If you watch the annotated video linked above the vmax I could see is 1m02s in and appears to be 846mph which would be mach 1.10 at sea level, but is registered on the video as mach 1.26 – Darren H Mar 07 '20 at 17:52
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    Capsules don't tumble in the lower atmosphere. It's either spinning or stable. – Joshua Mar 09 '20 at 16:12
  • You might expand your answer to include the issues to overcome to be in a re-entry capsule with a personal parachute. 1. It would need to launch to space with you, so extra fuel to get it there. 2. You would need to put it on before you started your re-entry. 3. If it is on your back, the seats will need to be redesigned. – James Jenkins Mar 10 '20 at 14:23
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I don't see anyone mention here the aspect of heat.

You say from a space capsule, but don't state a maximum altitude. To use a capsule, I assume you mean above the atmosphere. This means on reentry heat would be an issue. The friction of the atmosphere on the jumper as they decelerate from frictionless travel and orbital maintenance speeds.

This is an interesting article on it.

https://www.huffpost.com/entry/what-is-the-maximum-altitude-someone-could-come-back_b_58bf2f54e4b070e55af9e8d5

The question would be, say they jumped from geostationary orbit. Unlikely, but just say. They'd need to decelerate just to reenter. As a non vehicle they'd have little space for fuel, but little mass. Could they even carry enough fuel to reduce speed enough for a warm reentry when they hit the atmosphere. I'd say no...

I'd say this is probably the limiting factor rather than much else... The speed required for altitude maintenance, vs fuel for deceleration and how much can be carried, to keep the reentry within the temperature requirements AND limit the yaw forces excerpted on the body as you hit the gases in the upper atmosphere. These might be more dangerous!

The balloon works, because it is in essence stationary. There are limits to that technology, from orbit would be very different.

Rob
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    I almost wrote an answer like this until I re-read the first sentence of the question: "The space capsule has mostly survived re-entry, but the capsule's parachutes fell off." So the scenario takes place fairly close to landing after the capsule has already dissipated nearly all of the heat and energy associated with reentry. – uhoh Mar 07 '20 at 21:10
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    @uhoh Indeed, I think the related question on parachuting down from orbit has that part covered pretty well. – Fax Mar 08 '20 at 17:18
  • The heat on reentry is not from friction with the air. It is caused by the capsule compressing the air in front of it. – Mr. Wrong Mar 09 '20 at 14:19
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    @Mr.Wrong surface friction happens when air molecules hit the capsule surface, which will throw the molecule back and create compression. I'm not sure that the compression on a capsule isn't just a manifestation of normal air friction, just more visible because of the extreme parameters involved. – toolforger Mar 09 '20 at 20:44
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    @toolforger I don't think that's accurate. Surface friction is defined as a force that opposes the relative lateral motion of two touching surfaces, not as something that causes molecules to bounce off. Maybe the fluid friction of the air helps with compression though, that I don't know. – Fax Mar 09 '20 at 22:47
  • @Fax I meant friction between gas and surface. – toolforger Mar 10 '20 at 22:09