Thermal management for CCD performance on the Advanced Camera for Surveys (ACS)

The Advanced Camera for Surveys, an instrument containing two CCD cameras and a MAMA detector, is being build by Ball Aerospace and Technologies Corporation for NASA. The instrument will be placed in the Hubble Space Telescope during a space shuttle mission in December 1999. The CCD detectors need to operate at a temperature below -80 degrees C in order to avoid unacceptable dark current. This cooling is achieved through detailed thermal design which minimizes the parasitic load to a 4K x 4K array with 15 micron pixels (61.4mm x 61.4mm) and cools this Wide Field Channel (WFC) detector with a combination of thermo-electric coolers (TECs). This paper will describe the innovative thermal design necessary to maintain the WFC CCD at its cold operating temperature while providing the means to reject the heat generated by the TECs. It will focus on optimization techniques developed to manage parasitic loads including material selection, surface finishes and thermal isolation. The paper will also address analytical techniques developed to characterize TEC performance. Finally, a comparison with the STIS CCD design currently operating in the Hubble Space Telescope will be made.