Global Navigation Satellite Systems Engineering, Policy, and Design
Japan launched its second Multi-Functional Transport Satellite (MTSAT-2) on February 18, opening a new phase of precision air navigation and air traffic control (ATC) over the western Pacific Ocean.
By Inside GNSS
Like some behemoth rocket ship launched in the 1970s, the Global Positioning System sails on through an expanding universe of users and applications, seemingly imperturbable, successful beyond the expectations of its creators, an enormous momentum carrying it into the third millennium.
Like some behemoth rocket ship launched in the 1970s, the Global Positioning System sails on through an expanding universe of users and applications, seemingly imperturbable, successful beyond the expectations of its creators, an enormous momentum carrying it into the third millennium.
To all appearances, GPS is prospering more than ever: a second full signal (L2C) is becoming available to civil and commercial users, a denser ground monitoring system being built out, improved accuracies squeezed out of the algorithms and operational practices at the Master Control Station in Schriever Air Force Base, prices dropping on products with more features and functions than ever, hundreds of millions of receivers in use around the world. A follow-on generation (Block IIF) of satellites with a third civil signal (at the so-called L5 frequency) is being built by Boeing for launch beginning in 2007.
Since its first satellite launch 28 years ago, GPS has blazed a trail for satellite-based positioning, navigation, and timing. Thanks to GPS, global navigation satellite systems have gone from being a technological unknown to becoming a widely recognized utility. GPS, a model and inspiration to its imitators across the oceans.
Or is it?
In fact, for some years now GPS has been a victim of its own success. Performing better than advertised, the system has suffered from budgetary pilfering for other defense programs and risks getting lost in the shifting maze of diffuse dual-use management responsibilities.
“History has shown that the Air Force has had chronic difficulty in adequately funding GPS, even in the absence of the more expensive GPS III satellites,” observes a high-level Defense Science Board (DSB) task force report on GPS issued late last year. “If the Air Force continues to use its GPS investments as a funding source to offset other space/aircraft programs, then GPS service continuity will remain in jeopardy even without the more costly GPS III.” (See article “Bold Advice” in this issue.)
Meanwhile, an Air Force Space Command projection puts the worst-case probability of the GPS constellation falling below its fully operational capability (FOC) of 24 space vehicles sometime between 2007 and 2012 as 20–40 percent. Indeed, the task force argues for a 30-satellite constellation to ensure robust coverage in “challenged environments.”
The timelines for the last three GPS satellite development and launch programs — Block IIR, IIR-M, and III — all slid to the right, as they describe schedule delays these days.
Intermittently starved for fuel, with sporadic guidance from the helm, will new resources reach the system before its speed inevitably begins to slow, threatening its being overtaken by other GNSS vehicles?
Okay, that’s the bad news.
The good news is that no one connected to the program wants to let one of the world’s leading U.S.-branded utilities slip into the shadow of the other GNSSes under development. And steps are under way to ensure that doesn’t happen.
New Game Plan
A long-awaited next-generation program, GPS III, spent well more than hundred million dollars on conceptual studies and several years jogging in place before receiving a renewed go-ahead from the Department of Defense (DoD). The Fiscal Year 2006 (FY06) federal budget allocated $87 million for GPS III. The FY07 budget will be finalized soon in Washington, and current indications are that GPS Block III will receive at least $237 million, according to the GPS Joint Program Office (JPO). Of course, GPS III funds have been zeroed out before.
Current plans call for GPS JPO decision this summer that chooses among proposals submitted for separate space vehicle (SV) and operational control (OCX) segment contracts. Once acquisition strategies are formally approved in Washington, release of the GPS Block III SV request for proposals (RFP) are expected to be released by mid-February and later in the spring for the OCX RFP, according to JPO.
“Minor adjustments are being implemented in the program planning to reflect an incremental development and delivery approach for both acquisitions that will provide increased GPS capability sooner and more frequently over the life of the program,” the JPO told Inside GNSS. Nonetheless, an upgrade in the control segment to accommodate the new generations of satellites is behind schedule, which means that the capability to operationally control those signals will not be available until 2009 at the earliest, according to the DSB task force.
Modernizing Technology
In terms of its fundamental design, the Global Positioning System is nearly 35 years old. More recent spacecraft designs using modern electronics, new rubidium clocks, better satellite management techniques, and navigation message enhancements have improved performance. But the design of the key resource for manufacturers and users, the GPS signals-in-space, is essentially the same as when the first satellite was launched in 1978: a C/A-code on L1 (centered at 1575.42 MHz) and P/Y-code military signals at L1 and L2 (1227.60 MHz).
Over the next five years, however, this situation will change dramatically.
Beginning with SVN53/PRN17, the first modernized Block IIR (IIR-M) satellite built by Lockheed Martin and launched last September 25, GPS has gained a new open civil signal at L2 (centered at 1227.6 MHz). A third civil signal, L5 (centered at 1176.45 MHz) will arrive with the Block IIF satellites now scheduled to begin launching in 2007.
Both IIR-M and IIF satellites will offer new military M-code signals at L1 and L2 with “flex power” capability of transmitting stronger signals as needed. The L5 civil signal will be broadcast both in phase and in quadrature, with the quadrature signal being broadcast without a data message. Air Force Space Command expects to have a full complement of satellites transmitting L2C and M-code signals by 2013; for L5, fully operational capability is expected by 2014.
Generally, the new signals will be characterized by longer code sequences broadcast at a higher data rate and with slightly more power. Beginning with the IIR-M satellites, the Air Force will be able to increase and decrease power levels on P-code and M-code signals to defeat low-level enemy jamming — a capability known as “flex power.”
These new signal features will support improved ranging accuracy, faster acquisition, lower code-noise floor, better isolation between codes, reduced multipath, and better cross-correlation properties. In short, the new signals will be more robust and more available.
Looking farther ahead, another civil signal at L1 is planned to arrive with the GPS III program. Under a GNSS agreement signed with the European Union in June 2004, this will be a binary offset carrier (BOC 1,1) signal similar or identical to that of the Galileo open signal. This is expected to simplify the combined use of GPS and Galileo signals. Nominal first launch date for a GPS III spacecraft is currently 2013.
Modernization will also take place in the ground control segment. Six GPS monitoring stations operated by the National Geospatial-Intelligence Agency (formerly the National Imagery and Mapping Agency) have been folded into the existing five Air Force GPS monitoring stations (which includes the Master Control Station at Schriever AFB, Colorado.) This will eliminate blank spots in coverage and support Air Force plans to monitor the integrity (or health) of civil signals as well as military signals.
New Political Structure
Under a presidential national security policy directive (NSPD) released in December 2004, a National Space-Based Positioning, Navigation, and Timing (PNT) Executive Committee and Coordination Office have taken over from the Interagency GPS Executive Board (IGEB). Mike Shaw, a long-time GPS hand on both sides of the civil/military interface, stepped in toward the end of 2005 as the first director of the PNT coordination office.
Establishment of the PNT committee — now cochaired by deputy secretaries of defense and transportation, Gordon England and Maria Cino, respectively — kicked GPS leadership up a notch from that of the IGEB. Other members include representatives at the equivalent level from the departments of state, commerce, and homeland security, the Joint Chiefs of Staff and the National Aeronautics and Space Administration.
The committee had met once shortly after its formation under President Bush’s NSPD, but a January 26 gathering marks its first with the current leadership. In addition to getting acquainted with one another and the PNT topic in general, the agenda covered such issues as the DSB task force report, modernization and funding of GPS, and the new UN International Committee on GNSS (see article "What in the World is the UN Doing About GNSS?" in this issue).
Without a director and coordination board in place, the executive committee was unable to get on with many of the tasks assigned it by the presidential directive, including writing a five-year plan for U.S. space-based PNT and appointing an advisory board of outside experts. With Shaw on board, the coordination board now has seven staff members detailed from agencies represented on the executive committee.
A charter for the advisory board has been drafted and awaits approval by the committee, as does a draft of an international PNT strategy prepared by the State Department under the direction of Ralph Braibanti, who heads that agency’s space and advanced technology staff.
By
DSB Task Force Members
Co-Chairmen
Robert Hermann, Global Technology Partners, LLC
James Schlesinger, MITRE Corporation
DSB Task Force Members
Co-Chairmen
Robert Hermann, Global Technology Partners, LLC
James Schlesinger, MITRE Corporation
Task Force Members
John Darrah, Institute for Defense Analyses
William Delaney, MIT Lincoln Laboratory
Arnold Donahue, National Academy of Public Administration
Kirk Lewis, Institute for Defense Analyses
USAF Gen. James McCarthy (Ret), U.S. Air Force Academy
Steve Moran, Raytheon Corporation
Ruth Neilan, NASA Jet Propulsion Laboratory
Robert Nesbit, MITRE Corporation
Brad Parkinson, Stanford University
James Spilker, Stanford University
John Stenbit, Private Consultant, former Assistant Secretary of Defense for Networks and Information Integration (ASD NII)
USAF Gen. Larry Welch (Ret), Institute for Defense Analyses
Executive Secretary
Ray Swider, ASD NII
Recommendations from a high-level Defense Science Board (DSB) Task Force on the Global Positioning System, if implemented, would profoundly alter the way that GPS is managed and operated: a significantly redesigned and enlarged satellite constellation, a larger contractor role in running the system, more focused responsibility and authority for GPS, and permanent elimination of Selective Availability.
A memo from U.S. Secretary of Defense Donald Rumsfeld, drawing on the task force analysis and recommendations, has been drafted to provide guidance to departmental leaders and the Air Force officials responsible for overseeing and managing the program.
The DSB presented the group’s analysis and recommendations in a 109-page report, “The Future of the Global Positioning System,” signed by Under Secretary of Defense Kenneth Krieg and released publicly in early December. In a far-ranging critique, the report identifies potential gaps in sustainment of the GPS satellite constellation, delays in upgrading the operational control segment, and diffuse lines of authority within the Department of Defense (DoD). It calls for changes in how the United States funds GPS, how DoD manages the system and acquires military user equipment, and how the U.S. Air Force contracts for modernized GPS infrastructure and operates the satellites.
The ultimate significance of the report probably depends on the willingness and perseverance of its co-chairs, former defense and energy secretary Jim Schlesinger, and former National Reconnaissance Office director Robert Hermann, to advocate vigorously for the product of the task force’s labors.
Schlesinger briefed Rumsfeld and Deputy Secretary of Defense Gordon England, who also co-chairs the National Space-Based Positioning, Navigation, and Timing (PNT) Executive Committee (NPEC). The DSB report was on the committee agenda for its January 26 meeting.
Established by Krieg’s predecessor Michael Wynne, the task force’s objective initially had been framed to address competitive concerns in light of Europe’s move to implement its own GNSS, Galileo.
“Without significant DoD movement on GPS, the introduction of Galileo may marginalize GPS to an expensive military use only system,” Wynne wrote in an April 9, 2004, memo to DSB Chairman William Schneider, Jr.
Within a couple of months, however, the signing of a US/EU agreement on cooperation in GPS and Galileo matters broadened the focus of the task force — fortuitously, one might argue. President Bush’s policy directive on space-based positioning, navigation, and time further influenced the scope and emphasis of the group’s work.
An impressive mix of old GPS hands and former defense leaders comprised the task force — a gathering of what used to be known in less gender-sensitive days as “graybeards” or “wise men.”
“It was a unique confluence of expertise and leadership that we won’t have again for some time,” says Jules McNeff, vice president of strategy and programs for Overlook Systems Technologies, Inc., who staffed the task force and oversaw the drafting of its report. McNeff himself has more than 20 years invested in GPS, both inside and outside of DoD.
Rattling Cages
After 18 months of study, more than a dozen outside briefings, and deliberations, this “unique” task force produced a trenchant volume of solidly reasoned findings and recommendations (The full report can be download from the Internet at <http://www.acq.osd.mil/dsb/reports/2005-10-GPS_Report_Final.pdf>.)
Inevitably, such a collection of strong-willed, independent free-thinkers with a broad mandate produced some real zingers. Among those proposals:
• Permanently eliminate Selective Availability (SA), the ability to degrade positioning accuracy in open civil signals “with the objective of deleting the hardware and software overhead for its implementation from throughout the future system.”
• Change the constellation to a three orbital plane configuration with 30 satellites, rather than the current requirement of 24.
• “Selectively” integrate technical personnel from private contractors into direct satellite monitoring and control operations at the Master Control Station at Schriever Air Force Base — a break from long-standing tradition of only uniformed Air Force personnel operating the satellites.
• Prepare for discussions regarding possible use of Galileo services for military purposes by NATO member nations.
• Require each U.S. military service to fund its own R&D program to best ensure position and timing information is integrated into equipment and operational capabilities. (The function is currently coordinated by the NAVSTAR GPS Joint Program Office.)
• Designate a single focal point within the Office of the Secretary of Defense responsible for all GPS policy and oversight matters.
• Limit GPS III satellite weight to permit launch of two satellites on a single mid-size launch vehicle, including the transfer, if necessary, of the Nuclear Detonation Detection System now on board GPS satellites to other host spacecraft.
Leadership and Capacity
Throughout the report’s analysis and recommendations, two concerns stand out: the task force’s strong desire to see a greater GPS system capability funded, built, and brought on-line in a timely fashion, and the perceived need to create a clear, unified line of authority and responsibility for GPS — what McNeff refers to as “a single belly button” that can be pushed to get GPS the attention it needs.
But just sustaining the GPS constellation at its current 24-satellite fully operational capability (FOC) level is at risk, according to the task force, as a result of budgetary uncertainty and delays in modernization programs. States of the task force findings:
“The current on-orbit inventory is 28 satellites; however, with expected failures, the AF Space Command December 2004 PNT Functional Availability Report reflects a nominal probability between 5–20 percent and a worst-case probability between 20–40 percent that the constellation will fall to fewer than 24 satellites in the 2007– 2012 period based on current satellite replacement schedules.”
Moreover, the capability to operationally control new GPS L2C and L5 signals will not be present in the GPS control segment until 2009 at the earliest, the report suggests.
Upgrading the Block IIR and IIF satellites to include M-code, L2C, and L5 signals, along with an annual rather than multi-year purchase strategy, nearly doubled the cost of those spacecraft. Looking ahead, the price tag for GPS III satellites will be nearly double that of the preceding generation. As a way to mitigate the expense of the GPS III program, satellites should be designed so as to allow two to be launched at the same time, even if this means eliminating unrelated functions such as NDS.
“The concern that the DSB has is that, if GPS III becomes another massive satellite, the department can’t afford it,” task force member Brad Parkinson told Inside GNSS. “GPS really needs 30 to 36 satellites, but the Air Force requirement is only 24.” Increasing the strength of GPS transmissions should not pre-empt the goal of populating the constellation with more spacecraft, adds Parkinson, who was the first director of the GPS Joint Program Office. “Geometry is more important than extra power.”
As for the leadership issue, one of the report’s recommendations proposes, “The Secretary of Defense should also clarify lines of authority and responsibility within the Department to eliminate ambiguity regarding GPS responsibilities that hinders decision making internally and that perpetuates the perception externally that the DoD has lost sight of its GPS stewardship responsibilities.”
Noting the President’s creation of the PNT Executive Committee, which occurred during the task force’s deliberations, the report says the new policy body “affords an opportunity for all stakeholders to correct deficiencies of the former Interagency GPS Executive Board [IGEB].” That assessment stems largely from the fact that the President’s national security directive creating the executive committee also elevated the level of its leadership to deputy secretaries of transportation and defense.
Nonetheless, reflecting the difficulty of the IGEB to gain sustained participation from its co-chairs, the task force recommends, “If Deputies do not routinely participate, then designated representatives to the . . . PNT Executive Committee . . . must be formally empowered to speak for and act on behalf of their respective Deputies for all matters coming before the [committee].”
Says Parkinson, “The [PNT] executive committee can do some good if it gets the attention of people who can make some changes.”
Mike Shaw, director of the National Space-Based PNT Coordination Office that will provide staff support for the executive committee, says he hopes the office will exercise “more insight responsibilities.” By this Shaw means looking into the agencies involved with GPS and identifying “disconnects” the prevent a common exercise of GPS policy, and then putting this information “in front of senior people” who can make the needed changes.
Glen Gibbons
NovAtel Inc.
The Defense Science Board (DSB) Task Force report focuses primarily on project strategies for correction of a number of known GPS deficiencies, with the impetus to fix things being driven by the potential future impact of Galileo. There are some good thoughts and several opportunities for improvement.
The President’s U.S. Space-Based Positioning, Navigation, and Timing (PNT) Policy announced in December 2004 already highlights areas where GPS and GPS assets are vulnerable to jamming. The DSB Task Force report once again highlights this area of vulnerability, especially for civilian users.
As the supplier of GPS reference receivers to the FAA Wide Area Augmentation System (WAAS) network and participant in the development and supply of the Galileo Reference Chain receivers for the Galileo ground control system, NovAtel has proposed an approach using a combination of antenna array and signal processing for protection of the NovAtel network reference receivers. These extensively tested and qualified national networks could substantially improve GPS signal monitoring – if only the GPS control segment could access data from the WAAS networks in US, Japan, Europe, India and even China.
NovAtel supports the initiative to permanently increase the GPS constellation to 30 satellites, and we are ready for the new L2C and L5 signals. More space vehicles means a greater probability of seeing good geometry signals, and more signals at different frequencies will improve system accuracy and signal reliability. The DSB report does not, however, appear to consider the combined use of Galileo and GPS, which together will provide up to 60 satellites. This will really improve signal reliability and usability!
Keeping pace with the coming of Galileo is a recurring theme and the threat of a competitive system runs throughout the report. However, it does not really support the need to actively monitor and use Galileo for national programs such as WAAS and Local Area Augmentation Systems (LAAS). NovAtel has already fielded a commercial dual-mode GPS/Galileo 16 channel receiver, which can provide users with the benefits of new signals and which works with both systems.
Such receivers could be readily added to the existing WAAS reference receivers. Moreover, NovAtel expects to be deeply involved in Galileo and GPS receiver development for many years to come.
As the world moves into a GPS/Galileo dual-constellation environment, where dual use will be pervasive, it seems strange that the U.S. Department of Defense may have to remain reliant on single-mode GPS while the rest of us benefit from the improved accuracy and reliability which GPS and Galileo together will provide.
Tony Murfin
Vice President, Business Development
NovAtel, Inc.
Lockheed Martin
The Defense Science Board report thoughtfully addresses many key issues as the government looks forward to and works to define future generations of the Global Positioning System. Many of the issues raised in the report have been examined by industry and the Air Force as part of the GPS III architecture and requirements studies.
The report will serve as an important resource as the Air Force finalizes its plans to acquire next-generation space and ground architectures. GPS III is a major focus area for Lockheed Martin, and we stand ready to help the Air Force create a next-generation system that will address the challenging military transformational and civil needs across the globe, including advanced anti-jam capabilities, improved system security and accuracy, and reliability.
Steve Tatum
Sr. Manager, Communications
Lockheed Martin Space Systems Co.
EADS Space Services
The DSB Task Force report provides a very interesting and fair overview of the Global Positioning System challenges from a performance, competitiveness and governance point of view in view of the upcoming European alternative “Galileo.” As a major actor of the future Galileo PNT system, EADS has a particular interest in the GPS evolutions and policy, especially in the field of cooperation with leading U.S. manufacturers.
The Task Force position is particularly appreciable for the navigation industry as it recommends promoting “opportunities for cooperation,” “true civil interoperability,” and considering “alternative means of funding and governance” for GPS to facilitate its international support. The underlying purpose of this collaborative approach is to improve the commercial and cost efficiency related to the PNT civil signals.
Through its recent site distribution agreement, Galileo has made a significant step forward and will provide in the near future increased satellite signal availability worldwide for navigation purposes. It is indeed a primary objective to promote the combination of the GPS and Galileo constellations for civil users in order to improve significantly the overall positioning accuracy and integrity.
Consequently, the report supports the definition of an international civil signal standardization allowing combined GPS-Galileo receivers. This common effort is necessary to facilitate a widespread usage and certification of the signals in the commercial sector. Therefore, all parties should sustain the systems interoperability with the “full disclosure of an open signal structure” and well defined geodetic and time reference transformations in receivers.
EADS also welcomes the task force proposal to “explore cooperative exchange of monitoring information” provided by the WAAS and EGNOS systems as well as a “collaborative approach” to manage and monitor both systems for better performances.
Finally, we consider that the adoption of a separate strategy and governance for the GPS military and civil activities would facilitate the system modernizations, international cooperation, and augmentations focused on the civil particular interests, while maintaining a superior military capability.
To conclude, we regret that tangible directives have still not been issued by the U.S. authorities in the direction initiated by the US-EU agreement of June 2004. It would add great benefits to the user community to initiate the creation of joint entities aimed at addressing the performance, the standardization, and the vulnerability of the GPS and Galileo signals across the Atlantic.
Martin U. Ripple
Director Galileo Program
EADS Space Services
The Boeing Company
We continue to execute on our commitment to GPS IIF production, with a goal to make the IIF the most capable and reliable navigation satellite to join the constellation. We also look forward to seeing the customer’s requirements for GPS IIIA when the request for proposal (RFP) is issued. We’re excited about the new IIIA program and await the competition.
I believe that the majority of the [DSB] comments relate to the future of GPS requirements and that is the purview of the GPS Joint Program Office (JPO). Boeing is ready to respond to the requirements, with whatever DSB recommendations are included. The job of the JPO is to take the opinions of all appropriate experts and meld them into a future roadmap and set of requirements which are sent to industry to propose and build. Again, Boeing stands ready to respond with a compelling proposal.
Mike Rizzo
Director, Navigation Systems
The Boeing Company
L-3/Interstate Electronics Corp.
In general, the DSB report is “right on.” Their assessments regarding current shortfalls and urgent needs bring to light the vulnerabilities that our current war fighter is faced with when depending on GPS. It is true that improved satellite coverage is needed for challenged (e.g. urban) access, modernized GPS availability to the war fighter is too far out in time, and enhanced anti-jamming (AJ) capability is not being adequately funded or fielded.
The report makes a good point about the need for sufficient, but not excessive AJ capability in user equipment. Industry has demonstrated scalable, cost-effective AJ solutions that include hardware and software-only augmentations that satisfy the DSB’s recommended minimum acceptable level of 90 dB jamming resistance. These capabilities are easily and readily incorporated into user equipment, yet there are few programs in place to incorporate and deploy it.
Agencies like the Office of Naval Research (ONR) and Air Force Research Lab (AFRL) are financing technology programs that include AJ improvements for GPS; however, these are not pointed at fielding new equipment for the war fighter. Case in point — the Modernized Receiver Card Development Program, which is in place to help establish “proof of design” for modernized GPS does not require this type of AJ enhancement.
Hopefully, with the promulgation of the DSB report more military agencies will recognize the emerging jamming threat and programs will begin requiring the deployment of more AJ capability for GPS user equipment.
L-3/IEC agrees with the report’s assessment that the new PRONAV security architecture is essential to providing the needed Information Assurance improvements to military GPS (although one might argue with the details in the DSB’s comparison of performance benefits that PRONAV provides).
However, one must be cautious with considering the permanent removal of SA or, even more importantly, with opening up DoD acquisition policies to allow non-military GPS equipment. The gamble is the price our war fighter pays by having the wrong positioning, navigation, and timing (PNT) information because he’s using vulnerable commercial GPS signals. That price can be the difference between life and death.
Carlton Richmond
Chief GPS Technologist
L3 communications, Interstate Electronics Corp
