Thursday, July 21, 2011

More Paper Rocketry...

I'm missing the boat... I was going to go take the ferry to visit the Cape May Zoo, today, but after I watched Atlantis return I dawdled, lay down for a bit, and now I'm sitting here working up paper rockets, again. This goes back to GURPS space, and from there to Greg Porter's VDS and now Stuff!, which I highly recommend.
When I 'design' stuff for near future space adventure, or whatever, I'm not really doing anything but folding paper airplanes, drawing paper rockets. In this particualar case, a 'Single Stage To Orbit', with a crew return vehicle for a payload. Leave the tanks, engines (or return those) and residuals on orbit, hung from the bottom of a space tether, lifted up to the mid-point, or out to the high end of the tether.

       Assume the CRV or payload is 5 metric tonnes, 5,000 kg
       Assume, further, that the SSTO is one or two orders of magnitude larger; or 200 tonnes
       Assume that we need 1.5 G acceleration to lift off, call it 3 million newtons, and the thrust to mass ratio is 50 to 1, so that the engines mass 3% of Gross Lift Off Mass, or 6 tonnes
       A 10 to 1 fuel to dry mass ratio, ~91% LOX/LH, 182 tonnes, 156 tonnes of LOX, 26 tonnes of LH
       LOX is dense, but go with 160 m^3 for the oxidizer tank and 360 m^3 for the fuel tank
       The LOX tank is a 7 meter sphere sitting on top of the 9 meter LH tank
       Go with 500 m^3 of structure, at 1 tonne per m^3, is 5 tonnes
       Assume power supply and avionics can be brought in under 1 tonne
       Running total is 17 tonnes dry, 199 tonnes wet, 10 to 1 fuel to dry mass ratio
       Sloppy estimate of $1m per tonne at launch is ~$200 million
       At $5K per kg of dry mass vehicle, 12,000 kg, that would be $60 million plus fuel.

One launch per week is 50 vehicles a year (two weeks off 8-). $3 billion, for 250 tonnes of cargo and passengers... and 600 tonnes of bootstrap mass. Perhaps as much as 50 tonnes of water?

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