Vertical Alignment Technology for Large-Aperture Space Optical Remote Sensing Cameras

With the advancement of international remote sensing technology, the effective aperture of China’s space remote sensing cameras has gradually increased, accompanied by rising demands for production efficiency. Consequently, the alignment methods and manufacturing processes for these cameras must continually evolve. Due to the significant gravity-induced deformation of large-aperture cameras in the horizontal optical axis state, which cannot be ignored, this paper proposes a vertical optical axis alignment technology. This approach addresses key challenges such as precise assembly and positioning of large-aperture mirrors, elimination of gravity-induced errors, and extraction of the optical axis reference in the vertical state, ensuring alignment accuracy while improving efficiency.

Figure 1: Key Processes and Core Technologies of Vertical Alignment Route

Additionally, the article introduces intelligent alignment units. Practical applications demonstrate that adopting this technical framework enhances pre-assembly precision, shortens development cycles, and resolves issues such as difficulties in detecting the optical axis reference in the vertical state and ensuring consistency between ground alignment results and in-orbit performance.

The Optical Alignment process of remote sensing cameras is a critical step in their development, encompassing all assembly and adjustment procedures from components to fully integrated optical-mechanical systems. The alignment quality directly impacts the final imaging performance. In recent years, China has completed numerous specialized remote sensing missions, achieving meter-class apertures for in-orbit cameras with excellent alignment results. Traditional horizontal optical axis alignment methods, with alignment cycles of approximately 90 days per camera, sufficed for low-volume, customized missions. However, as commercial remote sensing systems—such as the "16+4+4+X" large-scale satellite constellations—become mainstream, the traditional R&D model faces challenges, including prolonged production cycles and low automation, failing to meet high-volume alignment demands.

To address the requirements for future large-aperture cameras and batch production, vertical alignment technology effectively mitigates gravity deformation caused by camera weight and extended cantilevers. 

To achieve high-efficiency manufacturing of large-aperture cameras, it is essential to shorten alignment cycles, ensure consistency, identify and overcome core alignment challenges, optimize processes, and establish intelligent alignment units.

High-Precision Assembly Technology for Large-Aperture Mirror Components
A novel "discrete" support method is employed to achieve highly reliable, lightweight fixation of large-aperture mirrors. This involves bonding thermally matched blocks to the mirror’s back or side support points, connecting them to flexible support structures, and constraining all six degrees of freedom.
To ensure positional accuracy between support pads and the mirror, a 3D coordinate-based open-space rigid body positioning method is used. Nominal support pad positions from the design model are referenced in the coordinate system, and a six-axis adjustment device precisely aligns and fixes the pads. Finally, optical-mechanical adhesive is uniformly injected to solidify the structure. Figure 2 illustrates the assembly result.

Figure 2: Support Pad Assembly for GEO-Eye2 Camera Mirror

Gravity Error Elimination Technology
This technology involves finite element modeling of the mirror and its support structure to analyze gravity-induced deformation. The mirror assembly is flipped 180° vertically, and surface parameters are measured in both orientations. By comparing experimental data with simulation results, true gravity errors are identified and removed. Figure 3 shows surface measurements before and after error elimination.

Figure 3: Gravity Error Detection and Elimination. (a) Measured surface with gravity errors; (b) Surface after error removal

Optical Axis Reference Extraction Technology
By strategically positioning 2-3 laser trackers and multiple target ball mounts, spatial coordinates of six reference points around the camera are simultaneously measured. This links the positions of four instruments, establishing spatial relationships between the focal plane, optical axis, view axis, and camera reference mirror to extract the optical axis reference.

Figure 4: Schematic of Optical Axis Reference Extraction

For future batch production, intelligent alignment systems are critical. For example, an "Optical Surface Intelligent Detection Unit" automates surface inspection (Figure 5). In lens alignment, system aberrations are analyzed to calculate optimal positional adjustments for Optical Components via iterative control, achieving precision without manual intervention, thereby improving efficiency and consistency.

Figure 5: Schematic of Intelligent Mirror Surface Detection System

Conclusion

The breakthroughs in vertical alignment technology and the development of intelligent alignment units are applicable to future medium- and large-aperture remote sensing cameras, meeting diverse alignment needs—especially for high-volume missions like low-orbit dense constellations.

Additionally, the core algorithms for intelligent alignment leverage computer-aided techniques to compute globally optimal relative positional deviations of optical components based on system aberrations. High-precision six-degree-of-freedom platforms then adjust component poses. This technology extends beyond remote sensing to fields such as astronomy and aviation.

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