Stellar Reference Sensors or Star Trackers are often an integral sensor component in a spacecraft attitude control system, especially in systems that require high pointing accuracies. A star tracker at the most fundamental level is a high-precision visible camera capable of imaging stars and reporting their positions with respect to some fixed reference axis. Virtually all modern star trackers utilize a suite of space qualified electronics along with a Charge Coupled Device (CCD) as the image sensor. All of these components are susceptible to both transient and cumulative damage effects from the high-energy radiation in space. Typically, the most susceptible component is the image sensor, which can experience not only lifetime accuracy degradation through displacement damage and total ionizing dose effects but also can be affected by transient signals generated by the passage of high energy particles through the imaging area. These transient signals can be mistaken for star signals or overwhelm mitigation algorithms, and on several occasions, have caused operational star trackers to cease operation for a period of time. This paper will discuss how the radiation environment affects the design and operation of visible imager based star trackers and by extension, other imaging sensors utilized on spacecraft.
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