http://www.dtic.mil/cgi-bin/GetTRDoc?AD=AD465422&Location=U2&doc=GetTRDoc.pdf
As now recorded in the West Virginia Coal Association's R&D Blog, as US Air Force 1965 CO2 to Fuel Conversion | Research & Development | News, which details the "Catalytic Reduction of Carbon Dioxide to Methane and Water"; the United States Air Force had worked, in the early 1960's, to improve, essentially, the Sabatier technology, wherein Carbon Dioxide is chemically reduced, and made to synthesize, primarily, Methane.
Either water or oxygen, as we read it, depending upon how the balance of the reaction is set up, are generated by the Sabatier reaction as by-products; and, the Air Force, at times, seems to indicate that those by-products are their main targets.
In fact, the Sabatier reactor aboard the International Space Station is, as we've documented, used for the regeneration of oxygen, with the co-produced Methane being ejected overboard; although, again as we've documented, NASA also plans to use Sabatier technology on the planet Mars to synthesize rocket fuel, via Methane synthesis, from the primarily Carbon Dioxide Martian atmosphere.