Advanced CCD Imaging Spectrometer

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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.

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.[1]

The CCD sensors of ACIS operate at −120 °C (−184 °F) and its filters at −60 and −50 °C (−76 and −58 °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.[2] Radiation in space is another potential danger to the sensor.[3]

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.[3]


  1. ^ "Science Instruments". Chandra X-ray Observatory. NASA / Smithsonian Astrophysical Observatory. 19 September 2013. Retrieved 20 January 2017. 
  2. ^ Roy, Steve; Watzke, Megan (13 November 2003). "Chandra Advanced CCD Imaging Spectrometer (ACIS) update". NASA. Retrieved 20 January 2017. 
  3. ^ a b Grant, Catherine E.; Bautz, Mark W.; Ford, Peter G.; Plucinsky, P. P. (24 July 2014). "Fifteen years of the Advanced CCD Imaging Spectrometer". Proceedings of the SPIE 9144, Space Telescopes and Instrumentation 2014: Ultraviolet to Gamma Ray. 91443Q. arXiv:1407.6677Freely accessible. Bibcode:2014SPIE.9144E..3QG. doi:10.1117/12.2055652. 

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