Microgravity research in space is a complex activity where the often scarce resources available for the launch, accommodation, and operation of instrumentation call for a careful experiment planning and instrument development. In this paper we describe a module of the Selectable Optical Diagnostic Instrument, that has been designed as a compact optical diagnostic instrument for colloidal physics experiments. The peculiarity of the instrument is the combination of a novel light scattering technique known as near field scattering and standard microscopy with a low-coherence laser light source. We describe its main design features, as well as measurement results on colloidal aggregation taken on the International Space Station.