This test run completed a 100-hour full-scale simulated mission, less the reaction control system operation, to demonstrate the 1-day mission capability of the Mercury spacecraft. Again, as in earlier runs, the MA-9/20 flight plan served as the guideline, including the use of onboard supplies of electrical power, oxygen, and coolant water, with hardline controls simulating astronaut functions. During the 2-hour prelaunch hold, a small leak was suspected in the secondary oxygen system, but at the end of the hold all systems indicated a 'GO' condition and the simulated launch began. System equipment programing started and was recycled at the end of each 22 simulated orbits covering 33 mission hours. Test objectives were attained without any undue difficulty.