Spectroscopic Active Galaxies and Clusters Explorer

We present a concept for the payload SAGACE, the Spectroscopic Active Galaxies And Cluster Explorer, devoted to study the evolution of Universe structures using different observables, all of them in the mm/submm wavelength. The SAGACE payload is made of a passively cooled 3 m telescope, a cryogenic Fourier Transform Spectrometer (FTS) and detector arrays to be operated at 0.3 K by a <SUP>3</SUP>He fridge. The detectors are Ti/Au Transition Edge Sensor (TES) bolometers with a NEP<10<SUP>-17</SUP> W/Hz<SUP>12</SUP>. A phase-A study has been recently completed for this experiment, in the framework of the call for small missions of the Italian Space Agency.