Boeing will modernize the U.S. Air Force GPS network, including software and systems affecting its constellation of satellites amid increasing competition in space and concerns over global security.

Global Positioning Systems have proved extremely useful in less than half a century but concerns over hacker malware threats and terrorism have made GPS a high priority.

Although managed by the Air Force, the U.S.-led GPS network is free to use but requires constant investment to keep it up to date with competing systems already in space or trying to get there.

China is expanding its rival GPS-like network, Russia has deployed its own variety, the European Union is developing its version and other space-bound powers all have ambitions to compete rather than collaborate.

In addition, GPS and similar systems are under threat from "spoofing" attacks that involve an individual or computer program masquerading as another by falsifying data and thereby gaining an illegitimate advantage.

Spoofing presents huge risks to business, defense and security and societies on the whole. Scientists say the capture of a Lockheed RQ-170 drone aircraft in Iran in December 2011 resulted from a spoofing attack.

The Boeing Co. said Tuesday it will continue modernizing the GPS satellite constellation for up to five more years, extending the company's role in the vital military and civilian navigation network.

The Air Force recently awarded Boeing a $51 million, one-year contract with four one-year options. The contract covers GPS IIF satellite shipment to the launch site in Florida, pre-launch preparation, post-launch checkout, handover and on-orbit support, Boeing said in a statement from El Segundo, Calif.

"The contract provides mission continuity for the Boeing GPS IIF fleet as we continue to deliver on our commitments," Boeing Space and Intelligence Systems Vice President and General Manager of Craig Cooning said.

"With nine GPS IIFs still awaiting deployment, the contract scope includes supplying all support needed until the Air Force calls for the vehicles," Cooning said.

Boeing has been part of GPS since the network's inception in the 1970s. The company has produced nearly 70 percent of the satellites launched in support of the GPS constellation.

Boeing says it is on contract for 12 GPS IIF satellites, three of which have been launched into service. The IIFs provide greater navigational accuracy through advances that include atomic clock technology, a new civilian L5 signal and an improved military signal.

The next IIF is to launch during the second quarter of 2013. Boeing will complete production of the remaining ones by the end of the year.

"We have the capability to maintain the remaining IIF spacecraft to be delivered and the flexibility to launch up to three within a single year if required to sustain the network," Boeing GPS IIF program director Jan Heide said.

Boeing Defense, Space and Security has headquarters in St. Louis.

Although now a modern and sophisticated technology, the GPS design is based on ground-based radio-navigation systems developed in the early 1940s and used during World War II.