SIM has long been a high priority in Decadal Reports. Some excerpts:

"Despite the promise of interferometry carried out from the ground, the ultimate power of this technique will probably be fully realized only with a system operating in space, where no limits to the coherence size, angle, or time are imposed by the terrestrial atmosphere. NASA has been studying a number of possible space missions as a first step in interferometry from space. A concept that appears particularly appealing is to use interferometric techniques to achieve a 1,000-fold improvement in our ability to measure celestial positions. The mission requirement would be to measure positions of widely separated objects to a visual magnitude of 20 with a precision of 30 millionths of an arcsecond; a more challenging goal would be to measure positions with a precision of 3 millionths of an arcsecond. The Astrometric Interferometric Mission (AIM) would permit definitive searches for planets around stars as far away as 500 light-years through the wobbles of the parent star, trigonometric determination of distances throughout the galaxy, and the study of the mass distributions of nearby galaxies from stellar orbits. AIM would demonstrate the technology required for future space interferometry missions."

"The Astrometric Interferometry Mission has evolved into the far more capable Space Interferometry Mission (SIM). Measuring positions on the sky with unprecedented precision, SIM will enable the discovery of planets much more similar to Earth in mass and orbit than those detectable now, and it should permit astronomers to survey the Milky Way Galaxy 1,000 times more accurately than is possible now. We must begin planning now to take advantage of the discoveries these new facilities will make possible."

"The committee reaffirms the recommendations of the 1991 Astronomy and Astrophysics Survey Committee (NRC, 1991) by endorsing the completion of the Space Infrared telescope Facility (SIRTF), the Millimeter Array (MMA; now part of the Atacama Large Millimeter Array, or ALMA), the Stratospheric Observatory for Infrared Astronomy (SOFIA), and the Astrometric Interferometry Mission (now called the Space Interferometry Mission, or SIM)."

From Astronomy and Astrophysics in the New Millennium, 2001

"The panel believes that the present high level of commitment to the SIM mission is well merited, and it fully supports the launch of SIM."

"The scientific capability of SIM is enormous. The measurement of distance is arguably the most fundamental and difficult measurement in astronomy. The SIM goals will provide distance measurements of 1 percent accuracy to distances of several kiloparsecs and of 10 percent accuracy throughout the Galaxy, providing a firm foundation for the understanding of stellar astrophysics. At the same time, luminosity determinations for key classes of stars-for example, Cepheid and RR Lyrae variables-will reduce the calibration uncertainties in the cosmological distance scale. Distances to a selected sample of stars throughout the Galaxy will refine our understanding of galactic structure, and in particular the structure of the Galactic halo, thus tracing the distribution of dark matter.

Searching for planets near stars in the solar neighborhood is the most ambitious of SIM's goals. SIM should generate a preliminary survey of the local planetary population and a more exttensive survey of the jovian-mass planets. By detecting the shirts in stellar positions, the orbital parameters for these planetary systesm will be able to determine mass directly when combined with radial velocity techniques and will not leave any ambiguity about the masses of the extrasolar planets."

From Astronomy and Astrophysics in the New Millennium: Panel Reports
Report of the Panel on Ultraviolet, Optical, and Infrared Astronomy from Space, 2001
Full Decadal Report