The Moon-based Two-Channel Spectrometer, an international payload jointly developed by China and France, is planned to be onboard the Chang'e-7 orbiter. This instrument features a broadband observation channel covering 0.2–50μm and a longwave observation channel covering 5–50μm, enabling the measurement of Earth's outgoing broadband and longwave radiation from lunar orbit. The shortwave radiation can be derived by differencing the broadband and longwave measurements. The instrument is equipped with onboard calibration blackbodies for longwave calibration of both channels; however, due to constraints in power consumption and volume, no onboard shortwave calibration source is included for the broadband channel. To enable on-orbit shortwave calibration, this study proposes the concept of a solar calibrator, which, together with an optical aperture, forms the shortwave calibration module of the Moon-based Two-Channel Spectrometer. This paper first introduces the overall design and specifications of the lunar-based dual-channel Earth radiance spectrometer. Then, based on the operating principle of a thermistor-type radiometer, a theoretical model of the solar calibrator is established. To further ensure on-orbit calibration accuracy, pre-launch experimental calibration methods for the solar calibrator are studied. A radiometric power calibration method using a laser source and a low-temperature radiometer is proposed, as well as an irradiance calibration method using a solar simulator and the SIAR-2C absolute solar radiometer. Furthermore, experimental methods and correction models are developed to quantitatively describe the effects of temperature and angular characteristics on the radiometric calibration coefficient, providing support for the ground validation and in-orbit application of the solar calibrator.
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