Space Shuttle Orbiter Oxygen Partial Pressure Sensing and Control System Improvements

The Space Shuttle Orbiter Pressure Control System uses an electrochemical oxygen partial pressure (PPO2) sensor with an amplifier to provide continuous monitoring and control signals to maintain oxygen concentrations in a two gas cabin atmosphere. Due to manufacturing complications, the need for a replacement sensor was identified. A program was initiated by NASA/Johnson Space Center (JSC) to develop a longer life sensor which would satisfy all of the existing interface requirements without modifications to the remainder of the system. As a result, a low cost, high accuracy, replacement sensor has been developed and is planned for use on future Shuttle Orbiter missions. In addition to the oxygen sensor, a redesign of the amplifier assembly has been proposed which will provide higher accuracy and greater output signal gain adjustment. The increase in gain adjustment will provide increased sensor utilization time.

Because of commonality of the oxygen sensing hardware and schedule requirements the SPACEHAB Program is responsible for initiating the development and certification of the amplifier re-design.

These design enhancements to the Orbiter oxygen sensing and control system should result in significant cost savings. The savings are a result of increased life of the basic sensor, maximization of the useful sensor output range through increased amplifier gain and streamlined production methods. The sensor has undergone qualification testing and additional performance testing is being conducted at the NASA/JSC Crew and Thermal Systems Division. First flight usage of the new sensor is planned for mid-1992. This paper describes the design, development and testing of the new oxygen sensor and the design of the replacement amplifier.