National Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology
Wesley Traub, Stuart Shaklan, and Peter LawsonJet Propulsion Laboratory,
California Institute of Technology
The Spirit of Lyot ConferenceUniversity of California - Berkeley, 4-8 June 2007
Prospects forTerrestrial Planet Finder
(TPF-C, TPF-I, & TPF-O)
National Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology
Traub/Shaklan/Lawson
Purpose of Talk
• Exoplanet detection science is maturing rapidly• Exoplanet characterization science is in its childhood,
and needs data on all nearby planets (not just transits) tobegin maturing
• We are told that science mission funds are scarce• Dilemma: how to get data cheaply?
• We may need to revise our view of desired science:- More Jupiters & zodis?- Fewer Earths?
• Nevertheless, let us remain prepared for better times,and missions that could give head-turning orworld-view changing science
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Exoplanet Mission Discovery Space
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Scalable Architecture vs Science Yield
* very aggressive IWA assumption1-2 µm25, 622.56 mJWST and occulter
3-8 µm; R= 20 25, 80 02.52@1m,B~12mFourier Kelvin Stellar Int.
0.5-1 µm; R= 10 219, -- 3, --2*1.5Visible Nuller
0.5-1.5 µm; R= 10290, 47016, 29 2.5*2.5Pupil Mapping (PIAA-C)
0.5-1 µm; R= 10230, 3807, 153.52.5Pupil Mapping (PIAA-C)
0.5-1 µm; R= 10130, 2406, 133.52.5Band Limited Mask orShaped Pupil (C)
COST UNDER $1B
0.5-1.5 µm; R= 7570, 7828, 642.54 +50mocculter
External Occulter
0.5-1.5 µm; R= 75550, 71048, 99 2.5*4Pupil Mapping (PIAA-C)
0.5-1 µm; R= 75460, 58025, 563.54Pupil Mapping (PIAA-C)
0.5-1 µm; R= 75320, 54019, 363.54Band Limited Mask orShaped Pupil (C)
7-18 µm; R=25160, 19070, 1502.54 @ 2mB ≤ 400m
Emma-X Array (I)
COST RANGE $1B-$2B
0.5-1.5 µm; R= 75580, 80073, 1403.58 x 3.5FB-1 Coronagraph withPupil Mapping (PIAA)
0.5-1 µm; R= 75390, 68041, 8548 x 3.5FB-1 Coronagraph withBand Limited Mask
7-18 µm; R=75440, 460190, 3802.54 @ 4mB≤600m
Classic-X ArrayInterferometer
COST OVER $2B
Spectraλλ, R
# Jupiters # Targets
# Earths # Targets
IWA(λ/Dmax)
PrimaryMirror (m)Instrument Concept
5 Year Mission:25% detection25% characterization50% astrophysicsη(Earth) = 1τ(Jupiter) = 1
National Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology
Traub/Shaklan/Lawson
Summary: the path for exoplanet missions?
nothing
dazzling
head-turning
world-view changing
resu
lts
cost
current prospects
future prospects
National Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology
Traub/Shaklan/Lawson
Community Effort
UNIVERSITY FUNDING ($K) from TPF-C since
JUNE 2002
STSci, 242
SAO, 210
BostonU, 564
CTM, 316
Florida, 171Princeton, 919
UCB, 286
UofHA, 662
TOTAL FUNDING = $ 3 ,3 7 1 K
TPF-C TOTAL TECHNOLOGY INVESTMENTS
since 2002 ($K)
ITT
10,360
Masks
1,906
HCIT
8,766
Xintetics
2,146
Princeton
919
UCB
286
Florida
171 UofHA
662BostonU
564
VN
798CTM
316
SAO
210
STSci
242
TOTAL = $30,154K
JPL $14,277K Industry $12,507K Universities $3,371K
National Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology
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TPF-C
National Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology
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HCIT Electric Field Conjugation Results
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Coronagraphy PrimerImage Plane Masks Pupil Plane Masks
Pupil Mapping (PIAA)Shearing Nulling Interferometry
Best so far, good aberration rejection,hard to achromatize, low throughput
Easy to manufacture, easy to achromatize,simplest design, low throughput, large IWA.
Closest to ‘ideal’ high throughput, smallIWA, challenging optics, unknown WFCissues.
No optics in image plane, mostcomplicated to implement, throughputsimilar to band-limited mask.
BL8Vortex
External Occulter
Broad band, uses standard telescope, largefloppy structure, limited mobility
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Shaped Pupil Fabrication
Silicon-on-Insulator wafers.DRIE process. 2-sided etching.Manufactured at JPL Microdevices Laboratory
10-9 mask10-7 mask with 3 lambda/D IWA
Smallest features ~ 5 microns.
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Shaped Pupil HCIT result(monochromatic)
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Model Validation
• Monochromatic contrast to < 10-9
• Explore variations in contrast with bandwidth– Null at 785 nm with 2% bandwidth– Measure contrast at 10% bandwidth without changing DM
• Agreement with model ~ 20%• Modeling shows path for improvement
– Performance limited by systematic mask errors (dispersion)– Optimal Lyot stop improves by ~ 2x
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Pupil Mapping (PIAA) Schematic
Courtesy of Olivier Guyon
National Aeronautics and SpaceAdministrationJet Propulsion LaboratoryCalifornia Institute of Technology
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After speckle subtraction using a 32 x 32 DM
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Coronagraph Summary• Direct Imaging of Terrestrial Planets: 6 years of Lessons Learned
– Community has established science requirements– Mission studies: observational completeness– Detailed engineering studies and analysis– Preliminary instrument concepts including astrophysics camera
• Technology Status– State of the art is 10-9 contrast in 2% bandwidth at 4 λ/D
(about the 4th Airy ring)– Shaped pupil masks are close behind, 6e-9 in 10% bandwidth.– Demonstrated stability in the laboratory for detecting Earths.– Other approaches including external occulters are at 10-6 – 10-7.
• Bottom Line– For <$1B NASA, 1.5 m coronagraph could detect and characterize
a few (<6) Earths, but significant R&D required– Already have the technology for a large sample of cold Jupiters.– A phased approach – a small coronagraph later joined in orbit by a
large occulter – may make the most sense.
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A Case StudyBand-limited 8th-order Mask
Excellent aberration rejection.Modest throughput.
1st pupil 1st imagebright star
mask 2nd pupil Lyot stop 2nd imagebright planet
8 m x 3.5 m aperturePlaces planets in ‘foothills’ of ‘Mt. Everest.’Large throughput, high resolution reducescontribution of exo-zodi.
ResultsDetailed engineering studies show wemeet thermal, vibration, and pointingrequirements. No show-stoppers.Detects 41 Earths, 390 Jupiters (η=1)
Mission Modeling ToolsWhich stars to look at,how long, how deep.
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Type IWA ( !/Dmax) Primary Mirror # Earths # Targets # Jupiters # Targets
BL8 4 8 m x 3.5 m 41 85 390 680
PIAA 4 73 140 580 800
BL8/SP 3.5 4 m 19 36 320 540
PIAA 3.5 4 m 25 56 460 580
Ext. Occ. JWST 25 62 71 78
BL8/SP 3.5 1.5 m 2.3 5 82 154
PIAA 2.5 1.5 m 4.5 9 105 186
PIAA 2 1.5 m 6 11 115 195
Completeness Results
Known RV: 10Known RV: 7
SoA: 1e-9SoA: 1e-7SoA: 1e-7
SoA: 1e-7
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A Phased Approach
• Fly small coronagraph• Characterize Jupiters & disks with existing technology.
– Could find a few Earths.– Discovery-class missions
• Follow with an occulter– Can observe the systems most likely to harbor Earths.– Allows time to develop external occulter technologies.– Telescope angular resolution comparable to JWST (80 mas).– TPF-O
• Approach: use proven technology for bright planets,then new technology for Earth-like planets.
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Useful coronagraph throughput
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Deformable Mirrors
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Coronagraph Stability Demonstration
Trauger & Traub, Nature 2007
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Small Scale TPF-C Attributes
• Telescope does not deploy.– Simple thermal shroud deployment– Standard solar panel and solar sail deployments
• Simplified observational scenario– Line-of-site dither for image subtraction– Circular aperture means no need for multiple rolls about line of sight
• Requirements– For terrestrial planets, much tighter stability requirements than FB-1– Lower throughput and smaller aperture, so integration times grow.
• Stiffer Telescope– Greatly reduce gravity sag relative to FB1– Stiffer structure relative to FB1 to reduce beam walk and aberrations
• End-to-end testing looks feasible– No major new facilities
• Easily fits in low-cost launch vehicles.
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Traub/Shaklan/Lawson
TPF-I
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Planet Characterization in Mid-IR
• Starlight suppression– Null depth & bandwidth– Null stability
• Formation flying– Formation control– Formation sensing– Propulsion systems
• Cryogenic systems– Active components– Cryogenic structures– Passive cooling– Cryocoolers
• Integrated Modeling– Modeling uncertainty factors– Model validation and testbeds
• Science requirements• Architecture trade studies
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Software validation at the ISS
Ground-based software validation
System Testbed
Broadband Nulling1 x 10-5 null25% BW
Ongoing Work
TPF-I Systems Manager
Peter Lawson
TPF ManagerDan Coulter
TPF-I ArchitectureOliver Lay, Project ArchitectStefan Martin, Design Team Lead
Mid-IR Spatial FiltersAlexander Ksendzov (PI)Formation Control
TestbedDaniel Scharf (PI)
SPHERES GuestScientist Program (MIT)
Fred Hadaegh (PI)
Planet Detection TestbedStefan Martin (PI)
TPF-I ScienceCharles Beichman, Project ScientistStephen Unwin, Deputy Project Scientist
Achromatic Nulling TestbedRobert Gappinger (PI)
Adaptive Nuller TestbedRobert Peters (PI)
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Technology for Mid-Infrared Nulling
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Broadband Nulling: Achromatic Nulling Testbed
• 3.7×10-5 null,& 25% bandwidth
• 2.0×10-5 null, with& 20% bandwidth(left)
• 5.0×10-6 null,& laser source
• Goal is 1.0x10-5 average null depth at 25% bandwidth centered at 10 micron.• Only the Adaptive Nuller has achieved comparable results
2×10-5 average null with 20% bandwidth
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Broadband Nulling: Adaptive Nuller
• In April 2007 demonstrated control to 0.2% and 5 nm, 8-12 microns• Null depths of 2×10-5 over a 32% bandwidth demonstrated
0 1 2 3 4 5 6 73.8
4.0
4.2
4.4
4.6
4.8
5.0 Phase Stability Run 1
RM
S Ph
ase
(nm
)
Time (Hours)0 1 2 3 4 5 6 7
0.05
0.06
0.07
0.08
0.09
0.10
0.11
0.12Intensity Stability Run 1
Per
cent
Inte
nsity
Diff
eren
ce (R
MS
)
Time (Hours)
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System Testbed: Planet Detection Testbed
Figure 8: Frequency spectrum of the nulling detector output.
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• Achieved Formation Control of FCT Robots with FF S/W Controlling the two robots using thewireless Inter-Spacecraft Communication (ISC), Timing, and Synchronization functions
• Formation Software to Robots H/W I&T• Integrated FF Inter-Spacecraft Communication (ISC) software (new capability)• Integrated Inter-S/C Clock Timing and Synchronization software (new capability)
S/C
Path
Planner
Formation
Controller
Control
Mapper
Leader Spacecraft
Control
Mapper
Follower(s) Spacecraft
Formation Mode Commander
Spacecraft Mode
Commander
Inter-spacecraft Communication (ISC) - Wireless
Formation and Attitude Control System (FACS)
Formation
State
Estimator
Formation
Path
Planner
Formation
State
Estimator
Formation
Controller
Sensor Data
Sensor Data Actuator Cmd.
Actuator Cmd.
Formation FlyingControl Architecture
Distributed Realtime Simulation Architecture
Ground TestbedPerformance Simulation
Formation Algorithm & Simulation Testbed(FAST)
Formation Control Testbed (FCT)
Formation Control Testbed
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MIT SPHERES at ISS
• JPL is participating in theSPHERES Guest ScientistProgram to allow testing ofTPF-I formation flyingalgorithms at the ISS
• Nominally 8 opportunities fortesting over two years
• Prof. David Miller (MIT)
• MIT completed a three-SPHERESformation maneuver during testing atISS in March 2007
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Summary
Highlights• Formation Flying Testbed now operational• Laser nulling exceeding 10-6
• Broadband nulling now within a factor of two offlight requirement:
– Adaptive Nuller Testbed demonstrates (5 nmphase and 0.2% intensity compensation)
– Adaptive Nuller Testbed achieves a2×10-5 null with a 32% bandwidth
– Current performance would add only 5% tothe integration time needed to detect Earth at15 pc
• TPF-I & Darwin now very well aligned– Both projects working with the same design– Performance estimates closely agree
TPF-I Technology Goals• Demonstrate 10-5 broadband mid-IR nulling• Demonstrate fault-tolerant algorithm for formation
flying in a ground-based lab and at the ISS
Record broadbandmid-IR nulls: 2 × 10-5
null @ 32% BW
Old co-planar geometry
New ‘Emma’ geometry
‘Emma’ geometryreduces complexity &
increases sky coverage
Simulated earthextracted at 5×10-7
contrast ratio
Precision performancemilestone upcoming in mid-2007
Formation Control Testbed
Adaptive Nuller Planet Detection Testbed
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State of the Art in Broadband Nulling
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TPF-I Key Features• Wavelengths: Mid-Infrared 6 – 20 µm• Contrast: Earth-Sun ~ 107 @ 10 µm• Biomarkers: O3, CO2, CH4, H2O
• Technique: Nulling Interferometry• Implementation: Formation Flying
Selsis
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Emma Three Telescope Nuller
• Combiner moved 1.2 km out of plane• Collectors are spherical mirrors (f = 1.2
km)• Simplified collectors; no deployables• This design by Alcatel
Linear DCB
TPF-I Darwin
Bow-Tie
X-Array Planar TTN
Emma TTN
Emma X-Array
TPF-Darwin
Stretched X-Array
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Collector: old vs new
Five layersunshade
15.3 m
Deployedstray lightbaffles
Deployed payloadcryo radiators
Cold SunshadeDeployment Booms
(4 pl.)
4-m diametertelescope aperture
4.5 mdiameter
3-mdiametermirror
Fixed 4layer
sunshade
Fixed radiators
Deployed secondarymirror and shroud
Classic design Emma design
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Collector spacecraft
• 3 m spherical mirror• Passively cooled• Readily scaled to smaller apertures• No deployables
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Combiner spacecraft: old vs newClassic design Emma design
Five layersunshade
Cold sunshadedeployment booms
Cryogenic nullingbeam combiner
15.3 m
Deployed payloadcryo radiators
Fixed 4 layersunshade
Fixed payloadcryo radiators
Cryogenic nullingbeam combiner
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Beam combiner spacecraft
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Mass and volume
• 3 m design = 6900 kg (w 30% reserve)• Mass saving of 30% over previous
design• Compatible with medium lift LV
– Delta IV M+– Ariane 5 ECA
• Scaling to smaller diameters– 3.0 m 6900 kg– 2.0 m 4800 kg– 1.5 m 4100 kg– 1.0 m 3700 kg
Inspired by Alcatel design
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Performance: Inner Working Angle
120 x 20 m array 400 x 67 m array
IWA = 25 mas
• Single Visit Completeness > 90%
IWA = 7 mas
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0
50
100
150
200
250
300
0 20 40 60 80 100
Mission time / weeks
# E
arth
s
Performance: detectable Earths
• From Sarah Hunyadi’s completeness code• Assumes 1 Earth per star• Good agreement with European analysis
3 m diameter
2 m diameter
1.5 m diameter
280
130
82
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Spectroscopic characterization
0
20
40
60
80
100
120
140
0 100 200 300 400 500 600 700 800 900 1000
Available time for characterization / days
# p
lan
ets
ch
ara
cte
rized
• SNR = 5 in 9.5 – 10 µm ozone channelηearth = 1
3 m diameter
2 m diameter
1.5 m diameter
1 yr 2 yr
48
70
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TPF-O
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Occulters
• Telescope big enough to collect enough light from planet• Occulter big enough to block star
– Want low transmission on axis and high transmission off axis• Telescope far enough back to have a properly small IWA• No outer working angle: View entire system at once
Target Star
Planet
TelescopeOcculter
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New Worlds Observer
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Fly the Telescope into the Shadow
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Binary Shape
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Performance
a=b=12.5mn=6F=50,000km
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End
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Summary
• We are exploring several approaches to TPF-C including 4 classes ofinternal coronagraphs, and external occulters.
• For internal coronagraphs, only Guyon’s PIAA approaches the theoreticallimit and may potentially enable Exo-Earth detection with a 1.5 m aperture.– If this approach is successfully developed, it can find up to ~ 5 Earth-like
planets (for ηEarth = 1) and requires an ultra-stable 1.5 m aperture telescope.• Phased approach may yield the best overall science return, and be
affordable over time.