In MaxQ and SPICE, the origin of a coordinate system is often defined by an “Observer” location. Coordinates and state vectors of “Target” objects are computed relative the the Observer (at the coordinate system’s origin).
There are also a few specially designated Observer/Target locations in MaxQ/SPICE.
| Observer / Target | It is |
|---|---|
| MOON, MARS, etc | Celestial bodies |
| [body] BARYCENTER | The point in space multiple bodies mutually orbit |
| SOLAR SYSTEM BARYCENTER | Solar System “Barycenter”. The point in space the Sun and Planets etc mutually orbit. This is “home” to everything else. |
| SSB | Short form for above |
| EARTH BARYCENTER | The point in space EARTH and MOON mutually orbit. |
| EMB | Short form for above |
An Observer location combined with a Reference Frame fully describe a coordinate system’s spatial and rotational positions. The only detail left to agree on is the exact coodinate system type - rectangular, spherical, or otherwise.
