In order to clarify the principle and method of spacecraft attitude measurement, further understand the importance of star trackers in aerospace applications and the difference from other attitude sensors, Here briefly introduces the situation of the main attitude sensors on spacecraft.

Celestial bodies maintain relative balance via gravitation and motion. Visually, all celestial bodies seem to be equidistant, and their relationship to the observer is like the relationship between a point on a sphere and the center of the sphere. This imaginary sphere with the observer as the center and an arbitrary length as the radius is called the celestial sphere.

Star tracker is an device to determine the attitude by measuring the orientation of the navigation star in the spacecraft coordinate system.