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July 07, 2007

Space Diving

Via Dizzy comes this.

So, you're in orbit, in a space suit, with a couple of parachutes. Why can't you just descend from orbit on said parachutes?

I'll admit to having had this rolling around the back of my mind for months: say you had a Space Elevator, wouldn't you end up attracting the base jumping crowd?

The thing I can't work out though is why it wouldn't work. Can anyone clear this up for me?

July 7, 2007 in Space | Permalink


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Because you're in ORBIT.
You had to apply a great deal of energy to get yourself up there, and now get to expend it getting yourself down. If you slow yourself down (you're doing about 25,000 mph at this point)you will drop to a lower orbit and eventually hit the atmosphere, slowing further due to friction while heating yourself up. Eventually at about 100,000 feet there will be sufficient atmospheric drag to deploy the 'chutes and your slightly charred self can drift merrily to earth.

Posted by: Robert | Jul 7, 2007 11:44:34 AM

As Eric Idle once said:

"Just remember that you're standing on a planet that's revolving, revolving at 900 miles and hour..."

Posted by: Unity | Jul 7, 2007 11:50:13 AM

Bollocks. It's perfectly safe and feasible.

"The highest-altitude parachute jump was made by Joseph Kittinger of the US airforce, who jumped from a balloon at 31,333 metres on 16 August 1960. He was in free fall for 4 minutes 36 seconds, reaching an estimated speed of 1150 kilometres per hour. He opened his parachute at 5,500 metres."

NB 31,333 metres = about twenty miles, about the edge of the atmosphere.

Posted by: Mark Wadsworth | Jul 7, 2007 12:17:55 PM

The trick to it is the freefall. The velocity of the fall must be below a certain speed when the parachute opens. If the astronaut is falling too fast, the parachute will rip apart.

Posted by: Charles Holden | Jul 7, 2007 12:27:51 PM

It depends on how attenuated the atmosphere is at the altitude of your orbit. If you are as far away as the moon, say, you'll die of old age before a parachute does any good.

Posted by: dearieme | Jul 7, 2007 12:38:17 PM

Because you'll burn to death on re-entry?

Posted by: Imli | Jul 7, 2007 1:40:33 PM

The issue isn't the altitude, but the velocity that you're going at while in orbit. 18,000 mph or so is one hell of a clip, and the atmosphere will have to slow you down first. For that, you'll need some kind of heatshield to absorb the heat generated by your deceleration.

Once you slow down to about Mach 1 or so in the upper atmosphere, simply jettison the heatshield and freefall away.

- Getting some kind of heatshield.
- Slowing down for reentry (some kind of retrorocket required.
- Remaining stable on reentry
- Choosing the right point to get rid of heatshield (preferably in a location where it won't fall on someone's head!)

For the Space Elevator, unless jumping from the station at geostationary orbit (where you won't go far anyway), you won't be in orbit. At a low altitude (say, less than 200 miles or so), you actually won't have much of an orbit at all (or to put it another way, your orbital trajectory will intersect the Earth not far from your jumping point) and it might be more practical (although with no atmospheric drag, you'll get up to one hell of a clip)

Posted by: Andy Cooke | Jul 7, 2007 2:08:06 PM

With an ablative shield, an astronaut could survive reentry. Encyclopedia Astronautica has a page of designs for crew recovery vehicles and other personal reentry devices.

The International Space Station keeps a Soyuz reentry capsule on standby in case of emergency.

Posted by: gdr | Jul 7, 2007 3:14:14 PM

An object in orbit will eventually be pulled in by the Earth's gravitational pull, depending on any forces that may already be acting upon the object. However, you would need something much thicker and better insulated than a spacesuit, to get through Earth's atmosphere (also with the pressures acting on the spacesuit). Even if you could get past this barrier, you would have a very high chance of landing in some water (in which case you would need a way to shed the spacesuit very quickly) or in a very cold place.

Posted by: Opinionated | Jul 7, 2007 3:28:48 PM

How about "Beam me down, Scotty"?

Works for me every time.

Posted by: Roger Thornhill | Jul 7, 2007 4:35:45 PM

Andy, fair point, but there is such a thing as geo-stationary orbit, as you yourself point out. How high up does a geo-stationary satellite have to be? anybody know?

Tim adds: It's either 23k km or 23 k miles. Can't remember.

Posted by: Mark Wadsworth | Jul 7, 2007 4:51:31 PM

It's 23,000 miles. F***, that's a long way up, that's a tenth of the way to the Moon.

Interestingly, from the point of view of the Moon, Planet Earth is a geo-stationary satellite. Think about it!

Posted by: Mark Wadsworth | Jul 7, 2007 6:16:49 PM

Not sure I'd want to try it if I could. With my luck, I'd probably drop smack dabble into the middle of a hole in the ozone layer and end up in another dimension (or one of the 7 layers of Hell).

Posted by: Internet Ronin | Jul 7, 2007 6:53:29 PM

I'll admit to having had this rolling around the back of my mind for months: say you had a Space Elevator, wouldn't you end up attracting the base jumping crowd?

We've had several inquiries along those lines. Jumpers will need to make sure they move far away from the ribbon - from certain angles it will be hard to see and running into it at speed will be unpleasant. Or fatal.

Base jumpers might be deterred - the current plans call for the thing to be way the heck out in the middle of the ocean; it would not be cool to land in the water miles and miles away from your recovery boat.

Brian Dunbar

Posted by: Brian | Jul 7, 2007 8:31:15 PM

There was something in the news just the other day about a company starting up to offer high-altitude (and eventually orbital) parachute jumping.

They reckoned that you'd need a spacesuit able to withstand 350C for about 10 minutes as you re-enter, iirc. Not too much of a technical challenge these days, surely?

Posted by: sanbikinoraion | Jul 9, 2007 12:41:15 PM

Regarding the Space-Elevator:
Has anybody yet reflected on the electric aspects of such a future invention to be functioning like Benjamin F's lightning conductor ?
Of course any metal would be impossible to be
used, as the electric current of 300 kV and up to 100 Mio Amps may cause melting before anything can be lifted or downed.
But carbon-fibres are supposed to be well conductive too.
Any isolative or nonconductive threat might by
condensation of tropospheric waters be acting as
a short-time-conductor just enough Coulombs to
evaporate the water condensed and burn down the
So the updated Jack'sonian Beanstalk-Variation may have to stay in the old book with the Ogre ?
Isn't it a shame for NASA to have supported such ideas primarily ?
Does anybody know, how this
Planetary unique spheric electrical Field-Generator in High-Vacuum and dryness-secured layered gaseous nitrous & nitric anhydrides at critical parameters triple points is actually
working ?
Are there any Specialist's Publications known ?
It will certainly be extremely dangerous to try and put up similar experimental conditions in any how-ever-high-powered and supported Laboratory.
Who knows anything along these lines of mesospheric realities ?

Posted by: klas | Mar 11, 2008 6:32:58 AM