Cracking and Storing Water on Orbit

[simonbp]

I was looking at the new set of Centennial Challenges yesterday (http://prod.nais.nasa.gov/eps/eps_data/118924-OTHER-001-001.doc) and the first one got me thinking; it proposes a demonstration of an orbital LOX/LH2 (liquid Oxygen/liquid Hydrogen) fuel depot. One of the caveats is that the LH2 and LOX only have to be liquid and separate for the last 14 days of the 120 day storage period, meaning in principle, you could store it for the preceding 106 days as plain old water. I know the actual cracking of water on orbit is feasible, as the Elektron device does this on the ISS right now, but it produces gaseous Oxygen and vents the Hydrogen overboard. What would, therefore, be the feasiblity of an on-orbit LH2/LOX production and liquification facility?

Simon

[Jim]

liquification is a power hog.  Compressors and radiators would be required.  It would be a big spacecraft. Keeping the water liquid would take some power or sunlight.  Excess hydrogen could used for attitude control (H2 engines burn at a different mixture ratio than water).