Early warning satellite

An early warning satellite is an artificial satellite that detects ballistic missile launches in order to provide rapid early warning of a potential missile attack. Modern examples are often multi-purpose vehicles also supporting other wide-area reconnaissance roles.

Early warning satellites normally use infrared sensors that detect the heat of the rocket engines on the missiles. These engines produce enormous amounts of heat that can be easily detected at very long range, through clouds or smoke. Looking down from above, the system provides warning as soon as the missile clears the silo, compared to radar systems which may have difficulty spotting the relatively small targets against the ground. Additionally, the IR detectors are entirely passive, making them more difficult to jam.

Among the major EWS systems are the United States' Defense Support Program, Russia's (originally launched while still the USSR Oko fleet, and the Chinese Tongxin Jishu Shiyan. The European Union has advanced plans for similar systems, but to date no fully operational system has been deployed.