The complex space camera in geostationary orbit experiences significant changes in external thermal flux, leading to large temperature variations within the camera. The thermal stability and uniformity of optical components directly affect the imaging quality, thus requiring a large amount of high-precision active thermal control to provide the optimal operating temperature conditions for the camera. Geostationary satellites have multiple functions and limited resources, so the design of the active thermal control system for large space cameras must satisfy high-precision temperature control requirements while also being integrated to meet constraints on weight and power consumption. However, the traditional architecture using central processing unit (CPU) and digital signal processor (DSP) as control units is not well-suited for high integration design requirements, and the high thermal control power requires power management to meet the energy requirements of the entire satellite.
This article analyzes the characteristics, difficulties, and index requirements of thermal design for large geosynchronous orbit cameras, and proposes an integrated electronic active thermal control scheme with field programmable gate array (FPGA) as the core control unit. By utilizing the high-speed parallel processing capability and rich interface resources of FPGA, the scheme achieves high integration and high precision active thermal control for complex space cameras. To meet the requirements of large dynamic range temperature measurement, the measurement error is quantitatively analyzed, and a polynomial correction method based on least squares is proposed to correct the temperature measurement error within a large dynamic range. To address the problem of multiple heating circuits and high temperature control accuracy, a differentiated temperature control strategy is designed, which combines high-speed open-loop temperature control and fuzzy incremental proportion-integration-differentiation (PID) temperature control. This enables the 108 main heating circuits of the camera and the blackbody temperature control to work collaboratively. A comprehensive reliability strategy is also developed to handle possible exceptional situations. To address the problem of high heating power, a thermal control power off-peak strategy is designed. The heating plates are controlled in a time-sharing manner, and the thermal control power is dynamically and continuously monitored to limit it within the set range while ensuring the temperature control accuracy of the key components such as the camera’s motion mechanism, optical system, and compressor.
The thermal control precision, control strategy, and power management function of the active thermal control system for a large space camera in a geosynchronous orbit were tested through ground laboratory experiments and verified in orbit with temperature field changes and temperature control conditions. The ground precision resistance was measured, and the temperature accuracy was found to be -0.186?0.363 K within a temperature range of -120?100 °C (Fig.5), which is better than the required accuracy of ±0.5 K. The in-orbit temperature field and temperature gradient changes (Table 5 and Fig.6) within a year meet the component’s working temperature and temperature gradient requirements, verifying the rationality and correctness of the active thermal control system design. The control precision of the camera during a 7-h heating period in one orbit was measured, and the temperature accuracy was found to be better than ±1 K, with a standard deviation of less than 0.5 (Table 6 and Fig.7). The obtained accuracy is better than the required accuracy of ±1 K. The power management function effectively limits the camera’s thermal control power consumption in the set range (Fig.8).
An active thermal control system for a large space camera in geostationary orbit is designed, with the camera instrument management unit FPGA as the core control unit. To address the large dynamic range of temperature measurement, a polynomial correction method based on least squares is proposed to correct temperature measurement errors in a wide dynamic range. To address the issue of high heating circuit count and precision control requirements, a differentiated temperature control strategy is designed that combines high-speed open-loop temperature control and PID temperature control. This strategy enables the 108 camera body heating circuits and the blackbody temperature control to work together. A comprehensive reliability strategy is designed for possible abnormal situations. To address the problem of high heating power, a thermal control power off-peak strategy is designed to limit the heating power in a set range while ensuring the temperature control accuracy of critical components such as the camera’s motion mechanism, optical system, and compressor. Ground-based tests show that the temperature measurement accuracy in the range of -120?100 ℃ is between -0.186?0.363 K, which is better than the requirement of ±0.5 K. In-orbit temperature field changes have validated the rationality and correctness of the active thermal control system, with a main body temperature control accuracy of better than ±1 K, and the power off-peak function effectively limits the camera power consumption in the set range. The space camera has been operated in orbit for six years, and the in-orbit active thermal control system has been working stably, meeting the needs of long-term, high-performance operation of large cameras in orbit.
