Astronaut Gregory J. Harbaugh at work on HST, with the assistance of astronaut Joseph R. Tanner (out of frame) on remote manipulator system (RMS). After replacing the HST's Solar Array Drive Electronics (SADE), Harbaugh and Tanner replaced the Magnetic Sensing System (MSS) protective lids with new, permanent covers; and they installed pre-cut insulation pieces to correct tears in the telescope's protective covering caused by temperature changes in space.