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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.html and 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)

gg

gg

5

The peak of the interference pattern occurs at zero OPD to star

detectordelay line

beam combiner

telescope 1 telescope 2

Internal path delay

f = fringe position on detector0

detectedintensity

Pathlength control to ~ 10 nm 50)required for high fringe visibility.

B

How Does SIM Work?

External path delay

d = differential 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)

GuideCorner Cube

ScienceCompressor

GuideCompressor

External METBeam Launchers

External MetrologyBeams

Guide Interferometer Fields of ViewScience Interferometer

Field of Regard

Astrometric Beam Combiners (ABCs)

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MetrologySubsystem (MET)

Collector Subsystem (COL)

Real Time Control (RTC) Subsystem

Precision SupportStructure (PSS)

Flight Segment Elements

CombinerSubsystem (CMB)

Spacecraft System (SCS)

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MetrologySubsystem (MET)

Collector Subsystem (COL)

Real Time Control (RTC) Subsystem

Precision SupportStructure (PSS)

Flight Segment Elements

CombinerSubsystem (CMB)

Spacecraft System (SCS)

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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

SiderostatAnd 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”

d s B c= • +

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G G

G G

G GGuide

W

W

W

W

NR R

RR

R

The Field Of Regard covers Orion. 1302 red giants form the grid of reference stars.