Design of Compact Large Field Off-axis Three-mirror Space Optical System Based on Freeform Surface
In the realm of modern space exploration and remote sensing technology,reflective optical systems play an indispensable role.These systems are distinguished by their absence of chromatic aberration,broad operational bandwidth,effective stray light suppression,and their capacity for lightweight and compact design compared to transmissive systems.These attributes confer significant advantages in the application of space cameras.Particularly under the demands for high resolution and wide field of view,reflective optical systems emerge as the preferred choice due to their unique benefits.In an effort to diminish the physical footprint of space optical systems and reduce the associated costs of launching remote sensing satellites,this paper delineates the formulation of the initial structure for such a system,grounded in the principles of primary aberration theory.This research presents the design of an innovative off-axis three-mirror optical system characterized by an"annular contour",facilitated through a methodical,gradual optimization strategy concentrating on the field of view and surface morphology.The proposed system boasts a focal length of 2 000 mm,a field of view spanning 5°X5°,an F-number of 12.5,and an external envelope circle diameter measuring 750 mm.Integral to this design is the employment of XY polynomial freeform surfaces for the primary and tertiary mirrors,and Zernike polynomial freeform surfaces for the secondary mirror.These selections were motivated by their capacity to minimize aberrations and enhance the system's imaging performance.By applying the surface shape parameters of these freeform surfaces,we conducted simulations to generate two-dimensional sagittal height maps for each of the three mirrors,thus facilitating a rigorous analysis of the optical system's theoretical capabilities.The results from this design process indicate that the imaging quality of the sy(s)tem aligns closely with the diffraction limit.Specifically,the maximum Root Mean Square(RMS)spot diameter across all fields was recorded at 8.38 pm,thereby falling beneath the threshold of twice the pixel size of the targeted detector.This level of performance signifies not only the system's acute resolution capabilities but also its potential for high-fidelity image capture,crucial for remote sensing applications.Furthermore,the system demonstrates a significant degree of energy concentration,with a maximum relative distortion measure of 1.88％,and a maximum wavefront error marked at 0.053λ.Impressively,the wavefront error across all visual fields remains superior to λ/18,thereby underscoring the system's exceptional optical performance and its alignment with stringent imaging standards.The completion of a tolerance analysis further corroborates the robustness of the system's imaging quality,affirming its capacity to fulfill the requisite performance metrics under a variety of operational conditions.This level of reliability is pivotal,especially given the harsh environments and the demanding nature of space deployments.The development of this compact,cost-effective off-axis three-mirror optical system represents a significant leap forward in the field of space optics,particularly for applications in remote sensing.By harnessing advanced optical design principles and leveraging the unique advantages of freeform surfaces,this study not only achieves remarkable improvements in system compactness and performance but also lays a solid foundation for future innovations in satellite imaging technology.The methodologies and insights gleaned from this research may well inform the design and optimization of next-generation space optical systems,driving further advancements in earth observation,environmental monitoring,and beyond.
Optical designOff-axis three mirrorFreeformLarge field of viewXY polynomialZernike polynomialSpace camera
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维普
