Why the different Apollo RCS fuels? Nov 22, 2011 7:39:31 GMT -4
Post by ka9q on Nov 22, 2011 7:39:31 GMT -4
Although these fuels are liquids at STP, you did recently point out that N2O4 has an uncomfortably high freezing point. It can present a thermal control challenge especially if you expect to be in eclipse for a long time. I suppose if that's an insurmountable problem there's always IRFNA.
N2H4 also has a high freezing point, and while the methylated hydrazines have much lower freezing points they're not suitable for monopropellant engines.
What about N2O (nitrous oxide)? I'm familiar with its use as an oxidizer in hybrid rockets, especially amateur high power rockets because it is far less toxic and corrosive than the other oxides of nitrogen. Its main drawbacks are lower performance than N2O4 and a much higher vapor pressure at 20°C: 58.5 bar. It can be kept liquid at room temperature if you don't care too much about the weight of the tanks but I suspect that's a much bigger deal in a spacecraft than in a low performance amateur rocket. Still, it was used successfully in Space Ship One.
I had forgotten that N2O also has a positive enthalpy of formation, meaning it can be used in a monopropellant thruster with a catalyst though the performance isn't great. Has anyone actually done this?