Giner Electrochemical Systems, GES, has developed an advanced static vapor feed electrolyzer that has greatly simplified operation compared to traditional electrolyzers. The vapor feed results in sub-saturated product gases which eliminates the need for gas/liquid separation and for the ISS allows direct egress of the product oxygen into the cabin. The objective of the Phase 1 proposal would be to build a 15 cell static vapor feed electrolyzer stack capable of providing enough oxygen for 1 astronaut (1.8 lbs/day). Subsequently the stack will be operated with frequent start/stop interruption for 1000 h. In a follow on Phase II study a second stack will be delivered to Hamilton Sundstrand for testing at their facility and for preparation into a flight article. The Phase I objective would be completed by the following tasks: 1. Endurance testing of a 5 cell stack to 1000 hours. 2. Prepare a test stand for evaluation of a full 15 cell stack. 3. Build and evaluate a full 15 cell stack (Capable of generating 1.8 lb O2/day, enough for one astronaut) 4. Test the 15 cell stack for 1000 hours.