Operating a telescope larger than the Earth: How the VSOP space VLBI mission is scheduled Original Research Article

The Japanese VLBI space observatory programme (VSOP) mission is one of the most complex scientific endeavors ever attempted. It involves coordinating a spacecraft with detailed pointing constraints that vary on time scales ranging from years to hours, tracking stations in four different countries, ground radio telescopes in nearly 20 different countries with different capabilities at the VSOP observing frequencies, and correlation and tape copying facilities with four different recording formats. Scientific constraints on the quality of (u,v)-coverage obtainable force the scheduling to be done far in advance of the observation — over about 1.5 years time — so that the sources are observed when the orbital orientation is most favorable. In order that all these facilities work as a single astronomical instrument, the constraints on them also must be taken into account in the scheduling to the satisfaction of all parties involved, including the principal investigators as well as mission and observatory personnel. In this paper we outline the entire VSOP mission scheduling process. Special emphasis is placed on software required to decide when to observe the proposed sources and how to ensure the highest quality science while preserving the health of the spacecraft. We also discuss application of the process to the future space VLBI missions VSOP2, RadioAstron, and ARISE.