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Japan's Institute of Space and Astronautical Science (ISAS) plans to launch the Muses-B spacecraft for the VLBI Space Observatory Programme (VSOP) in late 1996. The orbiter will carry a radio telescope with an effective diameter of 8 meters into an elliptical Earth orbit with an apogee altitude of 22,000 km. This telescope will be capable of making VLBI observations in a VLBA-compatible mode, with the wide bandwidth data recorded at ground tracking stations. Three observing frequencies will be utilized: 1.6, 5, and 22 GHz. The elliptical orbit will provide the capability of making VLBI images at these frequencies with resolutions three times greater than is possible for ground VLBI. Ground radio observatories such as the VLBA have designated up to 30\% of their time for co-observing with VSOP. Continuum-source detection thresholds for baselines from VSOP to a single 25-m VLBA telescope are expected to be on the order of 100--150 mJy at 1.6 and 5 GHz, and about 500 mJy at 22 GHz.
The primary scientific goals of VSOP include the following:
\begin{list}{}{\itemsep -5pt} \item $\bullet$ High-resolution imaging of active galactic nuclei (AGN) \item $\bullet$ Monitoring of structural changes in superluminal sources \item $\bullet$ Surveying AGN for high brightness temperatures \item $\bullet$ Measuring proper motion as a function of redshift in AGN \item $\bullet$ Determining the distribution and spot sizes in OH and H$_2$O \item \quad maser sources \item $\bullet$ Measuring distances to H$_2$O masers \end{list}
The actual scientific experiments to be performed by VSOP will be selected by an open peer-review process, and all scientists are invited to propose.
