ccat · ccat will have an active primary supported by a carbon-fiber-reinforced-plastic (cfrp)...
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CCAT J. Glenn for the CCAT collaboration
CCAT will be a 25 m diameter Gregory telescope operating in the 0.2 to 2.1 mm wavelength range. It will be located at an altitude of 5600 m on Cerro Chajnantor in northern Chile. CCAT will deliver >80% Strehl ratio and <1/10th beam pointing error at λ=350 µm. CCAT will have an active primary supported by a carbon-fiber-reinforced-plastic (CFRP) spaceframe truss on an elevation over azimuth mount made of steel. Cameras and spectrometers with up to 1° field of view will be located at the two f/6 Nasmyth foci, which will be inside the elevation axle near the tertiary. CCAT will be inside a cylindrical enclosure to reduce wavefront and pointing errors due to wind forces and thermal deformation due to solar illumination.
Primary: CCAT will have an f/0.4 primary with 162 keystone-shaped segments, each with 16 machined aluminum tiles mounted on a ~2×2 m insulated CFRP subframe. Each subframe will be attached to the CFRP truss with 3 computer-controlled actuators. The truss will have a coefficient of thermal expansion of just a few ×0.1 ppm/K, so the surface control can be open loop, based on look-up tables for gravity and soak temperature.
CCAT requirements and estimated performance at λ=350 µm.
Optics: CCAT will have a profiled tertiary to correct aberrations. The field of view will be ~1° over the λ=0.35 to 2.1 mm band.
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-X Field in Degrees
Diffraction Limit
f6_OG_ter_corr.ZMXConfiguration 1 of 4
Strehl Ratio
Strehl Ratio vs Field
f/6 Gregory with tertiary corrector11/21/2012350 1e+003
Reference: Centroid
λ=350μm λ=1mm
0 -‐x field radius 1°
0 Streh
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Strehl ratio vs. field angle with a profiled tertiary. CCAT optical layout. The marginal rays are for ±0.5° field angle.
CFRP subframe
Aluminum 9le
CCAT segment.
Mount: CCAT will have an elevation over azimuth mount with hydrostatic bearings (for low friction) and direct drives (for high stiffness and zero backlash). The CFRP truss will connect to the steel mount via 2 concentric rings of blade flexures. The natural frequency of the complete telescope will be 5 Hz. The rotating mass will be 500 tonnes.
Secondary: The 3 m diameter secondary will use the same tile on subframe technology as the primary segments. The secondary will be mounted on a hexapod positioner that will be adjusted continuously to correct gravitational and thermal deformation of the support structure.
Tertiary: The 2.8×3.8 m tertiary will be mounted on a rotator in order to direct the beam to the active instrument.
Prototype segment actuator.
AZ drive forcer
AZ track
EL shock absorber
AZ drive magnets
AZ brake
EL drive forcer
EL drive magnets
EL brake
EL seismic restraint
AZ bearing
Enclosure: CCAT will be in a cylindrical enclosure with a sliding roof door and a folding front door. It will be possible to observe with the doors partly closed to reduce wind forces on the telescope.
Tertiary mirror. Prototype tertiary subframe (1.2×1.2 m).
CFRP subframe
Aluminum 9le
Rotator
Prototype truss struts. Truss node and strut fittings.
Invar node
CFRP strut Parameter Requirement Performance Notes Wavelength 0.35 to 2.1 mm Aperture 25 m Resolves submm
background, 1” positions Field of view 1° Limited by field curvature Emissivity <0.1 0.09 Half wavefront error <12.5 µm rms 12.8 >80% Strehl ratio
at λ=350 µm Offset pointing <0.35” rms 1/10th beam within 1° Pointing stability <0.35” hr-1 rms 1/10th beam hr-1 Scan speed >0.3°s-1 300 beams/s Scan acceleration >0.3°s-2 2 s turn around Scan following error <1.8” rms ½ FWHM beamwdith Scan pointing knowledge
<0.35” rms 0.42 1/10th beam
Pointing and scanning requirements scale linearly with λ.
The CCAT consortium includes Cornell University; the California Institute of Technology and Jet Propulsion Laboratory; the University of Colorado at Boulder, the University of Cologne and the University of Bonn; McGill University, McMaster University, the University of British Columbia, the University of Calgary, the University of Toronto, the University of Waterloo, Dalhousie University, the Western University; and Associated Universities, Inc. CCAT operates in Chile thanks to a Cooperative Agreement with the University of Chile and under the auspices of the Ministry of Foreign Affairs of Chile. The CCAT Engineering Design Phase is partially supported by funding from the National Science Foundation’s Division of Astronomical Sciences
Photo: George Gull/Cornell
f6_OG_ter_corr.ZMXConfiguration 1 of 4
3D Layout
f/6 Gregory with tertiary corrector11/21/2012
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CFRP subframe
Aluminum 9le
CFRP support
Secondary mirror and top end.
View over the CCAT site.
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