AOCS Requirements and Practical Limitations for High-Speed Communications on Small Satellites

Table 23

Sources of pointing error.

Spacecraft position errors:			Direction of error
	In-track	Displacement along the spacecraft’s velocity vector	Parallel to ground track
	Cross-track	Displacement normal to the spacecraft’s orbit plane	Perpendicular to ground track
	Radial	Displacement toward the center of the Earth (nadir)	Toward nadir
Note: these errors are dependent of the quality of the sensors used to determine the position of the spacecraft in the orbit
Sensing axis orientation errors:
	Elevation	Error in angle from nadir to sensing axis	Toward nadir
	Azimuth	Error in rotation of the sensing axis about nadir	Azimuthal
Note: these errors include errors in attitude determination, instrument mounting, and stability for control or pointing (e.g., jitter, thermal distortion).
Other errors:
	Clock error	Uncertainty in the real observation time (if applicable)	Parallel to the Earth’s equator