Editing Space Interferometry Mission (section)

==Instruments==

===Optical interferometry===
[[Image:Michelson Astrometric Interferometer Diagram.JPG|thumb|right|300px|How the Astrometric Interferometer works]]
Interferometry is a technique pioneered by [[Albert A. Michelson]] in the 19th century.<ref name=albert>"[http://planetquest.jpl.nasa.gov/technology/michelson.cfm Albert Michelson: The pioneer of interferometry] {{webarchive|url=https://web.archive.org/web/20070430082333/http://planetquest.jpl.nasa.gov/technology/michelson.cfm |date=30 April 2007 }}", NASA, PlanetQuest, ''Jet Propulsion Laboratory''. Retrieved 25 April 2007.</ref> Optical interferometry, which has matured within the last two decades, combines the light of multiple telescopes so that precise measurements can be made, akin to what might be accomplished with a single, much larger telescope.<ref name=inter/> It is the interaction of [[light wave]]s, called [[electromagnetic interference|interference]], that makes this possible. Interference can be used to cancel out the glare of bright stars or to measure distances and angles accurately.<ref name=inter/> The construction of the word partially illustrates this: interfere + measure = interfer-o-metry.<ref name=inter/> At [[radio wave]]lengths of the [[electromagnetic spectrum]], interferometry has been used for more than 50&nbsp;years to measure the structure of distant galaxies.<ref name=inter>"[http://planetquest.jpl.nasa.gov/technology/technology_index.cfm A new window on the universe] {{webarchive|url=https://web.archive.org/web/20070509123848/http://planetquest.jpl.nasa.gov/technology/technology_index.cfm |date=9 May 2007 }}", NASA, PlanetQuest, ''Jet Propulsion Laboratory''. Retrieved 25 April 2007.</ref>

The SIM Lite telescope functions through [[optical interferometry]]. SIM was to be composed of one science [[interferometer]] (50&nbsp;cm collectors, 6 m separation [baseline]), a guide interferometer (30&nbsp;cm collectors, 4.2 m baseline), and a guide telescope (30&nbsp;cm aperture).<ref name=davidson/><ref name=davidson3 /><ref name=astrorequest2>"[http://planetquest.jpl.nasa.gov/SIM/Documents/SIMLiteRFI-Final-highres.pdf SIM Lite Astrometric Observatory] {{webarchive|url=https://web.archive.org/web/20100625070629/http://planetquest.jpl.nasa.gov/SIM/Documents/SIMLiteRFI-Final-highres.pdf |date=25 June 2010 }} Response to the Request for Information from Astro2010", p. 8, Jet Propulsion Laboratory, April 2009. Retrieved 9 March 2010.</ref> The sophisticated guide telescope stabilizes instrument pointing in the third dimension. The spacecraft's operational limiting magnitude would have gone down to 20 at 20 millionths of an [[arcsecond]] (μas) and its planet-finding, astrometric accuracy of 1.12&nbsp;μas is for single measurements. The accuracy of its global, all-sky astrometric grid would have been 4&nbsp;μas.<ref name=davidson/><ref name=davidson3/><ref name=astrorequest2/>

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.<ref name=econ>"[http://search.ebscohost.com/login.aspx?direct=true&db=aph&AN=2969485&site=ehost-live A roadmap for planet-hunting]", ([[EbscoHost]]), Academic Search Premier, ''Economist'', 8 April 200, Vol. 355, Issue 8165, p. 87–89. Retrieved 26 April 2007.</ref>