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: and

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

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

8 Metrology Subsystem (MET) Collector Subsystem (COL) Real Time Control (RTC) Subsystem Precision Support Structure (PSS) Flight Segment Elements Combiner Subsystem (CMB) Spacecraft System (SCS)

9 Metrology Subsystem (MET) Collector Subsystem (COL) Real Time Control (RTC) Subsystem Precision Support Structure (PSS) Flight Segment Elements Combiner Subsystem (CMB) Spacecraft System (SCS)

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

14 Overall Configuration (stowed)

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

16 SIM Astrometric Measurements 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 Astrometric “Tiles”

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