The Jena-Optronik Optical Sky Stimulator (OSI) is a lightweight star sensor test device designed for space applications. It consists lightweight optical head for the projection, baffle mount, connecting harness, and a control computer. It is a universal test system for star sensors - plug & play ready - for both Jena-Optronik ASTRO 10 and ASTRO APS star sensors, but also compatible with third party star sensor. It also has a built-in HIPPARCOS based star catalogue.