The first military space mission was reconnaissance, and that remains the most important mission, offering capabilities that cannot be obtained by any other means. A number of countries possess military satellite reconnaissance systems, including the United States, Russia, France (in cooperation with Germany, Italy, and Spain), and Israel. China apparently has abandoned its reconnaissance satellite system. Japan has plans to develop an extensive reconnaissance satellite capability, and Canada, India, and Brazil operate "civilian remote sensing satellites" that have limited military uses. Since the late 1990s several private companies have offered to sell satellite imagery of increasingly high quality. Virtually any country can now buy detailed pictures of any place it wants to see.

At the most basic level, reconnaissance involves looking at an area of Earth to determine what is there. Among the ways this can be done from space, the primary methods are visual and radar reconnaissance...