Mechanical Design

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Mechanical Design
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Mechanical Design Status

• Mechanical design for Concentric V3 optical
  system began early January. First pass layout now
  complete.

• Mechanisms design has been considered.

• Just three more IGES models would help complete
  the design.

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Spectrograph on the CWS Plate
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NIFS Cross Section
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Spectrograph Plan View
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Spectrograph Assembly
Optical components distributed over CWS plate on
cantilevered support structures in a single
layer. Spectrograph is easy to maintain, some
focussing and servicing can be done in
integration frame.
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• Pick-Off Probe
• Probe 10mm thick, drilled for NIFS and OIWFS test
  projector
• Probe closely coupled to CWS. Does not touch
  baffle.

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Pick-Off Probe

• Probe 10 mm thick, drilled for science field and
  OIWFS test projector.
• Probe closely coupled to CWS plate, but does not
  touch OIWFS baffle.

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Pick-Of Probe Flexure Analysis

• Probe flexure is very small.

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• Pick-Off Probe
• Nearest guide star to science object 12.7
• Scatter inside probe from bright stars in field.

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OIWFS Guide Star Field

• Guide stars to 12.7 ? from science object.

• Bright stars may scatter into probe.

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Pick-Off Probe Scatter Analysis
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• Input Optics
• Cold Stop and sink
• Direct rays under f256 converter. These bypass
  cold stop but do not reach slicer.

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Spectrograph Input Optics
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Focal Plane Mask Wheel

• Twelve position wheel.
• Position repeatability about 30 ?m.
• Miniature version of NIRI Geneva drive and cam
  lock.

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Spectrograph Input Optics Issues

• How effective is the cold stop?

• Can stray light be baffled?

• Direct rays can pass under the focal ratio
  converter.
• Bypass cold stop but do not reach image slicer.

• lt 4 mm diameter footprint on filter.

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• IFU Image Slicer
• Pinned or staircase assembly
• Angular accuracy 30µrad Step 57µm. Accuracy
  -0.8µm per step.

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Staircase Image Slicer
Manufacture position
Operation position
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Staircase Image Slicer Mount

• Angular accuracy 30 ?rad gt 57?0.8 ?m step.

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Large Pinned Image Slicer

• 120?50?1 mm slices.

• 12 mm dowel pins.

• 15 mm thick anvils.

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Image Slicer Issues

• Manufacture of image slicer elements.

• Alignment of image slicer elements.

• Alignment of IFU1 mount.

• Stability under cool-down.

• Flexure of IFU1 mount.

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Mirror Array Manufacture
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• Pupil Mirror Generation.
• Needs x,y,z, Diamond Turning machine.
• No steps between mirrors.
• 0.76mm diamond tip radius.

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• IFU-2 Support.
• Crowded region.
• Triple Fold Mirror.
• Field and Pupil mirror arrays span beam.

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IFU-2 Mount

• Holds adjustable pupil and field mirror arrays.

• Holds fixed triple fold mirror.

• Crowded region requiring careful baffling.

• Pupil and field mirror arrays span the beam.

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IFU-2 Mount
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Plan view on IFU
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Collimator Mirror Mount

• Largest optical component (160?70 mm).

• Diamond turned 6061 aluminum.

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Collimator Mirror Mount
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Collimator Corrector Mount

• Coarse X-Y adjustment only.

• Non-circular shape.

• Held in compliant mount like NIRI lens mount.

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• Grating Wheel
• Seven gratings plus mirror in wheel.
• Bearing and lock mechanism need 3µrad stability
  to meet Gemini specification.

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Spectrograph Grating Wheel

• Heaviest mechanism ( 4.9 Kg).

• Seven gratings plus one mirror.

• Bearing and lock mechanism require 3 ?rad
  stability to meet Gemini flexure specification.

• Mounting
• Preloaded, deep groove, ball bearings.
• Vacuum-sputtered MDS lubricant.

• Careful bearing design.

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Spectrograph Grating Mounts

• Gratings held on adjustable three-point mounts.

• Cooled via straps to grating wheel.

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Spectrograph Camera Lens Mount

• Lenses mounted in aluminum tube with zero
  clearance when cold.

• Lens tube held on brackets from CWS plate.

• Tongue and groove system maintains alignment to
  detector.

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• Flat Ribbon Cable
• Run direct from hermetic connector to detector
  circuit card without twisting.

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Detector Mounting

• No remotely controlled detector focussing
  mechanism will be used.

• Detector in light-tight box.

• Detector pressed against a ceramic ring aligned
  to focal plane.

• Rigid circuit card.

• Short lead length to controller.

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Detector Circuit Board

• Dual flex-circuit from hermetic connector to
  circuit board.

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Baffling Design
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Baffling Issues

• The biggest sources of stray light are the
  detector ( 30) and the grating ( 20).

• The camera lens tube confines the stray light
  near the detector.

• The detector views a large solid angle to the
  camera tube.

• The gratings can not see directly out to the sky
  or telescope past the IFU and cold stop.

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Baffling

• Sheet metal baffles coated with Aeroglaze.
• Sheet metal baffles cover both motors.
• Plate baffles inside camera mounting tube.

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Baffling Philosophy
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Baffling Construction

• Sheet metal baffling.

• Light, simple, with sharp edges.

• Coat with Aeroglaze or similar IR black.

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Spectrograph Housing

• 8 mm thick, cast, light-tight box will enclose
  spectrograph.

• Air vent in cover.

• Labyrinths to pass wiring.

• Spectrograph radiation shields as for NIRI.

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Spectrograph Assembly

• Install optical components on support structures.

• Align optical components.

• Install baffling.

• Wire mechanisms.

• Install tie plate.

• Install cast light-tight cover.

• Install radiation shields.

• Assemble vacuum jacket.

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Summary of Issues

• Baffling efficiency of input optics?

• Alignment of image slicer?

• Alignment of pupil and field mirror arrays?

• Stability of all mounts, esp. the grating wheel?

• Baffling efficiency within spectrograph?

• Thermal gradients across CWS plate?

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Scattering Analysis
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Zero order from J grating 10.5º below camera axis
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Ghost from camera tube wall reflection
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Ghost Amplitude from OptiCAD Radiometer. For 400
launched rays Radiometer results for 20x20 bins
(1.668/(202))0.0044 rays/bin. Each bin
contains (2048/20)210485 pixels. Black paint
wall reflection 5 Assume Zero order is 10 Peak
ghost is (0.0044/10485).1 4.1E-8 per pixel
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Camera forward reflections 2 from 2 last lenses
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Detector back reflections For detector reflection
of 30
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Ghost patches on detector
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Ghost Amplitude from OptiCAD Radiometer. For 400
launched rays Radiometer results for 20x20 bins
(0.5777/(202))0.00144 rays/bin. Each bin
contains (2048/20)210485 pixels. Detector
reflection 30 Peak ghost is (0.00144/10485).3
4.1E-8 per pixel
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• With a reflection intensity of 4.1E-8 per pixel
  and a radial shift of about 0.8R what does shift
  and add do to this ghost?
• The ghost is about 9x7mm and contains about 194
  000 pixels. If we shift and add the ghost over
  every pixel we will have a central patch of
• (194 0004.1E-8)7.9E-3 per pixel.
• This is a very bright central bump but in
  practice the real added ghost effect will be
  smaller because the ghost will lie in strips over
  the OH lines. A strip ghost over a single OH line
  will be
• (9/.018)4.1E-82.0E-5 per pixel.

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Non-Common Path Phase Errors
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NIFS plus ALTAIR

• Artificial star from ALTAIR
• Differential flexure comparison
• Phase Maps, common path optics in NIFS

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• NIFS common path optics.
• Telescope focus -30mm to fill 2mm entrance
  aperture.
• Common path optics near focus see large changes
  in footprint.

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• Phase maps from NIFS will be small.
• We can make phase maps by warming the cryostat
  and moving the detector about -9mm. Our manual
  focusser is designed for about -3mm.