On-orbit star tracker recalibration: A case study

Abstract

Star trackers must be calibrated prior to flight so that they can make accurate measurements of star positions within the instrument field of view. This calibration is often performed in atmosphere and once the sensor is launched, it is not uncommon to observe a small shift in some of the calibration parameters. To maximize sensor performance, these parameter values must be corrected to better match the actual observa tions. In this paper, we explore the several practical strategies for on-orbit recalibration of star trackers. We consider both human-mediated batch-processing as well as autonomous, se quential algorithms. We base our results on orbital data from a number of Sinclair Interplanetary ST16 star trackers launched within the last year. Both approaches to on-orbit calibration can yield significant improvements both to sensor availability and geometric error.

An On-Orbit Calibration Method of Star Sensor Based on Angular Distance Subtraction

“…Then we can get the DiDj is about 256.1520, and the DjDk is about 256.3122, the difference between DiDj and DjDk could be small but significant. In this case, using (11) to equate them will bring some error. Therefore, in the actual experiment, we did not equalize DiDj and DjDk, but directly used the result of subtraction of (10), so that these points at special locations would not cause errors.…”

“…Z. Wang [10] established the angular distance error model and determined the variation range of the observation angular distance error. J. Enright [11], [12] suggested using the angular distance directly and adopting a new camera model for calibration. Although the method of angular distance is widely used, the calibration accuracy of the principal point is much worse than that of other parameters [13], [14].…”

A Star Sensor On-Orbit Calibration Method Based on Singular Value Decomposition

“…Let bold-italicw=[X,Y,Z]T be an arbitrary unit star vector [16] with respect to the camera reference frame, and its projection on the image frame is bold-italicp=[u,v]T. The perspective projection relationship between w and p can be represented as [22,24]:[]uv1=1z[]fu0u00fvv0001[]XYZ, where [u,v,1]T are the homogeneous coordinates of the point p , and fu and fv are:fu=fDu, fv=fDv, where f is the focal length and …”

“…According to the fact that the angular distance between stars is constant under the rotation transformation, Samaan [10] proposed an on-orbit calibration method based on the cosine residuals of the angular distances, and the detailed on-orbit calibration procedure was presented. Further studies were carried out by other members of the team; Singla [11] evaluated the performance of the calibration method based on angular distances; Griffith [12] explored approaches for the on-orbit calibration of higher order focal plane distorting effects; Woodbury [13] proposed an on-orbit calibration method based on the sine of angular distance, instead of the cosine; Liu [14] and Shen [15] concentrated on the improvement of the sequential estimation method; and Enright [16,17] suggested using the angular distances directly and adopting a new camera model for calibration. Although considerable studies have been done for the on-orbit calibration of star sensors, almost all of these were related to angular distances.…”

Autonomous Recalibration of Star Trackers

“…This manuscript expands upon an earlier study that presented our preliminary analysis of recalibration using orbital data [6]. We consider the efficacy of both batch and sequential reprocessing techniques.…”