As originally designed, the Shuttle Orbiter's fuel cells did not adequately monitor the health and status of individual cells. Even though the fuel cells were previously modified to add the Cell Performance Monitor (CPM) capability (which provided aggregate substack [32 cells] voltages to each fuel cell), they still did not provide the visibility the ground needed to determine that the individual cells (96 cells per fuel cell) for each fuel cell were healthy. This resulted in the premature termination of STS-83 mission. For new spacecraft systems design and development, it is critical that a worst-case scenario evaluation be performed on critical flight systems so that health status is available at the level required to determine the system’s health.