The need for space VLBI user assistance software is based on the fact that space VLBI observations are more complicated geometrically and operationally, then ground based VLBI. Moreover they are also one or two orders of magnitude more expensive, which justify a very careful preparation, optimization and care for the details.
The complications are due to the addition of an orbiting radio telescope to the network of ground radio telescopes. Consequently the station network geometry is changing fast and continuously in both the terrestrial and the celestial reference frame. Observational limitations should be taken into account due to the orbit geometry and technical constraints of the satellite. Although the orbit can be considered fixed in the celestial frame for a short period of time, it may change considerably on the longer term, due to the gravity field harmonics of the Earth and other perturbations. Therefore the optimal periods for observing a given source depend on this "orbit evolution". Space VLBI also requires a complicated scheme of tracking, telemetry and control operations. Because there are no hydrogen masers on the satellites, the on board oscillators are slaved to ground-based frequency standards via two way link from the telemetry stations. The VLBI data from the satellite, during one observing session, may be recorded on magnetic tapes in short sections at several telemetry stations, each with different clock characteristics.