Spaceborne lidar has a high orbit and wide observation range, which facilitates the accurate and rapid acquisition of large-scale three-dimensional spatial information. It is a key research area, both domestically and internationally. Spaceborne lidar has been increasingly used in marine remote sensing and topographic mapping. With the continuous development of China's space laser altimeter, the measurement accuracy has increased from 5.0 m to 0.3 m. The stability requirements of the optical-mechanical structure continue to increase and the measurement accuracy also increases at the same time. Simultaneously, the laser itself is also a highly sensitive component of the optomechanical instrument. There can be shape and position errors of the onboard interface owing to factors such as production, emission vibration, and changes in satellite temperature. These errors lead to a deviation in the optical axis of the laser altimeter. The traditional installation method considers the rigidity requirements of the instrument rather than the precision requirements. In this study, the core accuracy of the altimeter is considered to be the main optimization goal. The flexibility of the supporting structure is optimized to isolate a part of the deformation caused by the outside surroundings. This ensures that the optical accuracy of the laser altimeter is better than that of the traditional method.

This study designs the support structure of an altimeter based on the kinematic installation method. The rigidity of the optical plate of the laser altimeter is enhanced, and the rigidity of the supporting structure is reduced as much as possible while meeting the requirements of the satellite. Thus, most structural deformations caused by changes in the mechanical and thermal environments are isolated. The flexibility of the support structure is implemented by the arcuate hinge, and the parameters of the arcuate hinge are optimized to set reasonable flexibility. The structural deformation of the deck which is caused by the change in the mechanical and thermal environments is transmitted to the equipment by comparing their stiffness values. The carbon fiber composite honeycomb panel is equivalent to an aluminum panel with a certain thickness using the equivalent method. The relative stiffness of the instrument and deck at the installation point is obtained using finite element analysis. The range of the errors is set according to the temperature and structural deviation ranges provided by the satellite. The optical axis stability performance of the laser altimeter under the support structure designed in this study is obtained by stiffness calculation and statistical analysis of the errors. Mechanical and thermo-optical tests are designed to verify the conclusions of the analysis.

The stiffness ratio between the support structure and the optical plate is 1∶8 (Tables 2 and 3) by structural optimization. The test shows that the first-order frequency of the device reaches 88 Hz (Fig.7). The statistical analysis of the errors shows that the optical axis change of the laser altimeter is only approximately 8.5 μrad (Table 7) under the interference of the external environment. The analysis results above imply that the supporting structure designed in this study can satisfy the requirements of the structural rigidity of the satellite. Additionally, it can protect the optical performance of the laser altimeter from structural deformation of the platform. The change in the optical axis of the laser altimeter is approximately 30 μrad (Table 8) before and after the mechanical vibration. The mechanical stability of the structure satisfies the optical requirements. During the thermo-optical test, the optical axis stability of the device is about 8.5 μrad (Fig.8), indicating that when the environment temperature alternates between high and low boundaries (20 ℃±30 ℃), the support structure can absorb most of the thermal deformation to ensure optical stability.

There are shape and position errors in the onboard interface due to factors such as production, emission vibration, and changes in the satellite temperature. These errors lead to a deviation in the optical axis of the laser altimeter. To reduce the influence of errors in the onboard interface, this study designs the support structure of the altimeter based on the kinematic installation method. The support structure is optimized by stiffness analysis between the deck and the laser altimeter. The error distribution of the onboard interface is analyzed using the Monte Carlo statistical method, and the errors in the installation area are determined as the analysis inputs. The analysis and experimental results show that the first-order fundamental frequency of the designed support structure reaches 88 Hz, the change in the laser emission-receiving optical axis caused by installation is approximately 8.5 μrad, and the change before and after mechanical vibration is 30 μrad. The thermo-optic test shows that the optical axis stability is 8.5 μrad between the high- and low-temperature boundaries. The designed support structure can satisfy the requirements of laser altimeter. The design ideas and test results in this study provide a reference for the design of similar type of laser load on satellites.