$LastChangedDate: 27-Oct-2009 $

# Local Frames

Local Frames

## Local frames used in CelestLab

Several local frames are defined in CelestLab:

- Local orbital frames: QSW, TNW and LVLH.

- Local frame tied to some ground location: topocentric North frame.

## QSW local orbital frame

The QSW local orbital frame is defined as follows:

- Origin: center of mass of the satellite
- Q (X axis): unit vector from the planet center to the satellite
- W (Z axis): unit vector in the same direction as the orbit's angular momentum vector (that is, perpendicular to the orbit plane)
- S (Y axis): unit vector chosen so that the (X,Y,Z) trihedral is direct.

## TNW local orbital frame

The TNW local orbital frame is defined as follows:

- Origin: center of mass of the satellite
- T (X axis): unit vector in the direction of satellite's velocity vector
- W (Z axis): unit vector in the same direction as the orbit's angular momentum vector, that is, perpendicular to the orbit plane
- N (Y axis): unit vector chosen so that the (X,Y,Z) trihedral is direct.

## LVLH local orbital frame

The LVLH local orbital frame is defined as follows:

- Origin: center of mass of the satellite
- Z axis: unit vector from the satelite to the planet center
- Y axis: unit vector in the opposite direction as the orbit's angular momentum vector
- X axis: unit vector so that the (X,Y,Z) trihedral is direct (if the orbit is circular, X is in the same direction as the velocity vector)

## Topocentric North local frame

The topocentric north local frame is defined as follows:

- X: unit vector in the horizontal plane and towards norh
- Y: unit vector in the horizontal plane and towards west
- Z: unit vector in direction of the local vertical