The 4 packages have the following functions in common:UV plotting routines, subsatellite (ground) track plotting routines and some form of elevation vs time or elevation vs azimuth of the source and the satellite(s) as seen from the VLBI or telemetry stations. We summarize the results of the intercomparisons of these functions as follow:
UV plots: FAKESAT and the SVPIS package agreed almost exactly except for the longer track lengths in the SVPIS plots near perigee.
The longer tracs at perigee may be due to diffrenet assumptions concerning the capability to rotate the spacecraft about its pointing axis during observations. Both packages agreed on the shape and orientation of the tracks and crossing points are both in the correct place. The SPAS UV plot didn't give correct information in both the track lengths and shape, orientation. The error will have to be corrected. The RASTRON package had a UVPLOT option which couldn't be activated because it is still under implementation.
SUBSATELLITE (ground) track plots : All four packages agreed correctly on the ground track plots. The perigee point and the path length and orientation are identical.
OBSERVABILITY plots: Satellite and source observability comparisons between the 4 packages are more difficult. Mainly because of the way in which each package displayed the final results.
The source observability comparisons gave the following:
The FAKESAT-SVPIS packages gave different scales for time with FAKESAT using GST(Greenwich Siderial Time) and SVPIS using (UT) or (Greenwich Mean Siderial Time:GMST). But after the appropriate conversion was carried out on the time scales and the various plots compared, agreement was found in all cases. (Note: SVPIS package uses the CHECK program to calculate a basic observing schedule and computes the rise-set times of the objects on the given start and stop dates at the horizon(0 degrees elevation.)). The uptime option within UVPLOT, however calculates rise and set times based on elevation limits of the ground radio telescopes. The FAKESAT package will only plot the EL vs GST curves to the elevation limit and compute the rise-set times accordingly. Once compensation is made for this the two packages agreed on the results.
The SPAS package provides two diagrams of the source observability, one is the elevation versus the azimuth position. The second is simply an observability timeline of the source from various VLBI stations including the satellites. The observability is defined to be above a given elevation angle at the stations (cut off) taking into account the telemetry, but not the satellite constraints. The data is output also in tabular form in preselected time steps. (Note: the FAKESAT and SPAS packages both do elevation versus another variable while the SVPIS package doesn't have such graphical output and only outputs the rise-set times in tabular form.) Comparisons of SPAS with FAKESAT gave good agreement for rise and set times of the sources.
The RASTRON and SPAS packages have quite similar graphical output and they agree numerically when comparing the rise and set times of sources. Thus they are also in agreement with the FAKESAT and SVPIS packages.
Satellite observability comparisons: Satellite line of sight timelines for the telemetry stations were given in RASTRON and SPAS. The data is also output in tabular form. The comparisons of rise and set times of the satellite showed agreement within a few minutes.