In the mid-1990's the technique of Very Long Baseline Interferometry (VLBI) will expand into space with the launch of the Radioastron and VSOP space VLBI satellites. These missions will provide a unique astronomical facility to the international astronomical community.
From the point of view of planning experiments, VLBI programs using spacecraft present a number of complexities over conventional, ground-based VLBI. Unlike ground VLBI antennas, the spacecraft does not have a fixed coordinate in the earth reference frame. Moreover, the operational and pointing contraints imposed on the spacecraft due to on-board instrumentation, cooling systems, etc. are complex and can change rapidly during an orbit and dependent on time of year. The ability to acquire data from the spacecraft also depends on the availability of a line of sight from the spacecraft to telemetry stations on the earth and the ability to establish a data down-link at the same time other constraints are met. These complications make it very difficult for a potential principle investigator (PI) to design an effective astronomical observing program without the aid of software tools. Such software is required both to allow a potential PI to assess the viability of a proposed scientific program and to assist in the design of an observing program that will maximize scientific return.
This document describes a suite of programs designed for this purpose to run
on an IBM PC or compatible computer. Through a graphical interface these
programs allow the user to manipulate observing parameters and proposed
allocation of ground resources to assess the effect on a scientific program.
There are three separate programs in the package, ground, uvplot,
allsky, all of which share a common style of user-friendly
interface.
Ground is a visualization tool which provides a view of the sub-orbital
track of the spacecraft on a specified date and the portion of the orbit for
which a telemetry link is possible.
Once a potential
observing date is determined,
uvplot provides a general purpose utility
to explore the effects of including or excluding various ground telescopes on
both the 
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coverage and the anticipated signal-to-noise ratio of the
correlated data on baselines to the spacecraft. Allsky allows
examination of the - coverage obtained
using a particular array of ground VLBI stations on a particular date, as
a function of source position on the sky. This is essentially equivalent to
running uvplot a number of times, for a series of source positions
making up a regular grid on the sky.