Space Interferometry Mission

SIM Lite

Artist's concept of the SIM Lite Astrometric Observatory in space
Names	Space Interferometry Mission PlanetQuest
Mission type	Space observatory
Operator	NASA / JPL
Website	NASA SIM Lite
Mission duration	5+1⁄2–10 years
Spacecraft properties
Manufacturer	Northrop Grumman
Start of mission
Launch date	Cancelled in 2010
Rocket	Intermediate class EELV
Orbital parameters
Reference system	Heliocentric
Regime	Earth-trailing
Main telescope
Type	Optical Michelson Interferometer
Diameter	2 × mirrors 50 cm (20 in) baseline 6 m (20 ft) 4 × mirrors 30 cm (12 in) baseline 4.2 m (14 ft)
Wavelengths	0.4–0.9 μm
Instruments SI Science Interferometer G1 Guide-1 Interferometer G2 Guide-2 Telescope

The Space Interferometry Mission, or SIM, also known as SIM Lite (formerly known as SIM PlanetQuest), was a planned space telescope proposed by the U.S. National Aeronautics and Space Administration (NASA), in conjunction with contractor Northrop Grumman. 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. SIM was postponed several times and finally cancelled in 2010.^[1] In addition to detecting extrasolar planets, SIM would have helped astronomers construct a map of the Milky Way galaxy. 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. The spacecraft would have used optical interferometry to accomplish these and other scientific goals.

The initial contracts for SIM Lite were awarded in 1998, totaling US$200 million. 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. SIM Lite was originally proposed for a 2005 launch, aboard an Evolved Expendable Launch Vehicle (EELV). As a result of continued budget cuts, the launch date was pushed back at least five times. NASA had set a preliminary launch date for 2015. As of February 2007, many of the engineers working on the SIM program had moved on to other areas and projects, and NASA directed the project to allocate its resources toward engineering risk reduction. However, the preliminary budget for NASA for 2008 included zero dollars for SIM.^[2]

In 2007, the Congress restored funding for fiscal year 2008 as part of an omnibus appropriations bill which the President later signed. At the same time the Congress directed NASA to move the mission forward to the development phase. In 2009 the project continued its risk reduction work while waiting for the findings and recommendations of the Astronomy and Astrophysics Decadal Survey, Astro2010, performed by the National Academy of Sciences, which would determine the project's future.

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. Accordingly, all SIM Lite activities were closed down by the end of calendar year 2010.