Staff members work under the reflection panel of China's Five-hundred-meter Aperture Spherical radio Telescope (FAST) in southwest China's Guizhou Province, Aug. 28, 2019. China's FAST, the world's largest single-dish radio telescope, will greet the third anniversary of operation that began in September 2016. (Xinhua/Ou Dongqu)

Staff members conduct maintenance operation in the feed cabin of China's Five-hundred-meter Aperture Spherical radio Telescope (FAST) in southwest China's Guizhou Province, Aug. 28, 2019. China's FAST, the world's largest single-dish radio telescope, will greet the third anniversary of operation that began in September 2016. (Xinhua/Ou Dongqu)

The feed cabin of China's Five-hundred-meter Aperture Spherical radio Telescope (FAST) is operated to go down before receiving maintenance in southwest China's Guizhou Province, Aug. 28, 2019. China's FAST, the world's largest single-dish radio telescope, will greet the third anniversary of operation that began in September 2016. (Xinhua/Ou Dongqu)

Staff members conduct maintenance operation for China's Five-hundred-meter Aperture Spherical radio Telescope (FAST) in southwest China's Guizhou Province, Aug. 28, 2019. China's FAST, the world's largest single-dish radio telescope, will greet the third anniversary of operation that began in September 2016. (Xinhua/Ou Dongqu)

A staff member conducts maintenance operation in the feed cabin of China's Five-hundred-meter Aperture Spherical radio Telescope (FAST) in southwest China's Guizhou Province, Aug. 28, 2019. China's FAST, the world's largest single-dish radio telescope, will greet the third anniversary of operation that began in September 2016. (Xinhua/Ou Dongqu)

A staff member conducts maintenance operation for the reflection panel of China's Five-hundred-meter Aperture Spherical radio Telescope (FAST) in southwest China's Guizhou Province, Aug. 28, 2019. China's FAST, the world's largest single-dish radio telescope, will greet the third anniversary of operation that began in September 2016. (Xinhua/Ou Dongqu)

The feed cabin of China's Five-hundred-meter Aperture Spherical radio Telescope (FAST) is operated to go down before receiving maintenance in southwest China's Guizhou Province, Aug. 28, 2019. China's FAST, the world's largest single-dish radio telescope, will greet the third anniversary of operation that began in September 2016. (Xinhua/Ou Dongqu)

A staff member conducts maintenance operation in the feed cabin of China's Five-hundred-meter Aperture Spherical radio Telescope (FAST) in southwest China's Guizhou Province, Aug. 28, 2019. China's FAST, the world's largest single-dish radio telescope, will greet the third anniversary of operation that began in September 2016. (Xinhua/Ou Dongqu)

A staff member conducts maintenance operation for the reflection panel of China's Five-hundred-meter Aperture Spherical radio Telescope (FAST) in southwest China's Guizhou Province, Aug. 28, 2019. China's FAST, the world's largest single-dish radio telescope, will greet the third anniversary of operation that began in September 2016. (Xinhua/Ou Dongqu)