Power Down Analysis for the Hubble Space Telescope Power Control Unit Replacement 2001-01-2217
During the fourth servicing mission (SM3B) of the Hubble Space Telescope (HST), the Power Control Unit (PCU) will be replaced to correct a fault that has appeared. The PCU controls the power from the solar arrays and the batteries to the entire telescope. The fault reduces the amount of battery power available and could result in a limit being placed on power usage in the future thereby seriously reducing science capability. Because all power goes through the PCU, power will be cut off to all HST components for the duration of the change out.
Since the maximum Extra Vehicular Activity (EVA) duration capability for the Orbiter Astronauts is eight hours, a thermal analysis was conducted to evaluate the effect of an eight-hour power off period on the HST components. This analysis was conducted using the HST servicing mission thermal timeline FORTRAN code and the Lockheed Martin proprietary code THERM. While the analysis encompassed the entire vehicle, this paper focuses on the Forward Section of HST, which includes all the equipment bays.
This paper presents the results of that analysis and the resulting component preheats developed in order to maintain all components above their minimum turn-on limits for an eight-hour power off period. It describes the preheats developed for the Advanced Computer, Communications Equipment (including the Multiple Access Transponder (MAT) and S-Band Single Access Transmitter (SSAT)), Science Instrument Control and Data Handling (SIC&DH), batteries and Reaction Wheel Assembly (RWA) as well as their corresponding cool downs during power off.