12 aug 2003 pg 1 s. shaklan national aeronautics and space administration jet propulsion laboratory...

12 Aug 2003 pg 1S. Shaklan

National Aeronautics and Space AdministrationJet Propulsion LaboratoryCalifornia Institute of Technology

The Terrestrial Planet Finder Coronagraph

Stuart Shaklan

TPF Coronagraph Architect

Jet Propulsion Laboratory,

California Institute of Technology

July 23, 2004


National Aeronautics and Space AdministrationJet Propulsion LaboratoryCalifornia Institute of Technology Overview

• History

• Science Requirements

• Trade Studies

– How aggressive to make the coronagraph?

• Baseline Mission Design

– Telescope

– Thermal Control System

– Coronagraph Instrument

• Technology Development

• …and into the future…


National Aeronautics and Space AdministrationJet Propulsion LaboratoryCalifornia Institute of Technology A Brief History of the Project

• 2000-2002: Industry/University teams conducted feasibility study

• Concluded that with suitable technology investment starting now, a mission to detect terrestrial planets around nearby stars could be launched by the middle of the next decade (2010–2020).

• Summary report available at: http://planetquest.jpl.nasa.gov/TPF/TPFrevue/FinlReps/JPL/tpfrpt1a.pdf

• In mid-2002, JPL set up Interferometer and Coronagraph pre-project teams

– Working toward a mission selection in 2006

• Science Working Group chartered in October 2002

• Spring 2004: NASA decided to fly a visible coronagraph first, followed by an IR interferometer.

• We are now working toward ‘Phase A’ project status.

– JPL is the project lead.– Goddard will build the

telescope.

Ball Aerospace 2000-2002 Pre-Phase A Final Architecture Review Concept:

Shaped pupil coronagraph

Off-axis unobscured system

4x10m elliptical off-axis monolithic primary mirror

High density deformable mirror for wave front correction

= 0.5-1.7 µm

1 AU orbit (L2 or Earth-trailing)


National Aeronautics and Space AdministrationJet Propulsion LaboratoryCalifornia Institute of Technology TPF Science Requirements

The minimum TPF must be able to detect planets with half the area of the Earth, and the Earth’s geometric albedo or the equivalent equilibrium effective temperature, searching the entire HZ of the 35 core-group stars with 90% completeness per star.

HZ = Habitable Zone = 0.7 – 1.5 AU scaling as sqrt(luminosity)

Flux ratios must be measured in 3 broad wavelength bands, to 10% accuracy, for at least 50% of the detected terrestrial planets.

The spectrum must be measured for at least 50% of the detected terrestrial planets to give the equivalent widths of O2, H2O, and O3 in the visible or H2O, and O3 in the infrared to an accuracy of 20%; we desire to detect CO2 and CH4 as well.


National Aeronautics and Space AdministrationJet Propulsion LaboratoryCalifornia Institute of Technology Distances, IHZ of 50 best targets

These are the 50 nearby stars that offer the best ‘completeness’ after 9 observations over 3 years.


National Aeronautics and Space AdministrationJet Propulsion LaboratoryCalifornia Institute of Technology Aperture Size

Wavelength (um) 0.5 0.6 0.7 0.8 0.9 1

Length (m) Distance in mas from center to 3rd minimum4 77 93 108 124 139 1555 62 74 87 99 111 1246 52 62 72 83 93 1037 44 53 62 71 80 888 39 46 54 62 70 77

10 31 37 43 50 56 62

Length (m) Distance in mas from center to 4th minimum4 103 124 144 165 186 2065 83 99 116 132 149 1656 69 83 96 110 124 1387 59 71 83 94 106 1188 52 62 72 83 93 103

10 41 50 58 66 74 83

Orbit a (AU) 0.7 1 1.2 1.4 1.5 2

Distance (pc) Star-planet separation (mas)10 70 100 120 140 150 20012 58 83 100 117 125 16714 50 71 86 100 107 14316 44 63 75 88 94 12518 39 56 67 78 83 111


National Aeronautics and Space AdministrationJet Propulsion LaboratoryCalifornia Institute of Technology Telescope Architecture Trades

Manufacture Launch Performance Integ. & Test Comment

6 x 3.5 monolith3 lambda/D requires extremely tight tolerances

8 x 3.5 monolith4 lambda/D better, possible mass problem

10 x 3.5 monolithNew facilities to build it, mass an issue

8 x 7 multi-segLow throughput, tight piston reqmnts.

15 x 3.5 2 segmentLarge primary-secondary distance > any test facility

12 x 3.5 2 telescopefew-pm piston req'mnt between 'scopes

Got milk?Well Beyond State-of-the-ArtChallenging


National Aeronautics and Space AdministrationJet Propulsion LaboratoryCalifornia Institute of Technology Baseline Mission Parameter Summary

• Aperture: 6x3.5 m off-axis Cassegrain

• IWA: 3 lambda/D

• DM: 96 x 96 actuators

• Bandpass: 500-600 nm (detection), 500-800+ nm (spectroscopy)

• Mask: 1-D linear 1-sinc^2 mask (others work as well)

• SNR = 4 per observation (photon-statistics limited)

• Solar Zodi: V=22.7 per sq. arcsec.

• Exo Zodi: 2x brighter than Solar Zodi (and double pass for 4x total )

• Total integration time: 1 year for detection (not including overhead)

• Total program length: 3 years for detection

• 50 targets

• 9 visits per target over 3 years

• Each visit requires 3 Line-of-sight roll positions (two 60 degree steps)

• Photometric sensitivity: delta magnitude = 25



• 2nd Order Dependence– Focus, Coma,

Spherical

• 4th Order Dependence– Tilt, Astigmatism,

Trefoil

• Other occulters exhibit different dependencies

(e.g.) Visible Nuller4th order focus sensitivity

Sensitivity to Low Order Aberrations

Radial Cosine (/D) Evaluated at 3 /D

Cm mm

2

Cm mm

4

m Cm m2

m Cm m4

Calculated using Fourier Plane mathematics and small wave front perturbations in a pupil plane.

Zernike C-matrix

These calculations form the

Zernike Sensitivity coefficients appear in worksheets:Rsinc28ar, lcos4ar, rcos4ar….

Green and Shaklan, SPIE 2003



Shaped Pupil Aberration Sensitivity

Green and Shaklan, SPIE 2004


National Aeronautics and Space AdministrationJet Propulsion LaboratoryCalifornia Institute of Technology Coronagraph Forms

ManufactureInner Working

AngleLow-order Aberration

Sensitivity Bandwidth Comment

HEBS glass continuous Bandwidth? Radiation?

Binary image plane mask Very different in each pol.

Shaped Pupil Mask

No design (yet?) for 3 lambda/D with elliptical aperture

Pupil RemappingHybrid approach looks promising

4-Quadrant Phase Masktheta 2̂ not theta 4̂ at center --> star leakage

4-beam nuller

~ 2x complexity of masks. Poor coverage in image plane.

UnfavorableTBDLooks good


National Aeronautics and Space AdministrationJet Propulsion LaboratoryCalifornia Institute of Technology TPF Architecture Coronagraph Description

TPF-Coronagraph PayloadM1

M3M2

f/20Polariz. BeamSplitter

M1

M2 M3

P1

P2

P2

DM(pair) MichelsonAssembly

RelayPupil f/60 (100)

PupilMask

OccultingMask

Image Relay f/20 (54)

CCDCamera

LyotMask

FocusMirror

M4 M5 M6

M7 M8 M9

Identical 2nd SystemCollimator

Mirror

Polarizer, WFS&C, Coronagraph, Spectrometer



Configuration Schematic

Dynamic Isolation

Optical Bench:Coronagraph Sensor

and Spectrograph

Primary Mirror Support Structure

(Aft Metering Structure)

Primary Mirror

Instrument Thermal Enclosure

Secondary Mirror

Deployed V-groove Thermal Shields (inner layer will act as baffle)

Deployed Solar Array

Spacecraft BusSpacecraft Equipment Support Panel:-thruster clusters (2)-fuel tanks (2)-high gain antenna (2)-sun shade

Science Payload-Telescope-Coronagraph System -Instruments

Spacecraft System



Sy

Amplitude & Phase Wavefront Correcting Deformable Mirrors

Fas

t Ste

erin

g M

irro

r

PolarizingBeam

Splitter

DispersingPrism

Insertable PickoffMirror

PlanetDetection

Spectrometer

Fine GuidanceCamera

Pup

il M

ask

Occ

ulti

ng

Mas

k

Lyo

t Sto

p

Focussing Mirror

RedundantInstrument

S Pol

P Pol

-100°C

-100°C

6DOFHexapodAcquisition

Camera CoronagraphDetectors

PrimaryMirror

Secondary Mirror

Fold MirrorLaser

Metrology

Telescope

Metrology

Coronagraph Optics

AcquisitionCamera

DeformableMirror Control

Detector ControlInstrumentComputer

ThermalControl

PowerOptical

Actuator Control

• • • •• • • • • •• •

CornerCube

0°C

Cor

onag

rap

hT

her

mal

Rad

iato

rs

Coronagraph Electronics

SunShade

PowerConditioning

PowerDistribution

Batteries

Pyro

Power

N2H4 N2H4

LLPP

P

Fill Drain

Propulsion

Sol

ar S

ail

Solar Arrays

Drain

FilterPressureTransducers Reaction

Wheels(6)

20 lbfThrusters

Branch A Branch B

Att

itud

e C

ontr

olA

ctua

tors

PropulsionDriver

Electronics

SpacecraftComputer

SpacecraftLoads

Transponder

Amplifier(50W)

3dB Coupler

HGALGATransmit

LGAReceive

HGALGATransmit

LGAReceive

+X/-X

Hi/Lo

Hi/Lo

+X Panel

-X Panel

Telecom

3 AxisGyros

AnalogSun Sensors

Att

itud

e C

ontr

olSe

nsor

s

Dynamic/Thermal Isolation

Key

Lau

nch

Su

pp

ort

Str

uct

ure

LV

Ad

apte

r

Lau

nch

Veh

icleSpacecraft

Optical Path

Electrical Interface

RF Path

Propellant Line

1 axis actuator

2 axis actuator

Thermal Path

Patch Antenna

Visco-elasticallyDamped booms

ThermalControl

System Block Diagram

StarTracker


National Aeronautics and Space AdministrationJet Propulsion LaboratoryCalifornia Institute of Technology Systems Summary

• Mission Overview– 2014 Launch Date– Earth Drift-Away orbit (ala SIRTF)

• 0.1AU/yr average earth separation rate• No cruise phase to operating orbit

– Delta-IVH launch vehicle with 5m x 19m fairing• 10,000 kg lift capacity to C3 of 0.4

– 5 year primary mission duration with consumables for 10 years• 6 month post-launch checkout and calibration• Planet search phase spans 3 years

– X-Band communications to 34m DSN• Continuous link capability & Hi Rate science downlink concurrent with data collection• Capability to downlink 3 days of stored data (~2Gb per day) in 1 8hr pass

• Systems Overview– Power: 3,000W solar array– Propulsion: 100kg Hydrazine in Blow-Down Mode

• No ∆V required• Provide safe sun point and some momentum management (solar sail is prime)

– Attitude Control: 3 axis stabilized• Star-trackers, gyros, sun sensors, plus instrument provided Acquisition Camera• 6 Reaction Wheels (Ithaco E Wheels)• Solar Sail with 1 axis articulation for balancing solar pressure torques

– Telecommunications: 256 kbps science downlink• X-Band transponder• 50W amplifier• 2 30dB HGAs with 2 axis articulation

– Thermal Control: V-Groove sun shade


National Aeronautics and Space AdministrationJet Propulsion LaboratoryCalifornia Institute of Technology Minimum Mission Configuration

X

Z

Secondary Mirror

Primary Mirror

Back end coronagraph optics

10m

6m

Z

Y

Tertiary mirror surface

Optical Bench

10m

3.5m



Deployed secondary tower

V-groove deployment boom

Spacecraft equipment support panel

Deployed HGA

Primary mirror thermal enclosure (coronagraph sensor and spectrograph inside)

Deployed solar array

Primary mirror (6m x 3.5m)

Cross section of deployed V-groove layers

Telescope and Secondary Mirror Assemblies

Secondary Mirror

Secondary Bracket

Acquisition Camera

Thermal Enclosure

Actuated hexapod

S/C thermal isolators

Optical BenchPrimary Mirror

AMS

S/CDynamic isolation

Thruster cluster (2 pl)

Spacecraft equipment support panel

Reaction wheels (6)

Spacecraft bus

Dynamic isolation (3 pl)

Propulsion tank (2 pl)Deployed v-groove platform


National Aeronautics and Space AdministrationJet Propulsion LaboratoryCalifornia Institute of Technology Laser Truss for TPF Coronagraph

Fiber Optics (2)

Beam Launcher

Corner cubePower, signal

Six metrology beams form an optical truss with ~0.3 nm resolution.In addition to the identified components, a stabilized NPRO laser (wavelength=1.3 um), a heterodyne frequency modulation system, and fiber distribution system are used. The laser and modulation system feed the beam launchers from a remote location on the s/c.

Corner cubes must be attached around the perimeter of the optics so as not to obscure the beam. They are required to maintain sub-nm piston (normal to optical surfaces) stability during observations.

For short design, we get ~ factor of 2 more precision with 1.6x more precise metrology.


National Aeronautics and Space AdministrationJet Propulsion LaboratoryCalifornia Institute of Technology Metrology System Configuration

Corner Cube with vertex removed

Beam Launchers

Isothermal Cavity



Stowed Mechanical Configuration

Stowed Configuration in Delta IV-H (19.8m gov’t standard)

5.08m (OD)

4.57m (ID)

12.192m

16.484m

Top View

19.814m

1.448m dia

Launch support cylinder – closed on both ends to control contamination on primary mirror


National Aeronautics and Space AdministrationJet Propulsion LaboratoryCalifornia Institute of Technology Deployment


National Aeronautics and Space AdministrationJet Propulsion LaboratoryCalifornia Institute of Technology Thermal Control Concept - Cocoon

V-GROOVE SHIELDS

ISOTHERMAL RADIANT CAVITY

BAFFLE

OPTICS BENCH

AFT OPTICS & CORONAGRAPH

PRIMARY MIRROR

SECONDARY MIRROR

PASSIVE METERING STRUCTURE

Cocoon Advantages:• Fully blocks sun light, earth or moon shine from telescope baffle at near

90º angle• Isolates baffle by keeping heat from sun in outer layers• Deploys in same direction as telescope baffle

V-Groove Radiator Cocoon:• Sunshine heats one side of radiator – outer v-groove shield heats &

emits IR light• Shiny surfaces reflect IR light outward into space



80 deg

100 deg

170 deg 190 deg

Telescope Steady-State Temperature for Two 20 deg Dither Cases (80 to 100 & 170 to 190)

Temperature (C) Distribution for all Sun Angles (variations<mC)

Delta Temperature (C) for Dither from 80 to 100

deg

Delta Temperature (C) for Dither from 170 to 190

deg19.0C

-142C -0.035C

0.041C 0.0014C

-0.0032C

Minimum Mission Thermal Modeling



Summary for PM Design with Optimized Segment PlacementBased on 80 to 100 deg Dither

Results for 170 to 190 deg Dither Using Optimized Segment

Placement80 to 100 deg Dither

Zernike Stead-State 3L/D Req RatioComp Resp (pm) Specs (pm) Req/Resp

4 0.14 2.29 16.217 0.19 0.29 1.47

11 0.09 0.14 1.6412 0.11 0.29 2.5313 0.07 0.29 3.86

170 to 190 deg DitherZernike Stead-State 3L/D Req RatioComp Resp (pm) Specs (pm) Req/Resp

4 0.02 2.29 126.527 0.06 0.29 4.88

11 0.01 0.14 22.7012 0.01 0.29 40.2813 0.03 0.29 9.93

Note: The results for PM with optimal segment placement are steady-state (conservative for dither)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

Thermal Modeling Continued



Dynamic Results 2 stage passive isolation

Reaction Wheels

Star Trackers

Observatory Structure-

Optics

GyrosIM

Controller (BW 10 Hz)ACS

Controller (BW 0.016

Hz)

Fine Guidance Sensor

0.1 mas IM stability

0.8 mas RB stability (pitch/yaw)

roll

pitch/yawFine Steering

Mirror

ACS Control

Image Motion Control

Sampled at 2 Hz

Sampled at 100 Hz

Reaction Wheels

Star Trackers

Observatory Structure-

Optics

GyrosIM

Controller (BW 10 Hz)ACS

Controller (BW 0.016

Hz)

Fine Guidance Sensor

0.1 mas IM stability

0.8 mas RB stability (pitch/yaw)

roll

pitch/yawFine Steering

Mirror

ACS Control

Image Motion Control

Sampled at 2 Hz

Sampled at 100 Hz

Rigid Optics Wavefront Error

Design meets requirements

passively

Flexible Primary Wavefront Error

Mode 8 exceedance can be avoided by running wheels above 4hz



Top 14 Contrast Contibutors

Major 14 Contrast Contributors

Source Cotributor Contrast (3λ/D)

Mask Leakage z3 4.34E-13Mask Leakage z2 4.33E-13Rigid Body Pointing Super OAP1 3.22E-13Rigid Body Pointing Super Fold Mirror 2 1.22E-13Rigid Body Pointing Super Fold Mirror 1 6.84E-14Thermal Structural Deformation Aberrations Secondary (z4 for dL ) 3.48E-14Thermal Structural Deformation Aberrations Secondary (z8 for dL ) 1.14E-14Thermal Structural Deformation Aberrations Secondary (z4 for Δf/f) 4.28E-14Thermal Deformation of Optics Primary (z4) 5.78E-14Thermal Deformation of Optics Primary (z12) 1.79E-14Dynamics Deformation of Optics Primary (z4) 2.23E-14Dynamics Deformation of Optics Primary (z8) 2.90E-14Dynamics Deformation of Optics Primary (z12) 1.79E-14 <Id> Total Dynamics Structural Deformation Aberrations Secondary (z4) 7.30E-14 Contrast at 3λ/D

6.75E-12 7.09E-12

Major contrast contributor in the Error Budget. The numbers shown do not include reserve factors.

0.09 mas 1-sigma per axis

0.8 mas 1-sigma per axis

dL = 217 pm 1-sigma

df/f =2.95e-11 1 sigma Z4=2.28 pm 3-sigma Z12=0.3 pm 3-sigma Z4=1.4 pm 3-sigma Z8=0.57 pm 3-sigma

Z4

Z8

Z12


National Aeronautics and Space AdministrationJet Propulsion LaboratoryCalifornia Institute of Technology Integral Field Unit

Detector

Lenslet Array

Collimator Optics

Grating

Camera OpticsFocal

Plane

Pupil Plane

AOFocus

ColdPupil

Filters

R. I. CollimatingSinglet

R.I. CameraSinglet

Reimaging Optics

Lenslet

Spectrograph

Slide from J. Larkin, presented at TPF-C Technical Interchange Meeting, June 9, 2004



Additional Instrument accomodations

Telescope Coronagraph

TelescopeField Stop

400nm to 950nm

0.95

um to

1.7u

mField at telescope focusCor. Camera f/# 54

Telescope f/# 20Field stop size 10.2 mm x 10.2 mmField stop size 17601mas x 17601mas

DichroicSplitter


National Aeronautics and Space AdministrationJet Propulsion LaboratoryCalifornia Institute of Technology Ecltel170: 2.5arcmin FFOV, 4 mirror

“Best Fit”


National Aeronautics and Space AdministrationJet Propulsion LaboratoryCalifornia Institute of Technology Conclusion

• Working toward a 2014 launch date.

• ‘Phase A’ start hoped for in January 2007

• Current Trades

– Telescope size: 6 – 8 m

– Sun-shade form and deployment

– Active or passive vibration isolation

– Cassegrain or Gregorian Telescope

• Technology issues

– Polarization: coating design and uniformity to eliminate cross-polarization

– Mask leakage: mask design with acceptable phase and amplitude errors

– Modeling: do our models have the right physics to characterize stability at picometer levels?

– Active Wave Front Sensing: can we actively stabilize speckles while we observe?

12 aug 2003 pg 1 s. shaklan national aeronautics and space administration jet propulsion laboratory...

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