Other Global Navigation Satellite Systems
GPS is sometimes referred to as a global navigation satellite system (GNSS). For many years, it was the only fully operational GNSS. Russia operates another operational GNSS known as GLONASS. The European Community and China are currently developing their own GNSS capabilities.
GLONASS
Russia has operated GLONASS since the 1980s. It is similar in design to GPS, but based on different technical standards. Like GPS, GLONASS offers a civilian service for peaceful worldwide use, free of direct user charges, and an encrypted military service. In the 1990s, the GLONASS constellation deteriorated, making the system less popular among users. Russia has prioritized the modernization of GLONASS and restored it to a 24-satellite constellation in 2011. The United States is cooperating with Russia towards GPS-GLONASS interoperability, both for enhanced PNT and combined search and rescue capabilities.
Galileo
The European Commission announced plans to develop an independent GNSS in 1999. Galileo is intended to be a primarily civilian system. It will offer an open (free) service, a commercial service, and a public regulated service designed for security applications. Current plans are to achieve operational status around 2015. Under a cooperative agreement signed in 2004, the United States and the European Community have designed common signals to be transmitted by both GPS and Galileo, enabling interoperability at the user level.