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What is SIM ?

The slides in this collection are all related and should be useful in preparing a presentation on SIM PlanetQuest. Note, however, that there is some redundancy in the collection to allow users to choose slides best suited to their needs. What is SIM ?.

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What is SIM ?

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  1. The slides in this collection are all related and should be useful in preparing a presentation on SIM PlanetQuest. Note, however, that there is some redundancy in the collection to allow users to choose slides best suited to their needs.

  2. What is SIM ? • SIM is a space-based optical interferometer for precision astrometry • 9 m baseline, Michelson beam combiner • SIM PlanetQuest could support a schedule that leads to a December 2011 launch, with a minimum 5-year mission lifetime • SIM has 3 basic operating modes • Global astrometry • Local astrometry • Synthesis imaging • How does it operate ? • SIM measures the white-light fringe position on 3 simultaneous baselines: 2 guide interferometers and 1 science interferometer • Using delay and angle feed-forward, the guides stabilize the science interferometer at the microarcsecond level • For more information visit the SIM web site: http://planetquest.jpl.nasa.gov/SIM/sim_index.htmland http://planetquest.jpl.nasa.gov/Navigator/sim_nav.html

  3. SIM Astrometric Performance Summary • Observational Band: 400 - 1000 nm • Global (all-sky) astrometry • Astrometric accuracy: 4 as (end of mission) • Faintest stars: V = 20 mag • brightness of a solar-type star at 10 kpc • Yields distances to 10% accuracy, anywhere in our Galaxy • Proper motion accuracy: 4 as / yr • Motion due to parallax at 10 pc is detectable in a few minutes! • Local (narrow-angle) astrometry • Measurements are made relative to reference stars (within ~1 • Astrometric accuracy: 1 as in one hour • This angle subtends a length of 1,500 km at 10 pc distance ! • Detect proper motion of Barnard’s star in 3 seconds !

  4. Astrometric Parameter Space • SIM will reach • V = 20 and 4 µas accuracy (global) • 1 µas accuracy (local) g g g g

  5. How Does SIM Work?  d = differential delay d = differential delay External path delay B telescope 1 telescope 2 detector detected intensity delay line Internal path delay beam combiner Pathlength control to ~ 10 nm (l/50) required for high fringe visibility. f = fringe position on detector 0 The peak of the interference pattern occurs at zero OPD to star

  6. Why go to space ? • Space has no air • Ground interferometers limited by atmosphere to ~1 mas over wide angles • High precision metrology measurements can be made • Space is quiet • Optical Path Difference (OPD) and pointing jitter are easier to control • Space can be made thermally benign • stable thermal environment  stability of optical system

  7. Instrument Configuration Guide Interferometer Fields of View Science Interferometer Field of Regard External Metrology Beams Guide Corner Cube Guide Compressor Optical Delay Lines (ODLs) Astrometric Beam Combiners (ABCs) External MET Beam Launchers Science Compressor

  8. Flight Segment Elements Precision SupportStructure (PSS) CombinerSubsystem (CMB) MetrologySubsystem (MET) Real Time Control (RTC) Subsystem Spacecraft System (SCS) Collector Subsystem (COL)

  9. Flight Segment Elements Real Time Control (RTC) Subsystem Precision SupportStructure (PSS) MetrologySubsystem (MET) Spacecraft System (SCS) Collector Subsystem (COL) CombinerSubsystem (CMB) Original image, to manipulate if desired.

  10. Flight Segment Elements • Instrument System • Collector (COL) Subsystem • Collects starlight • Combiner (CMB) Subsystem • Combines starlight from two collectors and measures position of resulting fringe • Measures OPD (optical path difference) • Metrology (MET) Subsystem • Measures motion of Science baseline wrt to Guide • Real Time Control (RTC) Subsystem • Performs all Instrument control functions • Spacecraft System • Precision Structure Subsystem (PSS) • Provides stable backbone structure to instrument • Traditional spacecraft engineering subsystems • CDS, S&M, ACS, Thermal, Telecom, Power, …

  11. SIM Launch Configuration (Without Solar Panels)

  12. Deployed Configuration

  13. Overall Configuration (deployed) Spacecraft COL Bay 1 PSS Truss TCC COL Bay 2 HGA LGA Star Tracker ODLs ABCs (3) Siderostat And DCC Solar Array Compressor

  14. Overall Configuration (stowed)

  15. SIM Configuration Vibration isolators Stowed PSS truss Contamination covers MLI covering of PSS truss and COL bay enclosures not shown Deployed COL bay enclosures Spacecraft

  16. SIM Astrometric Measurements Astrometric “Tiles” • Grid of stars is measured over entire sky • Grid is referenced to extragalactic objects • Position, parallax, proper motion are measured for all grid stars • Science targets are measured wrt grid • Grid is subdivided into 15 degree tiles • 5-7 grid stars per tile • Up to 50 additional science targets • Tiles centered on guide stars • Tiles overlap • SIM measures angle between stars in a grid. • S/C attitude is held fixed • Instrument scans over 15 degree tile B

  17. G G W Guide G G R N R R R R W W G G W The Field Of Regard covers Orion. 1302 red giants form the grid of reference stars.

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