Advanced CCD Imaging Spectrometer

The Advanced CCD Imaging Spectrometer (ACIS), formerly the AXAF CCD Imaging Spectrometer, is an instrument built by a team from the Massachusetts Institute of Technology's Center for Space Research and the Pennsylvania State University for the Chandra X-ray Observatory.

The instrument is capable of measuring both the position and energy of incoming X-rays.

It carries a special heater that allows contamination from Chandra to be baked off; the spacecraft contains lubricants, and the ACIS design took this into account in order to clean its sensors.

[3] As of 2014[update], after 15 years of operation, there was no indication of a limit to the lifetime of ACIS.

This allows for a measurement of the level of contamination, if present, as well as any degree of charge transfer inefficiency.