UMBRAS

Distant Screens: From Extrasolar Planets to

Eclipsing the North Star

http://umbras.org http://westminsterastro.org

Ian J. E. Jordan, December 6, 2005

Space Telescope Science Institute

UMBRAS Core Investigators

• Glenn D. Starkman, Craig G. Copi

– Case Western Reserve Univ.

• Mark Kochte, Dorothy Fraquelli, F. Hamilton, Charlie Wu. Ian Jordan–Computer Sciences Corporation @ STScI

• Helen M. Hart–Applied Physics Lab

• Paul Henze, George Sauter, Erich Bender, Brian Eney, Ron Smith –Westminster Astronomical Society, Inc.

• Alfred B. Schultz, Richard Lyon, Peter Chen, Jan M. Hollis, Ken Carpenter, Jesse Leitner, Richard Burns, Scott Starin

–NASA/Goddard

• Fred Bruhweiler–CUA/IACS

• Dennis Skelton–Orbital Sciences Coproration

• Ed Rowles–Blue Horizons

• Zolt Levay–AURA

• Bryce Roberts–U.C. Berkeley

An Outline for this Evening…

• Introduction: Extrasolar planets--to date.

• History & Workings of External Occulters

• Ground Demonstration w/ WASI participation.

Successful Planet Finding Techniques

Courtesy L. Cook, exoplanets.org

Transit

Courtesy: Penn State & Alex Wolszczan

Pulsar Timing

Candidates found: ~2-50

Candidates found: ~130

Microlensing

Direct Imaging& Coronography

Candidates found: ~3

Candidates found: ~4

Candidates found: ~2

Extrasolar Planet Count: 156, and growing!

2M1207 & GQ Lupi

Ground-based & HST surveys are starting to yield direct images of planets, but these are very far away from their parent stars, very large, and/or very young.

TPF: What is the problem?

TPF: Terrestrial Planet Finder … Detect & study earth-like planets around nearby stars.

• Earth < 0.” 1 from the sun when viewed from 33-light years away

(diameter of a quarter at 50 km).

• Sol appears 10-billion (1010) times brighter than earth.

Occulter: “covering up” the star improves star-planet contrast.

Before After

COSMOS

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Carl Sagan in COSMOS Episode 7 “The Backbone of Night.”

A Brief History of Occulters

<1962 Robert Danielson, Princeton Infinite Half-plane analysis1962 Lyman Spitzer, Princeton American Scientist “Beginnings &

Future…”

1972 Su-Shu Huang, Northwestern Resurrected Spitzer’s analysis1974 Gordon Woodcock, Boeing Occulter Vehicle Design1978 Hugh S. Hudson, UCSD, et.al. Shuttle-borne Pinhole Occulter Facility1978 James Elliot, Cornell Lunar occultation for LST, Hill Orbits

1980 Carl Sagan COSMOS "Backbone of Night" episode1985 Christian Marchal, ONERA Spergel-Kasdin-like Screen Shapes

1995 Jean Schneider, Obs. de Paris SCODOTEP1997 G. Starkman, C. Copi, CWRU IRIS (opaque occulter)1998 G. Starkman, C. Copi, CWRU BOSS (apodizing occulter)1998 Schultz, Jordan, Hart, et.al. UMBRAS (feasability studies)

2001 R. Lyon, A. Schultz, et.al. Occulter + Shaped Aperture /Apodization2005 W. Cash, et.al. New Worlds Observer (Marchal occulter)

Woodcock Occulter

~ 60-m diameter deployable “umbrella” packaged in a 2.5-m x 10-m upper stage.

BOSS Variable Transmission Screen Occulter

What is BOSS? -- It is a different kind of occulter mission.

BOSS employs an apodizing occulter without using multiple PSF suppression stages within the telescope.

Plot & Image courtesy of BOSS team, TRW, & JPL

Bus closeup

Tri-aspect Component Diagram

Constellation Configuration

in Space

Operations Cycle

TPF-C+O

Telescope-Occulter Control Block Diagram

• Telescope science imager takes picture(s)

• Pictures are measured to determine occulter position

• Error signal transmitted to occulter

• Occulter adjusts position & velocity

Sunward view of UMBRAS Occulter

Launching Multiple Occulters

Transit Time: Function of Separations

Ambient Earth-Sun L2 Accelerations

Earth-Sun L2.20,000 km Telescope-Occulter separation, with non-sail-like telescope & occulter properties for a likely typical TPF mission.

Dif

fere

ntia

l Acc

eler

atio

n M

agni

tude

(m

/s2)

Sun-Telescope-Occulter Angle (degrees)

•Brown solid = -gravitational (earth)•Black dotted = -gravitational (sun)•Green solid = ~ solar radiation pressure•Yellow solid = -gravitational (moon)•Blue dashed = max allowed gas leakage (10%)•Orange dotted = ~ nominal solar wind

NSTAR acceleration level

Science Ceiling

Why an Occulter?

Better suppression of the stellar PSF wings even with lower wavefront quality.

ASA: WFQ = /1000

ASA + O: WFQ = /100

ASA = Apodized Square ApertureWFQ = Wave Front Quality

Point Spread Function Slices using a 4-metre Telescope

Dawes’ Limit2.4-m V-band

Dawes’ Limit8-m V-band

Discovery Space Diagram

Exoearths fainter than mV=32 not plotted.

TPF-C goal.TPF-C goal + minimal Occulter.

Exoearth mV=29.5

M1V

K3V

G0V

A5V

M3V

M4V

M7V

B6V

Alpha Cen B

Alpha Cen A

Tau Ceti

Epsilon Eridani

Epsilon Indi

Pi3 Orion

Occulter vs Alternate Method Cost

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FL = Fresnel LensFFO = Free-Flying OcculterNIFF = Free-Flying Nulling InterferometerNIM = Monolithic Nulling InterferometerLAC = Large Aperture CoronagraphULSA = Ultra-Large Sparse ApertureSIM = Space Interferometry Mission

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The New Worlds Observer/Imager Concept

Ground ‘Tests’ of Occulters

FN =W2

z⋅λW = FN ⋅z⋅λ

D∝ z

W=occulter width; z=separation; =wavelength; D=aperture.

D=4m; z=20,000 km

W=D⋅constant

D=9mm;z=100m

Ground Test Equipment

• F/5 Televue 101-mm refractor.• Masked down to 11 & 24 mm.• Optional Barlow: system f/# from 50 - 100.• Mounted atop 8” + alt/az for stability.• ST-7X, TEC-cooled, 768x512 CCD camera.• M675X laptop data acquisition/storage.• Green laser for optical alignment.

• Hand-crafted (P. Henze) occulter-rig.• 12-inch diameter light shroud tube.• Square-rail optical bench.• Mid-tube occulter placement slot.• 1- and 2-inch square occulters.• 9” 1/10th-wave flat & mirror cell (GSFC).• Alt-az mirror mount.• Red laser for optical alignment.

Pic 15

Pic 11

Pic 27

Pic 25

Pic 3

Pic 6

Pic 4

9” mirror

765 x 510 9- pixels, 540-mm focal length, distance ~ 95 metres

Experiment Field of View.

25-mm (~ 15 pixels) edge occulter

626-second drift.

August 7/8, 2004

Occultation Movie

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Watch for

real

diffraction

lobes!

Movie C

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19:45 November 5, 2004, Drift 6, 24-mm aperture.

Theory & Experiment: ComparisonAdmittedly, this is red and green apples, but . . . .

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• Monochromatic, • Square aperture, • No wavefront error

• Polychromatic ~ 0.5, • Circular aperture, • Atmospheric induced wavefront error, • Atmospheric smearing

Sonine 4 Apodization

Unapodization

UMBRAS/WASI Occulter Demonstration Team October 31, 2004