Can the PFD Mask vary by Ascending / Descending Planes?

For polar orbiting non-GSO FSS systems, there can be a difference in orientation in the satellites between when the satellite is ascending or descending. This orientation could have an implication on the resulting PFD mask.

However the coordinate system in Rec. ITU-R S.1503-2 is north-orientated and there is no option to specify a different mask for ascending / descending directions.

The mask filed should be an envelope and hence the largest value over both ascending and descending directions should be used.

Note that S.1503-2 defines the angles as follows:

Figure 33: Definition of Azimuth and Elevation Angles
Figure 33: Definition of Azimuth and Elevation Angles

It should be noted that direction of the cartesian X, Y, Z vectors in this diagram are:

X: +ve in the East direction from the non-GSO satellite

Y: towards the centre of the Earth from the non-GSO satellite

Z: +ve towards the North direction from the non-GSO satellite.