STIS REPAIR OVERVIEW

Almost immediately after the August 2004 failure, the HST Project office at GSFC assembled a Failure Review Board (FRB). The board conducted a thorough review to identify the most likely cause(s) of the failure, to evaluate possible work-arounds, to recommend further testing to characterize the problem and/or establish whether or not STIS can be returned to use, and to consider any risks of identical failures occurring in other HST instruments.

The panel localized the failure to the power converter, and determined that no work-around existed to restore STIS operations. Since the Side 1 electronics are inaccessible while STIS is in place on HST, it was decided an attempted repair of the Side 2 electronics via a servicing mission was the only solution to restore STIS operations.

To repair STIS, astronauts will perform a spacewalk, referred to as an Extra Vehicular Activity (EVA), to replace one of the boards in the Side 2 Low Voltage Power Supply (LVPS-2) located within Main Electronics Box 1 (MEB-1). The repair is straightforward but requires diligence and Hubble engineers have designed special tools for the job.

STIS repair (STIS-R) represents a significant step forward in the ability to perform on-orbit spacecraft servicing. STIS-R is the first ever board-level operation that is planned for on-orbit execution by EVA astronauts. In addition, the tools and techniques developed as part of STIS-R have been of high value in preparing for repair of the Advanced Camera for Surveys (ACS). In fact, many of the elements included within ACS Repair are derived from STIS-R.