GLOBAL 

POSITIONING 

SYSTEM

A Comprehensive 

Assessment of 

Potential Options and 

Related Costs is 

Needed

Report to Congressional Committees

September 2013

GAO-13-729

United States Government Accountability Office
United States Government Accountability Office

Highlights of GAO-13-729, a report to 

congressional committees 

September 2013

GLOBAL POSITIONING SYSTEM

A Comprehensive Assessment of Potential Options 

and Related Costs is Needed 

Why GAO Did This Study

The GPS—a space-based satellite 

system that provides positioning, 

navigation, and timing data to users 

worldwide—has become an essential 

U.S. national security asset and 

component in daily life. The GPS 

program is being modernized to 

enhance its performance, accuracy 

and integrity. In 2013, the House 

Armed Services Committee directed

the Air Force to report on lower-cost 

GPS solutions. The committee also 

mandated that GAO review the Air 

Force report. GAO (1) assessed the 

extent to which the Air Force GPS 

report met Committee requirements; 

and, (2) identified additional 

information that is important in guiding 

future GPS investments. GAO 

reviewed the Air Force report, 

interviewed officials responsible for 

preparing it, and consulted subject 

matter experts from the positioning, 

navigation, and timing advisory 

community.

What GAO Recommends

GAO recommends the Air Force: 

(1) affirm the future size of the GPS 

constellation it plans to support; 

(2) ensure future assessments are 

comprehensive and include cost risk 

and the impact of options on all three 

GPS segments; and (3) engage the 

broader stakeholder community in 

future assessments of options. DOD 

concurred with these 

recommendations.

What GAO Found

GAO found the Air Force, the military branch responsible for Global Positioning 

System (GPS) acquisition, in its report on Lower Cost Solutions for Providing

Global Positioning System Capability, broadly addressed all four congressional 

requirements—system capability, implementation approaches, technical and 

programmatic risks, and estimated costs—for each option presented for the 

space segment. GPS consists of three segments—space, ground control, and 

user equipment—but the study only addressed the space segment, which 

accounts for the largest share of total GPS costs—more than half—in the Air 

Force’s current budget. The Air Force identified and assessed nine options for 

future GPS space segments, ranging in cost from $13 billion to $25 billion from 

fiscal year 2013 through 2030. The report assessed each option based on a 

constellation or collection of 30 total satellites instead of 24, which is the Air 

Force’s baseline GPS requirement for accuracy. This increase in total satellites

raises an issue with the constellation size the Air Force intends to support in the 

future. Air Force officials stated that the cost analyses supporting the nine 

options were high-level cost estimates. Although this may be expected given the 

time constraints and other limitations of the study, these estimates are not at a 

level that would support future GPS investment decisions. Table 1 identifies 

GAO’s evaluation of the Air Force report relating to congressional requirements.

Table 1: Extent Air Force Report Met Congressional Requirements and GAO Observations

Requirement Requirement met? GAO observations

System capability Yes, for the space 

segment

Each option is assessed on how long it would 

take the given option to achieve a constellation 

of 30 satellites; on signal integrity; and on its 

ability to accomplish its mission in the presence 

of adverse conditions or hostile actions 

(resilience).

Implementation 

approaches

Yes, for the space 

segment

Each option is assessed on its relative 

strengths and weaknesses, and potential 

courses of action are identified.

Technical and 

programmatic risks

Yes, for the space 

segment

The level (low, medium, high) of technical and 

programmatic risks associated with each option 

are identified.

Estimated costs of any 

recommended options

Yes, for the space 

segment

Relative rough cost estimates for each option 

are identified and comparisons across the 

options are indicated.

Source: GAO analysis of Air Force information.

Although the Air Force report is a good starting point, more information on key 

cost drivers and cost estimates, and broader input from stakeholders would help 

guide future investment decisions. Specifically, the key cost drivers include dual 

launch capability (launching two satellites on a single launch vehicle), navigation 

satellites (smaller GPS-type satellites yet to be developed), and a nuclear 

detection capability. The cost estimates also excluded the ground control and 

user equipment segments and cost risk. Further, the Air Force did not obtain 

inputs from some key stakeholders such as those from the GPS positioning, 

navigation, and timing advisory community. Consequently, without conducting a 

more comprehensive assessment that addresses each of these concerns, the Air 

Force is not yet in a position to make sound future GPS investments. 

View GAO-13-729. For more information, 

contact Marie A. Mak at (202) 512-2527 or 

makm@gao.gov. 
Page i GAO-13-729 Global Positioning System

Letter 1 

Background 3

Committee Requirements Broadly Addressed but Constellation 

Size Remains a Key Issue 8

More Information on Key Cost Drivers and Cost Estimates, and 

Broader Input from Stakeholders are Important for Future 

Investment Decisions 12

Conclusions 20

Recommendations for Executive Action 21

Agency Comments and Our Evaluation 21

Appendix I Scope and Methodology 25

Appendix II Comments from the Department of Defense 27

Appendix III GAO Contact and Staff Acknowledgments 30

Tables

Table 1: Extent Air Force Report Met Committee Report 

Requirements and GAO Observations 9

Table 2: GPS Space Segment Options and Key Assessment 

Information Identified by the Air Force 10

Figures

Figure 1: GPS Operational System and Its Three Segments 5

Figure 2: GAO’s 12-Step Cost Estimating Process 19

Contents 
Page ii GAO-13-729 Global Positioning System

Abbreviations

DOD Department of Defense

DOT Department of Transportation

GPS Global Positioning System

GPS OCX GPS Next Generation Operational Ground Control System

NASA National Aeronautics and Space Administration

NavSats Navigation Satellites

PNT Positioning, Navigation, and Timing

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Page 1 GAO-13-729 Global Positioning System

441 G St. N.W.

Washington, DC 20548

September 9, 2013

Congressional Committees

The Global Positioning System (GPS)—a space-based satellite system 

that provides positioning, navigation, and timing (PNT) data to users 

worldwide—has become an essential U.S. national security asset and a 

key component in economic growth; transportation safety; homeland 

security; and critical national infrastructure, supporting power grids and 

financial institutions, in the United States and abroad. In accordance with 

national PNT policy,1 the Department of Defense (DOD) develops and 

operates GPS, and an intergovernmental committee—co-chaired by DOD 

and the Department of Transportation (DOT)—manages the U.S. spacebased PNT infrastructure, which includes GPS. The Air Force, the military 

service responsible for GPS acquisition, is in the process of modernizing 

GPS to enhance its performance, accuracy, and integrity.2 This 

modernization effort is divided into three separate programs: the GPS III 

space segment, which comprises a constellation or collection of PNT 

satellites orbiting the Earth; a new ground control segment; and a military 

GPS user equipment segment. GPS III is an acquisition program to 

develop and field a new generation of satellites to supplement and 

eventually replace GPS satellites currently in use. The ground control 

segment, which operates the GPS satellite constellation, is being 

replaced for all existing and future GPS satellites. The user equipment 

modernization effort will provide the military services with new GPS 

receivers with enhanced capabilities to receive GPS signals in hostile 

jamming or otherwise availability-challenged environments (such as 

urban areas or mountainous terrain). The user equipment segment is 

managed by each of the military services for the weapon systems they 

own and operate.

 

1

 “U.S. Space-Based Positioning, Navigation, and Timing Policy” (Dec. 15, 2004 Fact 

Sheet) (available at http://www.gps.gov/policy/docs/2004/). 

2 We have previously reported on the challenges the Air Force faces in this effort. GAO, 

Global Positioning System: Significant Challenges in Sustaining and Upgrading Widely 

Used Capabilities, GAO-09-325 (Washington, D.C.: April 30, 2009), and GAO, Global 

Positioning System: Challenges in Sustaining and Upgrading Capabilities Persist, 

GAO-10-636 (Washington, D.C.: September 15, 2010).

 
 

Page 2 GAO-13-729 Global Positioning System

In its report accompanying the 2013 national defense authorization bill 

(H.R. 4310), the House Armed Services Committee directed that the Air 

Force report to the congressional defense committees on lower-cost 

solutions for providing GPS capability following the procurement of GPS 

III satellites.3 The committee noted that since its inception in the 1970s, 

the GPS space segment has remained generally the same, and that the 

evolution of satellite and user equipment technology, combined with 

today’s constrained budget environment, make this the right time to 

evaluate alternatives for the system. The committee provided that the Air 

Force report should identify (1) the system capability, (2) possible 

implementation approaches, (3) technical and programmatic risks, and (4) 

estimated costs of any recommended solutions. The Air Force submitted 

its report, Lower Cost Solutions for Providing Global Positioning System 

Capability, to the congressional defense committees on April 19, 2013.4

The committee’s report also mandated that we review the Air Force’s 

GPS report and provide our recommendations to congressional defense 

committees. To respond to this mandate, we reviewed the extent to which 

the Air Force GPS report met the Committee’s stated areas for reporting 

and also identified additional information that is important to guide the Air 

Force’s future investment decisions for GPS.5 To address the extent to 

which the Air Force met the Committee’s reporting requirements, we 

reviewed the approach, assumptions, and criteria the Air Force used to 

conduct its study. We also assessed the completeness of the information 

collected by reviewing the data collected and the reports that supported 

the Air Force’s report, and discussed the report with GPS program and 

Aerospace Corporation officials. The Aerospace Corporation is a federally 

funded research and development center that provides technical and 

scientific research, development, and advisory services to national 

security space programs. According to program officials, Aerospace 

Corporation officials participated extensively in the development of the 

report, most notably conducting the cost analyses. We did not 

independently verify the data the Air Force used in conducting its study. 

To identify additional or clarifying information that is important to guide 

 

3 H.R. Rep. No. 112-479, at 70-71 (2012). 

4 United States Air Force, Report to Congressional Committees: Lower Cost Solutions for 

Providing Global Positioning System (GPS) Capability, April 2013.

5 For purposes of this report, we term these stated areas for reporting as reporting 

requirements.
 

Page 3 GAO-13-729 Global Positioning System

future investment decisions, we reviewed the Air Force report and 

discussed it with subject matter experts6 from the PNT advisory 

community to obtain their insights on the GPS options identified, and 

information that could provide additional insights. We also assessed the 

process used to develop the cost estimates in the study to determine the 

extent to which they followed GAO’s 12-Step Reliable Process for 

Developing Cost Estimates assessment tool.

7

We conducted this performance audit from April 2013 to September 2013 

in accordance with generally accepted government auditing standards. 

Those standards require that we plan and perform the audit to obtain 

sufficient, appropriate evidence to provide a reasonable basis for our 

findings and conclusions based on our audit objectives. We believe that 

the evidence obtained provides a reasonable basis for our findings and 

conclusions based on our audit objectives. See appendix I for more 

information on our scope and methodology.

Every satellite has a bus and payload. The bus is the body of the satellite 

and is managed by the satellite control operations to maintain a desired 

location. It carries the payload and is composed of a number of 

subsystems, such as the power supply, antennas, and mechanical and 

thermal control equipment. The bus also provides electrical power, 

stability, and propulsion for the entire satellite. The payload includes the 

devices the satellite needs to perform its mission. This configuration 

differs for every type of satellite. For example, the payload for a weather 

satellite could include cameras to take pictures of cloud formations, while 

the payload for a GPS satellite would include equipment to pass 

navigation information from the satellites to receivers on Earth. Monitoring 

and operating of the satellite payload is done to collect data or provide a 

capability to the warfighter or civilian user.

GPS is a global PNT network consisting of space, ground control, and 

user equipment segments that support the broadcasts of military and 

 

6 For purposes of this report, a subject matter expert is either a government employee or a 

special government employee. A special government employee is an expert from 

academia or industry who is granted federal employee status when attending to certain 

government business.

7 GAO, GAO Cost Estimating and Assessment Guide Best Practices for Developing and 

Managing Capital Program Costs, GAO-06-3SP (Washington, D.C.: March 2009).

Background 
 

Page 4 GAO-13-729 Global Positioning System

civilian GPS signals. Each of these signals includes positioning and 

timing information, which enables users with GPS receivers to determine 

their position, velocity, and time 24 hours a day, in all weather, worldwide. 

GPS has changed the way the world operates, and underpins military 

operations as well as major sections of the economy, including 

telecommunications; electrical power distribution; banking and finance; 

transportation; environmental and natural resource management; 

agriculture; search and rescue; and other emergency services. GPS is 

used by all branches of the military to guide troop movements, integrate 

logistics support, and synchronize communications networks. In addition, 

many U.S. and allied precision-guided munitions are directed to their 

targets by GPS signals.

The space, ground control, and user equipment segments are needed to 

take full advantage of GPS capabilities. The GPS space segment, which 

accounts for more than half of the total GPS costs in the Air Force’s 

current budget is a constellation of satellites that orbit approximately 

12,500 miles above the earth. According to Air Force officials, current 

GPS requirements do not specify a number of satellites that are to be in 

orbit, but rather an accuracy threshold for the system. Based upon the 

threshold requirement for positioning and timing accuracy, the Air Force 

derived a constellation size of 24 satellites available 95 percent of the 

time. Due to the unanticipated longevity of some of the previously 

launched satellites, the constellation has at times exceeded the derived 

number of satellites. See figure 1 below for a depiction of the GPS 

segments.

GPS System Description
 

Page 5 GAO-13-729 Global Positioning System

Figure 1: GPS Operational System and Its Three Segments

GPS satellites broadcast encrypted military signals and unencrypted 

civilian signals that can be processed by GPS receivers to identify their 

location worldwide. Since the constellation became fully operational in 

1995, it has consisted of satellites from various generations of 

development and production, each introducing improved capabilities and 

additional signals. The latest generation of satellites in orbit—the GPS 
 

Page 6 GAO-13-729 Global Positioning System

IIF—broadcasts two military and three civilian signals. Additionally, the 

GPS constellation currently hosts a nuclear detonation detection system 

payload to monitor nuclear events on Earth.

The GPS ground control segment comprises the Master Control Station 

at Schriever Air Force Base, Colorado; the Alternate Master Control 

Station at Vandenberg Air Force Base, California; and various monitoring 

stations and ground antennas. Information from the monitoring stations is 

processed at the Master Control Station to determine the accuracy of the 

satellites’ clocks (for signal timing) and the precision of their orbits. The 

Master Control Station operates the satellites and regularly updates their 

navigation messages, transmitting information to the satellites via the 

ground antennas. The U.S. Naval Observatory Master Clock monitors the 

GPS constellation and provides timing data for the individual satellites.

The GPS user equipment segment includes military and commercial GPS 

receivers. A receiver determines a user’s position by calculating the 

distance from four or more satellites based on the time it takes each of 

the signals to reach the receiver. Military GPS receivers are designed to 

utilize the encrypted military GPS signals that are only accessible to 

authorized users; commercial receivers use the civilian GPS signal, which 

is publicly available worldwide.

The Air Force is in the process of modernizing the space segment under 

the GPS III program, which will incorporate advances over the GPS IIF 

satellites it is replacing, including a higher power military navigation signal 

to improve jamming resistance8 and a new civilian signal to allow users to 

receive GPS signals in combination with foreign satellite navigation 

systems. The acquisition strategy is to purchase up to 349 satellites 

following an incremental approach to replenish the current satellites in the 

constellation as they reach the end of their operational life. The original 

strategy was to purchase up to eight satellites in each of the first two 

increments and up to 18 satellites in the last increment. However, the 

 

8 A higher power signal increases resistance to jamming or confusion of military GPS 

receivers. This increases the likelihood the jammers will be identified by military forces 

and prevent obscuring of the GPS signal.

9 The first two satellites are developmental units, and the remaining 32 are expected to be 

production units.

Current Modernization 

Efforts 
 

Page 7 GAO-13-729 Global Positioning System

GPS program is drafting a modified acquisition strategy to streamline the 

last two increments into one to allow larger buying quantities to take 

advantage of economies of scale, making this an appropriate time to 

examine future GPS options. The Air Force has purchased four GPS III 

satellites to date, the first of which is expected to launch in 2015. The Air 

Force plans to incrementally increase the capabilities of the GPS III 

satellites as technology maturation occurs and funding allows.

The ground control segment is being modernized under the Air Force’s 

Global Positioning System Next Generation Operational Ground Control 

System (GPS OCX) program. GPS OCX is also being developed in three 

increments and will eventually allow DOD to take full advantage of the 

capabilities offered by the various satellites. The first increment is to 

deliver a capability to launch and initiate on-orbit testing of GPS III 

satellites; the next increment is to deliver a capability to command and 

control GPS II and GPS III satellites; and the final increment is to deliver a 

capability to make military and international signals operational.10

Software challenges have delayed availability of the command and 

control capability, which was previously planned for 2015 and is currently 

expected to be operational in late 2016 (final block is planned for 2017).

Each of the military services is managing modernization of its user 

equipment through the joint Military GPS User Equipment program, which 

is to develop modernized military GPS receivers that deliver improved 

capabilities for accurate, reliable, and available PNT service where 

current receiver performance might be compromised (e.g., jammed) or 

unavailable.

The 2004 U.S. Space-based PNT policy established a coordinating 

structure to integrate input from, and delineate the respective roles of the 

military and civilian departments and agencies for program planning 

(including identification of system requirements), resource allocation, 

system development, and operations. As part of the coordinating 

structure, an executive committee advises and coordinates among U.S. 

government agencies on maintaining and improving U.S. space-based 

PNT infrastructures, including GPS and related systems. The executive 

 

10 The original GPS satellites have been modernized in various generations of upgrades 

beginning with GPS IIA followed by GPS IIR, GPS IIR-M, GPS IIF, and GPS III, which is in 

development.

Broader Coordinating 

Structure 
 

Page 8 GAO-13-729 Global Positioning System

committee is co-chaired by the deputy secretaries of the DOD and the 

DOT, and includes members at the equivalent level from the Departments 

of State, Commerce, Homeland Security, the Interior, and Agriculture; the 

Joint Chiefs of Staff; and the National Aeronautics and Space 

Administration (NASA). The National Coordination Office for Space-based 

PNT provides day-to-day support for the executive committee.

The Air Force broadly addressed all committee reporting requirements in 

its assessment of future GPS options for the space segment. These 

requirements include evaluation of system capabilities, implementation 

approaches, technical and programmatic risks, and estimated costs. 

However, each of the options presented and evaluated is based on a 

GPS constellation of 30 satellites, whereas the Air Force’s requirement is 

for a 24-satellite constellation. The 30-satellite constellation assumption 

has a significant effect on the cost of the options studied. It also raises 

questions about what constellation size the Air Force is committed to 

fielding and maintaining in the future.

The Air Force GPS report identified and assessed nine options for the 

space segment of a future GPS which were developed as part of a sixstep process the Air Force used to conduct the study, to include:

• Define the purpose, scope, and decision criteria.

• Assess the user requirement or capability in operational context.

• Develop a broad trade space of all available options.

• Review the trade space with GPS Senior Advisory Group to select a 

small set of promising options and to develop criteria for assessing 

the down-selected options.

• Analyze the options and assess them against the criteria using 

modeling and analysis tools, and conduct a risk assessment for each 

option.

• Integrate all the findings and develop recommendations.

According to program officials, they focused the report on options for the 

space segment because it is the most costly part of the GPS. The space 

segment accounts for more than half of all GPS program costs in the 

current budget. For the space segment, we found that the Air Force’s 

report addressed all four Committee requirements for each of these nine 

options. Specifically, the report identified system capability, 

implementation approaches, technical and programmatic risks, and 

estimated costs, as provided for by the Committee. Each of the options 

Committee 

Requirements Broadly 

Addressed but 

Constellation Size 

Remains a Key Issue

Air Force GPS Report Met 

Committee Requirements 

for the Space Segment
 

Page 9 GAO-13-729 Global Positioning System

for the space segment is assessed to determine how quickly it could be 

fielded, implementation approaches, technical and programmatic risks, 

and space segment costs (to include the cost of launch). GPS program 

officials stated that the cost analyses that support the nine space 

segment options were not high fidelity estimates but instead estimated at 

a high level. Although this may be expected given the limited time 

provided to complete the study and prepare the report, the high-level cost 

estimates are not at a level that would support programmatic decisions. 

Table 1 below identifies our evaluation relating to the Committee 

requirements as well as our observations.

Table 1: Extent Air Force Report Met Committee Report Requirements and GAO Observations

Requirement Requirement met? GAO observations

System capability Yes, for the space segment Each option is assessed on how long it would take the given 

option to achieve a constellation of 30 satellites; on signal 

integrity; and on its ability to accomplish its mission in the 

presence of adverse conditions or hostile actions (resilience).

Implementation approaches Yes, for the space segment Each option is assessed on its relative strengths and 

weaknesses, and potential courses of action are identified.

Technical and programmatic risks Yes, for the space segment The level (low, medium, high) of technical and programmatic 

risks associated with each option are identified.

Estimated costs of any 

recommended options

Yes, for the space segment Relative rough cost estimates for each option are identified 

and comparisons across the options are indicated.

Source: GAO analysis of Air Force information.

Of the nine options the Air Force identified for the space segment, several 

relied on a core constellation of 18 to 24 GPS III satellites that would be 

augmented with other satellites to reach a total of 30. The last two options 

do not rely on a core GPS III constellation but would also consist of 30 

satellites. See table 2 for a description of each option as well as 

information on the results of the Air Force’s risk and cost assessments. 

Technical risk, for some of the options, includes the incorporation of 

technologies that are new to GPS. Programmatic risk includes areas such 

as establishing requirements, budgeting for funds, and obtaining approval 

of the acquisition strategy. The options are not presented in any particular 

order of significance.
 

Page 10 GAO-13-729 Global Positioning System

Table 2: GPS Space Segment Options and Key Assessment Information Identified by the Air Force

Option Description 

Risk assessment 

(technical/programmatic)

Rough order cost estimate for 

fiscal years 2013-2130 (fiscal 

year 2012 dollars in billions)

1 GPS III satellites with minimal changes (current 

baseline GPS program)

Low / Low

$23

2 GPS III satellites with all possible upgrades previously 

planned for the programa Low / Low-medium$25

3 GPS III satellites modified to launch two per launch 

vehicle 

Low-medium / Low-medium

$22

4 GPS III satellites modified to launch two per launch 

vehicle and augmented by navigational satellites 

(NavSats)b with all civilian and military signalsc

Medium / Medium-high

$20

5 GPS III satellites modified to launch two per launch 

vehicle and augmented by NavSats with limited 

civilian and military signalsd

Medium / Medium-high

$18

6 GPS III satellites modified to launch two per launch 

vehicle and augmented by PNT payloads hosted on 

other satellites in a more distant orbite

Medium / High

$21

7 GPS III satellites modified to launch two per launch 

vehicle and augmented by dedicated PNT satellites in 

a more distant orbitf

Medium / Medium-high

$22

8 Constellation evolves into all NavSats High / High $13

9 NavSat constellation augmented by 3 PNT satellites in 

a more distant orbit

High / High

$14

Source: GAO presentation of Air Force data

a

Includes enhanced command and control (i.e., sending “crosslinked” signals between satellites for 

improved signal integrity monitoring) and regional protection (i.e., high-power signals that can be 

transmitted over a combat zone for localized jam resistance).

b

The Air Force is conceptualizing NavSats as smaller, lower-cost PNT satellites that in options 4 and 

5 would be launched into orbit to augment an existing core constellation of 18 to 24 GPS III satellites.

c

Refers to PNT payloads that transmit the full complement of signals on GPS III satellites.

d

Refers to PNT payloads that only transmit selected GPS signals (two military and two civilian 

signals).

e

Hosted payloads in this case would involve navigation signal transmitters attached to commercial or 

other government satellites in geosynchronous-Earth orbit. Current GPS satellites are in mediumEarth orbit, at a distance of approximately 12,500 miles above the earth. Geosynchronous-Earth orbit 

is further still, where the Earth’s gravitational pull is such that objects orbiting at that distance circle 

the Earth once a day, with their position relatively fixed to the same spot on Earth.

f

According to program officials, GPS satellites in geosynchronous-Earth orbit have the advantage of 

broader regional coverage, but require more fuel on launch to reach their orbit, as well as more power 

to transmit signals over a farther distance.

GPS program officials noted that none of the options presented in the 

report represent a radical departure from the GPS III program, which they 

characterized as an essential investment for the health of the 

constellation. The GPS III program plans to eventually replace the 
 

Page 11 GAO-13-729 Global Positioning System

existing constellation with upgraded satellites that carry the nuclear 

detonation detection system payload. The first seven options presented in 

the Air Force report involve GPS III or some modification of it. 

Specifically, five options (numbers 3, 4, 5, 6, and 7) involve launching two 

GPS III satellites on a single launch vehicle (referred to as dual launch), 

and according to the Air Force report, are expected to substantially 

reduce costs by eliminating the need to buy launch vehicles for each 

satellite, as is currently practiced. Further, four options (numbers 4, 5, 8, 

and 9) entail fielding smaller, lower-cost PNT satellites—referred to as 

navigation satellites (NavSats)—yet to be developed satellites that would 

complement the core constellation of GPS III satellites in various 

configurations, or to replace GPS III satellites entirely. The NavSat 

concept is comparable to GPS III except that it is comprised of dedicated 

PNT satellites (without the secondary nuclear detonation detection 

system); and according the Air Force report, is expected to be 

significantly less costly than GPS III satellites due to the development and 

use of mass-reducing technologies.

According to Air Force officials, the baseline GPS requirement for 

accuracy drives a requirement for a 24 satellite constellation at 95 percent 

availability.11 However, each of the GPS space segment options the Air 

Force assessed is based on a constellation of 30 satellites. Therefore, it 

is unclear whether investment costs for these options will in fact be lower 

than the baseline cost of the current GPS III program. Moreover, based 

on the estimated costs presented in the report, basing all options on a 30-

satellite constellation may actually increase the overall GPS investment 

because the limited differences between the options assessed narrows 

the range of costs across the seven options that rely on a core of GPS III 

satellites.

Program officials noted that although the requirement is for 24 satellites, 

for the last seven years the Air Force has operated at least 27 satellites in 

the GPS constellation and, more recently, as many as 31 satellites due to 

the existing satellites outlasting the useful life originally estimated. We 

reported in 2010 that DOD predicted many of the older satellites in the 

constellation will reach the end of their operational life faster than they will 

 

11 The Air Force GPS report cites the same requirement—a 24-satellite constellation at 95 

percent availability.

Future Supported 

Constellation Size is 

Unclear
 

Page 12 GAO-13-729 Global Positioning System

be replenished over the next several years, decreasing the size of the 

constellation from its current level. Since the magnitude of error 

calculated by GPS receivers dramatically decreases as the constellation 

reaches 30 satellites, and program officials stated that users have come 

to rely on this increased accuracy over the last several years, the Air 

Force determined it was appropriate to assess options for providing this 

same level of service into the future. As a result, the report establishes a 

constellation of 30 satellites—an increase over the Air Force’s 

requirement for accuracy—as a baseline for each of the GPS options 

assessed. Program officials, however, acknowledged that there is 

reluctance to formally require the GPS constellation to be larger than the 

24-satellite requirement supported by the Air Force without the certainty 

of a corresponding growth in program funding. While a 30-satellite 

constellation may be justifiable, using that as a baseline in the study may 

have eliminated some lower cost options that may exist with 24 satellites. 

Additionally, given the uncertainty regarding the magnitude of future GPS 

investments, the DOD and civilian agency community would benefit from 

knowing which constellation size the Air Force is committed to supporting.

The Air Force GPS report identifies key drivers of cost and capability 

across the assessed options, but more information on each of these 

drivers is needed to fully assess their potential effect on the future GPS 

program. Similarly, additional information is needed on inputs for the cost 

estimates presented. This information includes analysis of costs and 

other potential options associated with the ground and user equipment 

segments, which were excluded from the study, as well as costs 

associated with the various technical and programmatic risks identified in 

the report. Assurance that best practices are followed for subsequent cost 

estimates would also benefit future investment decisions. Additionally, the 

Air Force was not required by the Committee to consult representatives 

from the broader PNT advisory community, but several of these 

individuals provided us with useful information relating to the options 

assessed. Future investment decisions would benefit from a broader 

outreach to gain the input and perspectives of other GPS stakeholders.

Development of dual launch capability for GPS III satellites, development 

of the NavSat concept, and the inclusion or exclusion of the nuclear 

detonation detection system payload, are key drivers of cost and 

capability between the GPS options assessed by the Air Force. For 

example, both the dual launch capability and the NavSat concept require 

use of technologies new to GPS with associated developmental risks, and 

More Information on 

Key Cost Drivers and 

Cost Estimates, and 

Broader Input from 

Stakeholders are 

Important for Future 

Investment Decisions

Information on Key Cost 

Drivers is Incomplete
 

Page 13 GAO-13-729 Global Positioning System

as key drivers of cost, they are factors that differ significantly enough to 

have a material impact on the analysis and the resulting findings, 

including estimated costs. Additionally, two of the NavSat options are 

based on the possibility that the nuclear detonation detection mission 

could eventually be transferred to another space-based system, but the 

effect of such a change on overall system capability was not fully 

considered in the report. To assess the options as a basis for making 

future GPS investment decisions, more information on each of these 

drivers is important to understand the full impact they could have on the 

future integrity, capability, and cost of the system.

For options 3 through 7, development of a dual launch capability for GPS 

III satellites is necessary, but a lack of detail in the Air Force’s report on 

the maturity of key technologies and cost considerations make it difficult 

to conduct a fully informed assessment of the viability of these options. 

Program officials indicated that this ongoing effort will require reductions 

in the size, weight, and power of the GPS III satellites, as well as 

development of equipment (adaptors) that will allow two satellites to fly on 

a single launch vehicle. According to program officials, these adaptors are 

nearing a high level of technology maturity. However, the report names 

various other components and technologies under development for this 

effort, such as lithium ion batteries and more efficient signal amplifiers, 

but does not indicate where they stand in terms of technology maturity. 

Instead, the report assumes that dual launch capability is fully developed 

and that demonstration of the capability will be ready in time to launch the 

seventh and eighth GPS III satellites (of potentially 32 production 

satellites). Consequently, it is difficult to assess the near- to medium-term 

feasibility and timeframes of all options that are based on dual launching 

GPS III satellites.

Additionally, the Air Force did not fully consider the cost impact of its dual 

launch approach. While cost savings may eventually be accrued from 

dual launches, the report does not address the acquisition and operations 

strategy—what is necessary to buy and conduct dual launches up front. 

For example, one of the subject matter experts we consulted identified a 

number of factors which would result in cost increases that offset some of 

the expected savings from not procuring a second launch vehicle. These 

include (1) taking the steps to ensure the constellation’s integrity would 

remain intact in the event of a launch failure, as two satellites would be 

lost in such an instance rather than one (e.g., Air Force officials would 

have to decide whether to orbit more spares to overcome the effects of a 

possible launch failure); (2) making changes at the manufacturing level to 

accommodate two satellites, such as the additional storage costs to hold 

Dual Launch Capability
 

Page 14 GAO-13-729 Global Positioning System

the first satellite until the second satellite is ready to launch; (3) ensuring 

launch site facilities are capable of processing two satellites essentially 

simultaneously, noting that discovery of an anomaly during launch site 

testing of one satellite could affect the other satellite; and (4) ensuring the 

additional support equipment and personnel necessary to support 

preparing two satellites for launch. This expert further acknowledged that 

none of these factors were “showstoppers” but suggested that they 

should be taken into consideration. Program officials noted that in 

developing the notional launch schedule for the options, they factored in a 

two percent probability of launch failure which is an industry standard for 

mature launch vehicle designs. However, they acknowledged that 

modifications needed on the launch vehicle to dual launch GPS satellites 

have not been demonstrated.

Some of the identified technical risks for the notional NavSat options may 

be understated given that they involve undertaking new acquisition 

programs with technologies not previously used on GPS satellites. For 

example, many of the initiatives to reduce satellite size, weight, and 

power underway for developing dual launch capability are also being 

explored for application on NavSats. We have found in our prior work 

relating to best practices for weapon system acquisition that programs 

employing technologies that are not fully mature tend to face challenges 

staying on budget and on schedule, which increases risk to the overall 

program.12 The Air Force report indicates that maturation of the NavSat 

concept is a prerequisite for many options assessed, including 

development of new satellite buses and payloads. These development 

efforts are assigned medium and medium-high technical and 

programmatic risk. While the report acknowledges that there are technical 

risks involved with developing higher efficiency signal amplifiers and other 

space, weight, and power reducing technologies, it concludes that none 

of these technologies is high risk. However, officials from the Air Force 

Research Laboratory, which is helping to develop some of these 

technologies for potential application on NavSats, noted that some of the 

new technologies are currently at a relatively low level of maturity (i.e., 

only tested in a laboratory environment), and will not likely be feasible for 

the GPS program until at least 2018. Moreover, one of the subject matter 

experts we consulted noted that there are other potential risks associated 

 

12 GAO, Defense Acquisitions: Assessments of Selected Weapon Programs, 

GAO-13-294SP (Washington, D.C.: March 28, 2013.

NavSat Development 
 

Page 15 GAO-13-729 Global Positioning System

with the NavSat options, such as not having a proven track record. This 

expert noted problems in the NavSat programs could result in the loss of 

user confidence in GPS that has been built up over decades of delivering 

a reliable satellite navigation service.

Details regarding technology maturity are also needed to better 

understand the cost impact of these options on the overall GPS program. 

For example, program officials acknowledged that savings from dual 

launching GPS III satellites could help offset some of the additional costs 

associated with development of NavSats. However, they noted that there 

would likely be significant initial development costs for the NavSats that 

would result in the need for a net budget increase in the near-term.

Additionally, a key aspect of NavSat capability relevant to civilian GPS 

users is not addressed in the Air Force report and without additional 

clarification, it is difficult to determine the impacts to these users. The 

report notes that one approach for reducing the size, weight, power, and 

cost of proposed NavSats, would be to reduce the total number of 

navigation signals they transmit. Specifically, under option 5 in the report, 

NavSats would broadcast two of four civilian signals and two military 

signals. Three of the subject matter experts we consulted noted concerns 

in part because determining which civilian signals to exclude would likely 

result in the prioritization of one user group over another, as the civilian 

signals have different applications. Air Force officials indicated that, 

option 5 is based on a larger core of GPS III satellites—which are 

required to carry all civilian signals—and augmented by a smaller number 

of NavSats. However, it is unclear how a core of GPS III satellites would 

compare with a combined constellation of GPS III satellites and NavSats, 

both required to broadcast all civilian signals.

Two of the NavSat options included in the Air Force report would require 

the eventual elimination of the nuclear detonation detection system 

payload from GPS satellites, and the report notes that as long as this 

mission is a priority and is planned to be hosted on GPS satellites, these 

options—and the low relative costs—would therefore not be viable. 

Elimination of the nuclear detonation detection system could have other 

effects on the overall capability of the GPS system not recognized or 

addressed in the Air Force report. For example, one of the subject matter 

experts we consulted mentioned that the GPS search and rescue 

function, a requirement for GPS III satellites, shares an antenna with the 

Nuclear Detonation Detection 

System 
 

Page 16 GAO-13-729 Global Positioning System

nuclear detonation detection system payload.13 Thus, the two options 

(numbers 8 and 9) that drop the nuclear detonation detection system 

completely would potentially forgo the search and rescue function as well. 

However, program officials said the search and rescue payload is 

relatively small and could be adapted to the NavSats without the nuclear 

detonation detection system, and also noted that in a mixed constellation 

of GPS III satellites and NavSats, there would likely be sufficient 

coverage for the search and rescue mission even if the search and 

rescue sensors were only on the GPS III satellites. Given the differing 

views of these officials and subject matter experts, this issue will need to 

be resolved as the Air Force pursues future assessments of GPS options.

The Air Force’s high-level cost estimates appear consistent across the 

options for the space segment, but the estimates do not include the other 

two key GPS segments. For its study, the Air Force defined affordability 

as the reduction in total ownership cost of sustaining GPS throughout its 

life cycle. However, without inclusion of the other two key segments of the 

system, the methodology used does not reflect true life cycle costs. 

Additionally, Air Force officials noted that the cost estimates developed 

for the report do not include cost risk. This leaves some question as to the 

ultimate usefulness of the cost estimates, risk rankings, or both. In 

addition, the Air Force did not apply all aspects of best practices in 

developing its cost estimates, which further reduces the usefulness of 

these estimates in decisionmaking. Finally, the Air Force did not obtain 

input from the PNT advisory community which may have helped inform its 

assessment. 

For a defense acquisition program, DOD defines life cycle costs as the 

total cost to the government of acquisition and ownership for a program 

over its full life.14 This includes the cost of development, acquisition, 

operations, and support (to include personnel), and where applicable, 

disposal. While the Air Force report indicates that the estimates are 

based upon life cycle costs, it does not include key elements necessary to 

 

13 According to Air Force officials, each group of GPS III satellites it procured can be 

contracted for additional capabilities. The search and rescue function will be available on 

GPS III satellites beginning with deployment of the ninth satellite.

14 Defense Acquisition Guidebook. (June 28, 2013) (available at 

https://acc.dau.mil/CommunityBrowser.aspx?id=654219). 

Cost Estimates are Not 

Comprehensive 

Estimated Overall Costs for 

Options Exclude Key Segments
 

Page 17 GAO-13-729 Global Positioning System

meet the definition of life cycle cost, thereby underestimating the total 

costs of the options and limiting their usefulness. The Air Force’s cost 

estimates for each option only included the space segment—satellite and 

launch vehicles—which it determined to be the only segment to have 

significant impact on overall costs. As mentioned previously, the space 

segment accounts for the largest share—more than half—of total GPS 

costs in the Air Force’s current budget. Under this methodology, program 

officials said options dealing with the ground control system were not 

included in the cost estimates because costs associated with adding 

capability to control new satellites were estimated to be a small 

percentage of the total GPS system cost, and would not provide a 

significant distinction between the options. However, this estimation, 

without the ground control segment, may not be valid given that there 

could be unknown cost and schedule risks for the ground control segment 

associated with modifications to accommodate new and different satellite 

vehicles. More specifically, while changes to the ground segment may not 

be a major cost differentiator between the options, they have presented 

significant challenges. For example, program officials said the costs of 

adding ground control capability for a new generation of satellites are 

known, but this is based on updates to the current ground control system. 

However, in our prior work, we also reported that modernization of the 

current ground control segment has been challenging, and has only 

enabled limited capability to control the new satellites, rather than 

facilitating full access to their new capabilities.15 Additionally, the ground 

control segment is being completely replaced as part of the GPS OCX

program, which according to Air Force officials, will eventually enable 

users to take full advantage of the capability offered by the GPS 

constellation, and is expected to cost nearly $3.7 billion through fiscal 

year 2017. This cost is significantly higher than initial planning estimates 

due to software and other challenges experienced thus far, and the extent 

and cost of this effort were not recognized in the Air Force report.

Additionally, two of the subject matter experts we consulted indicated that 

inclusion of user equipment could have benefited the study. The Air Force 

report did not assess any options that would require hardware changes to 

user equipment beyond what is already planned for user equipment 

modernization because of the large number of civilian receivers currently 

 

15 GAO, Global Positioning System: Significant Challenges in Sustaining and Upgrading 

Widely Used Capabilities, GAO-09-325 (Washington, D.C.: April 30, 2009). 
 

Page 18 GAO-13-729 Global Positioning System

in use. One subject matter expert noted that although the report cites this 

as the primary reason user equipment was not examined; civilian user 

equipment will continue to evolve by integrating GPS signals with signals 

from other global navigation systems, as well as with non-space-based 

PNT capabilities such as inertial navigation sensors, chip scale atomic 

clocks, and terrestrial radiolocation technologies. The expert noted that 

this could reduce some of the capability that the space segment needs to 

provide in the future. Based on our discussions with officials from the Air 

Force Research Laboratory, this could in turn potentially reduce the size 

and power requirements for the space vehicle and thereby the overall 

cost. 

According to Air Force officials involved in the study, the overall cost 

estimates do not include cost risk,16 which is defined as the risk 

associated with the ability of the program to achieve its acquisition 

strategy cost objectives. Similarly, identified technical and programmatic 

risks and their relative rankings do not generally appear to have a basis in 

cost. The options involving a constellation of all NavSats or at least a core 

of NavSats (numbers 8 and 9 respectively) both reflect high technical and 

programmatic risks. At the same time, the cost estimates for these 

options reflect the lowest development and procurement costs (excluding 

operations and sustainment costs) over the fiscal year 2013 to fiscal year 

2030 timeframe. We have found in our prior work relating to key practices 

for weapon system acquisition that programs employing technologies that 

are not fully mature tend to require more time in development or 

production and more funding than is initially anticipated.17 Without 

additional details as to how cost factors into the risk determination, it is 

difficult to know the relative utility of the Air Force’s cost estimates for 

making further GPS decisions.

Best practices in cost estimating result in accurate and credible cost 

estimates that management can use for making informed decisions. The 

methodology consists of 12 steps that we present in figure 2.

 

16 Although the Air Force report states that cost estimates include cost risk, program 

officials told us this was in error and that, in fact, cost risk was not included in the cost 

estimates.

17 GAO-13-294SP. 

Estimated Overall Costs for 

Options Exclude Cost Risk

Best Practices for Cost 

Estimating Could Improve 

Future Estimates
 

Page 19 GAO-13-729 Global Positioning System

Figure 2: GAO’s 12-Step Cost Estimating Process

These best practices represent an overall process of established, 

repeatable methods that result in high-quality cost estimates that are 

comprehensive and accurate, and that can be easily and clearly traced, 

replicated, and updated. We found that the Air Force followed some 

aspects of the 12-step process in developing its estimates for GPS 

architecture options, but did not follow others. For example, the Air Force 

defined the estimate’s purpose and identified some ground rules and 

assumptions, but did not perform sensitivity analysis and conducted 

minimal analysis of cost-related risks. This would be expected given the 

time constraints and other limitations of the study; however, to further 

assess its GPS options, more fully-developed cost estimates would be 

important in facilitating more rigorous comparisons across the options.

GPS has grown into a global utility whose multi-use services are integral 

to U.S. national security and transportation safety, and are an essential 

element of the worldwide economic infrastructure. As a result, any 

decision regarding GPS has far reaching consequences for many beyond 

DOD. This fact was clearly addressed in the national PNT policy which 

formalized the membership of the PNT executive committee to include 

other government departments and agencies that have a stake in the 

stewardship of GPS. This committee ensures that the national security, 

homeland security, and civil requirements receive full and appropriate 

consideration in the PNT decision process and facilitates the integration 

Consultation with Key 

Stakeholders Could 

Provide Additional Insights
 

Page 20 GAO-13-729 Global Positioning System

and reduction of conflicts of these requirements for PNT, as required. 

However, the Air Force did not seek input from those departments and 

agencies that are represented on the committee, including the 

Department of Transportation, which co-chairs the committee with DOD. 

These key stakeholders could have provided valuable insight on potential 

impacts of the options presented, as well as future needs arising from any 

changes to the GPS.

Several of the subject matter experts we consulted directly represent the 

stakeholders identified in the PNT policy. While these individuals largely 

believe the Air Force report is a good starting point for future GPS 

decisions, they provided additional, meaningful insights relating to 

potential risks and costs associated with the individual options as well as 

with ground control and satellite launch; user equipment capabilities; and 

the concerns and needs of various GPS users. According to Air Force

officials, they did receive input from individuals who advocated for the 

needs of non-DOD users, but acknowledged that these individuals did not 

directly represent those users or other stakeholders identified in PNT 

policy. While not specifically required by the House Armed Services 

Committee to seek input from others, obtaining input from key 

stakeholders, such as was provided by the subject matter experts we 

consulted, the Air Force may have been able to obtain additional insights 

as it developed and weighed the various GPS options. This was a 

sentiment shared by some of our subject matter experts who expressed 

concern over the lack of input from the civilian community.

The Air Force’s GPS report met the committee’s reporting requirements 

and serves as a good starting point from which to assess potential lower 

cost GPS options. The study focused on the space segment and as such, 

the options consist of various configurations of satellites and launch 

options—whether to launch satellites individually or in multiples. The less 

risky options appear to be relatively minor deviations from the 

department’s current approach in fielding GPS III, with the key decision 

being whether to launch one or two satellites at a time. Pursuing any 

options would likely require a near term increase in the overall GPS 

budget to achieve future savings—a challenge in the current fiscally 

constrained environment. Yet, the study used a larger constellation size 

than the Air Force’s current derived requirements and lacked the 

comprehensiveness that would allow the study to be used for future 

decision making. Based on acquisition best practices, there are actions 

the Air Force could take to improve the study results to include: identifying 

the constellation size to be supported; expanding the areas of 

Conclusions 
 

Page 21 GAO-13-729 Global Positioning System

consideration to include ground control and user equipment; more 

thoroughly defining and analyzing key capabilities and implementation 

approaches; and using a higher fidelity approach in assessing risk and 

estimating cost going forward. The Air Force could also benefit from 

greater consultation from the broader PNT stakeholder and advisory 

community, which could offer valuable perspectives relating to the overall 

approach for investigating future GPS options, as well as the relative 

merits and unknowns associated with each option analyzed. While there 

are a number of limitations in the study, it is valuable as a basis for 

substantive discussion of long-term GPS investments. Going forward, it is 

important for the Air Force to take a more comprehensive approach in 

assessing options for making sound future GPS investments.

To better position the DOD as it continues pursuing more affordable GPS 

options, and to have the information necessary to make decisions on how 

best to improve the GPS constellation, we recommend that the Secretary 

of Defense direct the Secretary of the Air Force to take the following three 

actions:

1. Affirm the future GPS constellation size that the Air Force plans to 

support, given the differences in the derived requirement of the 24-

satellite constellation and the 30-satellite constellations called for in 

each of the space segment options in the Air Force’s report.

2. Ensure that future assessments of options include full consideration of 

the space, ground control, and user equipment segments, and are 

comprehensive with regard to their assessment of costs, technical 

and programmatic risks, and schedule.

3. Engage stakeholders from the broader civilian community identified in 

PNT policy in future assessments of options. This input should include 

civilian GPS signals, signal quality and integrity, which signals should 

be included or excluded from options, as well as issues pertaining to 

other technical and programmatic matters.

In written comments on a draft of this report, DOD concurred with all three 

of our recommendations to better position the DOD as it continues 

pursuing more affordable GPS options, and to have the information 

necessary to make decisions on how best to improve the GPS 

constellation. DOD’s written comments are reprinted in appendix II.

DOD concurred with our first recommendation that the Secretary of the 

Air Force affirm the future GPS constellation size the Air Force plans to 

Recommendations for 

Executive Action

Agency Comments

and Our Evaluation
 

Page 22 GAO-13-729 Global Positioning System

support. In its response, the department stated the numbers of satellites 

are affirmed annually in the President’s Budget request. However, the 

budget shows satellite procurements over time and does not specify the 

target constellation size to meet current or future accuracy requirements, 

which has a direct impact on annual procurement costs. Additionally, as 

our report indicates, the Air Force report based all options on a 30-

satellite constellation while reporting a GPS requirement for accuracy of a 

24 satellite constellation at 95 percent availability. Therefore, the need 

remains for the department to more clearly and transparently identify the 

target GPS constellation size the department intends to pursue.

DOD also concurred with our second recommendation to ensure future 

assessments of options include full consideration of the space, ground 

control, and user equipment segments, and are comprehensive with 

regard to their assessment of costs, technical and programmatic risks, 

and schedule. In its response, the department stated that while 

consideration of the space and ground control segments should be 

comprehensive in these areas, the user equipment segment should be 

included in future assessments when those assessments include the 

fielding of new user equipment capability. As one of the subject matter 

experts we consulted noted, user equipment continues to evolve and 

could potentially embrace PNT technologies and capabilities that would 

reduce required capabilities for GPS satellites. As our report indicates, a 

comprehensive look at user equipment is warranted, especially given that 

the user equipment modernization program is in a pre-development 

phase.

Finally, DOD concurred with our third recommendation to engage 

stakeholders from the broader civilian community identified in PNT policy 

in future assessments of options. In its response, the department said 

stakeholders from the broader civilian community identified in PNT policy 

should be engaged in future assessment of options that include changes 

to the Standard Positioning System performance standard or to 

agreements or commitments the DOD has already made with civil 

stakeholders. However, as we noted in our report, considering the 

unknown effect on the civilian user community of some of the options 

presented, as well as potential future application of new technology for 

user equipment, comprehensive assessment of future GPS options 

should involve the broader PNT community, particularly those 

stakeholders identified in PNT policy.
 

Page 23 GAO-13-729 Global Positioning System

We are sending copies of this report to the appropriate congressional 

committees, the Secretary of Defense, and the Secretary of the Air Force. 

In addition, the report is available at no charge on the GAO website at 

http://www.gao.gov.

If you or your staff have any questions about this report, please contact 

me at (202) 512-2527 or makm@gao.gov. Contact points for our Offices 

of Congressional Relations and Public Affairs may be found on the last 

page of this report. Key contributors to this report are listed in appendix 

III.

Marie A. Mak

Acting Director

Acquisition and Sourcing Management
 

Page 24 GAO-13-729 Global Positioning System

List of Committees

The Honorable Carl Levin

Chairman, 

The Honorable James Inhofe

Ranking Member 

Committee on Armed Services

United States Senate

The Honorable Dick Durbin

Chairman, 

The Honorable Thad Cochran

Ranking Member

Subcommittee on Defense

Committee on Appropriations

United States Senate

The Honorable Howard P. “Buck” McKeon

Chairman, 

The Honorable Adam Smith

Ranking Member

Committee on Armed Services 

House of Representatives

The Honorable C.W. Bill Young

Chairman, 

The Honorable Paul Visclosky

Ranking Member

Subcommittee on Defense

Committee on Appropriations

House of Representatives
Appendix I: Scope and Methodology

Page 25 GAO-13-729 Global Positioning System

House Report No. 112-479 accompanying H.R. 4310, the National 

Defense Authorization Act for Fiscal Year 2013 directed the Commander 

of the Space and Missile Systems Center, U.S. Air Force, to provide a 

report to the congressional defense committees on lower-cost solutions 

for providing GPS capability following the procurement of the GPS III 

satellites.1 The Committee provided that the report should identify the 

system capability, possible implementation approaches, technical and 

programmatic risks, and the estimated costs of any solutions it 

recommends. The committee also mandated GAO to review the report 

provided by the Commander of the Space and Missile Systems Center, 

and to provide its recommendations to the congressional defense 

committees within 90 days after the Air Force report is received.

To determine the extent to which the Air Force’s report, Lower Cost 

Solutions for Providing Global Positioning System (GPS) Capability, met 

the requirements, and to identify additional information that could guide 

future investment decisions, we assessed the report and the approach, 

assumptions, and criteria the Air Force used to conduct the study. To 

accomplish this, we obtained and reviewed documents that supported the 

Air Force’s report. We then discussed the report and our preliminary 

analysis of the report with GPS program and Aerospace Corporation 

officials responsible for the report to obtain their perspectives and clarify 

aspects of the report. We also reviewed other relevant high-level space 

strategic documents including the National Space Policy2 and the 2008 

Biennial GPS Report to Congress.

3 To identify the technological 

advances available to the Air Force and the readiness of those 

technologies, we interviewed officials from Defense Advanced Research 

Projects Agency and the Air Force Research Laboratory. To identify 

additional or clarifying information that could help guide future investment 

decisions, we sent data collection instruments to ten subject matter 

experts from the Positioning, Navigation and Timing stakeholder and 

advisory community to obtain their insights on GPS options the Air Force 

identified, as well as information that could provide additional insights, 

and received responses from seven of them. These subject matter 

 

1 H.R. Rep. No. 112-479, at 70-71 (2012). 

2 National Space Policy of the United States of America (June 28, 2010) (available at 

http://www.whitehouse.gov/the-press-office/fact-sheet-national-space-policy).

3

 Available at http://www.gps.gov/congress/reports/. This was the last report available, as 

the biennial GPS reports were discontinued thereafter.

Appendix I: Scope and Methodology
Appendix I: Scope and Methodology

Page 26 GAO-13-729 Global Positioning System

experts were advisors to the National Space-Based Positioning, 

Navigation, and Timing Executive Committee or were identified by the 

National Coordination Office for Space-Based Positioning, Navigation, 

and Timing as experts in the field, and who were also government 

officials. To assess the completeness of cost estimates cited in the report, 

we assessed the process used to develop the cost estimates in the study 

to determine the extent to which they followed GAO’s 12-Step Reliable 

Process for Developing Cost Estimates assessment tool.4

We conducted this performance audit from April 2013 to September 2013 

in accordance with generally accepted government auditing standards. 

Those standards require that we plan and perform the audit to obtain 

sufficient, appropriate evidence to provide a reasonable basis for our 

findings and conclusions based on our audit objectives. We believe that 

the evidence obtained provides a reasonable basis for our findings and 

conclusions based on our audit objectives.

 

4 GAO, GAO Cost Estimating and Assessment Guide: Best Practices for Developing and 

Managing Capital Program Costs, GAO-06-3SP (Washington, D.C.: March 2, 2009).
Appendix II: Comments from the Department 

of Defense

Page 27 GAO-13-729 Global Positioning System

Appendix II: Comments from the Department 

of Defense
Appendix II: Comments from the Department 

of Defense

Page 28 GAO-13-729 Global Positioning System
Appendix II: Comments from the Department 

of Defense

Page 29 GAO-13-729 Global Positioning System
Appendix III: GAO Contact and Staff 

Acknowledgments

Page 30 GAO-13-729 Global Positioning System

Marie A. Mak, (202) 512-2527 or makm@gao.gov. 

In addition to the contact named above, Art Gallegos, Assistant Director; 

Andrew Redd; Emile Ettedgui; Jean Lee; Marie Ahearn; Karen Richey; 

Roxanna Sun; and Robert Swierczek made key contributions to this 

report.

Appendix III: GAO Contact and Staff 

Acknowledgments 

GAO Contact

Staff 

Acknowledgments 

(121114)
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