the new worlds observer: opening direct study of exo-planets using external occulters
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The New Worlds Observer: Opening Direct Study of Exo-planets Using External Occulters. Webster Cash University of Colorado & The NASA Institute for Advanced Concepts. New Worlds Contributors. Webster CashUniversity of Colorado Jim Green Eric Schindhelm Jeremy KasdinPrinceton University - PowerPoint PPT PresentationTRANSCRIPT
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The New Worlds Observer:
Opening Direct Study of Exo-planets Using External Occulters
Webster CashUniversity of Colorado
&The NASA Institute for Advanced Concepts
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New Worlds Contributors
Webster Cash University of ColoradoJim GreenEric SchindhelmJeremy Kasdin Princeton UniversityBob VanderbeiDavid SpergelSara Seager MITSteve Kilston Ball AerospaceTom BanksCharlie NoeckerJon Arenberg Northrop GrummanRon PolidanChuck LillieAmy LoGlenn Starkman Case WesternSally Heap Goddard Space Flight CenterMarc KuchnerKeith GendreauDon LindlerRick LyonDoug Leviton
and growing…
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Do there exist many worlds, or is there but a single world? This is one of the most noble and exalted questions in the study of Nature. St. Albertus Magnus (1206 – 1280)
scholar and patron saint of scientists
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Bringing Science FictionTo Life
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ExoplanetsThe Planets That Circle Other Stars
There are probably 10,000 within 10pc (30 light years) of the Earth. Indirect means have now found over 200.
If we can observe them directly, we will have a new field of astronomy every bit as rich as extragalactic.
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Boy Have We Got A Problem!
Courtesy of N-G
An Earth-like Planet Is 10 Billion Times FainterThan Its Parent Star
6pack vs Bill Gates entire fortune
Less Than 0.1 Arcseconds Away
One Hubble Resolution Element
AND
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Exploration & Science
One doesn't discover new lands without consenting to lose sight of the shore for a very long time. Andre Gide (1869 - 1951)
Science requires a hypothesis suggesting knowledge of the answer while exploration has no such conceit.
New Worlds is Exploration FirstScience Second
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Indirect Means
Over 200ExoplanetsNow Known
Mostly fromRadial VelocityMeasurements
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Direct Imaging is What We Want
Can We Ever Map Extra-Solar Systems In This Manner?
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Terrestrial Planet FinderMust be done from space because of the atmosphere
Telescopes must be corrected to PERFECTION – to suppress scatter: /5000 surface, 99.999% reflection uniformity
TPF is very difficult
NASA has not been good to TPF lately.They are on indefinite hold.
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TPF-ITerrestrial Planet Finder - Interferometer
Works in Mid-Infrared ~25microns
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TPF-I & DarwinMid-Infrared Interferometer
Multiple Large Cooled-IR Telescopes Combine BeamsNull Out Star at One AngleConstructive Interference at Nearby (Planet) Angle
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TPF-CTerrestrial Planet Finder - Coronagraph
Works in Visible Band
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TPF-CVisible Light Coronagraph
4x8mSpace Telescope
Starlight Stop
Planet Light
scatter
starlight
Planet light
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External Occulters
Let’s Resurrect an Old Idea– Spitzer (1962) appears to be the first
Just Keep the Starlight Out of the Telescope
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Occulter Diagram
Telescope big enough to collect enough light from planetOcculter big enough to block star
– Want low transmission on axis and high transmission off axisTelescope far enough back to have a properly small IWANo outer working angle: View entire system at once
NWD Starshade JWSTTarget Star
Planet
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New Worlds Observer
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Fly the Telescope into the Shadow
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Dropping It In
Note: No Outer Working Angle
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The Obstacle
Diffraction
Despite What They Tell You in Sixth GradeLight Does Not Move In Straight Lines
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Occulters
Several previous programs have looked at occultersUsed simple geometric shapes
– Achieved only 10-2 suppression across a broad spectral bandWith transmissive shades
– Achieved only 10-4 suppression despite scatter problem
http://umbras.org/BOSS Starkman (TRW ca 2000)
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Pinhole Camera Started this Effort With A Pinhole Camera IdeaA Pinhole Camera Meets The TPF Requirements:
Perfect TransmissionNo Phase ErrorsScatter only from edges – can be very low
Large Distance Set by 0.01 arcsec requirementdiffraction: /D = .01” D = 10m
@500nmgeometric: F = D/tan(.01”) = 180,000km
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NIACNASA Institute for Advanced Concepts
Vision Mission Proposal 2003 -- Rejected NIAC Phase I 2004 -- Accepted NGST Teams with New Worlds November 2004 – Meeting with NGST
– Pinhole Camera too Large – Can the Diffraction Problem of Occulters be Solved?
Has Anybody Applied the Princeton methodology? Beat My Head Against this Problem for the Next Five Months
SUCCESS!
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Extinguishing Poisson’s Spot
Occulters Have Very Poor Diffraction Performance– The 1818 Prediction of Fresnel led to the famous episode of:– Poisson’s Spot (variously Arago’s Spot)– Occulters Often Concentrate Light!
Must satisfy Fresnel Equation, Not Just the Fraunhoffer Equation
Must Create a Zone That Is:– Deep Below 10-10 diffraction– Wide A couple meters minimum– Broad Suppress across at least one octave of spectrum
Must Be Practical– Binary Non-transmitting to avoid scatter– Size Below 150m Diameter– Tolerance Insensitive to microscopic errors
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A Solution Exists
0A a
a 1
na
bA e
for
for
and
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Binary Shape
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Performance
A 50m diameter occulter at 50,000km will reveal Earths at 10pc
a=b=12.5mn=6F=50,000km
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Huygens-Fresnel Principle
0 ikrEE Ae dS
i r
F
s
F
s
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Fresnel Approximation
2
2 2 cos20 2
0 0
,
iksik ik sikF F
F FE e e
E e A e d di F
2
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0 20
0
iksikikF F
FE ke e k s
E e A J diF F
Then, if circularly symmetric:
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Now, Evaluate Candidate Apodization Function
n
a
bA e
1A
22
22
0
n
n
a ika ikFbF
a
k kE e d e d
iF iF
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Dimensionless Natural Units
ka
F
kb
F
k
F
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Electric Field at Center:
22
22
0
1 1n
ii
E e d e di i
22
221
1
nii
E e e di
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Integrate by Parts
2 1
2
nni
R n e e d
Yields E = 1+R where R is small as desiredAnd
This closed-form integral represents the electric fieldat the center of the shadow
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Continue Integrating by Parts
1! 1 1 !
n
n n n
n nR
Drop Small Terms
Dominant Term
If 2 >> n
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Binary Apodization
a
b
b
a a
b
b
a
2 2 cos cos
2
0
,2
ik ik s ik s
F F F
a
kR e A e A e d d
F
Difference between petalsand circularly symmetric
apodization.
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New Code
Still Need Computer Simulations e.g. Some Disagreement about Minimum Number of Petals Direct Fresnel 2-d integral is very slow
Princeton, Goddard , NGST, CU All Working on this
new cu code– Integrate Fresnel by parts– Yields edge integral --- like Green’s Theorem– Very Fast– Will Allow Diffraction Analysis with Any Error
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Shadow of 16 Petal Mask
Linear Log
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Effect of Petal NumberPetal Profiles
Radius(m)
0 5 10 15 20 25 30 35
Log10(Suppression)
-16
-14
-12
-10
-8
-6
-4
-2
0
2
6
48
12
24
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Simulated Solar System
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Discoverer Science Simulations
Jupiter
Saturn
Exo-Zodiacal
Starshade Shadow
Earth
Mars
Jupiter
Saturn
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Suppression vs Contrast
Those Charts are Suppression The Fraction of the Total Starlight That Makes It Into the Telescope
TPF Uses Contrast The Fraction of the Total Starlight that Ends Up Under The Image of the
Planet
Within an Occulter Contrast is Suppression Convolved With Telescope Response Function Typically Contrast is 100 times Better Than Suppression
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Additional Contrast from Telescope
10-7 10-610-8
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New World Observer Architecture
After NWD Proposal Submitted NGST looked at full-up system
4m Telescope Diameter Breakpoint
Two Starshades – one small and fast
Very Powerful Scientifically
Cost comparable to other missions on table
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The First Image of Solar System
JupiterSaturn
Uranus
Neptune
Zodiacal Light
Galaxies
10 arcseconds
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90
102030
405060
7080
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Spectroscopy
R > 100 spectroscopy will distinguish terrestrial atmospheres from Jovian with modeling
O2
H2O
CH4
NH3
S. Seager
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Spectroscopic Biomarkers
Water Necessary for habitabilityOxygen Free oxygen results only from active plant lifeOzone Results from free oxygenNitrous Oxide Another gas produced by living organismsMethane Life indicator if oxygen also presentVegetation Red edge of vegetation at 750nm
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Photometry
Calculated Photometry ofCloudless Earth as itRotates
It Should Be Possible to Detect Oceans and Continents!
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NWO Science
Result of Nature interviewsMany discussions with press and other
interested parties
It is Life Seeking that EVERYBODY wants
Just finding water planets enough, but its not what motivates the public
Can there be a bigger or more important question for astronomers?
New Worlds Observer can do it $2-3 Billion and 10 years
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Implementation
No pessimist ever discovered the secret of the stars or sailed an uncharted land, or opened a new doorway for the human spirit. Helen Keller (1880 - 1968)
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Tall Poles
Deployment of 35m shade to mm class tolerance
Acquiring and holding line of sight
Fuel usage, orbits and number of targets
Stray Light – particularly solar
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Lab Studies
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Tolerance AnalysisProceeds by perturbation analysisPitch or Yaw error – foreshortened to 1- in one dimension
2
12
0
ni y
y nR n e e y dy
csRR
Reduces to:
Proving
2 2 2
22 2222
(1 )
2 2
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2 2
(1 )
2
1
n
iky ikz
F F
ikF
y z aikziky b
F F
e e dydz
kE e
iF
e e e dydz
Where z=x/(1-)
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Starshade Tolerances
PositionLateral Several MetersDistance Many Kilometers
AngleRotational NonePitch/Yaw Many Degrees
ShapeTruncation 1mmScale 10%Blob 3cm2 or greater
HolesSingle Hole 3cm2
Pinholes 3cm2 total
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Scatter ControlView Nightside
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Deployment
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Triple LayeredMicro-meteor Protection
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Alignmentacquisition & hold
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L2 Orbit Favorable
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Planning the Mission
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Earth at 200km resolution. Oceans, continents and clouds are visible.
The New Worlds Imager
Young Water PlanetJPL
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Earth Viewed at Improving Resolution
100 km300 km3000 km 1000 km
TRUE PLANET IMAGING
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Solar System Survey at 300km Resolution
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NWI Concept
1500km
starshades
collector craft
combiner
50,0
00km
1500km
planet collimator
field star collimator
primary collector
to combiner
planet collimator
field star collimator
primary collector
to combiner
planet beams
field star beams
Delay Lines – Mixers - Detectors
planet beams
field star beams
Delay Lines – Mixers - Detectors
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Sims
Established that information is presentin the fringes and detectable.
How do we invert into images?Is this enough?
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Hypertelescope Problem
How Many Apertures Needed? One per pixel (no!)
Cost control of multiple craft
Formation Flying to Tolerance
Labeyrie has worked on this Amazing telescope even without starshades
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Conclusion By 2025
O2
H2O
By 2013
There is nothing in the above missionthat the people in this room could notimplement today.
Money for such a missionwill be available in twoyears. This is an obviouscandidate.