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26 September 1989 A Daylight Stellar Sensor Using A Charge-Coupled Device
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Abstract
Aircraft-mounted inertial navigation systems (INS) use stellar observations to improve accuracy of position and attitude. The INS provides a stable platform on which is mounted a two-axis gimballed telescope, which may be pointed to any of 57 stars of magnitude 2.5 or brighter. Only one target star appears at a time on the 6x6 arc-min field of view (FOV), with speeds up to 11 arc-min/sec. Previous implementations used optomechanical techniques to separate a star from a sky of up to 3000 fL luminance, allowing estimation to 5 arc-sec accuracy in the daytime and on the ground. This paper describes a more reliable implementation using a charge-coupled device (CCD) and high-speed microprocessor. Out of 385x288 pixels in the image section, only 30x30 are digitized each frame time of 10 ms. To reduce background shot noise, the charge accumulation duty cycle is varied so that pixel wells fill each frame regardless of sky brightness. Frame times are kept short to reduce dark noise and track fast-moving stars. During each frame time the microprocessor corrects each pixel for responsivity and background charge, averages over several frames, and forms a multipixel window. It then either searches an empty field for a star or tracks and interpolates to estimate the centroid of one already found. The sensor requires 52 in.2 PC board space and 4 W dc power. Ground tests on the first pre-production unit exhibit superior performance to its predecessor, tracking 2.5 magnitude stars in as much as 4000 fL urban skies.
© (1989) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
T. M. Duncan "A Daylight Stellar Sensor Using A Charge-Coupled Device", Proc. SPIE 1111, Acquisition, Tracking, and Pointing III, (26 September 1989); doi: 10.1117/12.977965; https://doi.org/10.1117/12.977965
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