Telescope, Star Tracker, Hard Mounted
Wednesday, September 20, 2006
A Hard Mounted Star Tracker telescope has been designed and developed using a large, two-dimensional focal plane array to image an extended field of view without requiring a scanning system. The Star Tracker is capability being rigidly mounted (strapped down / hard mounted) to the super structure. The accuracy of the Star Tracker is limited by (1) the focal plane array (CCD), (2) the dark current, (3) pixel response non-uniformity’s, (4) pixel surface structure, and (5) lens aberrations.
To achieve the required accuracy over the entire field of view, the CCD surface plane must lie within 5 μm of the desired image plane. The CCD surface plane is accurately measured relative to the heat sink, and the focal plane mounting shim ring is machined to fit. The shim ring is of a low thermal conductivity enabling the Star Tracker to operate with its lenses near room temperature. The laboratory measurements are interpolated to yield data that is applicable to the space flight orbital environment. By proper calibration for operational temperature, allowance for thermal expansion is not necessary. In flight and during calibration, the CCD’s are operated at a temperature of -40 oC ±5 oC by passively cooling the focal plane assembly to 0 °C with copper conductors to an external radiant radiator. Active cooling is achieved by applying power to a Peltier cooler.
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posted by JD52 @ 8:51 PM,