PARIS — Mitsubishi Electric Co. (Melco) of Tokyo will lead a team to complete Japan’s Quasi-Zenith Satellite System (QZSS) to enhance the precision of the U.S. GPS positioning, navigation and timing satellites over the Pacific Ocean region under a contract valued at $539.4 million, the Cabinet Office of the Japanese prime minister announced.

The contract calls for Melco to build one geostationary satellite and two spacecraft to be operated in highly elliptical orbit to complete the QZSS space architecture by 2017.

The contract is valued at nearly 50.3 billion Japanese yen, or $539.4 million at current exchange rates. A separate contract, valued at 117.3 billion yen, will be signed with a special-purpose company led by NEC Corp. to operate the system, which combined with the lone QZSS satellite already in orbit will comprise four satellites. The operational contract is for 15 years.

Japan’s first QZSS satellite was launched in September 2010. The program slowed after that as it became clear that Japan’s private sector was unwilling to manage QZSS as a business without substantial government guarantees. The same hesitation derailed Europe’s Galileo global navigation system before its financing was made the sole responsibility of European Union governments.

Japan’s Secretariat of Strategic Headquarters for Space Policy, part of the government’s Cabinet, estimates that GPS-only signals that are available with precision only 90 percent of the time in Japan will be available 99.8 percent of the time with the QZSS overlay. QZSS will carry six civil signals.

The secretariat has told international positioning, navigation and timing conferences in the past two years that the GPS-only L1S signal has a 10-meter horizontal accuracy in Japan that will improve to 2 meters with the addition of QZSS.

In addition to augmenting the medium-Earth-orbit GPS constellation of 24 operational satellites, QZSS will be able to send short disaster-warning messages to anyone with a mobile telephone.

India is planning a similar regional GPS overlay of its own. In North America, the GPS signals are verified by terminals placed on commercial telecommunications satellites in geostationary orbit. A similar system is operational in Europe, and Russia is planning one as well.

Russia’s Glonass and the U.S. GPS are the only two global satellite navigation systems in operation now, although China’s Beidou program has launched 14 spacecraft; that system is operational over Chinese territory and will provide global service when completed. Europe’s Galileo is scheduled to enter global operations in 2014.

In its March 29 announcement, the Cabinet Office said Melco and NEC won the contracts following a competitive bidding process that ranked each bidder. Details of the rankings will be published at a later date, the office said.

Peter B. de Selding was the Paris Bureau Chief for SpaceNews.