Modeling a large submillimeter-wave observatory

Abstract

The 25 meter aperture Cornell Caltech Atacama Telescope (CCAT) will provide an enormous increase in sensitivity in the submillimeter bands compared to existing observatories, provided it can establish and maintain excellent image quality. To accomplish this at a very low cost, it is necessary to conduct accurate engineering trades, including the most effective segment and wavefront sensing and control approach, to determine the best method for continuously maintaining wavefront quality in the operational environment. We describe an integrated structural/optical/controls model that provides accurate performance prediction. We also detail the analysis methods used to quantify critical design trades.

An imaging displacement sensor with nanometer accuracy

“…5,6 Measuring all six DoF at the edge between segments implies many more individual sensors are needed and is a new requirement beyond what is used or proposed for optical telescopes. So despite the allowable surface error for CCAT being a factor of a hundred larger than for an optical telescope the sensors are still challenging and the previously used edge sensors and proposed new designs for optical telescopes do not meet all of the CCAT requirements.…”

“…The segment design is described in Woody et al 4 . A closed loop control approach employing edge sensors which measures the relative displacements between neighboring reflector segments has been developed by Redding et al 5,6 . The critical requirement is to achieve a net ½ wave front error (HWFE) of less than 10 m, including the primary, secondary and tertiary optics.…”

The CCAT 25m diameter submillimeter-wave telescope

“…al. 14 The simulations include expected gravity distortions of the primary support truss as well as applying random piston, tip and tilt displacements of the segments. After removing the six rigid body motions for the whole primary all 6x162-6 = 966 Eigen modes are measured with high fidelity.…”