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JHotz
2005-Feb-03, 08:56 AM
Would it be worthwhile to launch a spacecraft from a high altitude balloon?

kucharek
2005-Feb-03, 09:38 AM
No. A rocket needs most energy to gain velocity. By the baloon, you just save the potential energy between the different heights. Let's assume a baloon that goes up 30000 meters.
To lift 1 kg of mass to 30000 m, you need m*g*h Joule, assuming g=10m/s^2, thats 300kJ.
To give 1kg a velocity of 8000m/s (needed for a low, circular orbit), you've to give him this kinetic energy, which is m*(v^2)/2 Joule.
8000*8000/2=32000 kJ

Compare the 300kJ you save with the 32000kJ needed and then think of the complexity of the operation of launching from a baloon.

Harald

ToSeek
2005-Feb-03, 03:09 PM
It's been done: rockoon (http://www.astronautix.com/lvs/rockoon.htm).

And amateurs are still doing it. (http://hiwaay.net/~hal5/HALO/SL-1/sl-1b-pre.shtml)

It's probably not a good way to get into orbit, but if the goal is just altitude, the balloons provide an easy way to get a "head start."

orangeSCT
2005-Feb-03, 03:28 PM
Speaking of launching from a balloon, what ever happened to the DaVinci project? Have they given up or is there still a plan for a launch? I always had my doubts that they were close when they announced a launch date right after SS1. I think they were more looking for publicity and a sponsor to help recoup some of there costs. I mean jeez..... look at their sponsor Golden Palace Casino :roll: .

JHotz
2005-Feb-04, 04:07 AM
No. A rocket needs most energy to gain velocity. By the baloon, you just save the potential energy between the different heights. Let's assume a baloon that goes up 30000 meters.
To lift 1 kg of mass to 30000 m, you need m*g*h Joule, assuming g=10m/s^2, thats 300kJ.
To give 1kg a velocity of 8000m/s (needed for a low, circular orbit), you've to give him this kinetic energy, which is m*(v^2)/2 Joule.
8000*8000/2=32000 kJ

Compare the 300kJ you save with the 32000kJ needed and then think of the complexity of the operation of launching from a baloon.

Harald


Thank you for responding to my post.

I think you have missed a point. Why do rockets launch pointed straight up? If a satellite wants to achieve a higher orbit it does not fire its thrust towards the earth. The thrust is directed opposite the direction of its orbit. If the launch began from orbit you would be correct. The reality is the atmosphere must be cleared before your formula applies. That is why rockets fly straight up.

If a rocket were to stop and hover it would be expending tremendous energy to stay at one altitude. Therefore the faster a rocket clears the atmosphere the less energy is wasted just fighting gravity. However the faster it flies through the air the more friction is created.

This line of reasoning tells me it actually takes many times the energy your formula calculate to clear the atmosphere.

Furthermore is a balloon is high enough, and therefore air resistance is low enough, a more efficient method of launch like and induction catapult may be used saving the fuel weight completely. Power could be provided by a reactor, beamed from the ground or beamed from space.