The European Space Agency's Planck satellite, launched on 14 May 2009, is the third-generation space experiment in the field of cosmic microwave background (CMB) research. It will image the anisotropies of the CMB over the whole sky, with unprecedented sensitivity ( ΔT T ∼ 2 × 10 −6 ) and angular resolution (∼5 arcmin). Planck will provide a major source of information relevant to many fundamental cosmological problems and will test current theories of the early evolution of the Universe and the origin of structure. It will also address a wide range of areas of astrophysical research related to the Milky Way as well as external galaxies and clusters of galaxies. The ability of Planck to measure polarization across a wide frequency range (30−350 GHz), with high precision and accuracy, and over the whole sky, will provide unique insight, not only into specific cosmological questions, but also into the properties of the interstellar medium. This paper is part of a series which describes the technical capabilities of the Planck scientific payload. It is based on the knowledge gathered during the on-ground calibration campaigns of the major subsystems, principally its telescope and its two scientific instruments, and of tests at fully integrated satellite level. It represents the best estimate before launch of the technical performance that the satellite and its payload will achieve in flight. In this paper, we summarise the main elements of the payload performance, which is described in detail in the accompanying papers. In addition, we describe the satellite performance elements which are most relevant for science, and provide an overview of the plans for scientific operations and data analysis.

Planck is a scientific satellite that represents the next milestone in space-based research related to the cosmic microwave background, and in many other astrophysical fields. Planck was launched on 14 May of 2009 and is now operational. The uncertainty in the optical response of its detectors is a key factor allowing Planck to achieve its scientific objectives. More than a decade of analysis and measurements have gone into achieving the required performances. In this paper, we describe the main aspects of the Planck optics that are relevant to science, and the estimated in-flight performance, based on the knowledge available at the time of launch. We also briefly describe the impact of the major systematic effects of optical origin, and the concept of in-flight optical calibration. Detailed discussions of related areas are provided in accompanying papers.

PLANCK is one of the scientific missions of the European Space Agency, devoted to observing the cosmic microwave background radiation with unprecedented accuracy. One of the key factors for the performance is the radiation pattern of the telescope, especially the sidelobe performance in the direction of hot celestial bodies such as the sun, Earth, and moon. The satellite will operate around the L2 Lagrangian point in deep space under cryogenic conditions. These conditions cannot be realized in an antenna test range for a payload of this size. The predictions for the performance under flight conditions therefore depend strongly on numerical simulations. The model to be used had never before been verified to this level of confidence. The challenge was to conduct a test campaign at frequencies up to 320 GHz (far beyond the normal range of the used CATR) with a very large object (the PLANCK RF Qualification Model with an aperture size of 1.5 m, l.e., more than 1500 wavelengths at 320 GHz) to demonstrate sidelobe levels down to -90 dB. A selection of the measurement results and comparisons with predictions are presented.

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