As the sophistication of national deep space exploration missions increases, the demand for high-precision exploration of extraterrestrial galaxies is increasing day by day. Taking the lunar exploration as an example, the lunar exploration project has planned specific tasks to acquire high-resolution three-dimensional (3D) terrain maps of the lunar surface. The high-precision optical stereo mapping camera is the key payload for achieving stereoscopic mapping of the lunar surface. In the deep space exploration domain, mapping cameras are required to withstand face far more rigorous challenges during both the launch and operational phases compared to Earth-orbiting satellites. As highly sensitive and complex precision aerospace equipment, extremely harsh conditions impose higher demands on the critical process of optical alignment for deep space exploration mapping cameras. To address these stringent conditions, adaptive responses are made in the structural and optical design of these cameras. Currently, there are only a few similar payloads successfully launched and operational worldwide, and their image resolutions are generally not high. Among them, the narrow angle camera carried by national aeronautics and space administration (NASA)’s lunar-reconnaissance-orbiter (LRO) is the one with the most comparable performance. Therefore, it is essential to study optical alignment processes of such cameras to ensure their excellent in-orbit performance after precise alignment.

Based on these characteristics of deep space optical mapping cameras, which include high integration, high lightweight design, and multiple boundary condition constraints, the force, thermal, and optical simulation analyses of these key components for the system are carried out. A dual-camera co-referenced alignment and detection scheme based on computer-aided adjustment has been proposed. A simulation model for sub-components is established, with adhesive shrinkage stress and forced displacement stress as objective functions. This enables targeted thermal and mechanical analyses of the primary and secondary mirror assemblies (Fig. 3, Fig. 4). Based on these thermal-mechanical analysis results, these coupling risks between surface deformation of the primary/secondary mirrors and system misalignment are prioritized. An optical simulation model is further developed to analyze distinctions caused by surface deformation and misalignment of the primary and secondary mirror assemblies (Fig. 6, Fig. 7). In order to ensure the precise alignment of the optical axes of two cameras under constrained conditions, the control of lens optical axis pointing should be managed at the optical design and optical manufacturing stages. Specifically, the optical axes of each reflective mirror need to be precisely extracted. Taking the primary mirror as an example, a null-compensator-testing based self-aligning optical axis extraction method has been proposed and applied to the high-precision extraction for the optical axis of the reflector (Fig. 8). Through comprehensive full-chain simulations that take into system aberration, optical axis, and distortion, these key variables for controlling distortion are identified (Table 3). These key variables enable iterative adjustments to achieve distortion compensation.

Using the aforementioned alignment methodology, strict control is implemented during the assembly of each reflector component. Surface shape test results for the primary and secondary mirrors before and after adhesive bonding are provided. Surface shape root mean square (RMS) of primary mirror remains stable at 0.02λ pre- and post-assembly (Fig. 9). Surface shape of secondary mirror RMS increases slightly from 0.013λ to 0.015λ post-bonding (Fig. 10). After initial system integration via the co-rotational alignment method, RMS of wavefront errors at three normalized fields are 0.106, 0.060, and 0.144, respectively (Fig. 12). Computer-aided alignment optimization further reduces these values to RMS of 0.087, 0.068, and 0.085 (Fig. 13), approaching the diffraction limit because of these residual high-order aberrations from mirror fabrication. After alignment, the integration and testing of lens assembly and detector assembly are carried out. Average modulation transfer function (MTF) across three fields exceeds 0.15 at the Nyquist frequency. The internal orientation element and distortion of the camera are measured by the precision-angle-measurement method. Focal length deviation is less than 3.5‰ of design specifications, and full-field distortion is less than 3.5 μm. Boresight alignment error relative to satellite reference axis measured by theodolites is 1.92′ (design target: 0°).

We propose a co-referenced alignment and detection scheme for the space mapping camera used in deep space exploration. Based on ensuring that key optical performance metrics of the camera meet requirements, it can rapidly achieve precise control of critical parameters for a stereo mapping camera such as camera boresight and distortion. By establishing thermal and mechanical simulation models for key components, and combining traditional computer-aided alignment method, the stress-free assembly of the secondary mirror is identified as a critical step in the alignment of a single-camera system. High-precision extraction of the optical axis for each reflective mirror is brought forward to the optical design and manufacturing stages, and a method based on null-compensator-testing for the optical axis is proposed and applied, thereby improving the initial alignment precision and the angle control precision between two cameras. A multivariable full-link simulation model is established to simultaneously meet these high-precision requirements for the angle between two cameras’ boresights and the system distortion. Ultimately, the alignment and testing of a spaceborne mapping camera for deep space exploration are successfully completed, with all performance metrics meeting required standards. This achievement addresses the challenging issue of optical alignment for lightweight, deep space cameras under multiple boundary constraints. It provides a technical foundation for the development of stereoscopic mapping cameras in future deep space exploration missions.