  We present a conceptual design for the input optical system for a
multi-object spectrometer operating at submillimeter wavelengths. The Mirror
MOS is based on a sequence of mirrors that enables low-loss propagation of
beams from selected positions distributed throughout the focal plane to the
spectroscopic receiver inputs. This approach should be useful for observations
of sources which have a relatively low density on the sky, for which it is
inefficient to use a traditional array receiver with uniformly spaced,
relatively closely packed beams. Our concept is based on assigning a patrol
region to each of the receivers, which have inputs distributed over the focal
plane of the telescope. The input to each receiver can be positioned at any
point within this patrol region. This approach, with only 4 reflections, offers
very low loss. The Gaussian beam optical system can be designed to produce
frequency-independent illumination of the telescope, which is an important
advantage for broadband systems such those required for determination of
redshifts of submillimeter galaxies.
