U.S. Space-Based Positioning,
Navigation, and Timing Policy
and Program Update
Briefing to the Fifth Meeting of
the GREPECAS ATM/CNS Subgroup
Lima, Peru
14 November 2006
Kenneth Alexander, Senior Advisor
U.S. National Coordination Office for
Space-Based Positioning, Navigation, and Timing (PNT)
Overview
• Introduction
• GPS Constellation & Performance
• Modernization Plans
• U.S. National Space-Based PNT Policy
• International Cooperation
• Summary
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 2
What is Space-Based PNT
• GPS is a space-based radio-navigation system
– Satellites broadcast precise, synchronized time signals and
data allowing users to estimate position, velocity, and time
• Augmentations improve performance of space-
based PNT systems such as GPS
• Space-based positioning, navigation, and timing
(PNT) includes:
– Global navigation satellite systems (e.g. GPS, GLONASS,
Galileo, etc.) and their augmentations
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 3
Global Positioning System
• Baseline 24 satellite constellation in medium earth orbit
• Global coverage, 24 hours a day, all weather conditions
• Four dimensional positioning worldwide
• Satellites broadcast precise time and orbit information
on L-band radio frequencies
• Two types of signals:
– Civil (free of direct user fees)
– U.S./Allied military
• Three segments:
– Space
– Ground control
– User equipment
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 4
U.S. Augmentations
Wide Area Augmentation (SBAS) Local Area Augmentation (GBAS)
Continuously Operating Nationwide Differential GPS
Reference Stations 5
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006
International Augmentations
Space-Based Augmentation Systems Differential GPS Networks
Global Differential GPS System International GNSS Service
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 6
Commercial GPS Applications Span
a Wide Range of Economic Activities
Satellite
Power Grid Financial Operations
Management Transactions
Personal
Navigation
Surveying &
Mapping
Trucking &
Shipping
Aviation
Communications
Network
Synchronization
Railroads Recreation
Fishing &
Offshore Boating
Drilling
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 7
New Applications
Developed Every Day
• Environmental monitoring
• Excavation/Open pit mining
• Child safety, E-911 and other
wireless applications
• Automatic snowplow guidance
• Spacecraft control
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 8
GPS: a Global Public Service
• Free access to civilian signals
– One-way broadcast, like FM radio
• Public domain documentation
– Anyone can develop user equipment
• Worldwide utility providing consistent, predictable,
dependable performance
– Critical component of global information infrastructure
• Owned and operated by the U.S. Government
– Acquired and operated by Air Force on behalf of U.S.
– Paid for by U.S. taxpayers
– Guided at a national level as multi-use asset
Available Now—Empowering the Future
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 9
Overview
• Introduction
• GPS Constellation & Performance
• Modernization Plans
• U.S. National Space-Based PNT Policy
• International Cooperation
• Summary
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 10
GPS Performance
1990s
• L1 C/A Signal
• Selective Availability On
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 11
Recent Launches
Providing worldwide position, navigation & timing
GPS IIR-12 GPS IIR-13 GPS IIR-14(M) GPS IIR-15(M)
23 Jun 04 06 Nov 04 25 Sep 05 25 Sep 06
1stModernized 2nd Modernized
GPS Satellite GPS Satellite
Next Launch scheduled for Thursday, 16 November 2006
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 12
Current Constellation
30 Operational Satellites
31 Operational Satellites
(with planned 16 Nov launch)
(Baseline Constellation: 24)
(Baseline Constellation: 24)
• 16 Block II/IIA satellites operational
• 12 Block IIR satellites operational
• 2 Block IIR-M satellites operational
– Transmitting new second civil signal (L2C)
• Continuously assessing constellation
health to determine launch need
– 2nd New IIR-M satellite launched 25 Sep 06
– Next IIR-M launch 16 November 2006
– 5 Additional Block IIR-M satellites
• Global GPS civil service performance
commitment met continuously since ‘93
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 13
GPS Performance
Current Commitment (since 2001)
13 m (95%)
13 m (95%)
36m or better (global worst case)
36m or better (global worst case)
• L1 C/A Signal
• Selective Availability Off
• Improved Orbit Determination
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 14
Civil GPS Performance Standards
U.S. commitments to civil GPS performance
documented in GPS Standard Positioning Service
Performance Standard (2001)
Performance Representative
Standard Performance
Global Accuracy
All-in-View Horizontal 95% 13 m 4m
All-in-View Vertical 95% 22 m 6m
Worst Site Accuracy
All-in-View Horizontal 95% 36 m 6m
All-in-View Vertical 95% 77 m 10 m
• In support of the service availability standard, 24 operational satellites must
be available on orbit with 0.95 probability (averaged over any day)
• At least 21 satellites in the 24 nominal plane/slot positions must be set healthy
and transmitting a navigation signal with 0.98 probability (yearly averaged)
System accuracy far exceeds current standard
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 15
Civil GPS Performance
7
Standard
6
5 4.6
RMS URE (m)
4.3
4
3.0
3 2.7
2.1
2 1.8
1.5
1.1
1
0
1990 1992 1994 1996 1997 1999 2001 2005
URE - Signal in Space User Range Error
Continuously Improving Performance
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 16
Ground Control System Expansion
Accuracy Improvement Initiative (AII)
South Africa
Alaska
Schriever AFB England
Vandenberg
AFB USNO Wash, DC
Bahrain
Cape Canaveral South
Korea
Hawaii
Ecuador Diego Garcia Kwajalein
Ascension
Tahiti South Africa Australia
Argentina
New Zealand
Master / Backup Control Stations: Provide navigation
estimation (ephemeris and clock), control the satellites,
control the operations network, and schedule missions
GPS / NGA monitor stations: Monitor navigation messages to
collect system performance metrics, collect environment
data, send data to OCS to calculate accurate satellite uploads
Ground antennas: Transmit navigation data / commands and
collect telemetry
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 17
Monitoring Before L-AII
GPS users on approximately half of the Earth’s surface (shown in
white) see at least one unmonitored GPS satellite 100 % of the time
A GPS satellite is considered to be “monitored” if it is seen by at least two GPS tracking stations; the minimum of two stations ensures that an alarm
is caused by a problem on the satellite and not at a tracking station. Monitoring enables GPS operators to identify errors in satellite transmissions;
further upgrades to GPS are needed to ensure that corrective action can executed with sufficient timeliness.
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 18
Monitoring After L-AII (2006)
No GPS users anywhere on the Earth’s surface ever see an
unmonitored GPS satellite
A GPS satellite is considered to be “monitored” if it is seen by at least two GPS tracking stations; the minimum of two stations ensures that an alarm
is caused by a problem on the satellite and not at a tracking station. Monitoring enables GPS operators to identify errors in satellite transmissions;
further upgrades to GPS are needed to ensure that corrective action can executed with sufficient timeliness.
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 19
Legacy Accuracy Improvement
Initiative (L-AII)
• All users see a small accuracy improvement
– Specialized defense systems see greater improvement
• More importantly, all users enjoy improved satellite
monitoring
• Additional tracking data eliminates monitoring gaps
– Without L-AII some satellites were out of view of any
tracking station for over two hours at a time
– Every satellite now “watched” by at least two tracking
stations at all times
• Controllers can now see satellite problems sooner
• User exposure to erroneous satellite signals reduced
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 20
Overview
• Introduction
• GPS Constellation & Performance
• Modernization Plans
• U.S. National Space-Based PNT Policy
• International Cooperation
• Summary
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 21
Why Modernize
• System-wide service improvements in:
– Accuracy
– Availability
– Continuity & Reliability
– Integrity
– Robustness against interference
• Multiple frequencies enables user equipment
ionospheric error corrections
• Interoperability with other GNSS constellations
• While maintaining Backward compatibility
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 22
Second Civil Signal (L2C)
• Designed to meet commercial needs
• Freely available since Dec 2005
– Currently on 2 satellites
– Will be on all future satellites
• Expected to generate over $5 billion
in user productivity benefits
Benefits existing
professional receivers
Increases accuracy Supports miniaturization,
for consumers possible indoor use
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 23
Third Civil Signal (L5)
• Designed to meet aviation safety
requirements
– ARNS band
– Higher power
– Wider bandwidth = 10x gain
– Longer spreading codes (10x C/A)
• May also enable global, centimeter-
level accuracy using new techniques
• Opportunity for international
interoperability
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 24
Fourth Civil Signal (L1C)
• Designed with international
partners for interoperability
– Specifically for interoperability
with the Galileo Open Service
• Modernized civil signal at
L1 frequency
Inside cities
– Original signal retained for
backward compatibility
• More robust navigation across a
broad range of user applications
• Improved performance in
challenged tracking environments
Under trees
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 25
GPS III
• Revised acquisition strategy
– Incremental block approach to reduce risk and
increase flexibility
– Separate contracts for space and ground segments
• Next-generation satellite bus accommodates
increased power requirements
• Provides L2C and L5 full operational capability
– In combination with GPS IIR-M and IIF satellites
• Delivers L1C for interoperability with Galileo,
QZSS and other potential systems
• Significant increase in system accuracy
• Improved availability of accuracy with integrity
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 26
GPS III Performance
Improved
resistance to
interference
1-2m
Estimated 1.8 m horizontal. • L1 C/A Signal (legacy users)
& 3.2 m vertical
Based on:
• Selective Availability remains Off
- Dual frequency • Improved Orbit Determination
- 95% Global Average • L1C, L2C, L5, L1C Signals with
- SIS URE: 0.25 meters
- UEE: 0.8 meters
new user equipment
Ref: GPS III System Spec
(SS-SYS-800) Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 27
Improving GPS Performance
with Augmentations - Today
.
Augmentations enhance GPS accuracy, monitor
integrity. and can improve availability
–<3 m Vertical accuracy with <6 sec time to alarm for aviation
– 2 cm Accuracy for real-time positioning, surveying, etc.
– Sub-centimeter accuracy for geodesy, geology, etc.
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 28
GPS Performance with WAAS (SBAS)
FAA developed Wide Area Augmentation System
(WAAS) to provide accuracy, integrity, availability
and continuity to support all phases of flight
Performance Representative
Standard Performance
Best Site Accuracy
Horizontal 95% 2.5 m .677 m
Vertical 95% 2.5 m .914 m
Worst Site Accuracy
Horizontal 95% 2.5 m 1.078 m
Vertical 95% 2.5 m 1.574 m
Based on observations from January to March 2006. Results are valid when the Localizer Approach
with Vertical Guidance (LPV) service is available. During this time frame, LPV was available 98% to
99% of the time.
SBAS fulfills rigorous user needs today
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 29
Overview
• Introduction
• GPS Constellation & Performance
• Modernization Plans
• U.S. National Space-Based PNT Policy
• International Cooperation
• Summary
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 30
U.S. Policy History
• 1983: President Reagan offered free civilian GPS access
• 1996: National GPS policy declared GPS a dual-use
system under joint civil/military management
• 1997: Congress passes law requiring civil GPS to be
provided free of direct user fees
• 2000: President Clinton turns off Selective Availability
• 2004: President Bush issues Space-Based PNT Policy
- Updates policy while retaining
principles in previous policy
- Recognizes changing national &
international scene since 1996
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 31
Growth in International Global
Navigation Satellite Systems (GNSS)
• Sep 2005 – 2nd civil GPS signal
• Dec 2005 –first Galileo test satellite
• Dec 2005 –3 GLONASS satellites
• 2006 – European EGNOS (non aviation)
• 2007 – WAAS LPV 200’ Decision Height
• 2007 – Japan MSAS ops and then future QZSS
• 2008 – European EGNOS aviation ops (Galileo I)
• TBD– Indian GAGAN and then future IRNS
• 2011 – European Galileo Phase II
• TBD China – Compass
Interoperability key to seamless global operations
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 32
U.S. Policy Goals
• Provide uninterrupted availability of positioning,
navigation, and timing services
• Continue to provide civil services that exceed or are
competitive with other civil space-based positioning,
navigation, and timing services and augmentation systems
• Meet growing national, homeland, economic security, and
civil requirements, and scientific and commercial demands
• Remain essential components of internationally accepted
positioning, navigation, and timing services
• Promote U.S. technological leadership in applications
involving space-based positioning, navigation, and timing
services
• Remain the pre-eminent military space-based positioning,
navigation, and timing service
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 33
National Space-Based PNT
Organizational Structure
White House
Defense
Transportation
National
State Space-based PNT Advisory
Executive Board
Commerce Committee
Co-Chairs: Deputy Secretaries Sponsor: NASA
Homeland Security Defense & Transportation
Joint Chiefs of Staff
Coordination
NASA Office
Host: Commerce
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 34
Key Executive Committee Actions
• 5-Year National Space-Based PNT Plan
– Plan is in draft and FY08 program assessment is in
progress
• Interference Detection and Mitigation Plan
– Department of Homeland Security coordinating U.S.
capabilities to detect and mitigate sources of
interference to GPS and its augmentations
• National Space-based PNT Architecture
– Led by DoD’s National Security Space Office and DOT’s
Research and Innovative Technology Administration
• In 2006, Executive Committee met four times
– Last meeting held October 27
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 35
U.S. Space-Based PNT
Advisory Board
• Board will conduct assessments and make
recommendations to accomplish policy goals
and objectives
– As tasked by the Executive Committee
– NASA is hosting Advisory Board
• Board established and membership being
finalized
– Includes 6 international members
• First meeting projected for February 2007
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 36
Web-based Information
• www.PNT.gov established to disseminate
information on the U.S. National Executive
Committee
– Contains information on Membership, Policy, the
Advisory Board, frequently asked questions, and recent
public presentations
• www.GPS.gov established to disseminate
information on GPS applications
– Brochure on GPS applications available in hardcopy
– Contains additional links to various other websites
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 37
www.PNT.gov
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 38
www.GPS.gov
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 39
Overview
• Introduction
• GPS Constellation & Performance
• Modernization Plans
• U.S. National Space-Based PNT Policy
• International Cooperation
• Summary
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 40
U.S. National Policy on Space-Based
Positioning, Navigation, and Timing
• Provide civil GPS and augmentations free of direct
user fees on a continuous, worldwide basis
• Provide open, free access to information needed to
develop equipment
• Encourage international development of PNT
systems based on GPS
• Improve performance of civil GPS & augmentations
to meet or exceed other international systems
• Seek to ensure international systems are
interoperable, or at a minimum, are compatible,
with civil GPS and augmentations
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 41
U.S. National Policy on Space-Based
Positioning, Navigation, and Timing
• Address mutual security concerns with
international providers to prevent hostile use
• Provide uninterrupted access to U.S. space-
based PNT services for U.S./allied national
security purposes
• Improve capabilities to deny hostile use of any
space-based PNT services without unduly
disrupting civil and commercial access
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 42
U.S. International Cooperation
• U.S. Government has engaged in
formal cooperative arrangements with
Europe, Japan, and Russia since 1996
– To ensure compatibility (non-
interference) and interoperability
with foreign systems
– To maintain and promote a level
playing field in the global market
• Additional efforts ongoing with
Australia, India, Brazil and others
• Multilateral cooperation established
through U.N. International Committee
on GNSS
– As well as ICAO, IMO, and NATO
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 43
GPS-Galileo Agreement
• In 2004, United States and European Community
signed agreement on GPS-Galileo cooperation
– Recognizing importance of compatibility and
interoperability for all parties
– Agreed to spectrally separate signals for military,
civilian, and public regulated services
• Agreed to implement a common, open, civil signal on
both Galileo and GPS III, free of direct user fees
• Working groups established
to continue cooperation:
– Compatibility and Interoperability
– Trade and Commercial Applications
– Next-Generation GNSS
June 26, 2004, press conference at U.S.-EU Summit in
– Security Issues Ireland (U.S. Sec. of State Colin Powell, Irish Foreign
Minister Brian Cowen, EU Vice-President Loyola De Palacio)
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 44
Caribbean and South America
• U.S. Government interested in expanding
cooperation to broader mutual interests
– Civil applications aviation and more
– Free market access, nondiscrimination
– International standards
– Workshop support
– WAAS test bed activities
Seeking continued dialogue with Governments
of Caribbean and South America
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 45
International Committee on GNSS
• Multilateral group chartered
through United Nations
– First Meeting: November 2006
• Purpose: Promote use of GNSS to improve efficiency
and security of transport, search and rescue, geodesy,
etc., particularly in developing countries
– Coordination among GNSS providers to ensure both
compatibility and interoperability
– Assistance to developing countries in use of PNT
services
– Focal point for international information exchange
– Forum for addressing future user needs
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 46
GPS/GNSS
Measures of Effectiveness
• Accuracy
• Bounded Inaccuracy
• Availability
• Continuity
• Integrity
• Resistance to Interference/Jamming
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 47
Spectrum Protection
• Protect spectrum for GNSS (GPS, Galileo, etc) and
other current/future critical systems from interference
– Degradation harms wide variety of plans and programs
– Ultra Wideband, Mobile Satellite Ventures, etc.
• Focus areas:
– Equitable spectrum management and coordination
– U.S. National Spectrum Management legislation
– Galileo cooperation for compatibility and interoperability
• Requires vigilance and early action on emerging issues
– World Radio Conference 2007 rapidly approaching
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 48
Managing Backup Capabilities
• New GPS and Galileo signals improve interference
resistance
• However, all GNSS systems are subject to interference
– Never totally eliminate threat of interference and other
disruptions that can have harmful consequences
• Galileo is not robust backup to GPS; nor GPS for Galileo
• Adequate independent backup systems and/or
procedures must be maintained in the future for critical
applications
– Must determine the minimum level of backup capability
recognizing constrained budgets
– Acceptable from safety and economic impact points of view
• Consider “fail soft” versus “equivalent” backup capability
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 49
Evolution of GPS Performance:
Cooperation
Improved
resistance to Improved satellite
interference availability
~1m*
Maintain Adequate GPS + Other GNSS Services
Backups for Critical
Applications • L1 C/A Signal (legacy users)
• Selective Availability remains Off
Improve Interference
Detection and • Improved Orbit Determination
Mitigation
• L1C, L2C, L5/E5, L1C Signals with
* cm level with new user equipment
augmentation
• GNSS Interoperability
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 50
Overview
• Introduction
• GPS Constellation & Performance
• Modernization Plans
• U.S. National Space-Based PNT Policy
• International Cooperation
• Summary
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 51
Summary
• U.S. policy promotes worldwide use of civil GPS, its
augmentations, and its interoperability/compatibility
with other GNSS systems, specifically Galileo
• GPS is getting better and will continue to improve
– First new GPS signal now available
– Augmentations enable high performance today
– Additional improvements will continue in the future
• International cooperation – a priority for all nations
– Compatibility and Interoperability of signals is critical to
maintaining and improving performance
– Adequate independent backup capability must be maintained
for critical applications
– Spectrum must continue to be protected
Progress through Partnership
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 52
Contact Information
Kenneth Alexander
Senior Advisor
U.S. National Coordination Office for Space-Based PNT
Herbert C. Hoover Bldg., Rm. 6822
14th and Constitution Ave, N.W.
Washington, D.C. 20230 USA
Ph: +1.202.482.5809
Fax: +1.202.482.4429
Ken.Alexander@pnt.gov
Presentation and other GPS information available at:
www.PNT.gov
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 53
Backup
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 54
Questions and Answers
• Isn't GPS controlled by the U.S. military?
• Has GPS ever been turned off by the military?
• Will the United States ever reactivate Selective
Availability, since there is a war?
• Has the U.S. Government thought about
privatizing GPS? If so, what would that mean for
the existing free access to GPS?
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 55
Isn't GPS controlled by the U.S. military?
• GPS is owned by the United States Government
and paid for by the U.S. taxpayer
– United States Government acquires, maintains and
operates GPS through the United States Air Force as a
dual use, civil and military system.
– The Air Force has successfully developed and operated
GPS as a multi-use system for the international
community since 1972
• Outstanding performance of GPS over decades
has earned the confidence of millions of civil and
military users worldwide.
• Management improvements and modernization
efforts directed by the President in his 2004
policy continue this support for multi-user
applications.
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 56
Has GPS ever been turned off by the
military?
• No. Since it was declared operational in 1995, the Global
Positioning System has never been deactivated, despite U.S.
involvement in wars, anti-terrorism, and other military
activities.
• Millions of users around the world have been monitoring
and recording real-time GPS performance on a continuous
basis since its inception. If the civilian GPS service had ever
been interrupted by its operators, the evidence would be
obvious and widespread. No such evidence exists.
Doesn't President's 2004 policy call for
deactivation of GPS during national security crises?
• No. The President’s policy does not include anything about
deactivating GPS. In fact, the policy declares GPS to be an
element of the nation's critical infrastructure that must be
protected against disruption.
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 57
Has GPS ever been turned off by the
military? (continued)
Policy reaffirms U.S. intent to deny hostile uses of space-
based PNT through Navigation Warfare. Navigation
Warfare involves protecting U.S. and Allied use of GPS
while simultaneously preventing hostile forces access
to space-based PNT services and preserving peaceful
civil GPS use outside of an area of military operations.
The U.S. is committed to fielding a range of necessary
denial options to prevent hostile use of space-based PNT
through regional denial of service, minimizing impact to
peaceful users outside the area of conflict.
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 58
Will the United States ever reactivate
Selective Availability, since there is a war?
• Prior to development of Navigation Warfare, GPS
employed a feature called Selective Availability, which
degraded civilian accuracy on a global basis. Selective
Availability was discontinued in 2000 and the United
States has no intent to ever use it again
• The United States does not intend to ever implement
Selective Availability again and is committed to
preventing hostile use of space-based PNT through
regional denial of service, minimizing the impact to
peaceful users
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 59
Has the U.S. Government thought about
privatizing GPS? If so, what would that mean
for the existing free access to GPS?
• There are no plans to privatize GPS
• President's 2004 policy
– Established new management framework for GPS and
its augmentations
– Reaffirmed U.S. Government will provide on a
continuous, worldwide basis civil space-based,
positioning, navigation, and timing services free of
direct user fees for civil, commercial, and scientific
uses, and for homeland security through the Global
Positioning System and its augmentations, and
– Provide open, free access to information necessary to
develop and build equipment to use these services
Fifth Meeting of the GREPECAS ATM/CNS Subgroup, 14 November 2006 60