2.1 ACS Repair During SM4

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After the failure of the side-2 electronics of ACS in January 2007, and the previous anomaly in the CCD low voltage power supply (LVPS) of side-1 in June 2006 the only functional channel of ACS has been the Solar Blind Channel.

NASA Headquarters has approved a plan for the execution of the ACS repair on SM4. The repair concept replaces the CCD electronic box (CEB) in the Wide Field Channel. The new CEB will be powered by a replacement LVPS that will be completely independent of the original unit, which failed in June 2006. While the highest priority is restoring the WFC, the ACS repair concept also provides a path for restoring the High Resolution Channel by powering the original CEB of the HRC channel with the new LVPS.

Most of the ground testing of the new electronics will be carried out during the fall and winter 2007, after the publication of this document. Some of the CCD performance may be impacted by the new electronics and by the eighteen months of continuous radiation damage without regular annealing cycles. These changes may include read noise, dark current, hot pixel contamination and charge transfer efficiency.

Observer should consult the ACS Web site:

http://www.stsci.edu/hst/acs/  

for the most up to date information on the predicted instrument performance and available observation modes. The information on the Web site will be updated regularly as our knowledge improves.

We will use this symbol to highlight trough the text all sections of parameters that could be affected by the ACS repair. Readers are encouraged to look for updates on the ACS Web site whenever they encounter such symbol.