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SYSTEMS ANOMALIES

For the first flight of a new Orbiter, the Discovery had remarkably few malfunctions. Those that affected the crew on the timeline are described below.

Ice Formation. During the third supply water dump, ice accumulated on and around the supply water dump nozzle. Nozzle temperatures were observed to drop sharply as the ice formed. Ice also formed later on the waste water dump nozzle. After going to a side-sun attitude for 2 days in an attempt to sublimate the ice, the RMS was finally used to break off the supply water ice formation. The waste water ice formation eventually sublimated entirely, but waste water dumps were discontinued. The ground personnel considered (without discussing with the crew) using one of the supply water tanks as a waste tank, but ultimately decided crew comfort and health were secondary to Orbiter turn-around time. It is recommended that those management personnel responsible for the crew's health and comfort be included and consulted during management meetings held to discuss Orbiter problems.

CRT 2 Failure. Approximately 3½ hours into the flight, CRT 2 failed. The crew had trained for satellite deployments considering this eventuality and waited until after all satellites were deployed to perform an IFM swap of CRT's 2 and 4. The successful IFM procedure took approximately 1½ hours and involved two crewmembers (see IFM section for details).

Fuel Cell No. 1 Substack Delta Volts Sensor Fail. Approximately 6 hours into flight, the fuel cell number 1 sub stack delta volts measurements went to zero. It was decided to bus-tie fuel cells 1 and 2 for the remainder of the flight until entry so that a change in a single cell performace in FC1 would show up as a shift in load sharing between FC1 and FC2.

Cryo O2 Leak. During the final sleep period, a 35 lb/hr cyro O2 leak was observed. The crew was awakened to perform the leak procedures and isolated the leak to the PCS O2 SYS 2 line. PCS System 2 was therefore lost for entry.

HYD Sys 3 Accum Pressure Decay. On flight day 4, the hydraulic system 3 accumulator pressure decayed rapidly and was determined to be caused by a three-way pilot valve leak. Circ pump 3 was turned on for the remainder of the flight.

Right MLG Strut Flat. On landing rollout, the Orbiter swerved to the right, requiring almost full left rudder to maintain track down the runway. The cause was determined to be a flat right main landing gear strut, caused by a leaking Schraeder valve.

APU EGT Sensors. Before the launch pad abort, it was decided to proceed with the launch with only two of six APU EGT sensors working. Neither of the EGT sensors on APU 1 were operable. The flight rules were changed to permit launching without working EGT sensors on the APU's. The crew feels strongly that if the APU EGT is such an important measurement that a "backup" EGT was added for redundancy, and if the crew, without any EGT sensors, would be reliant on the ground controller's call to react to a potentially explosive APU overtemp situation, then the flight rule permitting launch without EGT sensors should be readdressed.