How much fuel would we save if launching from orbit?

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Ben Fehrman

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Ben Fehrman asked the Naked Scientists:
If a space vehicle were to travel to the moon or Mars, but departed from an
Earth orbit rather than from the Earth itself, how much fuel would be saved on that trip?  And how much fuel would be used transporting the fuel needed to travel that far to orbit?  


What do you think?


Offline Soul Surfer

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How much fuel would we save if launching from orbit?
« Reply #1 on: 12/02/2009 18:16:41 »
Launching a spacecraft from orbit uses a great deal less fuel than launching from the surface of the earth.

Launching a tanker to carry the fuel into orbit uses a similar amount of fuel as would be used as starting from the earth's surface. so sending the spacecraft and the fuel in separate trips is unlikely to be more fuel efficient but assuming that boosters have a limited carrying capacity it does allow heavier loads to be sent to the moon by effectively sending them up separately.  However the transfer of fuel in space could be quite difficult.
« Last Edit: 12/02/2009 19:03:23 by Soul Surfer »
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Offline daveshorts

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How much fuel would we save if launching from orbit?
« Reply #2 on: 12/02/2009 18:51:56 »
The main advantage you get from putting things together in orbit is actually mass production. If you want to ship 1000 tonnes to the moon. You could build a massive rocket to lift it up there, but you would only ever use 1 or 2 of them and so you would have an immense R&D budget to build the thing, a few would explode on takeoff (as new rocket designs always do) and it would end up very expensive.

If on the other hand you fly 10 or even 100 smaller rockets, you can build a production line, get out all the bugs and make the whole process cheaper.

Saying that if you are building the same number of rockets, the large one will normally be cheaper, as you have to put guidance, monitoring systems etc on a rocket no matter how small it is. So there will be an optimum size of rocket to build to lift a certain amount of stuff into orbit.