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RE: starship-design: How to build a station.

> Quick correction - hydrazine *is* indeed a monopropellant.
> Example: on two
> of the satellites we operate, it is stored in liquid form
> under pressure, in
> titanium alloy tanks. Opening a tank valve results in the
> hydrazine liquid
> being pressure-fed to a thruster, where it passes over a
> catalyst bed and
> decomposes to provide thrust.
> Another method that can be employed is to use a small amount
> of oxidiser to
> provide a hypergolic reaction - the thermal energy causing
> decomposition.
> Once the oxidiser is used up, the reaction continues as the hydrazine
> rapidly decomposes.
> The catalytic reaction mentioned above is exothermic, which
> provides enough
> heat to start and maintain the decomposition process.

Thanks Chris, but both reactions you just described are bipropellant. The
catalytic reaction breaks the hydrazine down to liberate a small quantity of
oxygen for use as an oxidizer. The hypergolic reaction uses a mixture of
hydrazine - typically mono-methyl hydrazine mixed with an oxidizer such as
nitrogen tetraoxide to produce spontaneous combustion. Although both
reactions are exothermic, the hypergolic one is much more so. The key word
was the last one in your post - decomposition - as opposed to combustion.

I spent many years working with these fuels and acquired a healthy respect
and understanding of them, mostly by having the bejeesus scared out of me.
You have to be there when the leak check detector turns purple to