The Space Telescope Imaging Spectrograph (STIS) was installed in the Hubble Space Telescope (HST) in February of 1997. On May 16, 2001, the primary Side-1 package of support electronics failed, but STIS was able to continue operations using the redundant Side-2 electronics until August 3, 2004, when an electrical malfunction in a power supply forced cessation of STIS operations. On May 17, 2009, during the fourth EVA of SM4, astronauts Michael Good and Mike Massimino undertook an eight-hour spacewalk, during which they replaced the STIS LVPS-2 circuit board containing the failed component. This repair restored the STIS Side-2 electronics, allowing all three of the STIS detectors to be used for science observations.
In most respects, STIS after the 2009 repair operates in much the same way as it did prior to the 2004 failure. Most changes in performance are close to what had been expected. The degradation of the STIS CCD due to radiation damage and the modest changes in optical throughput are consistent with extrapolation of previously-observed trends. The biggest surprise is in the dark current for the NUV MAMA detector. It is several times larger than had been expected and is only slowly decreasing towards its expected range.