1993-07-01

Space Station ATCS Performance During Orbiter Berthing 932201

This paper documents the Space Station Freedom (SSF) Active Thermal Control System (ATCS) performance during approach/departure, berthing, and deberthing operations. Recommended fixed radiator orientations and radiator orientations as a function of the (β angle were used for SSF flights MB5 through UF-1. Radiator rotation restrictions impacting ATCS performance included plume loads during proximity operations, minimum clearances from the Shuttle post-mating, visual cues required for mating and/or SSF remote manipulator system, attitude perturbations, number of Orbital Replacement Units (ORUs) deployed and thermal radiator rotation joint bending moment response.
Three thermal models (TEA, ALPHA and TAURUS) performed the analyses on the MB5 through UF-1 mission builds. The study was divided into three parts pertaining to approach/departure, berthing, and deberthing. First, with SSF positioned in the pure gravity gradient mode the best locked radiator position was determined as a function of β angle. In the second part, the models determined the SSF ATCS radiator heat rejection capabilities as a function of β angle, and vehicle roll, pitch and yaw changes during the entire berthing operation. During this phase, the radiators were allowed to rotate to maximize heat rejection during the day, and minimize it during night. Another berthing scenario analyzed allowed the radiators to rotate until Reaction Control System/Control Moment Gyros (RCS/CMG) handover, when they were commanded to maintain the position they last had prior to handover. During the deberthing maneuver, the radiators rotated to the minimum environment except when commanded to lock during orbits 3 and 4.
The hottest environment values were used, along with End-Of-Life (EOL) radiator panel properties to determine SSF ATCS performance during mating operations. In examining the radiator heat rejection scenarios during approach and berthing, the ATCS provided the heat rejection required at some β angles for the 35°F set point in MB5 through UF-1. However, the deberthing and departure operations failed to meet the heat rejection requirements unless the set point temperature was raised or other methods were used to alleviate the problem. These methods included lowering the heat rejection requirements by powering down the station or performing the operations on the dark side of the orbit.

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