An Xray Interferometry Technology Roadmap

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An X-ray Interferometry Technology Roadmap
Keith Gendreau NASA/GSFC Webster Cash U. Colorado
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MAXIM Requirements Flowdown
SEU Science Objective
MAXIM Approach
Measurement Requirement
Key Technologies

• Angular Resolution 0.3 mas
• Qrs 2M8/D - 6M8/D
• Time Resolution 1 hour
• 2pRs/c10 hours
• Bandpass 0.1-10 keV
• K-lines from Carbon to Iron
• E/dE 50
• ASCA, Chandra, and XMM obs
• Area gt1000 cm2
• 10,000 Photons/frame
• (10 Photons/pixel/frame)

• Diffraction limited optics
• gtl/100 Flat
• long and skinny
• Thermal /Mechanical Stability
• CTE lt 10-7/K
• Precision Formation Flying
• X-ray CCDs
• Larger Arrays of lt 10 micron pixels
• Fast Readout (msec)
• 0.1 mas Line-of-Sight alignment knowledge.
• 100,000 finer than HST

Make a movie of a black hole, its accretion
disk, and its jets.
Understand the ultimate endpoint of matter.
To explore the ultimate limits of gravity and
energy in the universe.
Map doppler and gravitational redshifts of
important lines in the vicinity of a black hole.
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Basic MAXIM Design
Baseline
Fringes Form Here

• Each Channel Consists of 2 flats
• Primary mirrors determine baseline
• Secondary mirrors combine channels at detector.

To implement this basic design, you choose how to
group the mirrors.
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Original MAXIM Implementations
MAXIM Pathfinder

• Easy Formation Flying
• Optics in 1 s/c act like a thin lens

Full MAXIM- the black hole imager

• Nanometer formation flying
• Primaries must point to milliarcseconds

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Improved MAXIM Implementation
Group and package Primary and Secondary Mirrors
as Periscope Pairs

• Easy Formation Flying (microns)
• All s/c act like thin lenses- Higher Robustness
• Possibility to introduce phase control within one
  space craft- an x-ray delay line- More
  Flexibility
• Possibility for more optimal UV-Plane coverage-
  Less dependence on Detector Energy Resolution
• Each Module, self contained- Lower Risk.

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An Alternate MAXIM Approach Normal incidence,
multilayer coated, aspheric mirrors

• Optics demonstrated today with 1-2 Angstrom
  figure
• Multilayer Coatings yield narrow bandpass images
  in the 19-34 Angstrom range
• Could be useful as elements of the prime
  interferometer or for alignment
• Offer focusing and magnification to design
• May require tighter individual element alignments
  and stiffer structures.

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Technologies Status, Metrics, Mutual Needs
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Technical Components Mirror Modules

• Grazing Incidence Mirrors
• Grazing Incidence loosens our surface quality and
  figure requirements by 1/sinq
• Flatness gt l/100
• Simple shapes like spheres and flats can be
  made perfect enough
• At grazing angles, mirrors that are diffraction
  limited at UV are also diffraction limited at
  X-ray wavelengths
• Long and Skinny
• Bundled in Pairs to act as Thin Lens
• Thermal/mechanical Stability appropriate to gt
  l/100.

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What would one of these modules look like?
msin(g)
msin(g)
m
m/3 msin(g)
3/2md
2(wgap)msin(g) By 2(wgap)msin(g)m/3actuator
encoder ASSUME wgap5 cm Encoderencoder5cm S
in(g)1/30 --gt(10cmm/30)x(15cmm/3m/30) --gtm30
cm-gt 13cmx26cm
m/6
Gapmsin(g)
Pitch Control
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Technical Components Arrays of Optics

• Baselines of gt 100 m required for angular
  resolution.
• Formation flying a must for distance gt20 m.
• Miniaturization of ALL satellite subsystems to
  ease access to space.
• S/C Control to 10 mm- using periscope
  configuration (metrology to better than 1 mm).
• A system spanning from metrology to propulsion
• Individual optic modules are thin lenses with
  HUGE fields of view

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Technical Components The detector

• In Silicon, the minimum X-ray event size is 1 mm
• Large CCD arrays possible with fast readout of
  small regions.
• Pixel size determines the focal length of the
  interferometer Fs/qres
• 10 mm pixels -gt Focal lengths of 100s to 1000s of
  km.
• Formation Flying Necessary
• Huge Depth of focus loosens longitudinal control
  (meters)
• Large array sizes loosen lateral control
  (inches).
• High angular resolution requirement to resolve a
  black hole The Line-Of-Sight Requirement.

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Technical Components Line-of-Sight

• We must know where this telescope points to
  10s-100s of nanoarcseconds
• Required for ALL microarcsecond imagers
• The individual components need an ACS system good
  to only arcseconds (they are thin lenses)
• We only ask for relative stability of the LOS-
  not absolute astrometry
• This is the largest technical hurdle for MAXIM-
  particularly as the formation flying tolerance
  has been increased to microns

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Using a Super Startracker to image reference
stars and a laser beacon.
Super Star Tracker Sees both Reference stars and
the beacon of the other space craft. It should be
able to track relative drift between the
reference and the beacon to 0.1 microarcseconds.

• Both the optics spacecraft and the detector
  spacecraft can rotate to arcseconds- they are
  thin lenses
• Imaging problems occur when one of these
  translates off the line of sight
• We need to KNOW dx/F to 0.1 microarcseconds.
• AND We need to know a reference direction to the
  same level
• The CONTROL of the Line-of-Sight is driven by the
  detector size.

?o
dX
Beacon
F
?d
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Options to Determine Line-Of-Sight

• All options require beacons and beacon trackers
  to know where one s/c is relative to another.
• OPTION 1 Track on guide stars
• Use a good wavelength (radio, optical, x-ray)
• Use a good telescope or an interferometer
• OPTION 2 Use an inertial reference
• Use a VERY good gyroscope or accelerometer
• GP-B

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Summary of Key Technical Challenges

• The mirrors and their associated thermal control
  are not a tremendous leap away.
• Periscope implementation loosens formation
  flying tolerance from nm to mm. This makes
  formation flying our second most challenging
  requirement.
• Determination of the line-of-sight alignment of
  multiple spacecraft with our target is the most
  serious challenge- and MAXIM is not alone with
  this.

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Using Stars as a Stable Reference

• A diffraction limited telescope will have a PSF
  l/D
• If you get N photons, you can centroid a position
  to l/D / N1/2
• Nearby stars have mas and mas structure
• Stars move so you need VERY accurate Gimbals
• Parallax (stars _at_500 pc can move up to 40 mas in
  a day)
• Aberration of Light (as big as 40 mas in a
  minute)
• Stellar orbits, wobble due to planets
• Other effects

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An Optical Star Tracker

• A reasonable size telescope (lt1m diam.) _at_
  optical wavelengths will require 1012 photons to
  centroid to 0.1 mas.
• Practical limits on centroiding (1/1000) will
  need large F numbers
• Lack of bright stars requires complicated gimbals
  to find guide stars
• HST would barely squeak by with 15th mag stars

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An 100 mas X-ray Star Tracker

• A 1 m diffraction limited X-ray telescope
  (probably an interferometer) would need only 106
  photons to centroid to 0.1 mas
• A 1000 cm2 telescope would get 100 photons/sec
  from reasonable targets.
• 104 second integration times needed to get enough
  photons
• This is too big. And even then, there are not
  that many targets

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An 10 mas X-ray Star Tracker

• A 10 m baseline X-ray interferometer would need
  only 104 photons to centroid to 0.1 mas
• A 1000 cm2 telescope would get 100 photons/sec
  from reasonable targets.
• 100 second integration times
• This is too big.possibly
• And even then, there are not that many targets

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An Optical Interferometer

• Eg. SIM
• Metrology at picometers demonstrated in lab
• OPD control to nanometers
• Expensive?

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Local Inertial References

• Superconducting Gyroscopes
• Eg. GP-B Gyros will have drift lt 1/3 mas /day
• Superconducting Accelerometers
• Eg. UMD accelerometer sensitive to 10-15 m/s2
• Kilometric Optical Gyroscope
• Eg. Explored for Starlight- a BIG laser ring
  gyroscope
• Atomic Interferometer Gyroscopes
• Like a LRG, but with MUCH smaller wavelengths
• Laboratory models 10 mas/sec drifts
• ESA proposed Hyper mission

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Superconducting Gyroscopes

• Capitalize on GP-B technology
• Of all our options, this one has had a CDR
• Improve with better squids
• Readout is white noise limited
• Improve by requiring only hours-days of stability
  at a time
• Make the rotor have a larger moment- easier to
  read, but less stable over long times
• Use NGST/ConX Cryocoolers to replace cryogen
• Get rid of Lead bags
• Make lighter
• No need to find stars (no Gimbals)

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Superconducting Accelerometers

• 10-15m/s2 sensitivity exist now
• Need integrators
• Need higher sensitivity, unless used with other
  things

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Kilometric Optical Gyroscopes

• A Laser-Ring-Gyroscope with BIG area/perimeter
  ratio
• Resolution l/(area/perimeter)
• Use area bounded within space between multiple
  spacecraft
• Proposed for Starlight- but rejected in the end
• cost and technical reasons

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Atomic Interferometer Gyroscopes

• Same principle as a LRG, but use matter waves to
  make l many orders of magnitude smaller
• Benchtop demonstrations in lab are as good as
  best LRGs (10 mas/sec)- but should be much
  better
• ESA proposed mission Hyper based on these to do
  GR physics.