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°  

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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.