KH-11 satellites, also code-named KENNAN and CRYSTAL, were the first U.S. imagery intelligence space vehicles to digitize the pictures they take, and transmit them, in real time, to Earth. The first was launched in 1976 and the last in 1988. They also carry signals intelligence receivers, and were believed be SIGINT-only satellites until a low-level Central Intelligence Agency employee, William Kampiles, sold the technical manual to the Soviet Union in 1978.
Besides having a real-time capability, the satellites have a much longer operational lifetime, not limited by the supply of photographic film. This also frees payload to be used for more maneuvering fuel. They are operated by the National Reconnaissance Office, their imagery is analyzed by the National Geospatial-Intelligence Agency, and their SIGINT by the National Security Agency.
CRYSTAL may refer to the advanced KH-11 satellites with integrated infrared, as well as visual light, imaging. CRYSTAL may, alternatively, refer to KH-12/IKON systems. Some variants may use the cancelled MISTY stealth technology.
The optics have been described as similar to that of the Hubble Space Telescope, but pointing down rather than up. While the true resolution is not public, estimates in the 125-150mm (5-6") range are common, with some going into the 75mm/3" range.