Hubble Space Telescope first surviving mission power system design and performance

Abstract

This paper reports on the design and performance of the Hubble Space Telescope (HST) Electrical Power Subsystem and associated electrical Space Support Equipment during the First Servicing Mission (FSM) . The HST batteries and solar arrays were disconnected from the main load buses during the majority of the FSM. Electrical power to the HST equipment was provided by the Space Shuttle Endeavour fuel cells via electrical Space Support Equipment (SSE) which regulated the voltage and provided switching and distribution functions. The total power and energy use during the mission was less than expected but electrical models were accurate. There were two anomalies during the FSM. The f is t was the failure of one of twelve power converters in the SSE. Eight were required to meet the mission power requirements so this failure had no impact on the mission. The second was a short between two sections of the solar array. This solar array wing was later removed as planned and replaced with a new solar array. Overall the mission was a complete success with all primary and secondary objectives completed. FIST Electrical Power Svstem Design Figure 1 shows a simplified schematic of the HST Electrical Power System (EPS). The HST has six NiH2 batteries (520 Ah total capacity). The figure shows one third of the entire system. The power system has an unregulated bus providing 24 to 32 volts at the equipment interface, tracking the battery chargeldischarge voltage range. There are three separate distribution buses: the diode buses, the main buses and the essential buses. Two batteries are connected via diodes to each of the three diode buses. These &ode buses are electrically connected to each other and the main buses with power transfer switches which are closed during all normal operations. The diode Solar Array Trim Relays CCC Relays External Power