Saturday, August 06, 2011

We've Already Got Propellant Depots

The solution to so many space logistics problems is: use a bigger rocket. Propellant depots allow you to add another solution: use more rockets.

Now, for some reason, many people who are advocates of propellant depots object to just using existing space storable propellants because that would mean you'd need to launch more mass than if you used cryogenic propellants. Well, so what? More launches - that's a good thing!

We don't need technology development to make propellant depots work. They already work.. we already have one in orbit!

Suppose you want to send 100 tons to Mars transfer orbit. You need either 236 tons of storable propellant or 144 tons of cryogenic propellant (and that's being overly generous to cryogenics). Instead of 5 Falcon Heavy launches you now only need 3. So what? How much is that worth?

So, ya know, NASA has selected companies to study storing cryogenic propellants in space.. and that's great. Technology development, in general, is fantastic and it makes things better in the future. Unfortunately I'm already hearing people say "woohoo! Now we'll have propellant depots and we won't have to waste $38 billion on a heavy lift vehicle to no-where!". Well, no. We already have propellant depots and we already don't need heavy lift to go beyond LEO.

There is, however, a few things that we are in desperate need of.... the political will to go, anywhere, on the government side, and an outspoken willingness to go it alone, if necessary, on the commercial side.

5 comments:

  1. Music to my ears Trent.

    Now, for some reason, many people who are advocates of propellant depots object to just using existing space storable propellants because that would mean you'd need to launch more mass than if you used cryogenic propellants.

    Not even that much more mass if you use three body trajectories and Lagrange point staging. Lagrange points are very close to the edge of the Earth's gravity well. From there on you could use storable propellant, and even electrical propulsion, which would have much higher Isp still.

    But it's strange, isn't it? It's just like SDLV proponents who someone always try to sneak in an HLV without a convincing reason.

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  2. Aargh, I meant "somehow", not "someone".

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  3. Yeah.. also We've Already God Electric Propulsion, which is a great way to get storable propellant out to EML1/2.

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  4. And beyond, where the van Allens don't matter, say to LLO, GEO, a Mars Lagrange point and LMO. That way you could do propulsive LMO insertion and descent and TEI from the Mars Lagrange point.

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  5. Fantastic post. You hit this one out the park Trent. We could be doing shakedown cruises with a general purpose ship (capable of taking a dozen to mars or elsewhere) as soon as the $300m check clears. Put a dozen such ships in orbit and we have our depot relay. After positioning we could use Dragons for crew rotation between the ships.

    The pieces are falling together. No magic bullets required. Put a dozen ships 'halfway to anywhere' and work out the radiation issues live.

    How long before the Bigelow 7 becomes a land rush?

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