Advanced CCD Imaging Spectrometer

File:Chandra X-ray space observatory - ACISlabel-150.jpg

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.

ACIS is a focal plane instrument that uses an array of charge-coupled devices. It serves as an X-ray integral field spectrograph for Chandra. The instrument is capable of measuring both the position and energy of incoming X-rays.{{cite web |url=http://chandra.si.edu/about/science_instruments.html |title=Science Instruments |series=Chandra X-ray Observatory |publisher=NASA{{\}}Smithsonian Astrophysical Observatory |date=19 September 2013 |accessdate=20 January 2017}}

The CCD sensors of ACIS operate at {{convert|-120|C|F}} and its filters at {{convert|-60|and|-50|C|F}}. 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. Contamination buildup can reduce the instrument's sensitivity.{{cite web |url=https://www.nasa.gov/centers/marshall/news/news/releases/2003/03-198.html |title=Chandra Advanced CCD Imaging Spectrometer (ACIS) update |publisher=NASA |first1=Steve |last1=Roy |first2=Megan |last2=Watzke |date=13 November 2003 |accessdate=20 January 2017}} Radiation in space is another potential danger to the sensor.{{cite book |title=Space Telescopes and Instrumentation 2014: Ultraviolet to Gamma Ray |first1=Catherine E. |last1=Grant |first2=Mark W. |last2=Bautz |first3=Peter G. |last3=Ford |first4=P. P. |last4=Plucinsky |chapter=Fifteen years of the Advanced CCD Imaging Spectrometer |editor-first1=Tadayuki |editor-first2=Jan-Willem A. |editor-first3=Mark |editor-last1=Takahashi |editor-last2=Den Herder |editor-last3=Bautz |at=91443Q |date=24 July 2014 |series=Proceedings of the SPIE |volume=9144 |publisher=SPIE |doi=10.1117/12.2055652 |bibcode=2014SPIE.9144E..3QG |arxiv=1407.6677|s2cid=119124482 }}

{{As of|2014}}, after 15 years of operation, there was no indication of a limit to the lifetime of ACIS. Another design feature of the instrument was a calibration source that can be used to understand its health. This allows for a measurement of the level of contamination, if present, as well as any degree of charge transfer inefficiency.