GPS for Military Users: Current Modernization Plans and Alternatives

October 28, 2011

The U.S. military has come to rely on the Global Positioning System (GPS) to conduct many of its operations. The Department of Defense (DoD) is modernizing the system—in part to better counter deliberate interference—by purchasing new satellites and upgrading the systems that control the satellites.

In a study prepared at the request of the former Chairman of the Defense Subcommittee of the House Committee on Appropriations, CBO considers the implications of modernization plans for military users and assesses how those efforts are synchronized with DoD’s efforts to improve the capabilities of its GPS receivers. The study also examines three alternatives for improving the performance of the GPS for military users and estimates the budgetary consequences of those options as well as their effect on the ability of the GPS to operate in an environment where an opponent is trying to jam GPS signals.

Results in Brief

As DoD’s GPS satellites reach the end of their service lives, the department plans to replace them with ones that can counter deliberate interference by generating stronger signals. After examining DoD’s plan and other possibilities for upgrading the system, CBO finds that:

  • It will cost DoD roughly $22 billion from 2012 to 2025 to modernize the GPS under its plan.
  • An alternative approach—namely, improving military receivers to retain the GPS signal even in the presence of such jamming—would be less expensive than DoD’s plan for upgrading its constellation of GPS satellites by improving the signals.
  • Depending on how that alternative approach would be implemented—CBO examined three options—savings would be between $1 billion and $3 billion. The alternative approach would also yield benefits almost a decade earlier than DoD’s plan.
  • The alternative approach has some disadvantages, however. The improvements to military receivers could make them larger and heavier (and thereby less useful to personnel operating on foot) until they could incorporate the substantial gains that have been achieved in miniaturization in other applications.

DoD’s Plan Would Improve Antijamming Capabilities Through Stronger Signals At A Cost of $22 Billion

The GPS uses a constellation of at least 24 satellites, each of which transmits precise data on the time and its location. Receivers—both military and civilian—use the data transmitted by the satellites to calculate their own position. Since 1995 (when GPS became fully operational), the U.S. military has come to rely on the system to precisely locate both enemy and friendly forces, but the system can easily be swamped by interference.

In 2000, DoD initiated plans to reduce the system’s susceptibility to intentional interference or “jamming.” As a first step, DoD decided that GPS satellites would transmit additional signals, available only to military users, each of which covered a wider range of frequencies. Those signals, called M-code signals, are more difficult for enemy jammers to overwhelm and can improve the ability of military receivers to operate in the presence of jammers. Ten satellites capable of transmitting M-code signals were already in orbit as of August 2011.

Plan for the Next Two Decades: To maintain the constellation as existing and new satellites reach the end of their service lives, DoD plans to launch a total of 50 satellites through 2030 starting in 2012. Of those 50, the department has already purchased—but not yet launched—10 GPS satellites capable of transmitting M-code signals. DoD plans to acquire 32 more satellites—known as GPS III—that are capable of transmitting stronger M-code signals over the next 10 to 15 years. The new satellites—models include the IIIA, IIIB, IIIC—will increase the M-code signals by varying amounts and be developed and purchased in three phases. CBO expects that the department would need to purchase an additional 8 IIIC (above the 32 planned) satellites in order to have enough IIIC satellites in orbit to take advantage of its advanced capabilities (which include the ability to focus the M-code signals in a “spotbeam”).

Over the next 15 years, DoD also plans to develop software to control the M-code signals and the new GPS III satellites and to develop and purchase receivers that are capable of processing the M-code signals. DoD plans to have a new control system fully in place by the end of 2016. To make the entire planned system functional, however, additional control capabilities will need to be developed which may take many years beyond that time.

Cost: CBO estimates that it will cost DoD roughly $22 billion from 2012 to 2025 to complete this modernization of the GPS. That total would include the cost from 2012 onward to develop and purchase the 40 GPS III satellites (including $3.6 billion for the additional 8 IIIC satellites), to develop the software and capability needed to control those satellites and their signals, and to develop and purchase hundreds of thousands of military receivers capable of receiving and interpreting the M-code signals.

The Government Accountability Office and the Defense Science Board reviews of DoD’s plan raised several concerns, particularly regarding the plan’s focus on improving the satellites rather than the receivers and a lack of coordination in the plan in terms of the timing for improvements in satellites, control systems, and receivers. CBO has developed options by which it explores those concerns.

Options Would Provide Antijamming Improvements Sooner and At A Lower Cost

CBO examined three options that would provide antijamming improvements to military users sooner and at a lower cost than DoD’s plan. Those options focus more on improving the performance of receivers in a jamming environment and less on strengthening the signal that the GPS satellites transmit. Compared to the estimated $22 billion cost for DoD’s plan, CBO estimates that:

  • Option 1 would save $2 billion by improving current military GPS receivers by fitting them with better antennas and by adding inertial navigation systems.
  • Option 2 would save $3 billion by capitalizing on a DoD research and development program that enables current GPS receivers to integrate information received via the Iridium commercial communications satellite network (through a program known as High Integrity GPS, or iGPS).
  • Option 3 would save $1 billion by including the improvements of both Option 1 and Option 2.

Three items are common to all of the options and account for the bulk of the costs—nearly $18 billion. First, DoD would purchase 40 GPS III satellites (the same number as in DoD’s plan) but confine those purchases to the IIIA model. Second, under DoD’s plan as well as all the options, DoD would continue to develop the ground control system. And third, DoD would develop and purchase M-code-capable receivers in the same numbers under its plan and all three options.

Savings are primarily generated from canceling the IIIB and IIIC portions of the GPS III program; however, those savings would be partly offset by the cost to make improvements to the receivers under the three options.

Advantages of the Options

Compared with DoD’s plan, the options would yield greater improvements in reception and would yield improvements sooner. The options could increase the military’s antijamming capability in 2018, eight years before significant improvements would be realized under DoD’s plan (in 2026) when large numbers of M-code receivers could be in the hands of military. The technologies included in CBO’s options—those for improved antennas for GPS receivers, small inertial navigation devices, and iGPS—have already been developed.

Additional advantages of Options 2 and 3 come from augmenting the GPS constellation with the Iridium satellites in low-earth orbit. That fuller coverage would virtually ensure that receivers had a line of sight to at least one satellite, even in mountainous terrain and urban settings. In addition, because data can be received and updated frequently, receivers using iGPS can determine their position with almost the same accuracy as would be possible using data from IIIC satellites.

Disadvantages of the Options

All of the options would require additional power and hardware additions to existing receivers, making the devices bulkier and less convenient—especially for those on foot. Another disadvantage common to the options is that they would forgo the improvements offered by the IIIC satellites, so military (and civilian) users would not benefit from the increased power of the M-code signals within the spotbeam and the increased precision in positioning. A final disadvantage shared by Options 2 and 3 is the dependence on the commercial Iridium satellite constellation and support network, which is not controlled by DoD.

This study was prepared by Frances M. Lussier and Christopher Murphy of CBO’s National Security Division.