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PhilKravitz

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PhilKravitz

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russ_watters

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PhilKravitz

If one buy the joules per kilogram required to reach orbit from the electric company in the form of electricity it is well let see

1 kilo to say 1e4 m/sec using 1/2*m*v^2 is 5E7 joules

so 1 kilowatt hour at 20 cents from con edison is 3.6e6 joules for 20 cents. So 5E7 joules would cost about $3. Of course there are always losses in any system but even with only 10% eff. that would be $30 per kilo to orbit as far as energy costs are concerned. But rockets cost roughly $10,000 per kilo.

I do like the beamed power solutions I have been seeing articles about recently. Beam power to the "rocket" in the form of microwaves or as laser light.

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russ_watters

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There is a lot more than just energy required to launch a rocket. TheIf one buy the joules per kilogram required to reach orbit from the electric company in the form of electricity it is well let see

1 kilo to say 1e4 m/sec using 1/2*m*v^2 is 5E7 joules

so 1 kilowatt hour at 20 cents from con edison is 3.6e6 joules for 20 cents. So 5E7 joules would cost about $3. Of course there are always losses in any system but even with only 10% eff. that would be $30 per kilo to orbit as far as energy costs are concerned. But rockets cost roughly $10,000 per kilo.

I do like the beamed power solutions I have been seeing articles about recently. Beam power to the "rocket" in the form of microwaves or as laser light.

http://www.braeunig.us/space/propuls.htm

Bob S

*photons are an extremely poor source of momentum transfer, in terms of thrust per unit energy.

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Kinetic energy may be written (Newtoninan classical mechanics)I do like the beamed power solutions I have been seeing articles about recently. Beam power to the "rocket" in the form of microwaves or as laser light.

E

So the momentum p is, for a given classical energy E

p = sqrt(2mE

So classically, photons have no mass and therefore can transfer no momentum.

Relativistically, however

p = E

where E

So there is a very small momentum transfer with photons.

Bob S

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mheslep

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There must have been some prior looks at some kind of pre-launch acceleration tower for heavy lift vehicles, to save on launch fuel? It appears that a 3g (?) acceleration along, say, a 1000M 'elevator' tower takes the vehicle to ~250 m/s = sqrt(2 * 3g * height) before it needs to burn its own fuel. This would be the heavy lift version of what is already done with air launched rockets such as Pegasus.

Edit: Listing problems/comments here as they occur to me:

I suppose what I'm looking for here are the right terms for which to google, as nothing pops up under the terms I have used above.

Edit: Listing problems/comments here as they occur to me:

- A launch failure might destroy not only the vehicle but the significant investment in the vehicle pre-launch elevator.
- Drag incurred at low altitude (250 m/s) forces the vehicle to give back some energy gained by using the elevator. (Meaning the launch needs to move from the Cape to Pike's Peak :tongue:)
- Fuel savings: ~2kg of LOX per metric ton of payload pre-accelerated to 250 m/s [using a savings of 15 MJ combustion energy per kg of LOX to reach 13 kJ of kinetic energy per kg of payload at launch velocity]. So on the shuttle for instance at 2000 mt launch weight, this would save 4 mt of LOX, not counting mechanical structure savings, etc.
- Mechanical complexity of the elevator. Lifting a 2000 mt vehicle slowly is achievable with current technology. Lifting and accelerating something to 150 m/s is achievable with current technology. Doing both things together might be quite difficult - rapidly changing large moments along the tower, etc

I suppose what I'm looking for here are the right terms for which to google, as nothing pops up under the terms I have used above.

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