Design of a Low-Aberration Variable-Magnification Optical Stimulator for Vision System Hardware-in-The-Loop Testing

The increasing interest in spacecraft autonomy raises the need for a trustworthy approach to perform Verification & Validation. In particular, vision-based navigation algorithms have established themselves as effective solutions to determine the spacecraft state in autonomy, with low-cost and versatile sensors. Nevertheless, thorough testing must be performed on ground to understand the algorithm robustness and performance in flight. A dedicated simulation framework must be developed to emulate the orbital environment in a laboratory setup. This paper presents a methodology to design and develop a low-aberration optical facility for visual sensors. The proposed methodology foresees two steps. First, a preliminary design is performed to identify the range of possible components to use in the facility according to the requirements. Then, a detailed optical design is performed to optimize the number and properties of the lenses composing the optical systems. The final design is compared against the preliminary one to show the superiority of the optical performance achieved with this approach. The proposed methodology is exploited to design and integrate a physical facility able to accommodate cameras with different characteristics (e.g., sensor size and focal length) while ensuring accurate stimulation. Besides these results, this work also presents a subpixel-accuracy geometrical calibration procedure to correct the geometrical errors due to component centering and misalignment. The estimated calibration is pivotal to compensating residual geometrical errors, enabling the stimulation of the camera at tens of arcseconds accuracy. Finally, two applications are presented to show the versatility of the developed setup in accommodating different cameras and in simulating heterogeneous mission scenarios.