How possible are 'space jumps'?

Question

Have you seen the first of the two new Star Trek movies? Kirk (Chris Pine), Sulu (John Cho) and a red shirt perform something really awesome in this film: They jump from space down to a planet, basically only protected by some suit.

My question(s): Is a jump from actual space down to Earth possible? If yes, how? What are the actual problems related to it? Has it ever been researched? If yes, what was the outcome?

Let's assume two scenarios for my question. One jump from the true edge of space at 100 km altitude and another jump from 400 km, the approximate altitude of the ISS. Both jumps happen from fixed positions relative to the Earth's surface (not from an orbit, of cause). Imagine someone doing a base-jump from a gigantic tower.

Intuition tells me that rapid deceleration once deep in the atmosphere would not even be the issue. Trouble should come from heat caused by friction and its 'disposal', although I am not sure about that.

Giving some context to this question, first of all, there was Project Excelsior, in which Joseph Kittinger did similar jumps, among them one from an altitude of 31.33 km, in 1960. Further jumps of this kind happened within projects Red Bull Stratos, during which Felix Baumgartner jumped from a maximum altitude of 38.97 km in 2012. Both projects featured jumps from within Earth's atmosphere by definition, to be more precise from the stratosphere. Although, both parachutists experienced a rather long phase of virtual free fall before they 'hit' the 'atmosphere', as they described it.

A while ago I had to deal with sounding rockets. Straight up to about 100 km in powered flight and immediately straight down again in 'free' fall. Temperature measurements on the outer shell indicated a maximum of about 250°C +/- 50K on re-entry, although the temperatures had already reached about 70°C at apogee because of the high-speed ride upwards. I dug for an example in terms of speed and deceleration on the way down and made a plot, here it is:

It is only from 87 km, but it should do the trick. The object was a cylinder, about 2.5m in length and 0.3m in diameter, weighing something less than 100kg (weight and dimensions are slightly similar to a human body). Yes, it did tumble. You can see the parachute opening at about 6km. The peak-deceleration on the way down was at about 5.5 G, within limits for a human to survive. It includes the one G, which you experience here on Earth's surface. Be careful with the data above 60km - it is GPS data, which sucks at high altitude and high vertical speeds. If someone is interested in, the rockets were Improved Orions.

Answer 1

From this question on Physics.SE:

But other than that, there is no reason why a man couldn't be lobbed from behind Jupiter, make a slow-down loop around the Moon, then spiral down to Earth... given some marvelous suit that will withstand the atmospheric entry.

From this question on Felix Baumgartner:

Note that even if he jumped from "infinity", he would only reach the escape velocity which is 11,200 m/s for the Earth, just like the slowest meteoroids. I guess that a good enough (and cooled) suit inspired by NASA rockets might be capable of protecting a human against such relative speeds even though for generic surfaces, they would almost certainly start to burn at the surface.

However, it wouldn't be pleasant to slow down from such speeds in the atmosphere. ;-) You see that if you uniformly slow down from 10 km/s to 0 km/s while flying through 10 km of the atmosphere, the penetration through the atmosphere takes about 2 seconds. However, getting from 10 km/s to 0 km/s in two seconds means that the deceleration is 5000 m/s/s or 500 g. I guess that not even he could survive that. ;-)

So the interesting bit of information I get from those two is that your trajectory is going to be key. You couldn't drop straight in, so like the space shuttle, you will need to have a long glide path. This will give you lower friction, leading to a lower g-loading and lower temperatures. Obviously you will then need more stored air - as this could take some time, and possibly thicker ablative material on your suit (I haven't got numbers on this, but while the temperatures may be a bit lower, you are still going to have to ablate to protect the contents of the suit)

You might need winglets or other control surfaces to manage this glide slope.

In fact - you'd be better off with a capsule...

Answer 2

While Rory's answer is close, let me give a few additional details.

1. The orbital speed is about 7.8 km/s in low Earth Orbit.
2. If you are orbiting, you will not fall straight down. It just won't happen. In fact, the maximum speed would result from a minimal burn, which would take you through the atmosphere quite slowly.
3. You will start slowing down to an extent at around 50 km high, which is where re-entry really starts.

So, there are 2 scenarios which should be discussed.

1. The straight down approach- Think the Felix Baumgartner freefall record of 39 kilometer (24 mile), but about 500 km high.
2. The slow approach- This would be more like the space shuttle.

The straight down approach- Somehow you are on a space station, and you need to abort. You only have a rocket, and no spaceship. So you fire enough to stop your orbital velocity, and fall straight down. This sequence of events is rather unlikely, BTW.

Your max speed would likely be around 2000 m/second. Let's say you hit the atmosphere at 10 km, that would give you a time to decelerate of 10 seconds. That's about 20g of acceleration, not enough to kill you, but it wouldn't be a pleasant experience.

In the second one, you are only slightly falling vertically. Your G force wouldn't be anything more than that of the space shuttle. Presumably, if you could design the suit just right, it would work, but it would likely be extremely heavy, and risky.

Bottom line, I believe it could be done in either case, but it would be rather dangerous. The hardest part would be starting the de-orbit maneuver, and building the suit just right.

Far more likely is the ability to survive an aborted launch, such as the Challenger. You might be going very fast, or high, but these types of things are more likely to happen inside of the atmosphere, slowing you down considerably.

Answer 3

Sure. Why not. You'll want some sort of heatshield of course.

Or this more practical design:

Or this earlier, less convincing concept:

It looks like the fall from a $100\,km$ tower is survivable in terms of G's. I assumed a $100\,kg$ person and a $2\,m$, $100\,kg$ heatshield and other equipment. Assuming a blunt body $C_D$, I get a ballistic coefficient of about $40{kg\over m^2}$. Integrating that fall through a standard atmosphere with gravity properly varying with altitude, I get a maximum velocity of $900\,{m\over s}$, and a maximum acceleration of $2.8\,G$.

The fall from a $400\,km$ tower is problematic. Then the maximum velocity is $2400\,{m\over s}$, with a maximum acceleration of $16\,G$. For a ballistic entry, you can't really get it much below $14\,G$, at an optimum $C_D$ of about $7{kg\over m^2}$ (a much larger heatshield). Perhaps with some lift you could mitigate the G forces, but then the fall wouldn't be straight down anymore.

Answer 4

If I'm reading the question correctly, this is a question about how difficult the engineering challenges are.

Given the data in the question itself(amazingly helpful) the real question is keeping the person you're dropping from being crushed/catching fire. I believe the density of air and the spirit of the question prevents effective parachuting at high altitude. Your space jumper is going to free fall for some time, decelerate as they hit the atmosphere, then presumably open a traditional parachute(at traditional terminal velocity) and land safely.

Hitting the atmosphere after free fall if you are a sounding rocket or person is nonfatal(by crushing), albeit unpleasant. 5 g is completely survivable, even without countermeasures.

So that leaves breathing(not too hard, just some oxygen) and heating problems from air compression. The design of heat shields is actually to maximize the drag coefficient and minimize the heat load, so if you're willing to bring like a toboggan made of ceramic composites to push the air out of the way, certainly. (Could be strapped to your back. Envision a ninja turtle lying on his back with legs and arms pointed straight up) If you want to dive headfirst Captain Kirk style you are going to have to have more than just a viewpane. It might be possible, but it would not be safe.

However, if you want to sacrifice dignity, lying on your back with an aeroshell could, in my estimation, be an entirely practical way to fall from geostationary orbit.

Answer 5

Science Fiction has shown several interesting possibilities for surviving the reentry, most notably, either a suit that's got a high thermal load, or an ablative shield that one rides down.

Science fact has an even more interesting possibility: the shuttlecock mode. Inspired by a badminton shuttlecock, Scaled Composites uses it as the reentry mode for the SS1 and SS2 spacecraft; SS1 rose to a level where atmosphere was no longer useful to affect attitude of the craft.

A system of extensible vanes could be used to generate a shuttlecock drogue; a high expansion foam or gas into rolled tubing could generate a nice large drogue effect, and keep friction levels from reaching thermal danger to the suited astro-parachutist.

The issue is one of not entering at a speed sufficient to damage the drogue and/or astro-parachutist.¹ And that's a de-orbit issue.

Likewise, the Aerobraking inflatable shield exemplified in A.C. Clark's 2010: Odyssey 2 is from an actual proposal to NASA (by Clark, if I remember correctly). NASA finally got around to testing the idea in 2012... IRVE-3 passed initial tests about a year ago - July, 2012.

A combination of an inflatable shield for the high speed portion², and then shuttlecock drogues after slowing enough to not be injured by atmosphere itself, and finally a parachute for final landing could make a jump from LEO or even GTO survivable. Whether or not the rig is of a practical weight as an escape system is as yet dubious, but the technology does exist.

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¹: Noting that speed, in this case, is purely relative to the atmosphere. Orbital velocity is about 7.8 km/sec for low earth orbit; surface speed at the equator is about 0.46 km/sec. So that's a considerable large amount of speed to shed: about 7.3 km/sec.
Also note: Kittinger and Baumgartner had a near-zero relative velocity due to use of a lighter than air vehicle. Any speed below about 0.1 km/s is a non-issue - 360 kph isn't too much of a problem, and the drogue can handle well more than that.

²: That's the point while still above surface speed, yet below orbital speed.