I think you underestimate the amount of pressure hydrogen tanks are under. You need pretty large solar panels to power the compressor alone. So large that you c

I think you underestimate the amount of pressure hydrogen tanks are under. You need pretty large solar panels to power the compressor alone. So large that you can better charge a battery over a day or two. Why engineer a new kind of ICE when electric engines and batteries are already ready to go as they are both needed for the flight to the moon? Also, you don't want explosions in space. Especially not when supplied with oxygen tanks.