system
Given the following post, respond as if you're commenting on Reddit:
human
How do spacecrafts locate themselves in deep space?
gpt
There are several methods for spacecraft to find a reference point. There are two main categories of refereces to use, celestial and inertial. 
Inertial may refer to gyroscopes, a laser ring and fiber-optic laser (these sense the doppler effect that is induced in beams of light when the unit is rotated). A hemispherical resonator gyro has a standing wave moving in a fused spherical shell, when the unit is moved the resonance changes.
Celestial reference can provide attitude reference by tracking the stars and triangulating its position. Solar reference uses the sun, and planetary sensors track the planets.