The Johns Hopkins University Applied Physics Laboratory (JHU/APL) is currently developing a prototype star scanner design incorporating a variation on the V-slit design concept, called the N-slit, which is intended for deployment on future NASA spacecraft missions, such as the Radiation Belt Storm Probe (RBSP). In order to effectively test and evaluate alternative designs, including optics, sensors, and tracking algorithms, we have developed a laboratory testbed that simulates celestial objects, including stars down to a specified magnitude. We do this by creating a light-hermetic dome-shaped projection environment using light emitting diodes of specified brightness coupled to the dome exterior via fiber-optic patch cords, which can be adjusted by current bias and selected for color, if necessary, to simulate stars over a particular range of magnitudes required for the desired system accuracy. We also simulate the spacecraft platform spin dynamics using a two-axis servo-actuated mount for the star tracker test unit within the dome. This same actuator or a similar assembly can then be transitioned to actual field tests for sensor down-select and full functionality demonstrations prior to follow-on spacecraft-qualified design. We will describe the design, construction, calibration, and operation of this simulator and preliminary results of star scanner sensor evaluation using a photomultiplier-based N-slit sensor.