SPIDER: A balloon-borne large-scale Cmb polarimeter

SPIDER is a balloon-borne experiment that will measure the polarization of the Cosmic Microwave Background over a large fraction of a sky at ∼ 1° resolution. Six monochromatic refracting millimeter-wave telescopes with large arrays of antenna-coupled transition-edge superconducting bolometers will provide system sensitivities of 4.2 and 3.1 μKCMB √s at 100 and 150 GHz, respectively. A rotating half-wave plate will modulate the polarization sensitivity of each telescope, controlling systematics. Bolometer arrays operating at 225 GHz and 275 GHz will allow removal of polarized galactic foregrounds. In a 2-6 day first flight from Alice Springs, Australia in 2010, SPIDER will map 50% of the sky to a depth necessary to improve our knowledge of the reionization optical depth by a large factor.