Isn't it written in stone that you have to put more energy into water than can be extracted from it? Answered
I can see how astronauts could need oxygen from water on the moon, but haven't we always been told it takes more energy to separate the molecules than can be gained from burning them?
In reply to a response from my last question, I referenced something I read a long while back. It was about deep space probes extracting water from Mars or other planets and using it for fuel to go even further (faster I'm assuming).
So sure, astronauts need to breathe, and would be able to recoup some of the lost energy from the hydrogen, but how would an unmanned space probe benefit from such a loss of energy?