The proposed 10-2000 GHz frequency range covers all of the peak of the CMB (for "backlight" observations of galaxy clusters and gravitational lensing of CMB temperature and polarization anisotropies), an the CIB emission coming from the highest redshift objects. It complements the frequency coverage of two major space missions currently under study, the Origins Space Telescope and SPICA in the far-infrared, and that of the Square Kilometer Array at radio frequencies.

The spectro-polarimetric observations of the microwave sky will be performed by a large space mission carrying three main instruments that observe at varying spectral and angular resolutions.

Two of these instruments will be located at the focus of a large (3-m class) cold (8 K) telescope, providing arcminute scale angular resolution at 300 GHz. A broad-band, multifrequency, polarimetric imager will provide sensitive observations of the CMB and of SZ effects, while a moderate spectral resolution (R = 300) filter-bank spectrometer will map the IR background and atomic and molecular lines out to high redshift. These instruments will comprise tens of thousands of mm and sub-mm detectors, which will be cooled to sub-kelvin temperatures for sky background-limited performance.

On the same platform (or on an independent spacecraft) absolute spectroscopy across the entire frequency range will be performed by a Fourier-transform spectrometer (FTS) consisting of one or a few independent FTS modules, covering the full 10-2000 GHz band with spectral resolution ranging from 2.5 to 60 GHz, angular resolution ranging from a fraction of a degree to a few degrees, and overall sensitivity better than 1 Jy/sr, 4 to 5 orders of magnitude better than that of COBE-FIRAS.

We envision 6 years of observation from an orbit around the L2 Sun-Earth point, with two different observing modes: a survey for about half the mission time, to map the entire sky as well as a few selected wide fields; and an observatory mode, during which the rest of the time will be made available to the wider scientic community for an opportunity to observe regions of specic interest.