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Its difficult to put this into the title.

I was watching the Redbull Jump and noticed that the height of this is at 39 kilometres (24 mi) the atmosphere pressure is at I believe about 0.4% of that at sea-level. I was imagining, what if a large satellite dragged a cable (bungie cord, rope) below it into the atmosphere and the person grabbed onto the cord that is below the satellite, from the position of the Redbull jump altitude. The satellite may or may not be geo-stationary. Since the atmosphere pressure is low, even if the cable was moving through the atmosphere, its air friction would be relatively low and therefore its movement through the atmosphere wouldn't be much of a concern. Maybe there would be a lower chance of the cable breaking, also less cable length and therefore less weight could be used.

Would this be a better way to get an object into space when compared with a full cable from the satellite to earth as in the traditional space elevator idea http://en.wikipedia.org/wiki/Space_elevator. Can you compare and contrast the two options against each other?

Photo of Red Bull Jump http://i.imgur.com/thjAO.jpg

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2 Answers 2

up vote 3 down vote accepted

The practical lowest orbit is around 300km and a velocity of 8km/s - around 26 times the speed of sound at the altitude of the balloon jump.

So imagine the mass of a 300km long rope and even with a thin atmosphere there is quite a lot of friction on something moving at Mach 26

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This indicates that a geostationary orbit, or something close to it, is preferable. But it doesn't address whether or not skipping out the final 39km to the ground would be an advantage over dropping it to the ground, for packages which can be raised up to that level in the atmosphere. –  Niel de Beaudrap Oct 15 '12 at 15:45

Your biggest issue is simply that without a tether and a counterweight, your cable is effectively just sitting in a very precarious equilibrium (at best). Moving any weight up the cable causes the cable to be pulled downwards, and unless you counter this somehow, your cable will eventually fall to the ground. In fact, the friction of the atmosphere itself (however small it may be) will eventually drag it down, unless you provide some kind of constant thrust to counter it.

The space elevator design works around this problem using a counterweight - the weight itself is placed in a position so that it would "fly away" if it wasn't tethered to the ground. This means that the cable is effectively being pulled away from the ground, and it is this force which allows you to traverse it without it falling back down to the ground. It's basically harnessing the earth's rotation (and the strength of the cable) to keep the cable in position.

Aside from this, you'd typically want your space elevator to be a lot longer than just a few hundred kilometers to get the best practical uses (e.g. you'd have to be around 50,000km to have escape velocity without any additional thrust). So basically, the first 39km isn't really the problem.

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