Boeing [BA] will wrap up production of its three remaining Global Positioning System (GPS) IIF satellites by the end of 2013, according to a company spokeswoman.

Boeing is under an Air Force contract for 12 GPS IIF satellites, three of which have been launched into service with a fourth on deck for launch in the second quarter of 2013, company spokeswoman Paula Shawa said in an email. Shawa said the satellites that wrap up production this year began construction in the second quarter of 2012. Shawa said Boeing currently has five GPS IIF satellites in storage.

The Air Force also recently awarded Boeing a $51 million, one-year contract with four one-year options. Shawa said the December 2012 contract covers GPS IIF satellite storage in a controlled environment, shipment to the launch site at Cape Canaveral Air Force Station, Fla., pre-launch preparation, post-launch checkout, handover and on-orbit support. The contract allows Boeing to continue modernizing the GPS constellation, according to a company statement.

Boeing GPS IIF Program Director Jan Heide said in a statement the company is capable of launching up to three GPS IIF satellites a year if required. The company last launched a GPS IIF satellite in October on one of United Launch Alliance’s (ULA) Delta IV rockets, despite an engine anomaly, which the Air Force is still investigating. ULA is a joint venture between Boeing and Lockheed Martin [LMT].

GPS IIF provides greater navigational accuracy through advances that include atomic clock technology, a new civilian L5 signal and an improved military signal.