Space Interferometry Mission - Instruments - Optical Interferometry

Optical Interferometry

Interferometry is a technique pioneered by Albert Michelson in the 19th century. Optical interferometry, which has matured within the last two decades, combines the light of multiple telescopes so that exquisitely precise measurements can be made, akin to what might be accomplished with a single, much larger telescope. It is the interaction of light waves, called interference, that makes this possible. Interference can be used to cancel out the glare of bright stars or to measure distances and angles accurately. The construction of the word partially illustrates this: interfere + measure = interfer-o-metry. At radio wavelengths of the electromagnetic spectrum, interferometry has been used for more than 50 years to measure the structure of distant galaxies.

The SIM Lite telescope functions through optical interferometry. SIM is composed of one science interferometer (50 cm collectors, 6 m separation ), a guide interferometer (30 cm collectors, 4.2 m baseline), and a guide telescope (30 cm aperture). The sophisticated guide telescope stabilizes instrument pointing in the third dimension. The spacecraft's operational limiting magnitude goes down to 20 at 20 millionths of an arcsecond (μas) and its planet-finding, astrometric accuracy of 1.12 µas is for single measurements. The accuracy of its global, all-sky astrometric grid is 4 µas.

SIM's design since 2000 consists of two light collectors (strictly speaking, they are Mersenne telescopes) mounted on opposite ends of a six-meter structure. The observatory will be 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.