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Posted by: Zvezdichko Mar 3 2007, 09:32 PM

Hmmm... the braking engines are said to be "hydrazine engine", but what does it mean? Is the oxidiser dinitrogen tetroxide and is the fuel hypergolic?

Posted by: mcaplinger Mar 3 2007, 10:03 PM

QUOTE (Zvezdichko @ Mar 3 2007, 01:32 PM)

Posted by: edstrick Mar 4 2007, 08:30 AM

Hydrazine (whichever one... there are different varieties, as there are different "alcohols") in this context is a chemically unstable monopropellant. Like hydrogen-peroxide, it semi-violently breaks down when exposed to something it doesn't like (catalyst), forming superheated vapors. You feed it into the center of a "catalyst bed" though some kind of injection system under pressure that I'd presume is equal to that of the rocket chamber, it decomposes and comes out screaming out of the catalyst bed into the engine chamber and then out the nozzle.

Monopropellants are not very efficient. Their specific-impulse (bounce-per-ounce) is sucky, but ...

THEY'RE SIMPLE.

Mars landings ... you need to slow from a few hundred miles-per-hour, not thousands. Atmosphere, heat shields, and parachutes do that. You can afford some modest hover time, too, at a not horrendous expense in propellant mass.

The K.I.S.S. principle holds here very nicely. KEEP IT SIMPLE, STUPID!!!

Posted by: Zvezdichko Mar 4 2007, 09:24 AM

edstrik: you made it looking like a steam engine

Posted by: djellison Mar 4 2007, 10:35 AM

On principle, hydrazine thrusters ARE simpler than a steam engine

Heat the cat, open the valve...bingo.

Doug