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M.Shao , B. M.Levine, G. Vasisht, C. Zhai, J. Sandhu JPL, B. F. Lane, Draper Labs, R. Woodruff, G. Vasudevan, Lockheed-Martin,

R. Samuele, Northop Grumman, K. Havey, ITT, M. Clampin, R. Lyon, NASA/GSFC, O. Guyon, U. Arizona, V. Tolls, SAO,

Dilute Aperture Visible Nulling Coronagraphic Imager (DAViNCI)

© 2008 California Institute of Technology. Government sponsorship acknowledged.

IWA = 38mas @800nm, 0.5um to 1.7um converage (25%BW)Science of an 8m telescope at the cost of a 2.5m telescope

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2 April 10, 2023

Outline

• Instrument and Mission Overview- 4 1.1m telescopes, inside of a 4.5m fairing. Nulling coronagraph

• Equal collecting area to a 2.2m telescope, but telescope costs much lower than a filled aperture on axis 2.2m telescop

- Team X cost ~1.15 B total cost, includes launch vehicle and 5 years of mission operations. Cost roughly equal to a ~2.5m coronagraph

• Science Case- 38 mas IWA @ 800nm (Inner Working angle ~25mas @ 500nm)

- Exo-Earth science equal to ~8m 2/D coronagraph , or 76m occulter (vs 50m) at 166,000 vs 72,000 km.

- Science instrument R~80 spectrometer 0.5um to 1.7um, 25%BW at a time.

• Team X study

• Technology needs and status- Detecting a planet with 1% False Alarm

- vis nulling coronagraph testbed, segmented MEMs Deformable Mirror

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3 April 10, 2023

DAViNCI: Dilute Aperture Visible Nulling Coronagraph Imager

• Main mission- Astrophysics Strategic Mission Concept Studies

(ASMCS) Flagship class mission ($1.2 B)

• Image and take spectroscopic measurements for Earth-like exo-planets up to 150 nearby stars

• Reduce costs by using four 1.1 m telescopes (spatially separated to create a dilute aperture array) to produce the resolution of a large aperture telescope

• The payload acts as a coronagraph by using interferometry to null the central star’s signal

/s

s

CCD

Figure 1: Imaging with nulling interferometry. A fringe pattern is superimposed over the star and planet to be imaged, the star is placed at the bottom of a deep, achromatic destructive (null) fringe, while planet on the constructive fringe is transmitted.

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4 April 10, 2023

DAViNCI Concept

Sun shade

Spacecraft in 5m Fairing

4 x 1.1m telescopes based on NextView CRS

Three-axis stabilized spacecraft bus

Sun Shade provides thermal insulation, while allowing the target to be observed within ~45 deg of the Sun, any target is observable 75% of the time.

Spectra of Exo-Earth inWinter and Summer

NGST

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5 April 10, 2023

B=2.2m Baseline 4.2m Tip-Tip

At its longest baseline, Davinci has an Inner Working Angle of IWA~38mas @ 780nm

Roughly equal to ~8m coronagraph working at 2 /D

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6 April 10, 2023

Discovery Space DAViNCI

Max star-planet sep > IWA*1.2

101

102

103

100

101

102

103

Inner Working Angle milliarcsec

# t

arg

et

sta

rs# target stars versus IWA < 30pc Contrast > 6e-11,

4x1.1m DAViNCI and 8m telescope with 2λ/D Coronagraph

4m telescope with 2λ/D Coronagraph

# Stars ~ IWA-3

2m telescope with 2λ/D Coronagraph

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Imaging Planets with a Nulling Coronagraph

• Because of the null pattern an image needs ~3 rotations to produce an “normal” looking image of all the planets outside the IWA.

• In the presence of a significant exo-zodi signal, one approach is to difference two images at two different epochs when the planets have moved. - Without zodi subtraction the

angular resolution of the image may need ~3 airy spots between the planet and star.

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8 April 10, 2023

DAViNCI Science Case

• DAViNCI, with 4x1.1m telescope has the same science potential (for Earths @ 1AU) as a 7~8m (PIAA) coronagraph.- Davinci 38mas IWA @ 780nm (Oxygen)

- Spectroscopy from 0.5um to 1.6um. (25% BW at a time) # targets at 1.6um is ~ 1/8 of the number of targets at 0.8um.

- # potential targets ~ IWA-3

• How many targets are needed?- What’s a good guess on eta_earth? (30% of stars have sub-Neptune

planets (5~50 Mearth), from 0.03 to 0.3AU) ~10% of stars have a terrestrial planet in the HZ.

• DAVINCI has significantly less collecting area (roughly equal to HST) than a GIANT filled aperture coronagraph. But it’s adequate for a search of 100~150 Earths- An Earth @10pc is 29.5 mag. HST ACS (F606W) takes 4.5hrs to get a

SNR=6 image of a 29.5mag star. ACS83620

- Our calculations show ~10 Hrs to detect an Earth @ 10pc for DAViNCI

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9 April 10, 2023

Science I

• Photon throughput has 3 components- Optics/detector efficiency

- Coronagraphic mask transmission @ IWA (70%)

- Lyot mask efficiency (no glass in primary if photons don’t get to detector)

• DAVINCI has ~100% Lyot efficiency- In a Lyot coronagraph, working at 2~4 /D, there is a mask at a

reimaged pupil (Lyot stop) that “blocks” the starlight diffracted by the coronagraphic mask. Lyot efficiency of TPF-C/FB1 ~ 30% @ 4 /D

- With 100% Lyot efficiency, DAVINCI has roughly ~1/2 the sensitivity of the TPF-C FB1, 8m*3.5m coronagrah

- DAVINCI sensitivity is comparable to a 4m Lyot coronagraph because of 100% Lyot efficiency

• The Major advantage of DAVINCI is that it has an inner working angle of ~38mas @ 780nm (Oxygen line) equal to an 8m coronagraph working at 2 /D.

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10 April 10, 2023

Team X Mission Study Summary

• 1.5* Cost of Probe Class Mission

• High Level Mission Description - Launch Vehicle: Atlas V 521

- Orbit: Earth-Trailing

- Launch Date: 2020

- Mission Lifetime: 5 years

- Observation strategy:

• Planet Detection, orbit determination (or confirmation of SIM orbit)

• Exo-Earth Spectroscopy

• Instrument Description- 4 element dilute aperture imaging interferometer using (‘COTS’

telescopes) on (Dual) Variable baselines

- Dual nullers for deep and wide null with imager and (R=80) spectrometer

See Poster by Levine et. a.l.

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11 April 10, 2023

DM3

FiberBundle Array

Phase Plates

Null Beam CombinerAssembly

Combiner/Nuller Instrument

DM1

T1 / T2Nuller

Bright

T1-2 Dark T3-4 Dark

ScienceCamera

WFSCamera1

Phasesteppingdither

Shutters

DM Control

Single fibers with matched properties as the fiber bundle

Lenscompensator

PhasePlates

DM2

T3 / T4Nuller

Bright

Shutter

PhasePlates

WFSCamera2

DM Control

PupilRemapLens

To Pupil GeomMechanism

ACS Camera

Pupil Geom. Camera

ACS Camera output with pupil camera allows Phase diversity WFS as well!

Filters

TranslationStage

slit

Beam launcher

Dichroic mirror

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12 April 10, 2023

Cost Advantages of Dilute/Segmented Aperture Telescopes• Mulitple telescopes are cheaper

- Telescopes #2,3,4 are ~ 50% of the cost of #1.

- If cost ~ D2.5 then 4 1.1m’s is less than ½ the cost of a 2.2m.

- DAViNCI telescopes are On-Axis (not off-axes unobscured)

• Technology for diffraction limited segmented and dilute aperture telescopes was demonstrated on Keck >10 years ago. (JWST)- Technology for SIM (picometer level dilute aperture telescope/interferometer

in space) is also in hand.

- There is a known ~fixed cost for the metrology and structure/mechanisms for DAViNCI.

• Instrument (Nulling coronagraph) is roughly the same complexity/cost of a Lyot coronagraph with DM’s for phase and amplitude control.- DAViNCI instrument maybe more expensive because of the very wide 0.5um

~ 1.7um wavelength coverage. (rather than 0.5um~0.8um)

• Spacecraft - (Vibration) requirements similar to other coronagraphs

- Thermal stability requirements ~100X less sensitive than coronagraphs that use telescope rotation for speckle subtraction. (Post coronagraph inteferometer)

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13 April 10, 2023

DAViNCI Team X Cost (round 2)

Team X Instrument Study 2009

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14 April 10, 2023

Technology Status/ Near Future Plans

• Define Starlight suppression versus Contrast- Starlight suppression of 10-7 = contrast of 10-10, 10-9

• Finding a planet in a sea of Speckles, and measuring its orbit- Measuring the planet’s orbit. In the double blind test, we set a

threshold of 1% FAP (False Alarm Probability)

• If one takes the spectra of a dot in an image, without an orbit. We don’t know if that spectrum belongs to a HZ planet.

• In fact we don’t know that we haven’t taken the spectrum of a speckle, that by accident is 6 times brighter than the “average speckle.

• Starlight suppression demonstration (in a single mode fiber, 2006)

• High Contrast demonstration (vacuum nuller with DM)

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Steps to Direct Detection

• Starlight suppression- Optically remove starlight

• High contrast (dark hole)- Remove starlight where the

planet is supposed to be

• Speckle subtraction- Subtract out the residual

speckles even in the dark hole there are speckles

-5 -4 -3 -2 -1 0 1 2 3 4 510

-10

10-9

10-8

10-7

10-6

inte

nsity

Lambda/D

If we have 10-7 suppression

1st airy ring < 2x10-9

3 /D < 2x10-10

6~8x10-10 contrastTrauger et al 2006

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Detecting Terrestrial Planets in the HZ

• Goal is to detect a planet in the presence of speckles with a ~1% false alarm probability.- Conducted simulations on speckle statistics

• Brightest speckle vs “average” speckle flux, calculate contrast needed for 1% FAP Planet detection

- Speckle subtraction. There are a couple of ways to do speckle subtraction, How accurately do we need to subtract speckles, in order to see the planet (with 1% FAP)

• Simulation (because it was computationally simple) was of a 4 lambda/D lyot coronagraph, gaussian coronagraphic stop and hard edge lyot stop.- Purpose of the simulation was to look at direct detection in the same way that

astromery and RV has looked at planet detection. Setting a threshold, that results in 1% FAP, and looking at the implications.• At the threshold of detection the ½ the images of a planet will be above

the threshold and ½ the images of the planet will be below the threshold.• Also, 1% FAP means a lot of images “by eye” will look like planets, but

be below the 1% FAP threshold.

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Why Do We Need 1% FAP?

• Planet is outside the IWA most of the time but observable only 32% of the time.

• 30 deg inclination is the “Average” inclination

IWA ~ 0.7* Max star-planet sep => planetis observable over ~32% of its orbit.

• An orbit within 1 deg of face-on is ~100 times less likely than an orbit within 1 deg of edge on.

If we look at 100 stars 4 times a 10% FAP means 40 false alarms.

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There Will Be Lots of 1~30 Mearth Planets

Mordasini, et. al. 2009a

•In one image, the true earth could be inside the IWA, or have it’s sun-lite side facing away from us.•At the same time, a non-HZ planet could appear to be in the HZ because of orbit phase and inclin.•A Jupiter, with it’s sun-lite side facing away from us, could appear as bright as the Earth.•A dot in the image could also be a bright speckle

A claim that a planet in the HZ has been found NEEDS an orbitA claim that a planet is a terrestrial planet in the HZ needs Astrometry

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Statistics of Dark Hole in Image Plane

• Speckles are caused by gaussian random phase and amplitude errors. ~30pm rms ~ 3e-4 amplitude errors.- Average speckle background ~4e-

10.

• Speckle statistics- Exponential intensity distribution

(not gaussian)

- Mean speckle = std(speckles)

- Probability of a bright (4~5X mean) speckle much higher than for gaussian distribution.

0 1 2 3 4 5 6 710

-4

10-3

10-2

10-1

100

I(30,30)/ <I(30,30)>

Pro

babi

lity

Intensity at a location obeys exponential probability distribution function

4000 samples, at (7.5,7.5)/D

exp(-z)

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Brightest Speckle in an Image

• Probability distribution of the brightest speckle in an image, and the cumulative probability of the brightest speckle.

• If we set the threshold of detection at ~ 12X the “Average” speckle, there is a ~1% false alarm probability.

• Detecting a planet 1.2e-10 as bright as the star with 1% FAP requires the average speckles to be suppressed to ~1e-11.- A threshold of 1.2e-10 means that

a planet a flux of 1.2e-10 will be detected 50% of the time.

0.5 1 1.5 2 2.5 3 3.5 4

x 10-8

0

200

400

600

800

1000

1200

1400

max intensity

num

ber

of

sam

ple

Histogram of maximal intensity over the working region, totally 4000 samples

meanstddev=1.5e-0083.3e-009

2 4 6 8 10 12 14 16 1810

-4

10-3

10-2

10-1

100

Imax

/ <I>

Pro

babi

lity

Fitting of the probability distribution function

4000 samples=2=3=4

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Speckle Subtraction and Wavefront Stability

• Starlight suppression to 1e-11 contrast is extremely difficult and has not been demonstrated. 1e-11 optical contrast is not needed if we can measure (and subtract) out the speckle pattern in post processing.

• There are two techniques- Telescope roll (Occulter roll?)

• Speckles have to be stable as you roll the telescope

- Post coronagraph WFS. (DAViNCI)

0 2 4 6 8 10 12 14 16 18

10-3

10-2

10-1

100

detection threshold I/<(I)>

Fal

se d

etec

tion

ratio

False detection ratio, N=2500 samples, 50pm AO phase residual, 3pm random drift

1% FAP means detection threshold has to be set ~12X the rms fluctuations in the “Differenced” image.

IWA

Positive image

Negative image

4e-10 speckles to be “stable” to 1e-11implies the wavefront from the telescopeis stable to ~2.5 picometer over 2~4 hrs as two images are recorded for speckle sub. SIM optics are stable to ~40pm/90sec.

Cumulative Prob Brightest Speckle pair Diff Image

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• To reduce the wavefront/thermal stability requirement. DAViNCI measures the residual speckle pattern and the science image simultaneously.

• This will be tested in the VIS-Nulling testbed under construction.

• The Post corongraph WFS measures the E-field after the coronagraph. (The fft^2 of which should be the residual speckle pattern.)

• Proper operation of this approach to speckle subtraction can relax the stability requirement of the telescope by up to 1000X. (to SIM-like requirements)

Instead of asking the telescope wavefront to Be stable to 2.5 pico-m for a few hrs, DAViNCI measures the speckles simultaneously with the science image.The great advantage is not just from avoiding a new invention, but the testing of a flight telescope to 2.5pm stability.

Post Coronagraph WFSfor PSF Estimation (Speckle Sub)

See poster by Sandhu et al.

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Visible Nuller (DAViNCI & EPIC) testbed

• In air test ~3months, in vacuum test ~3months from now.

• Measure surface of DM (deformable mirror)- Current mirror has significant

“scalloping”- Noise in the wavefront

measurement is ~1.4nm rms for a 0.5 sec integration. (and 5*5 sampling of each DM actuator)

- Sensing per actuator < 0.5nm rms (0.5s)• Need <30 sec to get noise down

to 100 picometers/DM actuator• Recent activities

- Characterizing DM (influence fn, gain)

• Future activities- Test image plane contrast- New DM, Fiber bundle amp+phase

control - Recently started assembly of Vac

test setup

Unpowered DM1024 element SpareMEMs DM with ~40dead actuators

Diff of 2 phase maps 5*5

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Next Gen Components Near Ready

• Two new components are needed in vac nulling testbed

• Coherent fiber bundle (Fiberguide industries) ~1um spacing of fibers.

• Segmented DM, with tip/tilt piston control (delivered from BMC) Delivered DM has 5 dead actuators, which will have to be masked by the lyot stop.

9.5 mm

600 µm

silicon substrate

1 µm max. stroke

3 mrad max. tiltmirror segment

electrostaticactuator

Predicted DM Performance

Mirror architecture

329 close-packed hexagonal segments

Actuation architecture

Electrostatic tip/tilt/piston control for each segment

Mirror segment geometry

600µm hexagon, with epitaxial polysilicon layer for mirror rigidity

Mirror segment material

Silicon, 1000 Å gold coating, near-IR and visible

Segment motion (piston)

1 µm range, 0.1nm resolution

Segment motion (tip/tilt)

600 arc-second range, 0.06 arc-second resolution

Segment flatness Surface roughness < 1 nm RMSFigure < 1 nm RMS Radius of curvature > 5 m

9.5 mm

600 µm

silicon substrate

1 µm max. stroke

3 mrad max. tiltmirror segment

electrostaticactuator

Predicted DM PerformancePredicted DM Performance

Mirror architectureMirror architecture

329 close-packed hexagonal segments 329 close-packed hexagonal segments

Actuation architectureActuation architecture

Electrostatic tip/tilt/piston control for each segmentElectrostatic tip/tilt/piston control for each segment

Mirror segment geometryMirror segment geometry

600µm hexagon, with epitaxial polysilicon layer for mirror rigidity600µm hexagon, with epitaxial polysilicon layer for mirror rigidity

Mirror segment materialMirror segment material

Silicon, 1000 Å gold coating, near-IR and visibleSilicon, 1000 Å gold coating, near-IR and visible

Segment motion (piston)Segment motion (piston)

1 µm range, 0.1nm resolution1 µm range, 0.1nm resolution

Segment motion (tip/tilt)Segment motion (tip/tilt)

600 arc-second range, 0.06 arc-second resolution600 arc-second range, 0.06 arc-second resolution

Segment flatnessSegment flatness Surface roughness < 1 nm RMSFigure < 1 nm RMS Radius of curvature > 5 m

Surface roughness < 1 nm RMSFigure < 1 nm RMS Radius of curvature > 5 m

• The MEMs continuous face sheet DM’s have ~20~30nm rms errors within 1 actuator. Due to stresses in the face sheet that’s part of the manufacturing process.

• Segmented DM ~ 6nm rms (BMCorp)

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Summary

• Dilute aperture coronagraphs can obtain images at 800nm of Exo-Earths around ~150 nearby stars at a small fraction of the cost of other visible direct detection concepts.- Very high angular resolution (Small IWA, 38mas) in a small package - Spectroscopy to 1.6um for ~20 targets.- Much much lower cost than a comparable 7-8m coronagraph working

at 2 /D. Leverage technology from SIM

• Technology progress: have demonstrated 10-7 suppression laser light, which is what’s needed for 10-9~10-10 contrast.- A full imaging demonstration experiment has started.

• Use similar wavefront control technology to lyot coronagraphs• New approach is speckle subtraction w/o telescope stable to

2.5pm/4hrs.• DAViNCI from a cost/science point of view is playing in a different ball

park from other (Large) vis coronagraph concepts• The nulling coronagraph architecture is also compatible with on-axis, &

segmented telescopes. If a dedicated TPF is never flown, but only as an instrument on a large GP telescope, A nulling coronagraph instrument at 100~200M would be much less expensive than an external occulter.