The primary goal of the ground-based calibration effort is to perform a comprehensive characterization of ACS which will serve as a baseline and reference for on-orbit calibrations and data processing. The pre-launch verification of the optical performance of the camera provides a good understanding of the working instrument in a simulated on-orbit environment and allows the acquisition of calibration files that would be difficult, even impossible, to obtain in orbit. It also permits the early detection, diagnosis, and resolution of potential problems. Ground-based testing of ACS makes use of facilities, apparatuses, and stimuli developed for previous HST instruments, making improvements wherever possible by applying the lessons learned from those earlier programs. During the various phases of ground calibration, a wide array of calibration items will be addressed in accordance with the Contract-End-Item Specifications, from determining the properties of the detectors to verifying the flight software.
The ACS ground calibration effort consists of several major campaigns, such as thermal vacuum campaigns (Feb-Mar 1999, Jun-Jul 2001) and RAMP+RAS/Cal at GSFC, and RAS/HOMS at BATC (Feb-Mar and Oct-Nov 2001). These are interspersed with a wide variety of activities, all subject to the location, schedule, and availability of the instrument. A chronological summary and additional details on the calibration campaigns are available. ACS has been fully configured with the flight build detectors HRC Build 1 and WFC Build 4 since Dec 2000 and the majority of the ground calibration data has been acquired in the following year (up to the verification campaign at the Kennedy Space Center in Dec 2001).
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