1.4 Failure of Side-2

STIS stopped science operations on 2004-Aug-03, due to the failure of a power supply within the Side-2 electronics. Between 2004 and the Servicing Mission 4 in 2009, STIS remained in safe mode: the instrument and its on-board computer were switched off but the heaters remained on to ensure a stable thermal environment.

The failed unit delivered power to all the mechanisms within STIS, including the aperture wheel, the Mode Select Mechanism, and the CCD shutter. At the time of the failure, STIS was in idle mode, in which the light path is completely blocked (a precaution to prevent over-illumination of the MAMA detectors). In the absence of a working power supply, the mechanisms could not be moved from their current positions. STIS therefore remained inoperable until Servicing Mission 4 (SM4).