Methods to improve the accuracy and performance of star sensors

Improve the static accuracy of star sensors.

The constraint relationship between the accuracy of the star sensor and the focal length, pixel size, number of pixels and field of view of the star sensor is shown in Figure 1. During the optical design and assembly process of the star sensor, the diffuse spot signal of the optical imaging point needs to occupy 3×3 pixels to ensure that the star point extraction accuracy of the star sensor reaches sub-pixel accuracy (0.1 pixels). The pixel size is usually about 10 microns, that is, the positioning accuracy of the star point is about 1 micron. Therefore, improving the system pointing accuracy requires increasing the focal length, resulting in a corresponding reduction in the field of view angle.

In order to ensure the star map recognition performance, the number of arrays of detector pixels needs to be increased, the star photography capability needs to be improved, the exposure time needs to be increased, and the aperture needs to be increased, which will lead to a significant increase in the volume and quality of the entire star sensor. It can be considered star sensitive The improvement of the static accuracy of the sensor is basically at the expense of increasing the size and mass of the star sensor. Choosing a large area array sensor with an increased number of pixels results in longer system readout time and lower update rate.

Improve the dynamic performance of star sensors.

Dynamic performance has always been an important technical bottleneck for star sensors. When a star sensor is in orbit, its attitude is basically determined during the dynamic process. Therefore, it is particularly important to improve the dynamic performance of the star sensor. At present, when the angular velocity exceeds 0.1 (°)/s, the accuracy of the star sensor is difficult to guarantee, and when the angular velocity exceeds 0.5 (°)/s, it basically cannot work. At the same time, the movement of the star point during the exposure time of the star sensor will also cause the system’s accuracy and other indicators to drop significantly. Therefore, satellite system designs now almost all use the working mode that combines inertial sensors and star sensors.

Improve star sensor update rate

The star energy that the star sensor is sensitive to is relatively weak, so the exposure time is relatively long. At the same time, the area array of the sensor detector itself is relatively large, and the readout time is relatively long, so the update rate of the star sensor is generally low. Improving the update rate of star sensors and reducing the system’s dependence on inertial sensors is the most urgent technical problem that currently needs to be solved for star sensors.