Prospects for Terrestrial Planet Finder (TPF-C, TPF-I

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)


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



Exoplanet Mission Discovery Space



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



Summary: the path for exoplanet missions?

nothing

dazzling

head-turning

world-view changing

resu

lts

cost

current prospects

future prospects



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



TPF-C



HCIT Electric Field Conjugation Results



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



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.



Shaped Pupil HCIT result(monochromatic)



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



Pupil Mapping (PIAA) Schematic

Courtesy of Olivier Guyon



After speckle subtraction using a 32 x 32 DM



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.



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.



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



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.



Useful coronagraph throughput



Deformable Mirrors



Coronagraph Stability Demonstration

Trauger & Traub, Nature 2007



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.



TPF-I



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



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)



Technology for Mid-Infrared Nulling



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



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)



System Testbed: Planet Detection Testbed

Figure 8: Frequency spectrum of the nulling detector output.



• 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



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



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



State of the Art in Broadband Nulling



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



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



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



Collector spacecraft

• 3 m spherical mirror• Passively cooled• Readily scaled to smaller apertures• No deployables



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



Beam combiner spacecraft



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



Performance: Inner Working Angle

120 x 20 m array 400 x 67 m array

IWA = 25 mas

• Single Visit Completeness > 90%

IWA = 7 mas



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



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



TPF-O



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



New Worlds Observer



Fly the Telescope into the Shadow



Binary Shape



Performance

a=b=12.5mn=6F=50,000km



End



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.

Documents

Prospects for Terrestrial Planet Finder (TPF-C, TPF-I