TH 1 (Tianhui-1 = "Sky drawing") is a Chinese stereo-topographic mapping satellite operated by the People?s Liberation Army (PLA).
The satellites are built by the Hangtian Dongfanghong Weixing Corporation and the China Aerospace Science and Technology Corporation and the Chinese Academy of Space Technology (CAST). The satellites operate on a 500 km circular sun synchronous orbit. Electrical power is provided by two deployable solar panels that is stored on onboard batteries.
They are equipped with a three-dimensional survey camera and a CCD camera with a ground resolution of 5 meters, spectral region of 0.51 µm to 0.69 µm and with a camera angle of 25 degrees. Also on board is a multi-spectral camera with a ground resolution of 10 meters operating in four spectral bands of 0.43 µm to 0.52 µm, 0.52 µm to 0.61 µm, 0.61 µm to 0.69 µm, and 0.76 µm to 0.90 µm. The swath width of the cameras is 60 kilometers wide.
The Tianhui-1 satellites are part of the Ziyuan program that cover different civil and military earth observation as well as remote sensing programs. The ZY-1 program is focused on Earth resources and looks to have two distinct military and civil branches (this one being operated together with Brazil). These satellites are operated jointly by the Center for Earth Operation and Digital Earth (CEODE) and the Brazilian INPE (Instituto Nacional de Pesquisas Espaciais, National Institute of Space Research).
The ZY-2 program are reportedly used for aerial surveillance and are operated by the People?s Liberation Army (PLA). The ZY-3 series are used for stereo mapping and are operated by the State Bureau of Surveying and Mapping. There have also been indications that the development of Tianhui-1 program was merged with the Ziyuan-3 project planned for launch in 2011.
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