On the performance of Planck-like telescopes versus mirror aperture

Abstract

Future space mission like MAP and PLANCK will be able to shade new light on our knowledge of the Universe thanks to their unprecedented angular resolution and sensitivity. The far sub-degree angular resolution is obtained coupling usual detectors, radiometers and/or bolometers, to an optical system, namely a telescope. The wealth of cosmological information is encoded at high ℓ values (∼ 1000) which can be reached with resolution of about 10′. Distortions of the main beam resulting from the current focal plane arrangement and the optical design of the PLANCK satellite will degrade angular resolution and sensitivity per resolution element possibly compromising the final results. The detailed design of the PLANCK telescope is continuously changing with the aim of optimizing its performance. In the present work we present a methodological study on the relation between telescope optical design, focal plane arrangement and optical performances, focussing on the dependence of angular resolution on primary mirror aperture. Different independent approaches have been developed to quantify the impact of main beam distortions on cosmic microwave background (CMB) science yielding nearly the same results. The so-called PHASE-A telescope is unacceptable with respect mission main goals. Larger telescopes (namely with effective aperture ≳ 1.5 m) are therefore preferable. This paper is based on the PLANCK LFI activities.