Shijian

Shijian (simplified Chinese: 实践; traditional Chinese: 實踐; pinyin: Shíjiàn; lit. 'Practice', abbr. "SJ") is a series of satellites built and operated by the People's Republic of China. Some Shijian-series satellites have drawn significant concerns from the United States government and space observers who cite unannounced launches, undisclosed sub-satellites deployed in orbit, unusual orbital maneuvers, and demonstrated rendezvous proximity operations (RPO) including the close inspection and towing of other satellites.

Little is known about the series and what differentiates it from other experimental satellite series launched by China such as the Chuangxin (Chinese: 创新; pinyin: Chuàngxīn; lit. 'Innovation') series or Shiyan (Chinese: 实验; pinyin: Shíyàn; lit. 'Experiment') series. The China Aerospace Studies Institute of the United States Air Force asserts that Shiyan-series satellites play an earlier role in the systems development process testing various new technologies on a single bus while Shijan-series satellites are used to develop operational best practices and optimize the technologies previously tested on Shiyan-series satellites. In this regard, "Shijian" should be translated as "best practice", or "put into practice" while "Shiyan" ought to be translated as "experiment", "pilot", or "trial".