Space Interferometry Mission instrument mechanical layout

The Space Interferometry Mission, planned for launch in 2006, will measure the positions of celestial objects to an unprecedented accuracy of 4/spl times/10/sup -6/ are sec (about 1 billionth of a degree). In order to achieve this accuracy, which represents an improvement of almost two orders of magnitude over previous astrometric measurements, a ten-meter baseline interferometer will be flown in space. Starlight is collected by 33 cm diameter telescopes and combined to form fringes on detectors. To achieve the stated accuracy, the position of these fringes must be measured to a fraction of a wavelength of visible light. Passive vibration isolation and several layers of active control are used to stabilize the starlight wavefronts at sub-nanometer levels. Tight thermal control is coupled with very low CTE materials. Certain parts of the instrument need to be stabilized so that they move more slowly than the speed at which a baby grows.