Traditional star simulators are limited by short exit pupil distances (300?500 mm), which restrict their compatibility with large multi-axis turntables used in high-precision testing of star sensors. These limitations arise from the trade-off between extending the exit pupil distance and maintaining imaging quality, as longer distances often exacerbate optical aberrations and reduce illumination uniformity. Additionally, conventional illumination systems struggle to achieve high light efficiency and uniformity, leading to inconsistent star-point brightness. This study addresses these challenges by proposing a novel optical system design for dynamic star simulators, integrating collaborative optimization of projection and illumination subsystems. The primary objectives are to achieve a 700 mm exit pupil distance, ensure high modulation transfer function (MTF) values, minimize distortion and spot radius, and deliver 98% illumination uniformity. These advancements aim to enhance ground-based testing accuracy for star sensors in aerospace applications.

The projection optical system was designed using Zemax software with sequential ray-tracing mode. The Erfle eyepiece, known for its wide field of view (65°?75°) and long back focal length, was selected as the initial structure to accommodate the extended exit pupil distance. A polarizing beam splitter (PBS) was integrated to optimize the optical path layout, reducing stray light and controlling distortion. To achieve the target exit pupil distance of 700 mm, a stepwise optimization strategy was implemented: incremental adjustments of 50 mm were made to the exit pupil distance, followed by local optimization to correct aberrations. When local optimization failed, global optimization using the hammer algorithm was applied, with material selection constrained to H-K9L glass for PBS components to ensure manufacturability. Key parameters included an F-number of 7, a focal length of 384.7 mm, and a working wavelength range of 450?700 nm. For the illumination subsystem, LightTools software facilitated non-sequential ray tracing. A TIR (total internal reflection) lens was designed using PMMA material to collimate light from a 1 mm×1 mm LED source (550 nm center wavelength). The TIR lens featured dual surfaces: a refractive surface for low-angle light collimation and a reflective surface for high-angle light redirection. Compound-eye lenses were then employed to homogenize the collimated beam. The first compound-eye lens array split the beam into sub-sources, while the second array, positioned at the focal plane of the first, superimposed these sub-sources to achieve uniform illumination. The system’s performance was evaluated based on irradiance uniformity and divergence angle, with a target uniformity of 98% over a 35 mm×35 mm LCOS target area.

The projection optical system achieved a 700 mm exit pupil distance with a 55 mm diameter, surpassing traditional designs. At 61 lp/mm (Nyquist frequency), the MTF values exceeded 0.6 across all fields (Fig. 2), ensuring high-resolution imaging. The root-mean-square (RMS) spot radius remained below 8.2 μm (Fig. 3), matching the LCOS pixel size and minimizing centroid calculation errors for star sensors. Distortion was controlled below 0.4% (Fig. 4), critical for maintaining positional accuracy of simulated stars. Field curvature, though less critical for centroid detection, was constrained to <0.08 mm. Tolerance analysis reveals that 80% of Monte Carlo samples retain MTF of >0.56 (Table 3), validating the robustness of the design under manufacturing variations. The illumination subsystem demonstrated exceptional performance. The TIR lens achieved a collimation divergence angle of <24°, with optimized surface curvatures (refractive surface: -1.5 curvature, 20 mm radius; reflective surface: -1.165 curvature, 7.4 mm radius). Compound-eye lenses with 2 mm×2 mm spherical micro-lenses further homogenized the beam, achieving 98% irradiance uniformity across the LCOS target (Figs. 8 and 9). This uniformity ensures consistent star-point brightness, a critical factor for accurate sensor calibration. Additionally, the compact design of the compound-eye lenses reduced system volume compared to traditional light-pipe solutions.

This study presents a groundbreaking optical system design for dynamic star simulators, resolving the longstanding conflict between extended exit pupil distances and high imaging quality. By leveraging the Erfle eyepiece’s inherent advantages and integrating PBS-based path optimization, the projection system achieves a 700 mm exit pupil distance with MTF of >0.6 and distortion of <0.4%. The illumination system, combining TIR collimation and compound-eye homogenization, delivers 98% uniformity, addressing a key bottleneck in star simulator performance. These innovations enable precise testing of star sensors on large turntables, enhancing reliability in aerospace applications. Future work may explore material alternatives for thermal stability in non-laboratory environments and adaptive optimization algorithms for even longer exit pupil distances.