Large Dynamic Range Co-Phasing System Development

for Segmented Telescope Mirrors

Juan F Simar – ARC Phd StudentCentre Spatial de Liège

Université de Liège

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• Context

• Future Projects

• State of the art

• CSL Proposed Concept

• Activity plan

• Possible applications

• Conclusion

Outlook

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Context

Maximum On-ground monolithic mirror diameter (space

telescopes diameter are limited by

launcher capacity to 4m)

10m

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Context

Hubble Space Telescope (2.6m) and James Webb Space Telescope (6.5m) Comparison

Segmented mirrors are

folded in ground and

assembled in flight, due to

this, distances between

segments after assemblage

have an order of magnitude

of 100µm

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Context

Tip / Tilt Correction

Piston Correction

Note: Degrees and distance are exaggerated for explanation purpose

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Future Projects

Future Space Telescopes Projects

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State of the art

Spec JWST:

Tip / Tilt range > 0.3 arcsec

Piston range > 100µm

Today technology (JWST)

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CSL Proposed Concept

Coarse phasingRange 100µm (500µm target)

Resolution 300nm (100nm target)

Proposed rangeFine phasing

Range 300nm (400nm target)

Resolution 20nm (10nm target)

(Fine Phasing is under development in the frame of another CSL project)

Interferometric techniques to perform measurements

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CSL Proposed Concept

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synthsynth

synth

P

If λ1 is close to λ2 then λsynth is high and range of piston measure (P) is high

Coarse Phasing with beat technique

Beat techniques (Two waves mixing)

give a synthetic wave several orders of magnitude larger

than single wave components

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CSL Proposed Concept

As a part of Beat method studies, Heterodyne mixing techniques will be assessed in order to reduce the difference between λ1 and λ2 and

increase piston range measurement form 100µm to 500µm

Phase retrieval and phase diversity techniques will be assessed in order to be implemented as

coarse method sensing using Beat method

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Activity planFormation

Real Timealgorithm

implementation

Prototypingcoarse sensor

(open loop)Fine Phasing sensormonochromatic Φr

(open loop)

Φr = Phase retrieval

Φd = Phase diversity

Coarse phasing

Stacking fine and

coarse (open loop)

Measure method assessmentΦr, Φd + Beat ?

(another method can be implemented)

Close loop

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Possible applicationsBigger space telescopes

JWST (6.5m,year 2014)

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Possible applicationsEasy to launch space telescopes

(small segments)

JWST (6.5m,year 2014)

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Conclusion

-Co-phasing systems is a key factor in future space and earth observation missions