Millimeter-wave observations of the Sun have never been carried out from a space-based platform. This work presents a feasibility study for a full-disk 90 GHz radiometer designed to detect the radio emission of solar flares. Such a feasibility study has been carried-out in the frame of the ADAHELI (ADvanced Astronomy for HELIophysics) mission, whose phase A has been funded by the Italian Space Agency (ASI) and successfully completed in December 2008. First flare radiation mechanisms are introduced, showing that millimeter-waves are very sensitive probe of the highest energy electrons accelerated in solar flares. Then the fluctuation of the Sun to satellite radio path attenuation is studied by modeling the ionosphere as a charged plasma. Finally the science requirements and the system design are presented. The instrument architecture is based on a 25 cm dish antenna with f/D = 0.6 and a 45 deg offset of the feed. The receiver uses a direct amplification configuration with 8dB noise figure, 50 dB gain and 100 ppm gain stability. The target of 3 sfu radiometric resolution for a 1 s integration time is achieved with a 2 GRz pre-detection bandwidth.