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GPS Modernization: Space Force Should Reassess Requirements for Satellites and Handheld Devices

GAO-23-106018 Published: Jun 05, 2023. Publicly Released: Jun 05, 2023.
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Fast Facts

DOD has worked for years to upgrade GPS with a military-specific signal known as M-code. DOD plans to have the needed ground, space, and user equipment ready soon.

But it's unclear whether the current constellation of 24 satellites will meet some users' accuracy needs. Having 3 more satellites could help, but DOD may not be able to keep all 27 available consistently over the next decade.

Separately, DOD is working on new user equipment, including a new handheld GPS receiver. But the receiver will likely fall short of its performance goals, and military customers aren't committed to buying it yet.

Our recommendations address these issues.

person in military uniform holding a handheld GPS receiver

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What GAO Found

GPS is the principal source of positioning, navigation, and timing information for the U.S. military and its partners. The Department of Defense (DOD) has worked for more than 2 decades to modernize GPS with a more jam-resistant, military-specific signal known as M-code. Space Force, part of the Department of the Air Force, is responsible for GPS modernization.

The GPS system consists of three segments that cooperate to provide M-code: a ground control segment, a space segment, and user equipment.

  • Ground. In 2022, Space Force further delayed delivery of the ground control segment due to development challenges. This delay pushes delivery until December 2023 at a minimum. Space Force officials have not finalized a new schedule and acknowledged that remaining risks could lead to additional delays. GAO will continue to monitor Space Force's progress in adhering to its new schedule.
  • Space. Space Force met its approved requirement for 24 M-code-capable satellites on orbit, but determined that it needs at least three more to meet certain user requirements for accuracy. Building and maintaining this larger constellation presents a challenge. GAO's analysis indicates it is not likely that 27 satellites will be available on a consistent basis over the next decade. Unless the Air Force assesses its operational need for satellites to establish a firm requirement for a 27-satellite constellation, other DOD efforts could take priority, leaving the warfighter with GPS user equipment performing below the required capability levels.
  • User equipment. MGUE Increment 1 development progressed to the point where the military departments are ready to commence activities in support of testing and fielding it on the lead weapon systems. Delays and unexpected challenges could affect the fielding of capability for some systems. The figure below illustrates the integration process.

GPS User Equipment Integration

GPS User Equipment Integration

Space Force seeks to expand the use of M-code technology by developing a second increment consisting of an improved M-code chip and card, as well as a handheld receiver. Space Force lacks a major committed customer for the handheld receiver. The Army, the largest potential user of such a device, has its own plans for handheld receivers, and Marine Corps officials say the service is still considering its options. Without a sound business case for its proposed handheld product, Space Force risks expending significant resources without providing a benefit to military users.

Why GAO Did This Study

The Air Force launched the first GPS satellite capable of broadcasting the jam-resistant M-code signal in 2005. However, continued delays to the ground and user equipment segments prevent widespread use of the technology.

Congress included a provision for GAO to assess the cost, schedule and performance of GPS acquisition programs. This report assesses (1) risks and challenges to transitioning to a planned next-generation ground control system and how Space Force is mitigating them; (2) the extent to which Space Force identified and addressed risks affecting the space segment and delivery of M-Code capability; and (3) the progress DOD made in developing and integrating the M-code user equipment.

To conduct this work, GAO reviewed DOD's plans for GPS, its data on satellite reliability and launch schedules, and interviewed DOD officials.


GAO is making two recommendations to DOD: (1) assess the number of satellites necessary to meet operational needs, and (2) either develop a sound business case for the M-code capable Increment 2 handheld, or do not initiate the effort. DOD concurred with both recommendations.

Recommendations for Executive Action

Agency Affected Recommendation Status
Department of the Air Force The Secretary of the Air Force should ensure that the GPS program assesses whether an approved requirement for a 27-satellite M-code capable GPS satellite constellation is necessary to meet future operational needs. (Recommendation 1)
Closed – Implemented
In response to this recommendation, Air Force officials stated that they submitted a proposed clarification to the official GPS User Segment requirements document. This clarification would serve to ensure all GPS requirements documents are aligned across user equipment, M-Code satellites, and civilian signals. On August 3, 2023, the Vice Chairman of the Joint Chiefs of Staff signed a Joint Requirements Oversight Council Memorandum that approved the requirements modification. The modification itself reduced user equipment requirements to the level of accuracy delivered by a 24-satellite constellation. The mission of JROC is to assess joint military capabilities and to establish and approve joint performance requirements. DOD submitted this document to us in September 2023. After reviewing it, we consider this memorandum to meet the intent of our recommendation.
Department of the Air Force The Secretary of the Air Force should require that SSC produce a sound business case for the MGUE Increment 2 handheld prior to initiating the rapid prototyping phase of the middle tier of acquisition, or else not initiate the handheld rapid prototyping effort due to the absence of a sound business case. (Recommendation 2)
Closed – No Longer Valid
DOD awarded the agreement for the handheld receiver in July 2023, initiating the program as a rapid prototyping effort. With regards to the business case, DOD cited a nonbinding 2022 survey which sought rough estimates of demand for the receiver from the services. GAO had seen this survey while drafting the report and found it insufficient to resolve the issues with the receiver's business case. Given that the business case issues were not resolved before initiating the rapid prototyping phase of the middle tier of acquisition, the timeframe in which DOD could have implemented this recommendation has closed. As a result of DOD's actions, the recommendation can no longer be implemented and thus is no longer valid.

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