PARIS — Nearly two years of uncertainty about where the next-generation GPS satellite augmentation payload would find a home in geostationary orbit has apparently ended with an updated agreement between satellite fleet operator Satmex and GPS augmentation contractor Raytheon Integrated Defense Systems.

As a result, a Raytheon-produced payload to maintain the Wide-Area Augmentation System (WAAS) capability over the Americas will ride aboard Mexican satellite fleet operator Satmex’s Satmex 9 satellite, scheduled for launch in late 2015.

Fullerton, Calif.-based Raytheon and Satmex had originally struck an agreement in mid-2012 to put the WAAS payload on Satmex 9. The agreement followed the March announcement by Satmex that it was ordering two all-electric-propulsion satellites from Boeing Space and Intelligence Systems of El Segundo, Calif., as part of a four-satellite deal that included two other Boeing-built satellites for Asia Broadcast Satellite of Hong Kong.

The four satellites are to be launched in pairs aboard Space Exploration Technologies Corp. Falcon 9 rockets, with the first pair to launch in early 2015.

But Satmex’s commitment to the second of its two satellites was not as firm as it appeared at the outset. Satmex, whose financial situation was precarious — the company has since been purchased by Eutelsat of Paris — was uncertain about the business case for the second satellite and withheld final commitment until mid-2013.

U.S. Federal Aviation Administration (FAA) documents at the time said Raytheon had been having trouble finding a Satmex replacement.

By July 2013, however, Satmex was able to confirm the Satmex 9 order with Boeing. On Dec. 12, the company signed an updated agreement with Raytheon with the same basic terms as the previous deal, Satmex said Feb. 10 in a filing with the U.S. Securities and Exchange Commission.

Raytheon and the FAA in September 2012 signed a contract under which Raytheon would be responsible for finding satellite hosts for two WAAS payloads, called GEO 5 and GEO 6, to succeed the current WAAS payloads covering North America.

Using payloads on satellites in geostationary orbit 36,000 kilometers over the equator, the WAAS system validates the accuracy of the signals sent by the constellation of GPS positioning, navigation and timing satellites in lower-medium Earth orbit. These payloads also relay the corrected signals to GPS-equipped platforms, including aircraft.

WAAS is currently maintained with payloads on the Intelsat Galaxy 15 satellite, Telesat’s Anik F1R and Inmarsat’s I4 F3 spacecraft.

The Raytheon contract was valued at $249.7 million for two 10-year leases aboard geostationary-orbiting host satellites, which were scheduled to be operational by July 2015 and July 2018, according to the FAA.

Raytheon spokeswoman Cynthia Baker said in a Feb. 13 email that the original contract terms remain valid despite the hiccups with Satmex in securing a firm commitment.

Baker said Raytheon is “still in the process of selecting a candidate satellite for GEO 6 from several options.”

The 10-year lease contract with Satmex would begin in September 2017, assuming no delays in the satellite’s launch and deployment. As an all-electric satellite using Boeing’s xenon-ion propulsion system to power its way from the Falcon 9 rocket’s drop-off point to final geostationary position, Satmex 9 will spend several months in transit before reaching its final operating position at 116 degrees west longitude.

It will then take as much as a year to fully integrate the Satmex 9 WAAS payload into the GPS-augmentation network, which consists of 38 monitoring stations installed in the United States, Canada and Mexico, three master stations and  six Earth stations communicating with three operational WAAS satellite payloads.

WAAS-equivalent systems are in operation over Europe, Russia, Japan and China.

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