Download New Worlds Observer

Direct Observation of Exo-planets
Enabled by
Return to the Moon
Webster Cash
University of Colorado
November 30, 2006
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How Can We Make Use of Return to the Moon?
Future of Astrophysics is in
Large Structures and Formations
Will use Exo-planet Studies with Occulters as Example
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A Core Principle of Science
Fastest route to the science wins
Fastest is almost always the Cheapest
If we can’t save money using RTM, we should not even
consider it.
i.e. Nobody would ever again observe from the ground if it
weren’t vastly cheaper.
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What is the Financial Advantage
of RTM?
What can manned or robotic presence do to lower
costs?
What can “Luna Firma” do to lower cost?
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How Do We Save Money
Using Surface?
General Infrastructure
–Power, Communications, Maintenance
Astronomy Infrastructure
–Low Cost Instruments
–Permanent Telescope Mounts
Large Stable Platform
–Long Baseline Interferometry
–Vacuum Beamline
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Exo-Planets
Exo-planets are the planets that circle stars other than our
Sun.
There are probably 10,000 exo-planets 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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Occulter Diagram
Planet
Target Star
NWD Starshade
JWST
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
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Fly the Telescope into the Shadow
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Dropping It In
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Occulters
Several previous programs have looked at occulters
– First look by Spitzer (1962)
Used simple geometric shapes
– Achieved only 10-2 suppression across a broad spectral band
With transmissive shades
– Achieved only 10-4 suppression despite scatter problem
http://umbras.org/
BOSS
Starkman (TRW ca 2000)
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The Apodization Function
This Function Extinguishes Poisson’s Spot to High Precision
A    0
for
a
and
A    1 e
  a 


 b 
n
for
 a
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Off Axis Performance
The off axis performance shows a rapid rise to unit transmission
for the radii greater than the inner edge of the habitable zone
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Suppression of Edge Diffraction
Can Be Understood
Using Fresnel Zones and Geometry
The occulter is a true binary optic
–Transmission is unity or nil
Edge diffraction from solid disk is
suppressed by cancellation
–The power in the even zones cancels the
power in the odd zones
b
a
Need enough zones to give good deep cancellation
• Sets the length of the petals
–Petal shape is exponential
b is scale of petal shape
n is an index of petal shape
a is the diameter of the central circle
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Doing the Math (Cash, Nature 2006)
The Residual Intensity in the Shadow is
By Babinet’s Principle
Es  1  EA
Is  E
2
s
where EA is field over Aperture
So We Must Show
2 a ik  2
2  ik  2
ik  s cos
ik  s cos    a 






k
   e 2 F e F  d  d    e 2 F e F e  b   d  d   i
2 F  0 0

0 a


n

F is distance to starshade, s is radius of hole, k is 2/
To one part in
C  105
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Contrast Ratio
Preceding integral shows the contrast ratio is
–
 n!  F  
R n n

 a b  2 
n



2
– n is an integer parameter, typically n=6
To keep R small a~b
– this is the reason the occulter has that symmetric look
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Scale Model Lab Demo
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Data from Heliostat
by Doug Leviton
Shadow Map
Bottom at 1x10-7
Image of Backlit Starshade
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Starshade Tolerances
Position
Lateral
Distance
Several Meters
Many Kilometers
Angle
Rotational
Pitch/Yaw
None
Many Degrees
Shape
Truncation
Scale
Blob
1mm
10%
3cm2 or greater
Holes
Single Hole
Pinholes
3cm2
3cm2 total
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Simulated Solar System
(Using NIRCam of JWST)
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Discoverer Science Simulations
Starshade Shadow
Jupiter
Exo-Zodiacal
Jupiter
Saturn
Mars
Earth
Saturn
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NWD Sensitivity
Planet Mass (ME)
100
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Habitable
Zone
1
0.1
10.0
1.0
Semi-Major Axis (AU)
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The First Image of Solar System
Uranus
Galaxies
Zodiacal Light
Jupiter
Saturn
Neptune
10 arcseconds
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Spectroscopy
R > 100 spectroscopy will distinguish terrestrial
atmospheres from Jovian with modeling
H2O
O2
CH4
NH3
S. Seager
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Photometry
Calculated Photometry of
Cloudless Earth as it
Rotates
It Should Be Possible to Detect Oceans and Continents!
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What Will RTM Provide
Up To This Point?
 Refueling
Fly starshade back from L2 to rendezvous
Hugely extend life of instrument
 Thousands of targets instead of just hundreds
Repair
Patch micrometeor holes
Replace/Upgrade Electronics & Instruments
Telescope on Lunar Surface?
Difficult to hold starshade in position
No Financial Advantage
Probably Not…
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TRUE PLANET
IMAGING
3000 km
1000 km
300 km
100 km
Earth Viewed at Improving
Resolution
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Solar System Survey at 300km Resolution
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New Worlds Imager Concept
starshades
50,000km
primary collector
combiner
collector craft
1500km
field star collimator
planet collimator
to combiner
field star beams
Delay Lines – Mixers - Detectors
planet beams
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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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Sims
Established that information is present
in the fringes and detectable.
How do we invert into images?
Is this enough?
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Lunar Option
 Planet Imaging is exciting enough to justify the expense
level
 Appropriate Level of Challenge for 20+ years from now
Starshades in Orbit
1m Collectors
Delay Lines,
Beam Combiner, Detector
1m Collimator
Surface of Moon
4m Telescope
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Tradeoff
Pro
Con
Infrastructure
Moon Stable Bench
Predictable Bench
Refuel Starshades
Moon Rotates
100km class delay lines
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Can We Avoid Long Delay Lines?
Should We Look at Hybrids?
Takes out First Order Effects
Farther Away, Lower OPD
Starshades in Orbit
Relay
Delay Lines,
Beam Combiner, Detector
1m Collimator
Surface of Moon
4m Telescope
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Return to Moon
 Engineering presence in deep space via humans and
robots will greatly extend the lifetime and range of
New Worlds
 Should we place some telescopes on surface?
– Perhaps tiny telescopes make sense
– Can we image planets and black holes from surface?
 Stability, predictability and Infrastructure are Positives
 Rotation of Moon is a huge negative
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This is a new box. We have to think outside the old box.
 The old solutions and ways of thinking should be suspect.
 Perhaps, with enough work, we can find new solutions to
the problem that will tilt the answer toward the surface.
Have we given this enough thought?
– NO!
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