The military space program is a significant but largely unseen aspect of space operations. Nearly a dozen countries have some kind of military space program, but the U.S. program dwarfs the efforts of all these other countries combined.

Military space operations are divided into five main areas: reconnaissance and surveillance, signals intelligence, communications, navigation, and meteorology. Only the United States and Russia operate spacecraft in all five areas. Several other countries have long used communications satellites for military purposes. In the 1990s, several countries in addition to Russia and the United States began developing reconnaissance satellites.

Reconnaissance and Surveillance

Reconnaissance and surveillance involve the observation of Earth for various purposes. Dedicated reconnaissance satellites, like the United States's Improved CRYSTAL and the Russian Terilen, take photographs of targets on the ground and relay them to receiving stations in nearly real time. These satellites, however, cannot take...