SPIE Astronomical Telescopes ... · Figure 2. Cross section through the CCAT-prime telescope...
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SUBASSEMBLIES AND COMPONENTS Figure 4. Above – aluminum mirror panel showing backside light weighting and adjuster mounting points. Right – CFRP mirror backup structures consisting of a CFRP-AL-CFRP sandwich top plate and supporting CFRP truss. The primary is above, secondary below. The red elements are tuned CTE beams that minimize the HWFE due to imperfect mirror alignment from thermal effects. CONCLUSION We have completed the preliminary detailed design and simulation for a 6 meter crossed-Dragone telescope with a primary to secondary mirror surface area ratio near unity. This design is capable of meeting or exceeding the performance requirements for HWFE, PE, blockage and dynamics. There are clear advantages to this design configuration: • optics "buried" inside the mount, lower wind loading on mirrors • facilitates stray light control, reducing ground pickup • integrated shutter provides protection from sun, rain, snow, and ice • no tipping of instruments; improves stability, simplifies their design and mounting, easy to add co-rotator if desired • elevation axis runs through secondary minimizing gravitational distortions • symmetrical nature of mount allows for partial bore sight rotation by rotating beyond zenith and coming back around 180° in azimuth The Simons Observatory has adopted the same telescope design for their Large Aperture Telescope, but with a steel EL housing instead of Invar for mm observations. The next phase will be a critical design review, followed by a final design review then construction and assembly. First light is anticipated in 2021. CCAT-prime: a novel telescope for submillimeter astronomy. Stephen C. Parshley a and Jörg Kronshage b a Department of Astronomy, Cornell University, Ithaca, NY 14853, USA b Vertex Antennentechnik, GmbH, 47198 Duisburg, Germany www.ccatobservatory.org Acknowledgements: CCAT-prime funding has been provided by Cornell University, the Fred M. Young Jr. Charitable Fund, the German Research Foundation (DFG) through grant number INST 216/733-1 FUGG, the Univ. of Cologne, the Univ. of Bonn, and the Canadian Atacama Telescope Consortium. INTRODUCTION CCAT-prime is designed to operate in the millimeter to submillimeter (100 GHz to 1.5 THz) range with a 6-meter aperture, 7.8° diameter field of view (FoV) at λ = 3 mm. The telescope supports multiple instruments to cover the different science cases. The requirements include a one half wavefront error (HWFE) of less than 11 μm, a pointing error (PE) of less than 1.4 arcsec, and an emissivity of less than 2.8% for wavelengths longer than 850 μm (350 GHz). SIMULATED PERFORMANCE The overall performance of the telescope is simulated under various load cases. The steady-state effects of gravity, thermal gradients, uniform temperature changes, and wind are applied to the model. Wind loads are computed by CFD / FSI analysis. Relative deformations are calculated from the results and converted into one half wavefront error (HWFE) and pointing error (PE). Resonant frequencies are also calculated for the entire structure. TELESCOPE OVERVIEW The overall mechanical design is shown below. It is similar to a fork-structure (which we designate the yoke) elevation-over-azimuth mount without a reflector. Instead, the offset optics are contained inside what would normally be the secondary focus cabin, called the elevation housing, which shelters the reflecting surfaces from wind and solar illumination. A shutter closes the opening during periods of inclement weather. Rough overall size is 23 x 8 x 16 meters (L x W x H), with the elevation axis ~11 m above ground. Total weight is over 220 metric tons with ~200 tons moving in AZ and ~60 tons moving in EL. This section details the major components critical to the mechanical structure, starting at the reflecting surfaces and ending at the ground. Each component is optimized individually before being combined into the full telescope model for further total optimization which allows for parallel path development and leads to a good understanding of the sensitivity of the system to design changes. SPIE Astronomical Telescopes + Instrumentation Austin, Texas, USA, June 2018 9 m/s req. 9 m/s perf. 15 m/s perf. Blind pointing 6.9 5.4 5.8 Offset pointing 2.7 1.6 2.7 Scan pointing, sector 1 1.4 1.4 2.5 Scan pointing, sector 2 1.9 1.5 2.6 Scan following 6.9 1.6 1.6 Pointing stability 1.4 1.7 1.9 Component \ Error Type Grav. T, grad T, soak Wind Align. Mfg. Margin Comp. Total Mirror config. 4.2 0.3 3.5 0.0 2.0 0.0 1.0 5.9 M2 BUS 2.3 1.0 0.1 0.2 2.0 0.0 1.0 3.4 M1 BUS 5.1 1.0 0.1 0.4 2.0 0.0 1.0 5.7 M2 panel 0.8 2.2 0.9 0.2 0.0 3.0 1.0 4.0 M1 panel 0.8 2.2 0.9 0.2 0.0 3.0 1.0 4.0 Error Type Total 7.1 3.4 3.7 0.5 3.5 4.2 2.2 Telescope Total: 10.5 Figure 1. CCAT-prime telescope mechanical design model with major elements labeled. For reference, the opening in the elevation housing is approximately 7 m. Figure 2. Cross section through the CCAT-prime telescope highlighting science equipment spaces and access. Figure 3. Ventilation concept for CCAT-prime. The yoke traverse is insulated and maintained between 10-20° C while the yoke arms and elevation housing are ventilated to improve temperature uniformity within the structure. Figure 5. Elevation housing in cross-section through the telescope mid-plane with mirrors installed. The EL housing is an Invar beam structure with insulating cladding. Figure 6. Two views of the yoke structure and support cone, both insulated steel framework assemblies. Elevation drives are opposite the focal panel. A lift is provided to move personnel and small equipment between floors. Figure 7. Right – wind visualized by a streamline plot, wind speed 9 m/s, telescope oriented at -30° AZ & 30° EL, ρ air = 0.646 kg/m 3 . Left – resulting pressure distribution. Table 1. HWFE by component and error type, all in μm rms. Figure 8. Thermal gradient for a single mirror panel computed by a transient analysis after 300 s, peak-to-peak ~0.3° C Table 2. PE, all errors are in arcsec rms. Figure 9. Left – 2.6 Hz locked rotor AZ, 1 st mode. Right – 3.0 Hz locked rotor EL 3 rd mode. Both for 0° elevation. Modes are not pure, stiffening yoke should improve this. #10700-220 panoramic view from the CCAT high altitude site Cerro Toco Cerro El Chascón
Transcript of SPIE Astronomical Telescopes ... · Figure 2. Cross section through the CCAT-prime telescope...
SUBASSEMBLIES AND COMPONENTS
Figure 4. Above – aluminum mirror panelshowing backside light weighting andadjuster mounting points. Right – CFRPmirror backup structures consisting of aCFRP-AL-CFRP sandwich top plate andsupporting CFRP truss. The primary isabove, secondary below. The red elementsare tuned CTE beams that minimize theHWFE due to imperfect mirror alignmentfrom thermal effects.
CONCLUSIONWe have completed the preliminary detailed design and simulation for a 6meter crossed-Dragone telescope with a primary to secondary mirror surfacearea ratio near unity. This design is capable of meeting or exceeding theperformance requirements for HWFE, PE, blockage and dynamics.
There are clear advantages to this design configuration:• optics "buried" inside the mount, lower wind loading on mirrors• facilitates stray light control, reducing ground pickup• integrated shutter provides protection from sun, rain, snow, and ice• no tipping of instruments; improves stability, simplifies their design and
mounting, easy to add co-rotator if desired• elevation axis runs through secondary minimizing gravitational distortions• symmetrical nature of mount allows for partial bore sight rotation by rotating
beyond zenith and coming back around 180° in azimuth
The Simons Observatory has adopted the same telescope design for theirLarge Aperture Telescope, but with a steel EL housing instead of Invar for mmobservations. The next phase will be a critical design review, followed by a finaldesign review then construction and assembly. First light is anticipated in 2021.
CCAT-prime: a novel telescope for submillimeter astronomy.Stephen C. Parshleya and Jörg Kronshageb
aDepartment of Astronomy, Cornell University, Ithaca, NY 14853, USAbVertex Antennentechnik, GmbH, 47198 Duisburg, Germany
www.ccatobservatory.org
Acknowledgements:CCAT-prime funding has been provided by Cornell University, the Fred M. Young Jr. Charitable Fund,the German Research Foundation (DFG) through grant number INST 216/733-1 FUGG, the Univ. ofCologne, the Univ. of Bonn, and the Canadian Atacama Telescope Consortium.
INTRODUCTIONCCAT-prime is designed to operate in the millimeter to submillimeter (100 GHzto 1.5 THz) range with a 6-meter aperture, 7.8° diameter field of view (FoV) atλ = 3 mm. The telescope supports multiple instruments to cover the differentscience cases. The requirements include a one half wavefront error (HWFE) ofless than 11 μm, a pointing error (PE) of less than 1.4 arcsec, and an emissivityof less than 2.8% for wavelengths longer than 850 μm (350 GHz).
SIMULATED PERFORMANCEThe overall performance of the telescope is simulated under various loadcases. The steady-state effects of gravity, thermal gradients, uniformtemperature changes, and wind are applied to the model. Wind loads arecomputed by CFD / FSI analysis. Relative deformations are calculated from theresults and converted into one half wavefront error (HWFE) and pointing error(PE). Resonant frequencies are also calculated for the entire structure.
TELESCOPE OVERVIEWThe overall mechanical design is shown below. It is similar to a fork-structure(which we designate the yoke) elevation-over-azimuth mount without areflector. Instead, the offset optics are contained inside what would normally bethe secondary focus cabin, called the elevation housing, which shelters thereflecting surfaces from wind and solar illumination. A shutter closes theopening during periods of inclement weather. Rough overall size is 23 x 8 x 16meters (L x W x H), with the elevation axis ~11 m above ground. Total weight isover 220 metric tons with ~200 tons moving in AZ and ~60 tons moving in EL.
This section details the major components critical to the mechanical structure,starting at the reflecting surfaces and ending at the ground. Each component isoptimized individually before being combined into the full telescope model forfurther total optimization which allows for parallel path development and leadsto a good understanding of the sensitivity of the system to design changes.
SPIE Astronomical Telescopes + InstrumentationAustin, Texas, USA, June 2018
9 m/s req. 9 m/s perf. 15 m/s perf.
Blind pointing 6.9 5.4 5.8Offset pointing 2.7 1.6 2.7Scan pointing, sector 1 1.4 1.4 2.5Scan pointing, sector 2 1.9 1.5 2.6Scan following 6.9 1.6 1.6Pointing stability 1.4 1.7 1.9
Component \ Error Type Grav. T, grad T, soak Wind Align. Mfg. Margin Comp. TotalMirror config. 4.2 0.3 3.5 0.0 2.0 0.0 1.0 5.9M2 BUS 2.3 1.0 0.1 0.2 2.0 0.0 1.0 3.4M1 BUS 5.1 1.0 0.1 0.4 2.0 0.0 1.0 5.7M2 panel 0.8 2.2 0.9 0.2 0.0 3.0 1.0 4.0M1 panel 0.8 2.2 0.9 0.2 0.0 3.0 1.0 4.0Error Type Total 7.1 3.4 3.7 0.5 3.5 4.2 2.2 Telescope Total: 10.5
Figure 1. CCAT-prime telescope mechanical design model with major elementslabeled. For reference, the opening in the elevation housing is approximately 7 m.
Figure 2. Cross section through the CCAT-prime telescope highlighting scienceequipment spaces and access.
Figure 3. Ventilation concept for CCAT-prime. The yoke traverse is insulated andmaintained between 10-20° C while the yoke arms and elevation housing areventilated to improve temperature uniformity within the structure.
Figure 5. Elevation housing in cross-section through the telescope mid-plane withmirrors installed. The EL housing is an Invar beam structure with insulating cladding.
Figure 6. Two views of the yoke structure and support cone, both insulated steelframework assemblies. Elevation drives are opposite the focal panel. A lift is providedto move personnel and small equipment between floors.
Figure 7. Right – wind visualized by a streamline plot, wind speed 9 m/s, telescopeoriented at -30° AZ & 30° EL, ρair = 0.646 kg/m3. Left – resulting pressure distribution.
Table 1. HWFE by component and error type, all in μm rms.
Figure 8. Thermal gradient for a singlemirror panel computed by a transientanalysis after 300 s, peak-to-peak ~0.3° C
Table 2. PE, all errors are in arcsec rms.
Figure 9. Left – 2.6 Hz locked rotor AZ, 1st mode. Right – 3.0 Hz locked rotor EL 3rd
mode. Both for 0° elevation. Modes are not pure, stiffening yoke should improve this.
#10700-220
panoramic view from the CCAT high altitude site
Cerro Toco Cerro El Chascón
