On Monday, 19 June 2006, at 1:15 pm EDT (17:15 UT), the Advanced Camera for Surveys (ACS) issued status buffer messages indicating that the +15V and +5V power supply voltages in the CCD Electronics Box (CEB) were above their high limits, causing the ACS to suspend. This event occurred in a period with no ACS commanding and outside the SAA. A dump of the relevant data showed that a total of 36 CEB items exceeded limits at the time of the event.
At this point, the ACS is in a safe configuration, and further analysis is ongoing. Preliminary reviews of the telemetry and technical details about possibly affected components of ACS have been carried out. However, the root cause for the ACS suspend is still unknown. Further analysis and testing revolves around low-voltage power supplies as well as analog to digital converters. Analysis of ACS images taken before the suspend event shows no anomalies of any kind.
The further course of action will simultaneously prepare for further testing of the Side 1 electronics, which has been used since the installation of ACS, while preparing for a potential switch to the Side 2 electronics. The Side 1 tests will commence later this week, after verification that the tests will not harm the instrument. These tests will check various registers and voltages to pin down the location of the cause for the suspend.
Preparations for a switch to Side 2 involve procedure verification, Flight Software changes, as well as the definition of calibration and verification programs to be executed before the full ACS science program could hopefully continue. A switch to Side 2 could come as early as the week of 26 June, if the tests successfully show that this would be beneficial.
For the time being, no ACS science observations will be carried out. Measures are being taken to advance non-ACS observations to fill the available time.