Despite the low cost, these devices are quite sophisticated. Most of these
Satellites that require high accuracy attitude estimates (<1 arc-min) generally employ the use of star trackers. These sensors operate by taking images of the star field and matching observed patterns to an onboard catalog. For most star trackers, the availability of this attitude measurement is generally greater than 99% in ideal conditions [1]. However, in many cases, satellites are required to change their attitude, either continuously, as with Earth observation (EO) satellites, or periodically, as with space telescopes. For star trackers onboard such satellites, angular motion during imaging (slew) causes stars to smear out over a larger number of pixels than they would occupy in static imaging conditions.
This reduces the signal-to-noise ratio (SNR) of imaged stars, which decreases the detection performance of dim stars. Detecting less stars in each image ultimately impairs the accuracy and the availability of a star tracker attitude solution. Each star tracker claims to be tolerant of some amount of sensor slew; however, it is challenging to quantify the exact impact this angular motion has on sensor performance.This paper investigates the effects of slew rate on the availability performance of a star tracker. Specifically, we develop an analytical model of the intensity distribution of a star smear. We combine this model with star detection logic in a simulation-based approach to evaluate the effects of slew rate on star tracker availability.
We verify these results through lab testing and discuss further verification using field tests. Lastly, we propose two new measures of star tracker availability that both incorporate the effects of slew rate and represent improved modeling fidelity. Although the numerical results of this paper are specific to the Sinclair Interplanetary ST-16 star tracker, the models and methods developed are applicable to any star tracker with only minor modifications.Before we can begin discussing slew rate tolerance, we need to understand how sensor slew impacts the performance of a star tracker. The remainder of this section defines star tracker availability, introduces our test sensor and outlines the methods we use to measure detection performance as a function of slew rate.1.1.
Star Tracker Drug_discovery AvailabilityThe performance of a star tracker is generally described by two parameters: availability and accuracy. Accuracy is defined as the uncertainty in the attitude estimate. Availability is defined as the fraction of the celestial sphere, also known as firmament, over which a reliable attitude solution is possible. In this study, we only examine the effects of sensor slew on availability. For more information on how sensor slew affects star tracker accuracy, please see [2�C6].