  The BISOU (Balloon Interferometer for Spectral Observations of the Universe)
project aims to study the viability and prospects of a balloon-borne
spectrometer, pathfinder of a future space mission dedicated to the
measurements of the CMB spectral distortions. We present here a preliminary
concept based on previous space mission proposals, together with some
sensitivity calculation results for the observation goals, showing that a
5-sigma measurement of the y-distortions is achievable.
