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What advantage the "Space Elevator"?

The concept of getting to orbit via a "Space Elevator" has been around for years and seems to be gaining ground.

 

Leaving aside the practical difficulties such as manufacturing a strong enough filament, what would be the advantage?

 

Surely the "lift" would not only have to haul itself and its payload up to say the geosynchronous altitude but would also have to provide sufficiant energy to bring itself to the orbital velocity. Given that achieving orbit would probably take days rather than the shuttles' minutes, complex life support systems and supplies, with redundant systems, would also be required. Then again, energy would have to be supplied to negate the orbital speed on the way down.

 

Where exactly would be the savings over conventional orbital transition? Am I missing something?
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  • Asked by wilsr1
  • on 2009-11-24 09:56:59
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Categories: Technology.

Tags: energy.

 

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 wilsr1 says:

I still cannot see an answer to my question!

 

Anything in orbit - whether "free" or "tethered" - must contain energy by virtue of both height and speed. The potential energy is imparted by the energy used to crawl up the tether. But unless "horizontal" - ie., kinetic - energy is also imparted the lifted cabin would gradually fall behind as it climbed. So kinetic energy must surely be supplied as the height increased, otherwise as the cabin failed to keep pace with the tether it would drag the whole caboodle down? The only way I can think that a "horizontal" energy vector could be imparted is by reaction - and that requires reaction mass, which must be lifted as well.

 

Unless something like an ion engine was used to "fire" horizontally - in which case the trip would take a very long time!

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posted on 2009-12-08 01:47:22 | Report abuse

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 Paul_Pedant says:

Far as I can figure it, the kinetic energy is small compared with the potential energy.

For a one-kilogramme object on the equator at the base of the tether, it is already doing 40,000 km per day. At a geostationary height of 36,000 km, it would be doing 226,000 km per day. So it changes from 416 metres/second to 2616 m/s, which I make 2.42 MJ.

The potential energy of gravity, integrated from surface to 36,000 km, seems to come out at 37.7 MJ, so the potential energy outweighs the kinetic by about 15:1. (I have to admit my integration is a little flaky.)

I agree the tether will slightly lag the planet, but then the tether has a large weight outside the geosynchronous point to provide stability through centripetal tension. I would take the view that the kinetic energy is taken from the forward pull of the planet when objects ascend, and this is recovered when they descend. It would even appear that the tension due to the lagging tether would tend to pull the elevator up the tether.

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posted on 2010-12-29 22:34:03 | Report abuse

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