The Congressional Budget Office wants the Defense Department to scale back its plans for next generation Global Positioning System satellites and instead invest in and quickly deploy upgraded jam-resistant GPS receivers, an approach CBO estimates could save as much as $3 billion over the next two decades. The budget office described its findings in a report released Oct. 28.
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, Colo., 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 $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.
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:
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.
CBO said 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 $2 billion off the estimated $22 billion cost to develop all three GPS blocks and upgrade the control segment.
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 $3 billion from the projected $22 billion system upgrade cost, but cautioned this approach assumed the continued operation of the Iridium system.
Combine Options 1 and 2. This would result in jam resistance of 99.9 percent and save $1 billion, according to CBO.
Relying only on the block IIIA satellites would save $4 billion from development of the other two blocks and associated upgrades to the ground control segment, the budget office estimated.
Drawbacks to CBO's Approach
The downside to all three options is that U.S. troops would have to carry larger and heavier receivers, CBO said. New antennas and associated electronics would add four and a half pounds to a handheld unit that now weighs one pound, although component miniaturization could eventually lower that weight.
Today's GPS receivers can determine location within 10 feet, and Defense aims for position accuracy within six inches under its GPS III plan. The first CBO option -- improving receivers and adding inertia navigation -- would reduce position accuracy to three feet and the Iridium option could determine location within eight inches, the report said.
While the Defense plan would provide greater navigational accuracy, CBO said an appreciable number of M-code receivers capable of such accuracy would not be fielded until 2026. "The fielding of ancillary devices to augment existing military GPS receivers could begin in a few years, with appreciable numbers of improved receivers in the field by 2018. Consequently, the options could increase the military's anti jamming capability eight years before large numbers of M-code receivers could be in the hands of military users under [the Defense Department's] plan," the CBO report said.