The Function and Classification of Star Tracker

A star tracker is an optical device that measures the positions of stars using photocells or a camera. As the positions of many stars have been measured by astronomers to a high degree of accuracy, a star tracker on a satellite or spacecraft may be used to determine the orientation (or attitude) of the spacecraft with respect to the stars. In order to do this, the star tracker must obtain an image of the stars, measure their apparent position in the reference frame of the spacecraft, and identify the stars so their position can be compared with their known absolute position from a star catalog. A star tracker may include a processor to identify stars by comparing the pattern of observed stars with the known pattern of stars in the sky.

The main functions of star tracker

The main functions of various star sensors include:

1. Star map acquisition: capable of scanning the entire field of view and locating and outputting the positions of star image points within the field of view.
2. Star tracking: locate the star image points on the detection equipment, output the coordinates of the star image points in the image plane coordinate system, and be able to repeatedly locate the star image points and output corresponding coordinates on the updated star map for a period of time.
3. Automatic star tracking: During a period of time, star tracking can be performed without assistance, and new stars are automatically selected and tracked when the tracked star image points leave the field of view of the sensor.
4. Automatic attitude measurement: capable of measuring the orientation of the sensor in an inertial coordinate system without known or external attitude, angular rate, and angular acceleration.
5. Automatic attitude tracking: During a period of time, as the sensor moves within the celestial sphere, the star image points in the field of view are automatically selected and tracked, and automatic attitude measurement is performed.
6. Self protagonist rate measurement: Independently measuring the rotational angular rate of the sensor without relying on absolute attitude information.
7. Image download: Captures the instantaneous signal of the entire field of view of the detection device and outputs all image information to the user.
8. Star coordinate system navigation: external reference coordinates defined by a certain star (such as Earth, Sun), Measure the position of the sensor based on the reference system.
9. Inertial coordinate system navigation: Determine the position of sensors based on the inertial coordinate system.

Classification of Star trackers

According to the different functions mentioned above, star sensors are divided into five categories:

1) Star Scanner: The typical application of a star scanner is on spinning satellites, which detects the starlight pulse signal when scanning the celestial sphere through a narrow slit to obtain the satellite’s spin information. (Star scanners have been used before, It has been used for many years and has now been replaced by modern sensors.)

2) Star Camera: The basic function is to obtain star maps.

3) Star Tracker: capable of obtaining star maps and performing star tracking.

4) Autonomous Star Tracker: capable of obtaining star maps and performing automatic star tracking.

5) Star Navigation Sensor: It has the basic function of an autonomous star tracker and can navigate the star coordinate system.

Many models are currently available. There also exist open projects designed to be used for the global CubeSat researchers and developers community.Star trackers, which require high sensitivity, Adding bricks and tiles to the development of the aerospace industry.