28
$\begingroup$

It's now the late 23rd century and there are now hundreds of space stations, orbiting approximately at the height of the (now deceased) ISS, give or take a few kilometers. Lately, the International Space Fleet™ has been trying to find a way to get people back down to Earth without the need to use lots of rocket fuel for descents.

To do this, the ISF™ has decided to, rather than sending people down from stations in rockets that they're going to instead send people down by having them "skydive" to Earth. Let's assume that the following things are already in place:

  • There are now methods to keep people from blacking out at high speeds and high G-forces.
  • The "skydiver" has to manually operate the mechanisms on their suit, e.g, deploying parachutes, etc.
  • The "skydivers" leave and "dive" from the space stations at scheduled times to make sure there are no collisions, and that they land in the right-ish area.

Is this plausible in any way? If so, is there anything that needs to be changed to make it more plausible? If it's not plausible, or possible at all for that matter, then why? And if so, is there anything that could be changed to make if somewhat plausible?

EDIT: This question is not the same as this question. That question is asking if this kind of scenario is possible given some very tight constraints, in an earlier time period. My question is set in a completely different time period and has looser constraints.

$\endgroup$
  • 4
    $\begingroup$ @DanHenderson With the additional constraint that this time, what you drop is a human being who presumably want to survive to landing. This is nowhere near an answer, but Star Trek touches on orbital skydiving, with some summary here. $\endgroup$ – a CVn Oct 18 '15 at 13:33
  • 2
    $\begingroup$ Also been done in the Old Man's War universe. $\endgroup$ – dmckee Oct 18 '15 at 19:26
  • 2
    $\begingroup$ Not a duplicate -- the other question asks, "Given these resources, could someone parachute from the ISS?" This asks, "Is it reasonable to operate something that would allow you to parachute from the ISS?" The resources necessary is open. The answer to the previous question was no. The answer to this question is yes. $\endgroup$ – Brythan Oct 18 '15 at 22:40
  • 1
    $\begingroup$ Fictional story about sky diving from the space station (with modern tech) $\endgroup$ – user487 Oct 19 '15 at 3:08
  • 2
    $\begingroup$ Meta discussion. $\endgroup$ – HDE 226868 Oct 19 '15 at 15:37
46
$\begingroup$

Such a system has already been considered as an emergency evacuation system for space station, see the MOOSE.

It is like a backpack which contains basically the bare minimum to deorbit and try to survive reentry :

  • A small rocket to lose enough speed in order to lower your perigee (lowest point of your trajectory) enough to meet the atmosphere.
  • An polyurethane foam to shield you from the heat during reentry.
  • A chute to slow you down once you have reached a dense enough atmosphere.

It still require a rocket, but it will be really small given that the mass to decelerate if really low compared to an actual spacecraft (I have read somewhere that it would be about the size of a fire extinguisher).

Although it is really simple, it has never been actually deployed in a space station or a spacecraft, let alone used for an actual reentry.

$\endgroup$
  • 6
    $\begingroup$ Moose was always intentended as an emergency backup. It was never going to be a safe way to deorbit. Still +1 for the closest real world example. $\endgroup$ – Taemyr Oct 18 '15 at 8:56
  • 2
    $\begingroup$ The fire extinguisher comparison reminds me of a scene in Gravity. $\endgroup$ – kasperd Oct 18 '15 at 9:34
  • $\begingroup$ Oooh... I sense a gadget that's going to star in the next A-Team movie! Or maybe it's better suited for Machete 3? $\endgroup$ – oliver Oct 18 '15 at 10:27
  • $\begingroup$ I have just remebered a example from fiction : the Orbital Drop Shock Troopers (from halo ODST). I keep that in a comment, because it is not science based. $\endgroup$ – Quentin Oct 18 '15 at 11:12
  • $\begingroup$ Nice first answer, showing something that is reasonably close to a real life example doing what the OP is asking how to do. You might want to edit to clarify that the system was only considered, and never used in practice (Wikipedia claims it was shelved in the late 1960s, but needs more citations). Welcome to the site! $\endgroup$ – a CVn Oct 18 '15 at 13:28
15
$\begingroup$

The first and foremost issue is how is the person going to be decelerated? Orbiting the Earth involves moving at high velocity (@ 7.8 Kilometres/sec), and you need to shed some of the velocity if you are going to head towards Earth. This explains the rockets, etc that are currently used.

You could postulate something like a railgun or electromagnetic mass driver, but I think you can already see the problem; a dramatic reduction in velocity would involve either incredible acceleration or an improbably long "gun barrel" to keep the forces on the person reasonable. Other means of deceleration like an electrodynamic tether or Morovec "Rotovator" are going to be rather massive (essentially the space station itself), which is kind of beside the point.

Assuming the individual is decelerated below orbital velocity, they are still going to have issues on re entry into Earth's atmosphere. Unless they have somehow managed to get to zero velocity (i.e. subtracted the entire 7.8 Km/sec velocity needed to remain in orbit) they are going to hit the atmosphere at considerable velocity. The air will be rapidly compressed in front of them due to the velocity (the effect is the same as a piston in a diesel engine compressing the air in the cylinder, just much faster and on a larger scale), so the space suit, parachute, etc. will be subjected to incredible temperature stresses, far beyond what normal materials can withstand. (The heat shields of most spacecraft ablate to carry away some of the heat load; only Space Shuttle tiles don't do this and even they needed replacing on a regular basis).

While I suppose there is some sort of handwavium to get around these problems, in reality you will need to find a way for your character to survive being shot from a cannon many times faster than any rifle bullet, then hit the atmosphere at several "G" and be subjected to incredible temperatures, then be able to deploy some sort of arresting device to slow down and land.

I'll just get Scotty to beam me down instead.....

$\endgroup$
  • 1
    $\begingroup$ For reference, according to my (reasonably rough) calculations, a deceleration of 117 m/s would be sufficient to put an object from the ISS into an orbit that contacts Earth's surface. The good news is that with a very large, but not totally unreasonable gun, this could be done with safe accelerations. The bad news is that with this orbit you'll hit the atmosphere moving at over 8000 m/s. The other bad news is that you'll have accelerated your satellite, so if it needs to be in a particular orbit, it'll have to correct with rockets (and apply the same impulse as you would've needed) $\endgroup$ – Milo Brandt Oct 18 '15 at 1:15
  • $\begingroup$ Exactly the point. If you are still moving at many kilometres a second when you hit the Earth's atmosphere, then you will rapidly burn up on reentry. If you want to slow down enough to prevent that, then you will have to decelerate quite a bit more (and provide more inputs to the space station, something I failed to mention in the initial answer). $\endgroup$ – Thucydides Oct 18 '15 at 1:20
  • 1
    $\begingroup$ I don't think an answer to this question can be complete without discussing MOOSE. $\endgroup$ – Taemyr Oct 18 '15 at 8:56
  • $\begingroup$ @MiloBrandt the acceleration of the satelite might actually be useful in order to stabilize its orbit (currently ISS needs to be pushed up ever once in a while). $\endgroup$ – Paŭlo Ebermann Oct 18 '15 at 10:47
  • $\begingroup$ @MiloBrandt The 117 m/s for IIS orbital altitude sounds about right. See How could a 90 m/s delta-v be enough to commit the space shuttle to landing? on Space Exploration. (Full disclosure: it's my own question.) Of course, the Space Shuttle was pretty well built for re-entry; it'd take some serious retrofitting to be able to do the same thing with, say, basically just a spacesuit. $\endgroup$ – a CVn Oct 18 '15 at 13:24
9
$\begingroup$

Ignoring the technical limits, already quite well addressed above, there is an important other aspect, liability!

What happens if one idiot forgets to activate his parachute and goes splat? what happens if someone drops his luggage, which will be moving at such huge speeds that if it doesn't burn up in the atmosphere it will be lethal to anyone it hits, and potentially quite damaging to objects it strikes as well; not to mention what happens if a terrorist intentionally drops his 'luggage' in a preplanned time to strike something. What if someone falls asleep on the fall (this will take hours as a control fall!) and twists up his parachute etc.

In short, you can't allow an untrained layman to be responsible for his own return to earth. He could screw up, and no matter how much of an idiot he is you become liable for whatever he does. Not only is his own life in danger if he does, but so is anyone below him. Think about how much training you get for 'simple' sky diving, now imagine a system that is 3 times as complicated...

As an alternative I could see a drop pod being used. The concept is similar to the idea of skydiving, but with the entire drop pod doing the 'skydiving' for you. Everyone files into a pod and it's dropped into earth orbit. It handles deceleration, ejection of parachute etc. It also stores all the luggage that people wanting to return to earth are using and times it's drop and deceleration to 'land' in pre-planed parts of the world. Of course this is pretty similar to how shuttles already work, the only real difference would be to make the drop pod much smaller/lighter (so it can be brought back up to the space-station before the drop), probably with the pods somehow folding up or even being shipped 'unassembled' for easier transport up to the station. and with a heavier focus on cheaper deceleration methods. It's sounds far less exciting then the orbital sky diving, but it's really the same idea done in a way to be safe for untrained layman.

Of course you could still have orbital skydiving without a pod be an evacuation technique, or the next step to sky diving for a thrill seeker...with the limits of science mentioned in other questions.

$\endgroup$
  • $\begingroup$ +1 for the drop pod example. In fact, a number of sci-fi movies already use this, most notably Star Wars in Episode IV. $\endgroup$ – Nzall Oct 18 '15 at 22:10
  • 1
    $\begingroup$ Drop pods are not a good solution. In sci-fi that actually explains the tech, drop pods are employed from slightly within the atmosphere. The problem, like anything else entering the atmosphere, is that it needs to slow down, survive the temperatures, and then land. At that point this "pod" is nothing more than a shuttle, except you're going to have a damned hard time getting them back up again for the next passenger. $\endgroup$ – AndreiROM Nov 8 '15 at 4:00
  • $\begingroup$ How is the liability issue any different from liability in a normal skydive? That already happens on a worldwide scale, with all liability issues hammered out. $\endgroup$ – Peter Jan 20 '17 at 23:44
  • $\begingroup$ @peter the danger to the diver is significantly higher with many more things that could go wrong, and more importantly only those trained and certified can sky dive alone, while this example was suggesting letting laymans without certification dive. $\endgroup$ – dsollen Jan 23 '17 at 2:56
  • $\begingroup$ The opening sequence of Starship Troopers (the novel) features the drop pod idea prominently. One potential problem is the amount of "chaff" that is discarded during descent. $\endgroup$ – amfinley Feb 7 '18 at 18:13
3
$\begingroup$

I must object to the problem requirements.

Given the tech level I see no reason to require manual control of anything and every reason to think it's a bad idea.

Given that, yes, it can be done. There are two important issues: Deorbit and reentry heating.

First, deorbit: The posts above have attempted to deal with this with a gun type device which is problematic due to the barrel length. This is going at it backwards, a gun is absolutely the wrong answer. Don't push them off, pull them off: Your passenger is strapped into a ring which is then deployed outside (but still attached to) the station. When it's in position the passenger is ejected prograde at low velocity. They are still tethered by at least three cables, probably more for safety reasons. The passenger drifts forward as far as needed, the cables playing out as he goes. When he has reached the required distance they are wound back up quickly. Instead of a barrel that must withstand force in compression you have simple cables that only must withstand force in tension--much lighter, they can be much longer than the size of the station, a passenger can be deorbited from above ISS altitudes even. When the cables are fully rewound as the passenger zips through the departure point they disconnect, ready to be attached to the next passenger.

Second, reentry: This is the harder one to deal with as the plunge through the fire is very, very hot. I would handle this by making a cheap dish of foamed material (refinery slag from lunar mining makes a likely candidate.) While such a dish isn't going to be as good a heat shield as NASA builds we aren't so weight-limited when dealing with stuff built in space. The shield isn't going to be reused, either, so it can be a simple ablative design rather than the fancy stuff NASA put on the Shuttle.

During the trip through the fire the passenger is strapped to this dish to ensure their weight doesn't shift around. It extends enough around them to keep the center of mass ahead of the center of pressure so it's stable without flight controls. The back is covered by a thin layer of foamed material with a reflective layer on top--all you need to do is slow the entry of the heat, the shield is jettisoned before the heat bakes through.

At the right point pyro charges (the only equipment on the shield!) release the passenger from the shield. You do this while there still is some horizontal velocity left so the spend shield diverges from the passenger and won't smack him on the head when his chutes deploy.

$\endgroup$
1
$\begingroup$

Aside from the extreme heat experienced, re-entry also requires aerodynamic stability. The 8-9 g's experienced during the maximum braking portion of re-entry by astronauts indicates a substantial amount of pressure applied - if that pressure isn't applied evenly, the person is going to spin like crazy, more than enough to kill them.

It's one thing to enter a crouch for stability under the 1g of a free fall in the lower atmosphere. It's probably impossible to to maintain control of a human form when the aero braking force is 8-9 times higher. Thus, the blunt heat shield not only insulates, but provides a platform that can decelerate in a stable manner.

So you might think along the lines of a 'mini capsule', a blunt heat shield the person sits on to also provide the required aerodynamic stability on top of heat shielding, with side panels to protect them from the superheated ionized gases streaming past during the maximum G portion of re-entry. Perhaps some reaction jets to rotate the craft for steering... both Gemini and Apollo had an off center weight bias, so that rotating the craft during re-entry would cause the horizontal trajectory to change slightly.

A person isn't going to de-orbit (and survive the journey) in just a suit. Even if a suit that could insulate them from the extreme heat was developed, a person would die from the extreme forces of a spin or other gyrations that result from uneven aerodynamic braking.

$\endgroup$
1
$\begingroup$

You could use a Momentum Exchange Tether. I first saw this concept in the Neal Stephenson novel, Seveneves. The concept is that being on the end of the rotating tether, you get decelerated with respect to the surface of the Earth while the other end is accelerated. At the lowest point, you disconnect and just fall down, since you're now at almost zero horizontal velocity. The deceleration is (potentially) nice and slow.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.