The Herschel and Planck Space Telescopes

The European Space Agency launches in 2009 two flagship missions in the domain of submillimeter space astronomy. The Herschel Space Observatory is a common user facility featuring a 3.5 m aperture Cassegrain telescope passively cooled to 80 K. The Planck survey mission includes a 1.5 m unobscured aperture off-axis aplanatic telescope passively cooled to 40 K. Herschel will make pointed target observations of astrophysical objects and phenomena in the frequency range 448 GHz to 5.3 THz (or 672 to 55 mum wavelength). Planck, on the other hand, will map the entire sky by strip scanning at a spin rate of one revolution per minute covering a frequency bandwidth of 30-857 GHz (or wavelength from 10 to 0.35 mm). Its spin axis is pointed antisunward and can be oriented within a 10deg cone around that direction. The telescope line of sight is fixed at an angle of 85^deg to the spacecraft spin-axis. This paper describes briefly the specific telescopes developed for each mission; their design characteristics, the development process for each, their achieved performances (from on ground testing) and their expected performances in flight.