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Re: "build your own sputnik" (BBC article)

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Tue, 23 Oct 2007 23:57:21 -0400

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 ```> It's not reasonable to expect rockets to run as cheaply as airplanes: The claim was not that the total cost would be similar to airplanes, but that fuel would make up a similar portion (1/3 to 1/2) of the total cost. Thus \$10 worth of fuel per pound of payload translates into between \$20 and \$30 of total cost per pound of payload. Your arguments which follow all suggest a higher fuel consumption but provide no indication that costs other than fuel should make up a larger portion of the total cost. > Airplanes draw oxidizer from their environment; rockets must contain > and lift their oxidizer. Yes, that is extra non-payload weight, which increases the amount of fuel required to lift the craft. That amount of fuel costs \$10 per pound of payload. > Few airplanes generate enough thrust to lift the airplane vertically; > instead, wings allow a thrust less than the total weight of the > vehicle to lift the aircraft over time. Wings don't work in vacuum. Yes, spacecraft require a lot of thrust. Thus they need a fuel that provides such thrust. That quality and quantity of fuel costs \$10 per pound of payload. > Airplanes draw air from their environment to accelerate backwards for > thrust; rockets contain and lift all the mass they eject for thrust. That must mean that a spacecraft must eject more fuel to make up for not ejecting environmental air. That fuel is expensive - \$10 per pound of payload. > If you want an airplane comparison, picture a Boeing 747 flying on > afterburners that can lift it vertically, and fill the interior > with LOX. Sounds like a rocket, doesn't it? Yeah, and sounds like it would use a lot of fuel. Interesting that the fuel still ends up costing only \$10 per pound of payload. Of course, we all know it costs tens of thousands of dollars to put a pound of payload into orbit. I wonder where the rest of that money goes. Electronics are cheap. Fuel is cheap. Legal and political issues are negligible. It must be some kind of technical challenge - I just don't see how. > There's an astoundingly fantastic rocket primer at: > > http://www.projectrho.com/rocket/index.html It doesn't seem to explain anything about lobbying or permits. Oh, wait... artificial gravity... that explains why the technical challenges are so daunting. As if natural gravity wasn't troublesome enough :-D -- There are two ways of constructing a software design: One way is to make it so simple that there are obviously no deficiencies, and the other way is to make it so complicated that there are no obvious deficiencies. The first method is far more difficult.                     - C.A.R. Hoare -```

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