Abstract: The star sensor devices installed on a satellite platform require the on-orbit thermal control through a star sensor radiator. Because of the spatial interference between the star sensor radiator and the testing bracket of the star simulator, the star sensor radiator needs to be removed during the static star simulator test. In order to solve the problem, a testing bracket of the static star simulator in a confined space is designed after analyzing the installation process and the spatial characteristics of the star simulator; the miniaturized testing bracket is precisely sized by making use of the micro-deformation of the structure and the tolerance of the optical axis angle and the rotation angle. The static star simulator testing is therefore compatible with the installation of the star sensor radiator with the help of the miniaturized testing bracket, thus the risk in the AIT process of spacecraft is reduced, and the assembling efficiency is improved for the star simulator. The results of the static analysis and the on-board tests have verified the feasibility of the design.