Hubble Trouble

NASA Hubble Space Telescope Daily Report #4028

"WFPC2 WF4 Supplemental Darks - A anomaly has been found in images from the WF4 CCD in WFPC2. The WF4 CCD bias level appears to have become unstable, resulting in sporadic images with either low or zero bias level. The severity and frequency of the problem is rapidly increasing, and it is possible that WF4 will soon become unusable if no work-around is found. The other three CCDs {PC1, WF2, and WF3} appear to be unaffected and continue to operate properly. These darks are to supplement those in program 10748 to ensure sufficient dark frames for routine calibration. As the WF4 anomaly grows worse, we are beginning to see episodes where too many darks are corrupted and are unusable."

WFPC2 Advisories, StScI

"Partial repair of the WF4 anomaly: Over the last few days we tested a strategy to mitigate the WF4 anomaly by reducing the set point of one of the heaters in WFPC2. Specifically, at 12:28 UT on 9 January 2006 we reduced the upper set point of the WFPC2 Replacement Heater from 14.9C to 12.2C."