One of the main goals of the mission was the hunt for Earth-sized planets orbiting in the habitable zones of nearby stars other than the Sun.

Other important tasks would have included collecting data to help pinpoint stellar masses for specific types of stars, assisting in the determination of the spatial distribution of dark matter in the Milky Way and in the local group of galaxies and using the gravitational microlensing effect to measure the mass of stars.

Work on the SIM project required scientists and engineers to move through eight specific new technology milestones, and by November 2006, all eight had been completed.

In 2010, the Astro2010 Decadal Report was released and did not recommend that NASA continue the development of the SIM Lite Astrometric Observatory.

This prompted NASA Astronomy and Physics Director, Jon Morse, to issue a letter on 24 September 2010 to the SIM Lite project manager, informing him that NASA was discontinuing its sponsorship of the SIM Lite mission and directing the project to discontinue Phase B activities immediately or as soon as practical.

The spacecraft would have accomplished this task to an accuracy of one millionth of an arcsecond, or the thickness of a nickel viewed at the distance from Earth to the Moon.

The value of ηEarth (Eta_Earth), the fraction of stars carrying Earth-analog planets, will be estimated by the Kepler Mission some time before SIM Lite launches.

The Broad Survey would have looked at approximately 1,500 stars to help determine the abundance of Neptune-mass and larger planets around all star-types in Earth's sector of the Milky Way.

[8] Another task that the SIM was envisioned to perform for the future missions will include providing the orbital characteristics of the planets.

[8][9] With this knowledge other missions can estimate the optimal times and projected star–planet separation angles for them to observe the terrestrial (and other) planets SIM has detected.

Another key aspect of SIM Lite's mission was determining the upper and lower limits of star's masses.

Steven Majewski and his team planned to use SIM Lite to help determine not only the shape and size of the Galaxy but also the distribution of its mass and the motion of its stars.

[15] The first, fundamental galactic parameters, was aimed at answering key questions about the size, shape and the rotation rate of the Milky Way.

[12][13] The spatial distribution of dark matter in the universe is largely unknown; SIM Lite would have helped scientists answer to this question.

These numbers would enable scientists to estimate the spatial distribution of dark matter in the local group of galaxies, and by extension, throughout the universe.

NASA selected TRW's Space & Electronics Group, Eastman Kodak and Hughes Danbury Optical Systems to conduct the study.

[21] In August 2000, NASA asked project managers to consider looking at the Space Shuttle, instead of the previously proposed EELV, as a launch vehicle.

[24] The technological development phase of the mission was completed in November 2006 with the announcement that the eight, mission-technology-milestones set by NASA were reached.

[25] One of the new technologies developed for the mission were high-tech "rulers", capable of making measurements in increments a fraction of the width of a hydrogen atom.

The mission team also created "shock absorbers" to alleviate the effects of tiny vibrations in the spacecraft which would impede accurate measurements.

Another of the milestones involved combining the new "rulers" and "shock absorbers" to prove that the Space Interferometry Mission craft could detect the tiny wobbles in stars caused by Earth-sized planets.

The fifth of the technology milestones required the demonstration of the Microarcsecond Metrology Testbed at a performance of 3,200 picometers over its wide angle field of view.

[23][31][35] Between 2004 and 2006, contractor Northrop Grumman, the company designing and developing SIM, listed a launch date of 2011 on their website.

[34] The delay of the launch date was primarily related to budget cuts made to the SIM Lite program.

[34][40] The 2007 NASA budget stipulated, "SIM Phase B activity will continue while new cost and schedule plans are developed, consistent with recent funding decisions.

"[34] The funding decisions included a US$118.5 million cut over the FY 2006 NASA budget request for the Exoplanet Exploration Program.

[34] When SIM Lite entered what JPL terms "Phase B" in 2003 Fringes: Space Interferometry Mission Newsletter, called it a most important milestone on the way to a 2009 launch.

"[36] NASA, per the budget cuts, directed the SIM project to refocus its efforts toward engineering risk reduction.

[5][8][45] SIM's design since 2000 consisted of two light collectors (strictly speaking, they are Mersenne telescopes) mounted on opposite ends of a six-meter structure.

The observatory would have been able to measure the small wobbles in stars and detect the planets causing them down to one Earth mass at distances up to 33 light years (10 parsecs) from the Sun.