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Defense to improve GPS receivers: US Congress

US: In a report, the US Congressional Budget Office (CBO) suggested that the Defense Department should scale back its plans for next generation GPS satellites and instead invest in and quickly deploy upgraded jam-resistant GPS receivers. By this approach, the CBO estimated that as much as USD 3 billion can be saved over the next two decades.

The report, “The Global Positioning System for Military Users: Current Modernization Plans and Alternatives,” acknowledged that the options it presents would degrade location accuracy to a small degree, but the authors said an alternative approach would put improved receivers in the hands of troops eight years earlier than the Defense Department’s current plans would allow.

The military GPS system consists of at least 24 satellites in orbit at a time, a ground control system based at Schreiver Air Force Base, Colorado, and 400,000 receivers capable of picking up encrypted, military-grade signals from the satellites.

Though each of these segments needs to work together to take full advantage of the encrypted military signals and their anti-jam capabilities, the CBO report portrayed a disjointed effort with not much synchronization.

For example, the Air Force launched the first GPS satellite with an anti-jam military signal in 2005 and now has 10 in orbit, but Defense does not plan to field receivers capable of picking up that signal until 2017. The department will not replace all 400,000 military receivers (350,000 handheld units used primarily by the Army and Marines, with a number wired into vehicles) until 2030.

The upgrades to the ground control segment that are needed to manage the most advanced next-generation GPS satellites will not be completed until 2016, according to CBO.

In May 2008, the Air Force awarded Lockheed Martin Corp. a USD 1.8 billion development and production contract for the GPS III next-generation satellites, which will be delivered in three blocks, with each block providing improvement over its predecessor. The CBO suggested Defense focus its satellite dollars on the first block, IIIA, and drop the other two blocks, particularly the last, IIIC, which will include steerable spot beams to focus a high-powered signal on a spot on Earth 600 miles in diameter.

The budget office also suggested three options to current Defense plans for the GPS system, all of which would use the block IIIA satellites:

Option 1
Equip military GPS receivers with new antennas capable of rejecting signals from jammers and add an inertial navigation system, which uses motion sensors coupled with computers to determine location. The CBO explained this option could cut jammer interference by 97 percent. By 2018, Defense could begin deploying anti-jam receivers capable of picking up the M-code (the encrypted military code designed to improve jam resistance of GPS receivers). The budget office calculates this approach would shave USD 2 billion off the estimated USD 22 billion cost to develop all three GPS blocks and upgrade the control segment.

Option 2
Use the Iridium satellite system to Enhance GPS. This option would use the commercial Iridium satellite system to relay data from one or more of its 66 satellites to military GPS receivers to direct them to GPS satellites, thereby speeding GPS signal acquisition and improving accuracy. This option also envisions the use of inertial navigation and would result in receivers that could be deployed by 2018 that would reduce jammer interference by 99.7 percent, CBO said.

The budget office estimated that using Iridium to enhance GPS would cut USD 3 billion from the projected USD 22 billion system upgrade cost, but cautioned this approach assumed the continued operation of the Iridium system.

Option 3
Combine Options 1 and 2. This would result in jam resistance of 99.9 percent and save USD 1 billion, according to CBO. Relying only on the block IIIA satellites would save USD 4 billion from development of the other two blocks and associated upgrades to the ground control segment, the budget office estimated.

Source: Nextgov