In a cooperation of the Swedish Space Corporation, the Microgravity Research Center of the Université Libre de Bruxelles and the Institute of Geodesy and Photogrammetry at ETH Zurich, a system for the measurement of three-dimensional particle motion field in an experimental vessel under micro-gravity conditions has been designed and constructed. The system consists of four CCD cameras and a mirror system allowing a good photogrammetric network quality in combination with an extremely compact design. The paper shows the basic design of the system, discusses a calibration strategy and presents first results. The experiment unit was made for the MASER 8 sounding rocket JET experiment with the aim of a first direct observation of the so-called chemojet motion of free flying small growing crystals. It takes place in a reactor chamber with a dimension of 10x11x14 mm³, into which several hundred particles are injected during the flight. The particles are imaged by four synchronized CCD cameras. The chamber is illuminated from the backside via a milk-glass window. The front wall of the chamber is an observation window used for imaging the particles. According to the reliability requirements of 3-D particle-tracking-velocimetry (3-D PTV), the reactor chamber has to be imaged from at least three different directions. A fourth camera was added to enable the discrimination of two different particle substances via a special illumination in combination with a filter.