Cuddihy's Cut

Cuddihy's Cut on the events of the day....


Sunday, February 12, 2006

Lunar Architecture

Okay, evidently Blogger lets you post pictures now, so I'm more willing to spend some time blogging

I'm just starting this out (again), and I'm getting married next weekend to an awesome babe, so don't expect too much this week. (ha. nobody will read this for months if ever.)

Here's a start:

Over at Selenian Bookdocks Jon Goff posted an idea that piqued my interest: an entirely reusable LEO-->Moon-->LEO architecture, using depots in LEO and L1. The interesting thing to me was the idea of using propulsive braking for the return--even when it costs you Ginormous amounts of fuel.

I did a little excel check and found that, although it's physically possible, it's kind of nuts: for example, using LOX/Ker (Is 340s), with a bare-bones module of 7 tons, and a payload-to-drymass fraction of 0.17 (slightly better than any existing rocket), you need 223 metric tons of propellant at L1 to fuel your 40 ton LM.

Lets say you brought that propellant to L1 in a reusable LEO-L1 transporter that drops off 10 tons at a time, and uses aerobraking to get into LEO. that's 22 trips. Plus one additional trip to bring the lunar module. 23. And each of those trips is going to cost you 264 mT propellant in LEO. That's 6077 mT of propellant you need in LEO, just to accomplish one lunar mission.

One thing most depot-advocates argue for is that cheaper launchers with higher launch rates will lower the cost/lb to orbit. It becomes clear why they have to argue that if you actually run the numbers. At 6077 mT of payload, even if you use the (currently) hypothetical Falcon 9, at 9.3 mT to LEO, you need 653 Falcon 9s ($27 mil a pop, $17 bil total).

It's not hard to see why even CEV proposals that use L1 stayed away from depending on reusability .

That doesn't mean the resuability architecture idea should be thrown away, however.

MTF

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