posted 03-28-2020 02:18 AM               

Following recovery of the Mercury-Redstone 2 (Spacecraft 5) it was determined that during the launch of the Mercury-Redstone 2 mission, the ground ventilation inlet valve vibrated open, causing the cabin to depressurize through the negative-pressure relief valve and causing the suit circuit to command the emergency-rate mode of operation.

It was found that the snubber and its mounting bracket, intended to place a frictional load on the mechanical linkage connected to the valve, had been removed prior to flight. To prevent loss of cabin pressure, should this occur in future missions, a second spring-loaded flapper-type check valve was installed in the inflow line adjacent to and downstream of the inlet valve. A bypass switch was installed on the instrument panel which would allow the pilot to reset the emergency-rate valve and to return to the normal mode of system operation by removing the electrical signal from the solenoid on the suit-circuit-shutoff valve.

Upon recovery, water was found in the spacecraft, and the water was believed to have entered through the cabin outflow snorkel. This valve was of the ball-float configuration which was also used on the suit inflow snorkel. As a result, the outflow snorkel was changed to a diaphragm check valve which sealed if there was a hydrostatic head in the recovery compartment. The outflow valve itself was not changed.