Star trackers are electro-optical devices that are used to determine the attitude of satellite platforms. The test of star trackers is typically carried out by means of Optical Ground Support Equipment (OGSE). In this paper we present a new prototype of OGSE, the MINISTAR, recently developed by a consortium of Italian enterprises and the Applied Physics Institute of the National Research Council. The MINISTAR is a miniaturized electro-optical device able to generate synthetic images of dynamic star fields for the simultaneous test of up to three star trackers. Their performance can be evaluated in terms of its optics, electronics and on-board attitude software. The MINISTAR is able to perform a dynamic simulation of the apparent motion of the observed scene in order to test the star tracker in a realistic working scenario. It can be placed directly on the star tracker under test and, thanks to its reduced dimensions and weight, the test and validation phase can be performed while the star tracker is assembled on the satellite platform. The MINISTAR is also able to simulate the presence of large objects, such as the Sun, the Earth and the Moon, custom objects and disturbances like cosmic rays and stray light effects. The prototype has been built paying special attention to the employed materials and technology in order to minimize the weight and to ensure its compatibility with most star tracker models available on the market.

The validation of the correct functioning of star trackers is a crucial step for the success of any space mission. In recent years, there has been an increasing interest for the development of miniaturized, light-weighted test systems to be installed directly on the star tracker, opening the way to the test of completely assembled, on-board attitude sensors in pre-launch environment.Here we present the main technical characteristics of a new prototype, the MINISTAR, recently developed by a consortium of Italian enterprises and the Applied Physics Institute of the National Research Council. Besides its main technical features, here we present the results of a set of tests for its performance evaluation, with particular reference to its radiometric and geometric calibration in the laboratory. The MINISTAR can generate synthetic images of dynamic star fields for the simultaneous test of multiple star trackers (up to three head devices). The generation of dynamic star fields in a realistic scenario also includes large objects, such as the Sun or the Moon, and disturbances (e.g. cosmic rays and stray light effects).Thanks to its reduced dimensions and weight, the MINISTAR is suitable for the installation on the star tracker's baffle. Special attention has also been paid to the use of materials and technologies that could be compliant for vacuum operation in the future. Thanks to the design and construction of an interchangeable mechanical interface, the MINISTAR is compatible with the majority of star trackers available on the market.