| Term: | HERTN |
| Definition: |
Helio-Eclipitic Radial Tangential Normalcoordinate system. Typically centered at a spacecraft. The X axis (radial)is set as the primary axis, and is defined as the axis pointing from thespacecraft to the Sun. The Z axis (tangential) is set as the secondary axis,and is defined as that portion of the ecliptic rotational axis which isperpendicular to the primary axis. The Y axis (Normal) is defined as Z crossX. |