What To Do When You Receive an Exception Report
If there is a problem with observations, the Principal Investigator (PI) will recieve an HST exception report via email. The exception report will ask you to download your data from MAST, determine whether the S/N and/or flux of your data reached the expected levels, and determine from a quick-look inspection whether your data appears anomalous in any other way.
If you are unable to determine this in a timely manner, please contact the Help Desk. The Help Desk staff will work with the best available experts from the relevant telescope or instrument group to address and track your telescope and instrument-related questions and concerns in timely fashion.
Each instrument has different requirements for high quality data, and you can see recommendations for checks to be performed for each individual instrument.
In some cases, the Guide Star Acquisition process can only acquire a single guide star. There may be some degree of drift in roll which can happen over time, the degree of which can vary depending on factors such as the length of the exposure, time of an exposure or set of exposures, and the distance between the target and the guide star in the focal plane. This general principle applies to all instruments in the focal plane. For an ACS-specific example, please see GS ACQ Failed to Single Guide Star.