scope:

Description of Driving Event:

Inertial Upper Stage/Tracking and Data Relay Satellite (IUS/TDRS) instrumentation design allows active monitoring of only one of two Propellant Tank Assemblies (PTA's) during the countdown phase. The PTA's are isolated from each other until activated after IUS deployment. Therefore, the status of all PTA's can not be determined by monitoring one PTA. Pre-launch preparation procedures permit adequate determination of pre-flight PTA leakage status; pyrotechnic system design adequately protects against inadvertently commanded loss of PTA isolation; and structural design safety factors are adequate. However, no indicator is available to detect a flight-induced anomaly, thereby making the IUS status uncertain.