Rocket fuel from lunar water

For many years now, Bob Park has been writing What’s New, a highly opinionated and often sarcastic weekly column about issues relating physics to society and public policy.  Here’s a bit from the latest:

WATER: IS H2O A FORMULA FOR ROCKET FUEL? Even as I write this, the Lunar Crater Observation and Sensing Satellite is getting itself aligned in a lunar polar orbit. Its job is to look into deep lunar craters for any sign of the frozen water that some are certain is hidden in the shadows. It would be very expensive water. I told NASA that I would be happy to leave my garden hose out and they could come by and take all the water they want. They weren't interested. They wanted water on the Moon, where they could use it to refuel rockets. “Is water rocket fuel,” I asked? “Hydrogen is a component of rocket fuel,” I was told. “You have to split the water.” “Doesn’t that take energy,” I asked? “Excuse me,” he said, “my cell phone is ringing.”

(As of this writing, the latest column is not up on the web site; it was sent by email on Friday.)

For those who’ve never seen the column, this is a pretty typical sample in both content and tone.  If you like this sort of thing, then this is the sort of thing you’ll like.

Anyway, I’ve heard this sort of thing before: if we find water on the Moon, we can separate the hydrogen and oxygen to make rocket fuel.  One would hope that any physics student — or indeed a decent middle-school science student — could see the problem here: to separate the molecules requires precisely as much energy as you get back when you burn them.  So what are you getting out of this?  That’s Park’s point.

I find it hard to believe that NASA would be stupid enough to make this elementary error (or perhaps I should say that they would be stupid in this particular way).  And as much as I enjoy Park’s column, he does have his axes to grind, so you have to read him skeptically.  I should add that most of the time, his biases are on the side of the (metaphorical, secular) angels: He seems to be primarily animated by hatred of ignorance, superstition, and pseudoscience.

Anyway, it turns out that when people talk about using water as rocket fuel, they’re envisioning a future in which we have good ways of producing energy, but those ways aren’t portable: think nuclear power plants or massive arrays of solar cells.  If we had a nuclear plant on the Moon, we could do electrolysis and generate lots of hydrogen for use as a rocket fuel, which would be a lot more practical than putting the nuclear plant on the rocket itself.

That idea may or may not be realistic, but it isn’t crazy and stupid in the manner Park implies. (On the other hand, what he wrote is much funnier and pithier than what I just wrote.  Life is full of tradeoffs.)