NASA
JPL
SIM Planet Quest
Science Goals and Technology Status
M. Shao
JPL
NASA
JPL
Outline
• Basics of astrometry with a space interferometer (SIM)
• Technology of SIM
– Nanometer control of space interferometer
– Picometer knowledge of optical paths
• Science with SIM
– Exo-planets
– Astrophysics
• Other applications of SIM related technology
NASA
JPL
Basics of Interferometric Astrometry
Star-Baseline Geometry
The angle between the star and baseline creates an external
path delay x
External path delay
X= B*cos(q)
q
telescope 1
Baseline Vector B
telescope 2
If we know B, and can determine x, we can solve for the star
position q
NASA
JPL
Determining the External Delay
We determine the external delay by measuring the
length of an internal delay which exactly matches it
External path delay
x = B sin(q)
telescope 2
telescope 1
Internal path delay
beam combiner
delay line
Optical delay lines are used to vary the internal delay
NASA
JPL
Fringe Position as a Measure of Pathlength Equality
detected
intensity
External path delay
x = B sin(q)
0
telescope 2
telescope 1
detector
Internal path delay
beam combiner
delay line
The peak of the interference pattern occurs when the
internal path delay equals the external path delay
external delay
- internal delay
About Fringes
NASA
JPL
1.5
1
V
0.5
Narrowband
(laser) fringe
Dl ~ 0
1
0
-Fringes at all delays
-0.5
-1
-1.5
0
2
1 wavelength
4
6
8
1.5
1
-Number of fringes ~ Dl/l
-There is a well defined
central fringe
0.5
Wideband
(white light)
fringe
Dl >> 0
0
-0.5
-1
-1.5
0
2
4
6
8
-Fringe position tells us about position of source
-Fringe visibility tells us about structure of source
(extended sources have reduced fringe visibility)
NASA
JPL
Requirements on Fringe Stabilization
Vibrations blur out the fringe
1.5
1
0.5
10 nm rms
0
-0.5
-1
1.5
-1.5
1
0
1
2
3
4
0.5
50 nm rms
0
-0.5
-1
1.5
-1.5
0
1
2
3
4
1
0.5
200 nm rms
0
-0.5
-1
-1.5
0
Need real-time control of pathlength to
~10 nm (l/50) for high fringe visibility
1
2
3
4
Internal Metrology
NASA
JPL
Laser gauge measures internal delay
(adjusted by delay line, sensed by fringe detector)
Metrology
Starlight
telescope 1
optical fiducial
optical fiducial
telescope 2
detector
laser
Internal path delay
beam combiner
delay line
Laser path retraces starlight path from combiner to telescopes
External Metrology
NASA
JPL
SIM uses 2 guide interferometers looking at two guide stars (7 mag)
to define an inertial frame to < 1uas/1hr in knowledge.
External laser metrology measures the relative baseline vectors of
The two guide interferometers wrt the science interferometer
Guide 1 near
Center of field (15 deg)
telescope 1
optical fiducial
optical fiducial
telescope 2
Baseline Vector B
Guide 2 ~90 deg away
The physical baseline of SIM will move ~ 0.1 arcsec on a time scale
of ~30 sec. In data reduction, we define a “regularized” baseline that is
fixed in inertial space to < 1uas over ~ 1hr by using information from both
guide interferometers and the external laser metrology truss.
NASA
JPL
SIM Fringe Detector
(conceptual schematic)
Light is combined
A
2~3 arcsec
Field stop
B
Low resolution
Spectrometer ~80 channels
From 0.45 ~ 1.0um
Vibrating mirror
250Hz triangle wave 1um
CCD read out @ 8 samples/um
A Laser metrology system measures the optical
path diff (A-B) from the combining beam splitter to optical fiducials
at siderostat that defines the baseline vector.
NASA
JPL
Technology for SIM
• NASA (with the project, and review committees) defined 8
technology milestones (1-4 prior to start of phase B, 5~8 required
prior to start of phase C. All 8 were completed in July 2005.
• Nanometer control (realtime)
– Coarse pointing of spacecraft (0.1 arcsec)
– Siderostat (telescope) pointing to ~20 mas
– Delay tracking to ~10nm ~ 200 uas.
• Picometer knowledge (post processing on the ground)
– Total error budget for 1uas narrow angle astrometry is ~50
picometers. Individual component contributions in some
cases are required to be 1~2 picometers
– Photon noise from the star(s) is ~ ½ the error variance
• System integration/interactions and modeling
NASA
JPL
SIM Technology Flow
Component Technology
1999
Subsystem-Level Testbeds
4:Oct2002
2001
Metrology Source
System-Level
8:Jul2005
Absolute Metrology
4: Kite Testbed (Metrology Truss)
1999
Picometer
Knowledge
3:Sep2002; 5:Mar2003
6:Sep2003; 7:Jun2004
8: Overall system
Performance via
Modeling/Testbed
Integration
Multi-Facet Fiducials
Technology
Numbers before box
labels indicate HQ
Tech Gate #’s (1
1:Aug2001
1: Beam Launchers
1998
2000
3, 5, 6, 7: MAM
High Speed CCD
Fringe Tracking
Camera
Testbed
(single baseline picometer
testbed) Narrow & Wide
Angle Tests
TOM Testbed
(distortion of front
end optics)
through 8)
All 8 Completed
2:Nov2001
Nanometer
Control
Optical
Delay Line
1998
Technology Hexapod
Reaction Wheel
Isolator
1998
1999
STB-1 (single baseline
nanometer testbed)
2: STB-3 (three baseline
nanometer testbed)
NASA
JPL
System Testbed - 3 Baselines
(STB-3)
•
•
•
•
•
Fully functional model of SIM -3 interferometers, 15 external
metrology beams, 9-meter
flexible structure (emulates SIM
dynamics)
Demonstration of SIM
nanometer stabilization
technololgy
Proving ground for SIM control
algorithms
Validation of AEB allocations
for 2nd order errors via
overdrive (“whale-on”) tests
STB-3 completed Tech Gate 2
NASA
JPL
STB-3 on 9-meter Flexible Structure
NASA
JPL
Accurate White Light Fringe Phase
Measurement
• 1 uas accuracy with a 10m baseline => optical path accurate to
~50pm.
• The allocation to white light fringe
measurement is ~ 20pm or a
required accuracy of l/30,000
• Normal opd dither modulation
and demodulation isn’t accurate
enough
• Inten = 1+vis*sin(2pX/l + f) in
monochromatic light
~1000 sec
observation
NASA
JPL
White Light Fringe Phase 2
Inten = 1+vis*sin(2pX/l + f)
Measuring Inten(1-8), one
then solve for in a least sq’s
sense, f , vis etc.
Errors in the knowledge of
X produces both random and
Systematic errors
Systematic errors are due to
M1 M2
non-linearities in
M3
hysteresis in PZT
vibrations at the modulation
freq or harmonics
Random errors from
vibration at freq other than the modulation freq
M4
M5
M6
M7
M8
Errors in our knowledge of X result 1:1 in errors in f*l//2p
Random errors in X will average down ~sqrt(N), but systematic errors won’t
(and often the systematic errors can be ~ l/50 or larger
NASA
JPL
White Light Fringe Phase 3
• By measuring the modulator motion with laser metrology with
systematic errors < 10pm, and random noise < 10pm/sqrt(hz) white
light fringe measurements can be extremely accurate.
– However, the metrology data must be used when demodulating
the whitelight fringe.
– Normally we solve for the phasor components of the whitelight
fringe, in a least squares fashion
• [Vis*sin(phi), Vis*cos(phi), DC] = pseudo_inv * [M1…M8]
• The brute force approach to using the metrology data is to
calculate a diff pseudo_inverse for every modulator stroke
based on the X’s measured.
– However a much more computationally efficient route is
possible is the modulation waveform is highly repeatable.
• Fundamental limits (beside stellar photon noise) to w.l.
measurements are due to
– errors in the metrology system
– Errors in the timing of the metrology and ccd measurements.
NASA
JPL
The Micro Arcsec Metrology Testbed
Laser metrology measures the
position of the IIPS.
Test is to compare metrology to
whitelight (starlight) fringe
position.
IIPS
MAM
Interferometer
Examples of Systematic Errors
NASA
JPL
SIM Diffraction Testbed
Diffraction:
The metrology beam and
starlight beam are different
diameters, see different
obscurations.
Mask B
TEMPORARY STORAGE 1
0. 0070
14
12
10
phase meter (nm)
0. 0035
0. 0000
8
6
4
2
0
-2
-0. 0035
-4
-6
-500
-0. 0070
-0. 0070
-0. 0035
0. 0000
SIM Diffraction Testbed
FOB (X,Y)
0.000 0.000
SPACING (X,Y) = 0.93750E-04 BY 0.93750E-04 METERS
GRID (X,Y) = 256 BY 256
starlight
0. 0035
-400
-300
-200
-100
0. 0070
0
z (mm)
CFG 1
100
200
300
400
500
After propagating ~10 meters
the optical phase of the
wavefront of metrology and
starlight are different
Lockheed Martin Adv. Tech. Center
318 HRS 29 Oct 01
Torben B. Andersen
metrology
Beamwalk:
The metrology beam samples a different part of the optic
than the starlight beam. If the optical surface is perfect
at l/100 rms, the surface has 6nm hills and valleys.
If we want to measure optical path to 50 picometers we
have to make sure we sample the same hills and valleys
everytime.
NASA
JPL
Narrow-angle Astrometric Observations
Understanding
instrument
systematic errors is
essential for meeting
narrow-angle
performance at
1 as accuracy
Instrument Field
of Regard (15deg)
Guide star
1~2 deg
Repeat later with
Orthogonal baseline
Dq
Baseline B
Guide star
Grid star
Science target
Reference star
Guide star 2, 90 deg away
NASA
JPL
Sqrt(N) From 1 Chop to 10 chops
MAM test: 4 ref stars, 1 target star, (T, R1, T, R2, T, R3, T, R4 …. Repeat)
~20 runs conducted over ~1 week.
1 uas total error
0.7 to photon noise
0.7 to instrument
0.5 to science interf
0.5uas ~25 pm
Meet 25pm in 8 chops
Each dot is an 8 chop
average
Sqrt(N) Multiple Epochs
NASA
JPL
The data does show
That averaging multiple
8 chop data does improve
Accuracy.
8 chops
Small number statistics at
long integration
Times make a definitive
Statement difficult.
18*8 chops
There was enough data to calculate allen variance and get
some idea whether multiple epochs will get sqrt(N).
Data taken over ~1.5
weeks, interferometer
realigned daily
NASA
JPL
Wide Angle Astrometry
SIM goal is 4uas global astrometry (end of mission)
Single epoch accuracy ~ 10uas.
Wide angle test sequence looks at ~60 stars
over a 15 deg field of regard. (~1hr test)
Instrumental error vs position in
the field of regard.
Met milestone ~4 uas error (end of mission)
~10uas single epoch error.
Dominated by field dependent biases and
thermal drift over 1 hr (versus 90sec for NA)
NASA
JPL
Siderostat/Telescope Thermal Stability -Test Layout
NASA
JPL
SIM Science Team
Key Science Projects
Names
Institutions
Topic
Dr. Geoffrey Marcy
University of California, Berkeley
Planetary Systems
Dr. Michael Shao
NASA/JPL
Extrasolar Planets
Dr. Charles Beichman
NASA/JPL
Young Planetary Systems and Stars
Dr. Andrew Gould
Ohio State University
Astrometric Micro-Lensing
Dr. Edward Shaya
Raytheon ITSS Corporation
Dynamic Observations of Galaxies
Dr. Kenneth Johnston
U.S. Naval Observatory
Reference Frame-Tie Objects
Dr. Brian Chaboyer
Dartmouth College
Population II Distances & Globular Cluster Ages
Dr. Todd Henry
Georgia State University
Stellar Mass-Luminosity Relation
Dr. Steven Majewski
University of Virginia
Measuring the Milky Way
Dr. Ann Wehrle
NASA/JPL
Active Galactic Nuclei
Mission Scientists
Dr. Guy Worthey
University of Washington
Education & Public Outreach Scientist
Dr. Andreas Quirrenbach University of California, San Diego
Data Scientist
Dr. Stuart Shaklan
NASA/JPL
Instrument Scientist
Dr. Shrinivas Kulkarni
California Institute of Technology
Interdisciplinary Scientist
Dr. Ronald Allen
Space Telescope Science Institute
Synthesis Imaging Scientist
NASA
JPL
Global Astrometry
At any one time, SIM’s field of regard is 15
deg. In order tie the whole sky together,
SIM makes measurements over 4p in a
series of overlapping tiles.
Tile #3
Tile #2
Instrument Field
of Regard (15deg)
Grid star
Science star
Tile #1
Dq
Baseline B
NASA
JPL
What is the Grid?
•
A regularly spaced set of 10~12 mag stars that cover the whole sky, along
with 25~50 QSO’s that form a reference frame for SIM global and narrow
angle observations.
•
Grid stars:
Moderately bright (11 mag) ~1300 stars in a regular grid
pattern
– K giants were chosen because they are intrinsically bright, hence
distant, 0.9~1.5 Kpc
– At such a distance jovian planets would in general would produce nonlinear motions over 5 years < 4 uas.
NASA
JPL
•
•
•
•
•
•
•
Solving the Simple Grid
Each tile has ~7 grid stars, 7 delay measurements.
There are ~1300 overlapping tiles (per orange peel)
2 baseline orientation per tile
22 orange peels in a 5 year mission
The 5 yr grid has ~400,000 measurements
Astrometric variables ( RA, Dec, PM_RA, PM_Dec, Prlx) ~6500
Nuisance parameters (regularized baseline vectors xyzc)
~175,000
• Large least squares fit
• Approx results
– Position accuracy ~ 4uas (for single epoch accuracy 10uas)
– Proper motion accuracy ~ 2.5uas/yr
– Absolute Prlx accuracy ~ 4.5 uas
NASA
JPL
More on the Grid
• Time doesn’t permit me to more than mention some additional
issues being studied by the SIM project
• Zonal errors, the errors in parallax (or PM or position) from star to
stars have both a random and systematic component. (assuming the
actual delay measurements themselves are totally random)
– This limits the ability to for example determine the distance to an
extra galactic object by averaging the parallaxes of N stars in
that object
• Solving for field dependent biases. Many (most?) of the field
dependent biases in SIM will be stable over very long time scales. In
addition to solving for the baseline vector, per tile, it may be possible
to solve for field dependent biases. (numerical experiments have
shown this is possible if the field dependent errors are stable for
several 100 hrs.
• Using QSO’s. Todate numerical simulations have only looked at a
stellar grid. The use of a number of QSO’s may avoid some of the
zonal errors that arise from a star-only grid.
NASA
JPL
•
•
SIM Planet Science Overview
The SIM planet science program has 3 components.
Searching ~250 nearby stars for terrestrial planets, in its Deep Search
at (1 as).
– SIM will characterize targets for Terrestrial Planet Finder
• If planets are found via other means, direct imaging in visible or IR
using TPF, archival SIM can measure the mass of that planet with
an error better than 0.5 Earth Masses (Sun-Earth @10pc)
•
•
Searching ~ 2000 stars in a Broad Survey at lower but still extremely
high accuracy (4 as) to study planetary systems throughout this part of
the galaxy.
Studying the birth of planetary systems around Young Stars so we can
understand how planetary systems evolve.
– Do multiple Jupiters form and only a few or none survive during the
birth of a star/planetary system?
– Is orbital migration caused primarily by Planet-Planet interaction or
by Disk-planet interaction?
– Suitable information for young stars cannot be obtained from
radial velocity studies due to effects of rotation and stellar
active
NASA
JPL
Application of Narrow Angle Astrometry
Planet Detection
Detection Limits
SIM: 1 as over 5 years (mission lifetime)
NASA
JPL
Galactic Structure from Microlensing
NASA
JPL
Taking the Measure of the Milky
Way
• Unique, legacy, measurements of
fundamental parameters of the Milky
Way:
– Mass scale  Total mass
– Distance scale  Size
– Dynamical scale  Rotation
curve
NASA
JPL
Probe of Inner Galactic Potential
Before SIM
After SIM
• SIM will measure:
– Galactic rotation curve across entire disk
– Vcirc(R)  disk potential to 2-3%  2Ro
– Local mass volume density and column density
– Amplitude, pattern speed, shape, wavelengths, phase for large
non-axisymmetries:
• bars, warps, spiral arms
NASA
JPL
Mass of the Galaxy (Dark Halo)
• SIM is the only means for obtaining precision velocities in outer
Galaxy
• SIM can determine mass vs. radius to R > 200 kpc via
complementary methods:
– Jeans Equation: ~1000 random field giants, Galactic globulars
and satellite galaxies
– Stars in tidal streams (e.g., Sagittarius): Milky Way potential
from true 3-D orbits
Simulation: Formation of tidal tails
Polar ring galaxies:
proven gravitational laboratories
NASA
JPL
Dynamics of the Local Group
NASA
JPL
Physics of Active Galactic Nuclei
• Does the most compact non-thermal
optical emission from an AGN come
from an accretion disk or from a
relativistic jet ?
• Do the cores of galaxies harbor
binary supermassive black holes
remaining from galaxy mergers ?
• Can AGNs be used to ‘anchor’ the
SIM astrometric reference frame (the
grid) ?
NASA
JPL
Stellar Astrophysics Goals
• Precise Masses and Luminosities (binaries)
– Open clusters
– Selected classes of objects
• Population II Distance Scale
– Ages of globular clusters
– RR Lyraes as standard candles
– MS turnoff stars and subgiants in the halo
• Dynamics
– Black hole and RS CVn binary emission
– Paths of neutron stars and OB stars
NASA
JPL
Other Applications of SIM Related
Technology
• Interferometry and very precise measurements of
distance/wavefronts have applicability to both the TPF-C and
TPF-I missions.
• On a nearer time scale. We’re pursuing a number of
collaborations.
• With UCSC/LLNL, HIA, AMNH, UCLA etc. on Gemini GPI
(extreme AO)
• With BU, MIT, on Picture, nulling coronagraph/post coronagraph
calibration interferometer on a sounding rocket.
• Studies with UCSC/LLNL on TMT extreme AO/coronagraph
• Studies of TPF-C nulling coronagraph
• Proposal with GSFC on space nulling coronagraph
NASA
JPL
NASA
JPL
Block Diagram
Speckle nulling
telescope
Wavefront
Correction
f, amp
Coronagraph
/Starlight
suppression
Post
coronagraph
Wavefront
sensor
Camera
/spectrometer
/IFU
Post processing
Speckle subtraction
If average scattered light
= 10-10
½ speckles > 10-10
5% of speckles > 2x10-10
0.2% speckles > 3x10-10
For field of view ~32*32
1% false alarm =>
Speckles (after subtraction) < 0.2* planet flux
TPF project simulation
NASA
JPL
Block Diagram of Post Coronagraph
Wavefront Sensor/Calibration Interferometer
coronagraph
Starlight rejected
by coronagraph
Dither for phase
Shifting interferometer
•
•
•
Take ~50% of the output of the coronagraph
Interfere it with starlight that is rejected by the
coronagraph. (spatially filtered)
Two~three options
– In the pupil plane, measure the speckle
amplitude and phase, fourier transform to get
the speckle image at science camera.
– In the image plane measure speckle amplitude
and phase
To Science
Camera
To PCWS
Camera
Nulled output
To sci camera
Pupil
camera
Spatial
filter
Post coronagraph
Wavefront calibration
Fiber bundle
nuller
PICTURE
AO Coronagraph on a Sounding Rocket
NASA
JPL
•
•
B.U. (S. Chakrabari), JPL, MIT (Lane),
GSFC (Rabin), NGST, and LMCO
A mini-version of the TPF-C concept
study.
–
–
–
–
1 potential target, Jovian planet around E
Eri. (3e-8 contrast)
Selected Jan 2005, 2 flights Jan-Feb 2007
and July-Aug 2007.
CDR July 2005
Nuller, with calibration system (no fiber
bundle)
400 km
~500 sec in space
100 km
• Working at 1 l/D
–
E Eri
1000 element DM in 1 arm of nuller
New Mexico
NASA
JPL
Telescope Section Design
(Overall)
•
•
•
•
•
•
Sharpie mirror (50 cm, diff limited in UV
telescope) (GSFC)
Primary mounted using bipods and Al
support ring.
Carbon fiber support tube w/ flare.
Four vane spider for secondary
Second four vane spider for ST-5000
Cold plate under shutter for thermal
“dynamic stabilization”
NASA
JPL
Basic Design
Electronics
section
•
Three sections
– Electronics section
– Instrument section (Back end)
– Telescope section (Front end)
•
•
•
•
Telescope & Instrument evacuated at launch
All optics mounted at a single attachment plane at the
Telescope - Instrument bulkhead
Aft facing at launch
Observes through WFF shutter door
Instrument
section
Attachment
plane
Telescope
section
Shutter
door
NASA
JPL
Planar Optical Design – Isometric View
versionV1.15 30 June 2005
• 1000 element engineering grade
device at JPL for testing of HV drive
electronics/computer control for
PICTURE project
•1000 element flight DM in ~Nov/Dec
2005 at JPL.
NASA
JPL
Lab Demo of Closed Loop Nulling
Average closed loop
null 8x10-7, with
~1000 actuator DM
~8x10-10 scattered
light/airy spot
PICTURE
Requirement
TPF-C
Requirement
Update rate ~ 1.5 sec
(see IAU talk by Schmidtlin et. al.)