The SIM flight segment consists of the interferometer instrument systems and the spacecraft system.
The spacecraft system provides the essential engineering functions for flight operations including the structure, power subsystems, attitude control, propulsion, communication, and thermal control. The instrument system consists of the optics, actuators, sensors, and computers needed to make science observations.
The SIM instrument is a set of optical long-baseline Michelson stellar interferometers that will acquire and track fringe patterns resulting from the interference of starlight directed along different paths.
The SIM design uses three collinear interferometers mounted on a 10-meter long boom. Each interferometer collects light from two paired siderostats and combines them. Two of the three interferometers will acquire fringes from bright guide stars in order to make highly precise measurements of the spacecraft attitude. The third interferometer will observe the science targets and measure the target positions with respect to an astrometric grid of many thousands of stars distributed around the celestial sphere.
The first 6 months of the mission will be used for in-orbit checkout, after which science operations will begin in earnest.
Data will be stored on the solid state recorder and downlinked every 48 hours in 2-hour increments to each of the three Deep Space Network complexes. The science and engineering data will be processed by JPL's science instrument services and transmitted to the Interferometer Science Data Center for analysis.
