[kanox]

> Sure but can you refuel with more hydrazine on the Moon?

Water might be present on the moon in always-shadowed craters and it is not 100% proven. Those same craters might also contain other volatiles that could maybe be used to synthesize hydrazine or methane.

If water is found on the moon it could definitely be used to produce hydrolox which has amazing isp, ~450.

> Also, is hydrazine so efficient below 30 watts?

Hydrazine monopropellant is decomposed with a catalyst, it doesn't need external power.

If you need an external power source then you're competing against various ion thrusters which can get 10x the Isp. Maybe it's main advantage is extremely small size, or perhaps it gets higher thrust?