What is a star tracker and its application

Star tracker is a spatial attitude sensor that uses stars as a measurement reference, and the brightness of stars is generally required to be higher than+2 visible magnitudes;

Attitude information is an essential reference benchmark for spacecraft in orbit operation, and is also an important technical indicator to characterize the level and performance of spacecraft.

Measure the angle between a certain reference axis of a spacecraft and the line of sight of the star by being sensitive to the starlight of the star, measure the angular position of the star relative to the spacecraft, and compare it with the angular position parameters of the star in the ephemeris to determine the spacecraft’s attitude.

Due to the very small opening angle of stars, the measurement accuracy of star trackers is required to be high.

So far, star trackers are still the most accurate sensors for attitude measurement on spacecraft (capable of reaching angular second or even sub angular second levels), playing an irreplaceable role in high-precision surveying, remote sensing, and formation flying.

Advantages

High precision, angular second level, independent of orbital motion (available at any position in space, including low Earth orbit etc.)

Star trackers can provide angular and even sub arcsec level pointing accuracy, enabling three-axis absolute attitude measurement of space vehicles; The navigation star referenced by the star tracker coordinates is relatively evenly distributed throughout the entire sky.

Star sensors have become the attitude measurement equipment with the highest stability and accuracy, which can solve the problem of equipment attitude determination under Lost in Sight (LIS) conditions. Due to the advantages of high precision, light weight, long lifespan, strong anti-interference ability, diverse working modes (aerospace, aviation, shipbuilding, etc.), and low power consumption, star sensors have become the most prominent performance in various attitude measurement instruments and have become a research focus among various attitude sensors.

Disadvantages

Star trackers are susceptible to interference from stray light – it is necessary to avoid interference from the light emitted or emitted by celestial bodies such as the sun, Earth, and moon; It cannot be interfered by the satellite itself.

Mass is large, complex, expensive, and star recognition takes a long time.

Star sensors, as essential navigation equipment for spacecraft such as satellites, spacecraft, and rockets, need to withstand various complex environmental tests during their operation.
What is a complex environment? A complex environment refers to various external and internal factors that interfere with the normal operation of star sensors, including stray light, spatial radiation, and noise. Stray light mainly includes terrestrial light, moonlight, sunlight, etc; Space radiation mainly refers to high-energy particle radiation (generating transient effects, cumulative effects, etc.); Noise generally refers to the dark current noise and non-uniform noise of the detector itself. The existence of complex environments can affect the execution of star sensor algorithms such as star point detection and recognition, affect the functionality and performance indicators of star sensors, and prevent the smooth implementation of space missions. In practical engineering tasks, it has been found that in some complex environments, star sensors may experience poor accuracy or enter a long-term lost state during orbit.
How to improve the performance and stability of star sensors in complex environments is of great research significance.

application area

Star trackers have many applications in space science and satellite navigation, including:

1) Orbital control: Star trackers can measure the position of stars in real-time and adjust the orbit of satellites or spacecraft to ensure their stable operation in the expected orbit.

2) Navigation system: Star trackers can establish an ontology reference system corresponding to the Earth coordinate system, and provide support in the detection of nearby planets or small celestial bodies, pollution prevention, celestial imaging, and other aspects by obtaining their own position and attitude information.

3) Space science research: Star trackers are widely used to obtain data resources such as photos and images when spacecraft fly over other planets.

The research, development, and application of star trackers have gone through more than half a century. With the emergence of new materials, devices, and technological advancements, accuracy has been improved, power consumption has been reduced, and costs have been reduced. New types of star trackers with increasingly wide application fields are constantly being introduced.