What is the risk of a human fatality from continuing the mission of the Compton Gamma-Ray Observatory?
The increased risk to human life from another gyroscope failure (assuming that the shuttle option is not used) is due to the 10% probability of a gyroscope failure, which would force the use of the zero-gyroscope reentry mode. Since the two-gyroscope reentry mode has a fatality risk of 1 in 29 million, while the zero-gyroscope mode has a risk of 1 in 4.1 million, the increased risk is 1 in 48 million. Another risk is from a double failure of a critical subsystem. Because all critical subsystems are redundant, two failures of the same subsystem would have to occur for control of the spacecraft to be lost. Because of the redundancy, the casualty risk is about 1 in several million. These risk probabilities are the result of calculations by NASA engineers.
