  Fundamental information about the Universe is encoded in anisotropies of the
Cosmic Microwave Background (CMB) radiation. To make full use of this
information, an experiment must image the entire sky with the angular
resolution, sensitivity, and spectral coverage necessary to reach the limits
set by cosmic variance on angular scales >~10'. Recent progress in detector
technology allows this to be achieved by a properly designed space mission that
fits well within the scope of NASA's Medium-class Explorer program. An
essential component of the mission design is an observing strategy that
minimizes systematic effects due to instrumental offset drifts. The detector
advances make possible a `spin chopping' approach that has significant
technical and scientific advantages over the strategy used by COBE, which
reconstructed an image of the sky via inversion of a large matrix of
differential measurements. The advantages include increased angular resolution,
increased sensitivity, and simplicity of instrumentation and spacecraft
operations. For the parameters typical of experiments like the Primordial
Structures Investigation (PSI) and the Far InfraRed Explorer (FIRE), we show
that the spin-chopping strategy produces images of the sky and power spectra of
CMB anisotropies that contain no significant systematic artifacts.
