# How possible are 'space jumps'?

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.

• Great question. I've always thought the case of doing this from an orbit was particularly interesting. Some minimum amount of deorbit impulse applied to a personal re-entry suit. Heinlein's Starship Troopers realized. – Erik Jul 19 '13 at 21:41
• Actually, heat during reentry isn't caused by friction, it's caused by compression. – Don Branson Jul 20 '13 at 3:21
• It is awful how people just c&p numbers like "10km" etc. Plot based on actual data added to the question! – s-m-e Jul 20 '13 at 17:04
• On a related topic, there is this question on worldbuilding. – Quentin Jan 17 '17 at 8:56
• @MagicOctopusUrn Felix Baumgartner jumped from 128k feet, i.e. 39 km ;) He also held the record for two years only: The current record holder is Alan Eustace. He jumped from 136k feet, a little more than 41 km. – s-m-e Jun 20 '18 at 21:01

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.

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...

• Thanks for the answer. Well, capsules are boring and Kirk does not have winglets :-) I am asking about a 'simple' parachute-jump in a suit from a static position - straight down. – s-m-e Jul 19 '13 at 22:59
• @ernestopheles: In that case the answer is NOT. You go splat against thicker layers of air. You need to spiral down, reducing your orbit gradually. – SF. Jul 20 '13 at 9:07
• @SF. I added a plot to the question a while ago. I would not call it splat. Deceleration builds up rather smoothly to a survivable level. I am busy looking for some data from a 400km drop. It should look similar, with just a slightly higher peak deceleration. – s-m-e Jul 29 '13 at 20:57
• @ernestopheles: 360km of freefall above the atmosphere would get you to about 2650m/s. Then within next 25km or so you'd lose about all of this speed. That's about 14g on the average during that period. You can be fairly sure peak acceleration would be considerably higher, and AFAIR, 8g is survivable "sustained", 12g in short pulses, 14g causes significant injuries... In your case average deceleration over that critical 25km is 1.6g, peak - 5.5, you can expect similar proportions here, rough estimate - 48g, that definitely meets the definition of "splat". – SF. Jul 29 '13 at 21:50
• @SF. Fair enough, this basically almost rules out the 400km scenario. If you would like to compile this into a proper, systematic answer ... – s-m-e Jul 29 '13 at 23:29

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.

• Again, thx for the answer. I am actually not asking how one could come into position for such a jump or the likelihood of it happening. I am not asking for de-orbiting. I can punch some numbers into my calculator, ignore atmospheric drag (above '10 km') and will come to something like 2,000 m/s. But it kind of does not answer my question. Intuitively, the jumps described in my question can work somehow, we can hopefully agree on that - at the very least from the 'true' edge of space. So this answer is just too easy. – s-m-e Jul 20 '13 at 0:10
• @ernestopheles: I would argue that I do answer the question. Jumping from LEO is about the highest I could ever imagine someone jumping, so it should give you a pretty decent place to start. – PearsonArtPhoto Jul 20 '13 at 0:12

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.

• Good answer, thank you. The math is really interesting. Your results for the 100km scenario are at the same order of magnitude than what I saw with sounding rockets. It makes me think that your results for the 400km scenario are correct, too, virtually rendering it impossible ... – s-m-e Aug 26 '13 at 8:35
• I forgot to mention that you have to add $1\,G$ to the actual acceleration to get what the unfortunate occupant will feel. So the accelerations to be tolerated are $3.8\,G$ and $17\,G$ respectively. – Mark Adler Aug 26 '13 at 21:18
• It looks like the second guy is re entering in a potato – Antzi Sep 11 '15 at 19:29

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.

• Your first & second paragraph nail what the question is about :-) Thanks for the answer and welcome to this place. I would not entirely rule out high-altitude parachutes. There is good stuff, which works at high speeds and in thin atmospheres - see latest Mars landings. Your statement is similar to what my intuition tells me. Well, it is intuition, which is the point. But has it ever been researched? Has someone punched some actual numbers into computers or done some designing or testing? – s-m-e Jul 29 '13 at 23:40

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.

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.