- #1

PhilKravitz

You are using an out of date browser. It may not display this or other websites correctly.

You should upgrade or use an alternative browser.

You should upgrade or use an alternative browser.

- Thread starter PhilKravitz
- Start date

- #1

PhilKravitz

- #2

russ_watters

Mentor

- 20,963

- 7,587

- #3

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.

- #4

russ_watters

Mentor

- 20,963

- 7,587

- #5

- 4,662

- 5

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.

- #6

- 3,277

- 955

- #7

- 4,662

- 5

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

Last edited:

- #8

mheslep

Gold Member

- 317

- 728

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.

Last edited:

Share: