Planck Telescope: optical design and verification

The cornerstone mission of the European Space Agency (ESA) scientific program Herschel/Planck is currently in the design manufacturing phase (phase C/D). The Planck satellite will be launched in 2007, together with Herschel. Located around the L2 Lagrange point, Planck aims at obtaining very accurate images of the Cosmic Wave Background fluctuations. Working up to high frequency (857GHz, i.e. 350μm wavelength), Planck is expected to give sharper images than the recently launched WMAP satellite. The Planck Telescope is an off-axis (unobscured) Gregorian antenna, with a 1.5m diameter pupil, a small F-number (~1) and a large FOV (+/-5° circular), owing to place a large number of detectors (bolometers) in the focal plane. This paper presents the optical design, performance, and verification concept of the Planck telescope. The custom made sequential Hartmann system is described. Working at 10.6μm, it will directly measure the wavefront of the telescope in cryogenic environment i.e. at operational conditions. This will be a major milestone in the spacecraft development.