Space Interferometry Mission: taking the measure of the universe

In 1991 the Astrophysics Division of NASA's Office of Space Science convened the Space Interferometry Science Working Group to consider in more detail the science goals of a space interferometer mission to do wide-angle astrometry at optical wavelengths. In addition, the working group considered the merits of alternative mission concepts for achieving those goals. We describe the current state of the adopted mission concept, and review the candidate astrometric science program. In addition to the main goal of precision astrometry, the concept interferometer has a limited capability for high- resolution imaging using rotational aperture synthesis. A phase A start on this mission has been made in 1996, an launch is planned for 2003.