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SIM Configuration and How SIM Works

SIM Configuration and How SIM Works. What Does SIM Do?. SIM uses interferometers in space to measure angles between celestial objects incredibly accurately in order to deduce all kinds of new scientific conclusions. SIM does astrometry Astronomy = “star naming” Astrometry = “star measuring”.

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SIM Configuration and How SIM Works

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  1. SIM Configurationand How SIM Works

  2. What Does SIM Do? • SIM uses interferometers in space to measure angles between celestial objects incredibly accurately in order to deduce all kinds of new scientific conclusions. • SIM does astrometry • Astronomy = “star naming” • Astrometry = “star measuring” SIM does astrometry

  3. An Important Example of Using Astrometry • Deduce planets orbiting nearby stars • Motion of our sun (1990-2020) due to all planets in our solar system as viewed from 10 parsec (a little more than 30 light years) away Scales are ±0.001 arc sec= ± 1 milli arc second= ± 1000 micro arc sec~ ± 5 nano-radian Motion of star’s optical center is a few thousand micro arc seconds (μas) SIM could measure this motion with an accuracy of about 1 μas (~5 pico-radian) (quite a bit thinner than the line plotted here)

  4. What is a Michelson Interferometer? • Light from two collectors (telescopes) is combined optically onto a single detector. • When the two beams have traveled the same distance from the star to the detector, then the two beams interfere constructively. • Pathlength is adjusted to find this maximum brightness condition. • With this knowledge and precise measurements of SIM internal geometry, the angle to the target can be calculated. • It gives only one component of angle precisely • Two measurements are required with baseline rotated ~90° about line to star

  5. A Michelson Astrometric Interferometer ABC

  6. Siderostat Assembly (an old view) A “Siderostat” is a flat steering mirror that keeps the line of sight of telescope STATionary in SIDereal space. As the platform moves around, the Sid compensates. It also allows the line of sight to be aimed over a region of sky without moving the platform or the telescope. Telescope line of sight is rotated about two orthogonal axes centered on the front face of the Sid by a gimbals assembly. A corner cube retroreflector will also be mounted with its vertex here (see slide later on)

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