# Presentation: 524101

## 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.

- November 23, 2004

## 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**

- November 23, 2004

## 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 !

- November 23, 2004

**Notes:**
These represent the best current estimate of SIM capability.  

## Astrometric Parameter Space

- SIM will reach
- V = 20 and 4 μas accuracy (global)
- 1  μas accuracy (local)

- g

- g

- g

- g

- November 23, 2004

## How Does SIM Work?

*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**

- External path delay

- November 23, 2004

## 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

- November 23, 2004

## 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)**

- November 23, 2004

**Notes:**
This slide shows an oblique view of the L-15x configuration. 
As a result of the reorientation of the corner cubes, the external metrology truss was reshaped into a more symmetric triangular prism.  This was necessary to meet the constraints on the viewing directions of the corner cubes. The external metrology fields of the view of the various corner cubes are very constrained.  Many are at close to grazing angles.  The corner cube positions cannot be adjusted much before losing external met beams.  
The guides share a common baseline of length 8.9m.  The science baselines are now both 10m long.  There are 15 external metrology beams.  
The science telescopes are now back-to-back.  This has widened the base of the triangular end view.  It has also pushed up the top of the “tent” as constrained by the corner cube geometry.  
The inset figure shows the relation between the FORs and the Sun shades.

## Flight Segment Elements

- MetrologySubsystem (MET)

- Collector Subsystem (COL)

- Real Time Control (RTC) Subsystem

- Precision SupportStructure (PSS)

- CombinerSubsystem (CMB)

- Spacecraft System (SCS)

- November 23, 2004

## Flight Segment Elements

- Original image, to
- manipulate if desired.

- November 23, 2004

## 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, ...

- November 23, 2004

## SIM Launch Configuration (Without Solar Panels)

- November 23, 2004

## Deployed Configuration

- November 23, 2004

## 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

- November 23, 2004

## Overall Configuration (stowed)

- November 23, 2004

## 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

- November 23, 2004

## 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”***

- November 23, 2004

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

**G**

**G**

**G**

**G**

**G**

**G**

- Guide

- W

- W

- W

- W

- N

- R

- R

- R

- R

- R

- November 23, 2004