Solar UV Irradiance for Biological Exposure Experiments on the China Space Station

Exposure experiments that involve biological samples subjected to solar ultraviolet (UV) radiation (UVA, UVB, and UVC wavelengths) have advanced an understanding of biological responses in the harsh environment of space. These experiments provide insights about the role of such materials with regard to the origin and evolution of life and the development of protective strategies for long-term space habitation. A solar UV detector was developed to measure solar UV irradiance during exposure experiments as part of the Space Radiobiological Exposure Facility (SREF) on the China Space Station (CSS). This detector, which utilizes three SiC photodiodes, measures solar UV irradiance across three wavelength bands to determine UV doses received by exposed samples. Detector calibration is based on spectral solar irradiance data. From June 2023 to September 2024, the SREF completed three exposure missions that spanned a total duration of 465 days. Throughout these missions, the solar UV detector monitored the solar UV irradiance, which revealed periodic variations in the measured data that corresponded to changes in the solar beta angle and the CSS orbit. The cumulative radiation dose for the missions was 391 MJ m^-2 for UVA, 78.6 MJ m^-2 for UVB, and 30.1 MJ m^-2 for UVC.