arXiv:1002.0867v1 [astro-ph.CO] 3 Feb 2010 February 3, 2010 23:18 WSPC - Proceedings Trim Size: 9.75in x 6.5in main SAGACE: the Spectroscopic Active Galaxies And Clusters Explorer P. DE BERNARDIS 1* , D. BAGLIANI 2 , A. BARDI 3 , E. BATTISTELLI 1 , M. BIRKINSHAW 4 , M. CALVO 1 , S. COLAFRANCESCO 5 , A. CONTE 1 , S. DE GREGORI 1 , M. DE PETRIS 1 , G. DE ZOTTI 6 , A. DONATI 3 , L. FERRARI 2 , A. FRANCESCHINI 6 , F. GATTI 2 , M. GERVASI 7 , P. GIOMMI 5 , C. GIORDANO 1 , J. GONZALEZ-NUEVO 8 , L. LAMAGNA 1 , A. LAPI 9 , G. LUZZI 1 , R. MAIOLINO 10 , P. MARCHEGIANI 5 , A. MARIANI 3 , S. MASI 1 , M. MASSARDI 8 , P. MAUSKOPF 11 , F. NATI 1 , L. NATI 1 , P. NATOLI 9 , M. NEGRELLO 12 , F. PIACENTINI 1 , G. POLENTA 1 , M. SALATINO 1 , G. SAVINI 13 , A. SCHILLACI 1 , S. SPINELLI 7 , A. TARTARI 7 , M. TAVANTI 3 , A. TORTORA 3 , M. VACCARI 6 , R. VACCARONE 2 , M. ZANNONI 7 , V. ZOLESI 3 1 Dipartimento di Fisica, Universit´ a La Sapienza, and INFN sezione di Roma, Roma, Italy; 2 Dipartimento di Fisica, Universit´ a di Genova , and INFN sezione di Genova, Italy; 3 Kayser Italia, Livorno, Italy; 4 Department of Physics, University of Bristol, UK; 5 ASDC - ASI - Frascati , Italy, 6 INAF, Osservatorio di Padova, Italy; 7 Dipartimento di Fisica, Universit´ a di Milano Bicocca, Italy; 8 SISSA - Trieste, Italy; 9 Dipartimento di Fisica, Universit´ a di Tor Vergata, Roma, Italy; 10 INAF - Osservatorio di Roma, Italy; 11 Department of Physics and Astronomy, Cardiff University, UK; 12 Department of Physics and Astronomy, Open University, Milton Keynes, UK; 13 Department of Physics and Astronomy, University College London, UK; * e-mail: paolo.debernardis@roma1.infn.it The SAGACE experiment consists of a mm/sub-mm telescope with a 3-m diameter pri- mary mirror, coupled to a cryogenic multi-beam differential spectrometer. SAGACE ex- plores the sky in the 100-760 GHz frequency range, using four diffraction-limited bolome- ter arrays. The instrument is designed to perform spectroscopic surveys of the Sunyaev- Zeldovich effects of thousands of galaxy clusters, of the spectral energy distribution of active galactic nuclei, and of the [CII] line of a thousand galaxies in the redshift desert. In 2008 a full phase-A study for a national small mission was completed and delivered to the Italian Space Agency (ASI). We have shown that taking advantage of the differential operation of the Fourier Transform Spectrometer, this ambitious instrument can operate from a Molniya orbit, and can be built and operated within the tight budget of a small mission. Keywords : Cosmology, Clusters of Galaxies, Early Galaxies, Cosmic Microwave Back- ground, Space Experiments, Spectrometers 1. SAGACE Science Our knowledge of the mm/sub-mm sky is rapidly improving. Balloon-borne mis- sions and the recent WMAP all-sky survey have produced impressive maps of the cosmic microwave background (CMB), allowing the precise measurement of several cosmological parameters. The Planck 1,2 mission is producing maps of the whole sky in nine wavebands with exquisite accuracy, allowing a secure separation of the CMB signals from the Galactic and extragalactic foregrounds, and a massive shallow survey of Sunyaev-Zeldovich clusters. However, the spectroscopic exploration of the frequency range between 90 and 600 GHz is still completely undeveloped, since most of this range is not accessible 1