This description file informs on the usage of the spacecraft orientation      
on Mars Express.                                                              

The spacecraft orientation element defines the orientation of Mars Express
in respect to its spacecraft reference frame. The orientation is given as
a 3-tupel and Mars Express is typical flown forward: (0, 1, 0).
Mars Express can however be flown backward: (0, -1, 0). The spacecraft
reference frame equals the mechanical frame with the y-axes rotated by 180
degrees with respect to the z-axes.