magellan f/15 chopping secondary magellan sac meeting laird close (principle investigator)

1September 24, 2005 Magellan F/15 Chopping Secondary

Magellan F/15 Chopping Secondary

Magellan SAC Meeting

Laird Close (Principle Investigator)

Victor Gasho (Program Manager)

September 24, 2005


Project Overview• Develop Magellan f/15 Chopping Tip-Tilt secondary

–Si clad SiC Mirror

•Lightweight (~8 kg) using egg-crate rib structure and thin face-sheet

•Very Stiff (~900Hz)

• Low CTE (2ppm/C)

• High thermal conductivity (better than aluminum)

– Physik Instrumente HVPZT Tip/Tilt/Chop Stage

•Capable of 2 Axis chopping

•Reactionless (98% Goal)

• High speed (~1 kHz)


Brief Project History1) From the beginning it was

recognized that Magellan needed a low emissivity secondary mirror. Factor of ~3 gain in exposure time possible for Mid-IR science at Cass.

2) A conceptual design was made ~1995, and contract placed with Lockheed to produce a tip-tilt chopping SiC secondary for ~900k$.

3) Polished Reaction Bonded SiC was found rougher than ~100A rms --project canceled.

4) In 2002 a 1.3 M$ NSF MRI award (PI Close) was made to provide Magellan with an adaptive secondary with tip-tilt capabilities to be provided in the funded phase 1. Full AO was to be provided at a later date from another unidentified grant.

5) Applications for enough money to finish & commission the AO secondary were turned down by AODP (twice) and TSIP (once). No further funds identified at this point.6) NSF has denied year 3’s funding due to risk, cost, & management. NSF expects SAC decision on a successful approach by end of Sept. NSF approved CDR required in fall.7) On the Sept 9, 2005 the SAC unanimously directed Close & Gasho to pursue a lightweight f/15 tip-tilt chopping secondary and not continue with the adaptive secondary.8) Here is an overview of how we can accomplish the original goals of a low emissivity tip-tilt chopping secondary for MIRAC4 and deliver the funded MRI science (and optical speckle).


Preliminary Specs of Mirror

Material Si Clad Silicon Carbide

Diameter 641.47 mm

Mirror Mass ~8.0 kg

Mirror Surface Error 40 nm rms

Mirror Surface Roughness 20 Å rms

Support Mass ~160 kg

Mirror Moment of Inertia @ CG ~0.30 kg/m2

System Resonance Frequency >300 Hz

Chopping Movement +/- 45” sky @ 0.5 Hz

+/- 16” sky @ 2Hz

+/- 3.5” sky @ 10Hz

Tip/Tilt Movement +/- 0.5” sky @ 100Hz

Angular Resolution 0.010” sky

Chopping Mechanism HVPZT Reactionless

Coating Gemini Silver?


MIRAC 4 and f/15 Secondary Mounted


F/15 Secondary Swing ArmSwing Arm

•Allows for fast deployment.

•Borrowed from previous Magellan f/15 design.

•When in retracted position will intrude in aperature and block 0.15% light.

•Trade off of optical performance vs operational needs.


F/15 Secondary Assembly


F/15 Secondary SiC Mirror


PI Stage Chopping Simulation


Examples of Chopping Secondaries

• IRTF (Infrared Telescope Facility)• Mirror diameter: 244 mm (SiC)• Tip/Tilt range: ±250 µrad (PI PZT) • 10 Hz chopping• Resonant frequency: 490 Hz

• SOFIA• Mirror diameter: 350 mm (SiC)• Tip/Tilt range: ±10 mrad (CSEM Voice Coil)• 20 Hz chopping• Resonant frequency: 422 Hz

• UKIRT (United Kingdom Infra-Red Telescope)• Mirror diameter: 314 mm (Zerodur)• Tip/Tilt range: ±500 µrad (PI PZT)• Resonant frequency: 280 Hz • 6 Hz chopping


Example of Large Si Clad SiC Mirror


MIRAC and Tip Tilt Camera


Camera and Optics

~100” MIRAC FOV (~60mm Optics)

25 mm travel x-y stage (0.3 m accuracy)


Tip/Tilt Camera

• Andor iXon DV-860 Camera


Schedule


•Questions?

magellan f/15 chopping secondary magellan sac meeting laird close (principle investigator)

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