Surveillance or spy satellites may use optical imagery, radar, or radio signal interception to keep tabs on what is happening below. Some of these devices are highly maneuverable, allowing them to change their orbits in order to focus on a specific target. This capability makes these satellites especially challenging and popular subjects for satellite trackers. Flying in formations of three satellites together, the Flying Triangles intercept transmissions from ships at sea. Satellites have been used as navigation beacons since the launch of Transit-1B in 1960.
Many satellites perform scientific duties.
Some perform astronomical research or monitor the space environment. But many focus their attention here on Earth. They monitor our weather, making life-saving forecasts possible. Others measure the drift of continents, the temperature of oceans, the health of crops, or the migrations of wildlife. As our technology advances, the number of uses to which satellites are put continues to grow.