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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.

The Hubble Space Telescope (HST) was launched in 1990 and has undergone several Servicing Missions that have replaced and repaired various scientific and support hardware. As preparations begin for Servicing Mission Four (SM4) in 2008 and the life extension activities that follow, the Telescope Thermal Math Model (TMM) has been improved using the latest thermal analysis software and techniques. Several efforts have been made to improve the HST system-level TMM since launch. A brief history of the major model updates, as well as the motivation behind the changes has been provided. The current improvements have provided the HST systems-level TMM a greater level of detail, while making model control more user-friendly and the results easier to verify. Several modeling techniques useful for spacecraft thermal design and operations support are discussed.

This paper presents an overview of the thermal analysis and results of the Hubble Space Telescope (HST) Servicing Mission 3A (SM3A). The shuttle mission took place from December 19-27, 1999, with the servicing mission taking place December 21-25, 1999. During the mission, several components were replaced during three planned Extra Vehicular Activities (EVAs). Also, a New Outer Blanket Layer (NOBL) was installed on several bays to repair the damage to the Multi-layer Insulation (MLI) that was seen during Servicing Mission 2. The timeline analysis predicts temperatures for all HST installed hardware in order to determine if they will remain within their temperature limits for the duration of Servicing Mission 3A. The maximum electrical power required by the HST while attached to the Orbiter is predicted and compared to the documented maximum.