Quotes Of The Quarter
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"Telecommunications networks are heavily dependent on GPS for timing. If GPS ever went down, your cellular phone, or your pager, wouldn't work, and the wirelines (Bell companies, etc.) would have trouble." Edward Butterline, Telecomm Soultions, at GPSIC meeting
"Work being done now on the 2nd and 3rd GPS frequencies
is really important in the long term evolution and development of GPS."
Joseph Canny, DOT Deputy Assistant Secretary for Policy and International
Affairs
From The President: Ben Peterson
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It was an honor to be elected and serve as president of the Institute for this past year, and I thank you for the opportunity. The fine support of the national staff and numerous volunteers made the President's job easy.
I would like to highlight some of the accomplishments of the Institute over the past year. Some of these I was personally involved in, but many were solely due to the efforts of others.
Vol. 5 of the series of GPS red books was published.
The ION, in cooperation with NOAA, sponsored a series of comprehensive meetings or public forums on "modernization" issues to assist in the process of providing civil input into the design of the next generation of GPS satellites. Special thanks to Keith McDonald and David Minkel, who helped in arranging and directing these meetings, for their efforts.
ION conference proceedings became available on CD-ROM for the first time on a trial basis for the ION GPS-97 meeting, and plans are to continue this service on a permanent basis beginning with the 1999 Annual Meeting.
McDonald, a former President of the ION, was elected President of the International Association of Institutes of Navigation (AIAN). The U.S. ION proposal to host the next IAIN World Congress in June of 2000 was accepted.
The Institute partnered with the Coast Academy Center for Advanced Studies, and NOAA, in hosting, "Navigating the Uncertain Waters of the 21st Century: The Role of New Technologies in Building a Competitive and Secure Maritime Infrastructure" on May 22. The keynote speaker, Richard Clarke, was named later that day by President Clinton as the national coordinator for security, infrastructure protection and counterterrorism during Clinton's commencement address at the U.S. Naval Academy.
In additions to the partnerships with NOAA and the Coast Guard Academy, cited above, the Institute sought out and effectively partnered in other areas. For example, NIMA is co-hosting this year's Annual Meeting, and Draper Laboratory will be co-hosting the 1998 Annual Meeting.
Again, thank you for the opportunity to serve as your President
and for your support. I extend congratulations and wishes of good luck to
our new President, Frank van Grass.
From The Editor: Hale Montgomery
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The earnest search for civil and military enhancements that will better the lives of those using GPS in the next century has engaged the time and talents of a broad spectrum of persons in government, the private sector and academia.
A DOT official estimated informally that more than 100 persons are involved in the overall GPS "modernization" effort on the multi-agency Senior Steering Group alone, an ad hoc group reporting to the Interagency GPS Executive Board (IGEB). To this, add contributing groups in the military, in civil agencies, the private sector and academic institutions who are "working the problem" of making improvements to the Block IIF program of the 2000s, and one has a cast literally of 100s, performing on a national stage.
The ION, not to be overlooked here, has proudly contributed to the process. Starting in June last year at the Annual Meeting in Albuquerque, the ION decided to assist in the coordination of civil contributions to the GPS "modernization" plan, and subsequently cosponsored with the federal GPS Interagency Advisory Council (GIAC) a series of comprehensive public forums held in August, November, January and March.
Decision Point
This flood of findings is channeled intensely toward a meeting of the IGEB in mid-August when decisions compelled by program contract imperatives are due to be made on adding 2nd and 3rd civil coded frequencies to future GPS spacecraft. Some of the issues and policies involved are unique.
Never before has civil funding for the military-operated GPS program been tried. Finding new frequencies, always a contentious issue, will require a measure of international cooperation. And the IGEB is operating under a relentless timeline: any delay in deciding on civil add-ons could drive contract costs unnecessarily high. Grafting civil parts to a military body in space, like the dramatic first heart transplant operation where rejection meant life or death, involves some delicate policy surgery in the case of GPS.
The military appears to have its priorities in order - among other things, more signal power, minimal changes in user equipment and ground control, and secure ways to accommodate expanding civil use of the system without compromising the essential military mission of GPS. Pentagon leaders are more familiar with handling inter-service big buys, with coordinating requirements, contracting and funding for large programs. It's the civil side that has looked confounded and uncoordinated.
The Pentagon has the high-level Joint Requirements Oversight Commission, supported by the Independent Review Committee and others, to manage GPS options. On the civil side, the Analysis of Alternatives (AOA) group has been formed to feed civil inputs into the Steering Group and the IGEB.
Still, the civil enhancements are far from a done deal. Keith D. McDonald, former ION president, noted with prescience in the last ION Newsletter: "Frequently, there are political, institutional, financial and other factors that outweigh technical considerations." As the coach told his team that was leading in the playoffs: "It ain't over until the fat lady sings."
Pricing Options
Getting a handle on the added system costs for the protean "modernization" options that have been discussed is difficult. Ken Lamm, DOT Policy Office, offered some estimates on capital costs at the meeting of the Civil GPS Service Interface Committee in Alexandria, VA, in early April. He referred to them as "cost projections" or "total cost guess" to make the changes in Block IIF spacecraft and control segment, fiscal years 1999-2005.
An Update On WAAS And LAAS
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The Federal Aviation Administration's parallel programs to provide GPS-based navigation for aircraft - the wide area and local area augmentation systems, or WAAS and LAAS - are approaching some milestone events in the coming year.
Updates on the programs were presented by FAA spokesmen at the Civil GPS Service Interface Committee (CGSIC) meeting in Alexandria, VA in early April. At the same time, Keith McPherson of Airservices Australia presented a paper on an alternative augmented system now being tested in that country.
In a related development a week later, the Air Transport Assn. (ATA), representing the airlines, and the Aircraft Owners and Pilots Assn.(AOPA), a 340,000-member trade group that speaks for general aviation, issued a joint statement provisionally supporting both the WAAS and LAAS programs, but urging a slower, more measured transition to satellite-based air navigation (see Aviation Groups Offer Support below).
WAAS Program
The initial operating phase of WAAS is scheduled for July 15, 1999, Don Hanlon of the FAA toldthe CGSIC meeting April 8, but service then will be limited to less than 85 percent of the lower 48 states. That will be in an egg-shaped area in the center of the country; the heavily traveled U.S. Northeast, for example, will not have service.
The first WAAS aircraft receiver equipment should be available in the same time frame, Hanlon said. It may be years, however, before commercial, business and private aircraft owners install the equipment. Hanlon estimated that 70 to 80 percent of aircraft would have to be equipped with certified WAAS receivers before the system could be fully used for sole source navigation in U.S. airspace. Ultimately, if plans are realized, a single WAAS receiver could replace a suite of on-board electronics for en route, terminal, and precision approach navigation, while some ground-based airnav aids could be decommissioned. Precision flight embraces Category I approaches down to 200 feet altitude and two miles from the runway.
LAAS Program
Contracts for the full-scale development stage for LAAS, meanwhile, should be let by October. The development stage will continue until 2003; thereafter, procurement of actual hardware will begin, explained Ray Swider, FAA. The FAA is looking for commercial partners to develop LAAS. Eventually, 143 systems will be procured, composed of 31 Category I systems (the first to be installed), and 112 Category II/III systems at major U.S. airports. Cat III is to have the capability of bringing aircraft on instruments to within a few feet of landing on a runway.
LAAS will be a "lookalike" to present Instrument Landing Systems (ILS), using existing aviation VHF radio links and providing service within a 30 nautical mile radius of an airport. Asked if the technology would be deployed internationally, Swider replied, "I hope that the International Civil Aviation Organization (ICAO) will adopt the system and that it will become the international standard."
While the U.S. WAAS program relies on L-band commercial satellites to relay GPS corrections to aircraft, Airservices' McPherson described a system undergoing tests in Australia using the Optus domestic communications satellite for wide area relay of similar data via VHF. Costs would be substantially lower than WAAS. McPherson said tests had achieved accuracies of 0.6 meters to two meters. Some 13 other countries, he said, had approached Australia indicating interest in the program. Because of weather conditions differing greatly from the United States, and other reasons, Australia has no great need for LAAS.
The WAAS program, troubled by cost increases and delays, is under intensive review within top management at the FAA. ATA President Carol Hallet said, "The program appears to be suffering from unbounded cost growth, and potential operational benefits are eroding." In mid-April, turmoil continued within the program at the FAA with the dismissal of team leaders Larry Stotts and J.C. Johns from supervision of the WAAS and LAAS programs.
Aviation Groups Offer Support
In a statement issued April 16, ATA and AOPA recommended that WAAS as a sole means navigation service be implemented no earlier than 2001, pending the results of an independent risk assessment of the program and its sweeping impact on critical flight safety issues. Previously, the two organizations had taken discordant positions on WAAS and LAAS: AOPA strongly supported rapid implementation of WAAS; ATA highly favored LAAS, and offered no support to WAAS.
The two groups representing commercial and private aviation interests also recommended the FAA accelerate development of airspace and flight procedures for GPS-based navigation augmented by WAAS, and accelerate implementation of public-use LAAS services as part of test sites for the FAA's flight test program.
The FAA should not discontinue existing ground-based radio navigation services, the groups said, until user requirements for levels of safety and operational services can be provided by space- based navigation. Further, the two organizations said the FAA "should achieve consensus with the user community on a transition schedule" before changing to space-based systems.
Joseph Dorfler, ATA, said equipment changeovers for commercial aircraft would not be too costly if the refits can be done during regular maintenance intervals. He also pointed out that new space-based navigation gear could replace or substitute for expensive inertial navigation equipment, perhaps resulting in some cost savings.
But Dorfler, former head of the FAA satellite office, cautioned
that the transition to WAAS and LAAS will be "a non-trivial event.
This is a big change." Beyond the development of hardware that will
provide one-second integrity warnings for Cat III landings, certification
of equipment, development of new flight procedures, in lieu there of the
following, training of controllers and air crews, and other issues must
be resolved.
GPS Modernization - In Our Lifetime?
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Since January first of this year the Interagency GPS Executive Board (IGEB) working group has been meeting weekly to work on issues associated with new capabilities to be included in an improved Global Positioning System (GPS).
The IGEB was established by a Presidential Decision Directive (PDD) to address issues facing GPS in the future. The PDD formally recognized GPS as a 'Dual Use' utility. This move was a needed step in addressing the growing use, and requirements for increased capability needed by all users of GPS, not just the military.
In March, the IGEB announced that a second civil frequency would be placed on L2 and recognized support for a third civil frequency. This is good news since it took more than two years to reach this decision. Now, the critical question is: when will we have access to this new capability? The official word is by 2005.
Is this realistic? Acquiring the required funding and a clear commitment to begin the modernization program will be the determining factors on whether this new capability will be realized any time soon.
Limitations
If GPS were starting anew, the answers to these questions would be much easier to determine. There now have been 20 years of operational experience with one form or another of the GPS. Procedures and processeshave been established that, if not changed greatly, reduce the ability to improve GPS services. First, changes are limited by the one-for-one satellite replacement methodology of getting the new capability in space. Only when a replacement is needed is a satellite launched. With the life of the current satellites increasing (more than 10 years), the time between replacement is therefore also increasing. The currently constellation of satellites is being replaced with IIRs. Of the IIR series currently under production, one is on orbit and 17 are programmed for use prior to deploying any 'modernized' satellites i.e., IIFs. Due to contractual constraints, even with the IIF program we cannot expect the additional capability to be implemented until vehicle 7 of the IIF buy. That is, of course, unless the Air Force modifies the contract to provide the capability sooner. For this to occur requires additional funding not presently programmed.
Funding
Over the years, funding for GPS sustainment has minimally met the modest needs of the military. The accuracy and availability of the GPS system have been sufficient for their current operations. Only during the Gulf War period was there additional funding provided to immediately increase operational capability. For the military user, the major operational shortcoming of the current system is the susceptibility to signal interference either unintentional or deliberate. Though this problem is recognized, little research and development funding had been provided to correct the situation until recently. Historically, even in times of greater resource availability the DoD has not fully funded GPS. Even today there is a funding shortfall of more than 15 percent for the sustainment program.
The Air Force, the executive agent for the Department for Defense, does an excellent job operating the system. In the past it has funded the minimal current system. In 1997, DOT signed a memorandum of agreement stating that it would be responsible for funding the second civil frequency. Now with the understanding that GPS is broadening its services to meet the civil and commercial requirements, the Air Force should expect that some of the funding burden be provided by other agencies. With the opportunity of this occurring, the Air Force has energized the chain of command to put pressure on the Secretary of Defense to find more non-DOD money to support the GPS modernization program before it commits to modernization. For the Air Force this appears to be a golden opportunity to reduce even more the total obligation authority programmed for GPS, releasing it for use on other critical programs. As good as this sounds, the ability for the two Departments to come to an agreement on what each considers their fair share will consume more time than making the frequency decision.
Though there has been considerable activity for defining GPS modernization requirements, as of today there are no monies programmed to begin the modernized GPS. Currently, the modernization program is beyond the DOD five-year program planning process. For any new capability there must be money made available to the Joint Program Office in the fy1999 budget that Congress is working on now. As many know, it is much easier to work the next generation capabilities if unconstrained by funding realities. When the modernization program comes into the planning window the competition for money is intense and major trade-offs may be made. For the Air Force it is perhaps a choice of improving an already existing system (GPS), or using the funds to get a new yet-to-be-built F-22 fighter. The money for GPS modernization will come by reducing by two or three the total number of fighters that will be in their inventory. With or without a GPS modernization program the Air Force is entering a period (2002-2006) where all of its major new systems have funding demands that far exceed projected available funds. You may have recently seen symptoms of this with articles in the news talking about a two-year delay in the fielding of the F-22 and delays in the new launcher programs. It is in this environment that additional money is needed to begin the GPS modernization program. Under these conditions it is more than likely that start of the GPS modernization program also may slip two or more years, even though the IGEB is committed to seeing a second civil frequency by 2005. The IGEB does not possess the funding authority to make any of this happen. It can influence the respective departments and agencies but can not insure that the needed money is made available.
Facing Delays
The need for additional GPS capability is clearly recognized and yet the bureaucratic funding process and the competition that GPS will experience within DOD will ensure that GPS modernization will not begin anytime soon. Can we wait until 2012-2015 to have even limited capability?
Thus, today we desire to begin a new generation of GPS
services but we may be put on hold, or see our desires continually delayed.
What will change this picture is a unified message from all of the user
communities that engages the Executive Branch and Congress to recognize
the need for early implementation of these new GPS services, and act now
to fund. If the situation remains business as usual, we will have a well-defined
set of requirements to read and review - but no new capability on orbit!
The Price Of Success
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The addition of a second coded civil signal on future GPS satellites may have little effect on higher priced receivers, but it could significantly impact the price of handheld units manufactured for the mass consumer market.
James White, vice president of marketing, Magellan, a subsidiary of Orbital Sciences Corp., makers of the popular handheld Pioneer and its successor, the 12-channel Blazer-12 receivers, tells us that the way it looks now, a second civil signal "may add more expense to a consumer product than the market can bear." The Pioneer now sells for $100, the Blazer-12 for $120 retail.
In effect, the handheld of the future, circa 2005 and beyond when the Block IIF spacecraft enter the GPS constellation, may be a dual-frequency receiver, as contrasted with the present single frequency (L1) receivers. Presently, White says, that looks like it will mean two RF front ends and new correlators to accommodate a second signal.
Such upgrades would add weight, cost, size, perhaps greater battery power. And that means, as a preliminary engineering guesstimate, about $75 or $80 more per unit. Assuming no marked changes in receiver technology, and the market demanded dual-frequency units, that would raise the Pioneer to $175-80, and the Blazer-12, now $120, to more like $200, for the consumer trade.
As for a third frequency, if SA is off or suppressed around
that same timeframe, there probably would be no need to utilize it in a
consumer-oriented handheld receiver that requires far less capability than
precision instruments.
Aviation Divided On LORAN-C
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General aviation (GA) users generally support Loran-C as the best and most widely available backup navigation system for GPS; GA and marine users comprise the largest user community of Loran-C.
Commercial airlines oppose equipping fleets with Loran as a backup; they presently rely on VOR-DME and ILS ground-based radio systems as the prime means of navigation.
A draft report, meanwhile, of a Booz, Allen & Hamilton (BA&H) study commissioned by DOT on whether to extend Loran-C life to 2015 was being circulated in May among relevant government offices for review and comments. The U.S. Loran system is scheduled to be decommissioned in 2000, unless existing federal policy is changed.
Recommendations of the final BA&H report are not expected
to be sent to Congress, or made public, until June, according to Heywood
Shirer, DOT.
White House Announcement On GPS Civil Enhancements
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Following is the text of press release by Vice President Gore, issued March 30 through the White House, announcing a second civil GPS signal on L2 and the addition of a third civil signal at a frequency to be determined by August.
Washington DC-Vice President Gore today announced that a second civilian signal will be provided by the U.S. Global Positioning System.
This new civilian signal will mean significant improvements in navigation, positioning and timing services to millions of users worldwide-from backpackers and fishermen to farmers, airline pilots, and scientists, the Vice President said.
The addition of a second civil signal represents a strong commitment by the United States to civil GPS users worldwide and is a major step in the evolution of GPS as a global information utility. Much like the Internet, GPS is becoming increasingly indispensable for navigation, positioning, and timing by users around the world. Also like the Internet, GPS has become an engine of economic growth and efficiency as businesses and consumers continue to develop new and creative applications of this technology.
The addition of a second frequency will greatly enhance the accuracy, reliability and robustness of civilian GPS receivers by enabling them to make more effective corrections for the distorting effects of the Earths atmosphere on the signals from space. GPS has always provided signals on two frequencies for military users for this purpose. Todays announcement marks a new era in which civilians will have access to the same type of capability.
The decision announced today demonstrates that we can successfully balance the needs of civilian users with the demands of national security, Vice President Gore said. GPS civil signals are, and will continue to be, provided free of charge to consumers, businesses, and scientists around the world. We will continue to do everything we can to protect these GPS signals and to promote GPS applications for commercial, public safety, and national security purposes.
The addition of a second civil signal has been recommended by a number of expert panels, the most recent of which was the White House Commission on Aviation Safety and Security, chaired by the Vice President. Todays announcement fulfills a pledge made last March by the Departments of Defense and Transportation to reach a decision on a second civil frequency within a year. The Departments of Defense and Transportation co-chair an Interagency GPS Executive Board, created by President Clinton in 1996 to manage GPS and its U.S. government augmentations.
Background
The NAVSTAR Global Positioning System (GPS) is a constellation of 24 satellites developed, launched, and maintained by the U.S. Air Force that provides positioning, timing, and navigation signals free-of-charge to both military and civilian users worldwide.
A second civil frequency will allow receivers to measure the time of arrival for two signals that have passed through the Earths atmosphere and correct for the distortion introduced by passage from space to earth.
An improved location calculation will allow safety-critical users requiring dynamic, reliable capability to be more reliant on the GPS signal, improve the overall accuracy of the system for the average user, and allow the high-accuracy users (surveying, geodesy, weather forecasters, etc.) to determine their data in a faster, more reliable manner. In addition, the second civil signal will allow the safety-critical users to have a backup signal in the event of inadvertent disruption of the current civil signal.
The Interagency GPS Executive Board (IGEB) has selected the 1227.6 MHZ band (currently known as the L2 signal) for the addition of new civil capability. A third civil signal will also be added with a decision on the frequency to be made in August of this year. The decision on which of these two new signals the Government will pursue to become the safety-of-life service signal will also be madein August.
One of the key factors in deciding which frequency to pursue as the safety-of-life signal is a commitment by all members of the IGEB to have a safety-of-life service signal available by 2005.
The new signals, intended to be added to the GPS Block IIF satellites, will be available to all civil users worldwide. Internationally, interest has been expressed via the International Civil Aviation Organization (ICAO) in the use of a second GPS civil signal in conjunction with the Japanese MSAS and the European EGNOS augmentation programs.
Currently the GPS system is used by a wide range of users:
from cars and trucks on the nations highways to ships at sea and on inland
waterways; from civil aviation to satellites in space, from earthquake monitoring
equipment to surveyors to backpackers; new industries such as precision
farming; and the electrical power companies and long-distance phone systems
which derive timing and synchronization from the signals.
Modernization Options/Issues
By CDR David Minkel
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The IGEB decision of March 27th to add a second coded civil signal to the current GPS L2 carrier and a third signal on a frequency to be determined adds significantly to GPS capability. But there are many issues and decisions remaining to be resolved.
Assuming that the contract with Boeing for the Block IIF satellites can be timely negotiated, the new capabilities still may not be available until the launch of the seventh spacecraft (SV7), expected around 2004.
Spectrum Issues
Navigation services broadcast by GPS require approval by the International Telecommunications Union (ITU) under an allocation for Radio Navigation Satellite Services (RNSS). Signals used for aeronautical navigation, a safety-of-life application, also require, by international treaty, an Aeronautical Radio Navigation Service (ARNS) allocation as the primary user. Therefore, the proposed new GPS aeronautical navigation signal must have two allocations, RNSS and ARNS. Note, that allocation of the second ARNS signal on GPS would force other established systems wherever they exist to move if there is the slightest chance of interference to the new GPS signal.
Allocations are determined in an international forum, the World Radio Conference (WRC), held every two years and organized by the ITU. This group is comprised mainly of the communications sector. Getting an allocation can literally take years, and a WRC operates on a one nation-one vote rule, giving the smallest member equal status with the United States or other large nations.
Another spectrum consideration associated with the second ARNS GPS signal is that it must be at least 200 MHz from L1 (the "primary" ARNS) to provide adequate determination of ionospheric refraction. Lastly, any new GPS signals will probably need to be "in-band" (approximately 1000-1800 MHz) with the current GPS signals to prevent incurring excess costs for new antennas and other major spacecraft modifications.
Of the possible solutions, the "simplest" decision is to use L2 as the second ARNS and find a new third frequency for L3C. Then the only decision to be made for L2 is the signal structure of the C/A code; will it be the so-called split spectrum signal, or the "standard" C/A centered signal? Since L3C will not be used for ARNS, under this option, it only needs an RNSS allocation, greatly reducing the difficulty in finding a chunk of spectrum for it.
Along with determining where L3C is located, it also will be necessary to determine a signal structure for it. Since L3C will be an entirely new signal there is great latitude in specifying its waveform, or signal structure, because backward compatibility with existing equipment is not an issue. Other possibilities for the third signal are a high chip rate code (perhaps the P code), addition of an integrity message, WAAS-like differential correctors, and others.
Possible Centimeter Positioning
Frequencies currently being considered for L3C are 1205, 1227, 1250, 1312, and 1595 MHz. The advantages of 1312 and 1595 include superior wide laning capabilities with L1, resulting in wide lanes of 3.6 and 7.4 meters respectively for high accuracy carrier phase measurements and improved integrity. For an L3C at 1595, the wide lane assumes that L3C and L1 would both have a split spectrum C/A code. Such a change to L1 would, of course, have to be phased in to protect users with imbedded applications.
The general consensus is a 3-to-5 meter wide lane is ideal in that it is easy to hit with differential code, but signal noise is not unduly amplified as occurs with wider wide lanes. The expectation of an optimum wide lane is the ability to do centimeter level positioning at 100-200 km from a reference station. If L3C can be selected to obtain a useful wide lane, the DGPS network(s) currently being established by DOT could provide the basis of real-time centimeter level positioning for terrestrial and marine navigators throughout the United States.
ARNS Signal on L2
In contrast to the L3C option just discussed, putting the ARNS on L2 sounds simple and attractive, but it has its own set of warts. First, it limits the military's ability to modify their signal on L2. Also, the tried and true C/A centered signal form has great potential for signal fratricide when the military is forced to conduct NavWar. In any event, it is very likely the military would have to modify all of their user equipment. Also, a D0D-DOT agreement states that a C/A code on L2 will not be implemented before the DOD has fielded equipment to deal with a C/A code centered on L2. While this may seem contradictory to the IGEB decision, it points out that the definition of signal availability by 2005 is not well defined.
The split spectrum was intended to mitigate, or at least reduce, the signal fratricide issue and should be available sooner. However, the performance of this waveform is not well known and it might not be adequate for the ARNS purpose. The waveform is expected to have superior ranging accuracy, but it may be more susceptible to errors induced by multipath or receiver acquisition of the wrong C/A peak. This choice also assumes that an ARNS allocation can be obtained for L2. While this change in allocation does not seem to be an uphill battle, it hasn't been done yet and it will not be attained easily.
ARNS on L2
The other choice is to not place the ARNS signal on L2. In this case, L2 would be the third civil signal and the ARNS would go to one of two (currently) candidate frequencies - 1205 or 1250 MHz. In this case, the utility of L2 to the civil user becomes more limited than in the previous scenario. Additionally, establishing the ARNS on one of these two candidate frequencies is probably the most expensive with regard to impact on existing systems. The attractiveness of 1205 is that an ARNS allocation presently exists for that frequency; the problem lies in its potentially significant interference with the military's secure communications system, called JTIDS. The advantage of 1250 is little impact to JTIDS, but the downside is its impact on many existing domestic DOD and civil systems, as well as no existing ARNS allocation (with less likelihood of international support at the WRC due to existing systems in the band).
With respect to waveform, the second ARNS signal is a bit more limited than the third civil signal. The aviation sector desires a signal similar to the L1 C/A code to minimize the complexity of user equipment, and +/- 10 MHz of bandwidth for multipath reduction. However, modification of the signal on L2 is severely restricted because the military uses L2 as its primary signal.
No matter what the decision(s) made by the IGEB in August, there are no simple, straight forward answers. Any decision currently envisioned will impact domestic and international existing systems.
Editor's Note: CDR Minkel is acting deputy director
of NOAA's National Geodetic Survey.
Spectrum Issues And GPS
By Sally Frodge
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Worldwide spectrum management for systems (including GPS) to exist and operate legally is accomplished through the International Telecommunications Union (ITU). The ITU sector of most concern here is one dealing with radio frequencies (ITU-R). The ITU-R conducts its business through a series of working parties. Their findings and decisions are acted on by World Radio Conferences (WRCs) held about every two years. GPS could be critically affected by decisions made at the next WRC, WRC-2000.
One such pending decision involves a proposal to reallocate the lower portion of the GPS L1 band to Mobile Satellite Services (MSS). The proposal originally was made by INMARSAT and forwarded through the ITU process last year during WRC-97 by the CEPT and APT, European and Asian telecommunications consortiums, respectively; it again is on the agenda, at WRC-2000. The GPS L1 frequency is (and has been registered since the 1970's) to 12 Megahertz (MHz) around the center frequency of 1575.42 MHz. The MSS proposal is that MSS will be of the same status as GPS and the frequencies (1559-1567 MHz) will be shared, i.e., both systems would be Co-Primary. This would be tantamount to a "demotion" for GPS which is protected now as a full Primary system under the current allocation. This Primary status allows GPS to manage interference caused by other systems. Co-primary status would cause this upper hand in interference negotiations to be lost. This is particularly untenable for safety-of-life services where even momentary interference may cause an accident, or worse, loss of life. The MSS reallocation would be in the 1559-1567 MHz, where GPS L1 operates (see Figure 1).
Just as GPS is a worldwide, ubiquitous service, so too is MSS. The MSS commercial communications satellite technology is truly exciting, but the concern of worldwide interference to GPS is real, particularly as the MSS service expands internationally.
This proposal puts at risk existing and planned GPS equities - many of them safety-of-life services - not only in the United States, but around the world. Services such as the U.S. Coast Guard's differential GPS (dGPS) system are so successful for a variety of applications that there is widespread support for expanding the service Nationwide within the U.S. The FAA is working towards having in place the wide and then local area augmentation systems to support aviation operations. Timing for telecommunications is dependent upon GPS as a primary time reference source. Similar services are going in place around the world. The International Civil Aviation Organization (ICAO) has stated that the 1559-1610 MHz band is the only spectrum available today to support Global Navigation Satellite Services (GNSS). There already are filings on record to reserve frequencies for international systems to move GNSS services forward.
GPS, The Newest Utility
Like communications or energy services, GPS is an emerging utility and its place within the world of utilities is still in formation. It is a powerful enabling technology, with benefits far beyond U.S. borders, that has evolved to become a utility, supporting a wealth of extremely diverse applications, new industries and critical systems that form our basic infrastructure. Unlike other longer standing utilities such as telephone or power, GPS is relatively new and must mature. Unfortunately, this maturation must progress rapidly since the luxury of time is not on the side of GPS and its users. It is somewhat of an intriguing irony that INMARSAT, located in the United Kingdom, was the first to propose reallocation of GPS spectrum to MSS applications, yet it is the UK that supplies a majority of the GPS timing receivers for the U.S. telecommunications industry.
How did we get here?
These trends towards use of GPS in industry and as part of the infrastructure are not limited to the United States. Why, then, has the MSS proposal gone so far within the ITU-R process? It is unusual that the strong objections of the provider of an existing service such as GPS would not be listened to, particularly in light of the importance of GPS. Part of the confusion in the debate over this issue seems to be a general lack of understanding by MSS proponents that there are existing operational wideband GPS L1 C/A-code applications that require at least
20 Megahertz (MHz) of spectrum in order to perform as they currently do - not to mention planned applications that require wide bandwidth. The answer also at least partially lies in the fact that the GPS community needs to improve relations and visibility within this process.
Radio frequencies are managed within the United States by the Federal Communications Commission (FCC) and the National Telecommunications and Information Administration (NTIA) under the Department of Commerce. The FCC regulates private sector, state and local government spectrum; NTIA regulates the federal government spectrum. For international issues, the State Department accomplishes the final coordination, though much of the work in developing the U.S. positions on international spectrum issues is accomplished by the FCC, NTIA and other interested parties. Recently, the FCC put a Public Notice out for comment on the preliminary U.S. positions to the WRC.
This excellent opportunity to comment to the FCC on the importance of GPS was taken advantage of by some within the GPS community. Was your company or interest group among that number?
Most nations divide management of the spectrum in a different manner than the United States. Internationally, spectrum management processes are not necessarily dominated by government, but by private telecommunication interests represented by the Post Telegraph and Telephone (PTTs), or their equivalent. Representatives from these PTT's dominant voting at the ITU-R WRC's. International input to the PTT's, and thence to the WRC-99, arguably may be more important than commenting within the U.S. process, although both are necessary. The U.S. position remains against any reallocation within the 1559-1610 MHz band. To assure that the outcome of WRC-2000 results in no reallocation will require active involvement within the WRC preparatory process and within ITU-R. Since these preparatory processes close out as soon as this fall, action must be taken quickly.
Is there a 100 foot wide car problem?
There also is rising concern about the protection limit set for out of band (oob) emissions from MSS services coming on line in spectrum above GPS L1, from 1610-1626 MHz. This oob limit is -70dBW/MHz. This limit was generated through the work of the RTCA Special Committee SC-159 and published in the report "Assessment of Radio Frequency Interference Relevant to the GNSS". Though this work is excellent and protects aviation, some important main assumptions may not work as well for land or marine applications as they do for aviation. For example, the interference from MSS to the GPS-based GNSS receiver in an aircraft would be momentary and at a distance from an MSS handheld user terminal (i.e., a mobile phone)- no closer than 100 feet to an aircraft that is landing. Additionally, the aircraft antenna pattern can be maximized to seek satellite signals above the aircraft, while this may not be a practical solution for other modes and applications. Will the GPS in a car be 100 feet away from an MSS user unit? The FCC may issue further Public Notices or a Notice of Proposed Rule Making (NPRM) in this area. If there are concerns with the -70dBW value, they should be supported by technical analysis and other data and forwarded to the FCC at the time a NPRM is established. The FCC is required to post such actions publicly through the Federal Register and they also post actions on the FCC web site. Since this is a morass of information to wade through, the DOT site will be updated with information as it becomes available.
Where is this information?
There are several web sites that have been set up to assist those interested in becoming actively engaged in protecting GPS. The Department of Transportation (DOT) has had a web site at www.navcen.uscg.mil "RNAV SPECTRUM ISSUES" that focuses on GPS. The GPS Industry Council has set up a web site (www.trimble.com/gpsic); links to other sites are included on the DOT site under the Navigation Center. Users can find their ITU representative, background information, and updated information on this site as it occurs. The NTIA also has a specific area for WRC issues and other useful spectrum information at www.ntia.doc.gov. The FCC has a plethora of information at www.fcc.gov and the WRC-99 preparatory issues are under www.fcc.gov/wrc-99.
The author is in the Office of Technology Policy, U.S.
DOT.
Mobile satellite service (MSS) operators, led
by INMARSAT of the U.K., are not relenting in their attempts to gain use
of a portion of the GPS L1 spectrum for MSS. The three authors below, from
The Aerospace Corp., report on the latest developments in technical meetings
in Geneva.
GPS Spectrum Contested
By John Clark, Steve Lazar, and Srini Raghaven
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Supporters of the Global Positioning System (GPS) currently are involved in critical spectrum negotiations with operators of space-based Mobile Satellite Systems (MSS). The two groups recently concluded a technical meeting under the auspices of the International Telecommunications Union (ITU) in Geneva, Switzerland.
At issue is the MSS industry-backed proposal to reallocate the lower portion of the Radionavigation Satellite frequency band, 1559-1567 MHz, for MSS use. This reallocation would force spectral sharing between the MSS and the Radionavigation Satellite Services/Aeronautical Radionavigation Satellite Services (RNSS/ARNS), which includes safety-of-life services of GPS.
Surprise Initiative
INMARSAT came close to winning approval of a proposal it spearheaded during the World Radio Conference (WRC'97) meeting in Geneva last year for reallocation of spectrum to support INMARSAT's Horizons project. The concept of requiring a radionavigation safety-of-life system to share with MSS was unprecedented; but INMARSAT initially gained international support for their proposal outside of the ITU process.
When the sharing plan was finally introduced at the ITU, the U.S. delegation was largely unprepared to counter it. Historically, the ITU requires a minimum of two years for studying the implications of sharing between services. However, in 1997, this practice was not followed. Fortunately for GPS users, the U.S. delegation was able to negotiate time for further study based on two major points: 1) GPS is critical to every country's current or future infrastructure, and 2) sharing the band must be studied carefully under the aegis of the ITU before considering such a significant change to international radio regulations. WRC '97 concluded in November 1997 by adopting a resolution to study the possibility of sharing the band in question at its next scheduled meeting, WRC '99.
Following WRC '97, the U.S. formed a team composed primarily of the FAA, the GPS Industry Council, and the GPS Joint Program Office, with support from The Aerospace Corporation. In preparation for the recent technical meetings of ITU Working Party 8D (WP8D), this team prepared new and updated analyses which concluded that GPS cannot co-exist with in-band MSS. Many of these analyses passed U.S. coordination and, along with papers from the European Space Agency and France, were presented at the most recent WP8D meetings in Geneva. These papers showed that sharing with MSS would degrade not only GPS and its augmentations, but would impact the proposed European Navigation Satellite System (ENSS), as well as L-SATNAV services and others.
INMARSAT Unyielding
INMARSAT responded with two arguments. The first was a technical paper that showed that, if a C/A-code receiver used the narrowly defined bandwidth described in the paper, then the MSS signal would not degrade the GPS performance. Initial U.S. reaction was that the receiver definition was not feasible in practice. The second argument introduced the concept of "burden sharing." Here, INMARSAT proposed that new radionavigation systems below the L1 frequency should compromise with MSS usage by increasing their power levels and reducing their performance specifications.
This most recent technical meeting, held in April, concluded with a partial victory for GPS users. The documents drafted for introduction at the next (October 1998) ITU conference contain compromise language which, while stressing the risks of sharing spectrum with MSS to the safety-of-life users of GPS, do not unambiguously establish the U.S.-advocated levels of maximum interference limits. This compromise allows the U.S. and other GPS advocates to further refine the studies and positions in preparation for WRC '99. The MSS community is also expected to redouble their effort to gain the reallocation with more studies and even test results.
Readying for Next Clash
The U.S. delegation is now working on a strategy to prepare
for the October meeting of the ITU. Each of the principal organizations
mentioned above are addressing different aspects of the WRC '99 MSS sharing
resolution, based on analysis of receivers and GPS applications. They are
being coordinated into a more cohesive and substantive GPS defense. There
also are plans to continue an information campaign that reaches out to all
of the ITU members to show the importance of protecting GPS use. The goal
of the U.S. delegation is to prove by WRC '99 that MSS sharing with RNSS
in the 1559-1610 MHz band will seriously degrade GPS performance, and will
never be feasible due to the important safety-of-life aspects of the existing
and planned services operating within this band.
Section News
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Alberta Section. Two speaker presentations were given at the fourth Section meeting, held at the University of Calgary's University Club on March 26. Grant Chevellier of Chevallier Geo-Com explained how GPS-based positioning equipment mounted on bulldozers used in forests had lowered costs 25-30 percent, and lessened environmental damage. Randy Hrynyk and Travis Gray of CSI gave an update on the Canadian Prairie DGPS system, which has towers in place in Bassano, Alberta, Watrous, Saskatchewan, and Winnipeg, Manitoba. New officers elected at the previous meeting on Feb. 5 are Tony Murfin, NovAtel, chair; Mohamed Abousalem, Position Inc., vice chair; Nancy Cannon, Intelligent Databases International, Secretary; Dave Thompson, Challenger Surveys, Treasurer.
New England Section. Two major projects developed by the U.S. Department of Transportation's Volpe Center in Cambridge, MA, were the featured topics at the seventh meeting of the Section held at the Center the evening of April 16. The Enhanced Traffic Management System developed by Volpe is a real-time computer system used by the FAA to detect and manage air traffic congestion problems at major airports. The GPS-based Vessel Traffic and Navigation System is used to control ship traffic, and supporting ground resources, for more efficient use of the Panama Canal. Hosts for the meeting were Karen Van Dyke and Richard Wright of Volpe. New officers elected unanimously at the meeting: Frank Mullen, Chair; Van Dyke, vice chair; William R. Michalson, treasurer; Daniel Eying, Programs; Elliott Kaplan, Publicity, and Duncan Cox, Secretary. Information provided by Duncan Cox.
Houston Section. NASA Johnson Space Center in Clear Lake hosted the April 28 meeting of the Section, held at the Gilruth Center there. The first of two technical presentations was by Dr. Mike Lisano, The LinCom Corp., on the GPS Attitude and Navigation Experiment (GANE). GANE, flown on the Space Shuttle Endeavor in May 1996, was a form of testbed for the proposed GPS-based navigation and attitude determination subsystem for the International Space Station. Morgan D. Reed of John E. Chance and Associates, described FLI-MAP, an airborne survey system based upon on-the-fly kinematic differential GPS. It currently is being used for large scale corridor surveys of pipelines, railroads, electric tranmission systems, and riverbed surveys, among others. Earlier, at the January 28 meeting, Dr. James J. Allen of Sandia National Laboratory, talked on micromachiningg technology as applied to navigation. Allen passed around samples of amazingly small parts, e.g., an inertial navigation system that resides in a bullet to provide navigation and steering. Terry Filthaut of Bell Geospace presented an overview of "stealth" inertial technology used to augment subsurface imaging methodologies in the exploration industry. Extracts from Houston Section Newsletter.
Dayton Section. A luncheon meeting of the Section was held at the usual venue, the Wright-Patterson AFB Officer's Club, on March 17. Guest speaker Paul Logus, Directorate of Avionics Engineering, deputy for engineering, ASC, entitled his talk, "Navigation: Searching for the Holy Grail."
Greater Philadelphia Section of the ION dedicated its navigation library located at the Navigation Research and Development Center of ARL/PSU on 26 May 1998. Pictured in the photo at left, from left to right, are: Carla Sives (Galaxy Scientific), Joseph Corsello (NAVWAR), Alan Fesnak (Gnostech), Marvin B. May (ARL/PSU), Louis Pelosi (Pacer Intertech), and Woody Polter (Naval Surface Weapons Center).
From The ION Historian One of a series of columns by ION Historian Marvin
May. My two previous articles dealt with the demise of two venerable navigation systems, OMEGA and TRANSIT, both victims of the rapid and virtual universal adoption of GPS for radionavigation. In consonance with the theme of the session at the upcoming 54th Annual Meeting in June entitled "Navigation: Past, Present, and Future," we examine another radionavigation system with a prestigious past and present, but an uncertain future: Long Range Navigation (LORAN). The first published Institute of Navigation Journal, Volume 1, Number 1, dated March 1946, contains an article co-authored by Dr. Fletcher G. Watson and Henrietta H. Swope entitled, "The Planning, Growth, and Use of Loran, the New Long-Range Aid to Navigation." Loran was one of the first attempts to implement a long-range hyperbolic navigation system that could provide all-weather fixing information for both ships and aircraft at sea. While pre-World War II radio ranging and direction finding were not reliable at ranges exceeding 200 nautical miles, Loran provided patterns of fixed lines of position at sea based on groundwaves out to ranges of 700 miles from the shore-based transmitters. Loran was developed at the Radiation Laboratory of the Massachusetts Institute of Technology, and was undergoing its first tests on the day Japan attacked Pearl Harbor. By the autumn of 1942, after some modifications had been made and tested, naval vessels were carrying out trial operations in the stormy North Atlantic where convoying and antisubmarine operation required the best possible navigation. The results were sufficiently promising for the Navy to take over; the Coast Guard was assigned the responsibility of constructing and operating the shore stations. At the end of WWII hostilities, some 60 million square miles, encompassing three-tenths of the entire earth's surface, were covered by Loran patterns. This original system, which came to be called LORAN-A, featured groundwave coverage out to between 450 and 700 miles from the base line by day, and sky wave ranges to 1400 miles by night. Between about 1955 and 1970 it was deployed throughout the coastal regions of the northern Atlantic and Pacific Oceans, where it became probably the most widely used radionavigation aid. The need for a longer-range system became apparent, and by 1957 the concept of using time-difference measurements using both pulse envelope matching and carrier phase tracking, was developed. This system, which employed a lower frequency and higher power than LORAN-A to provide for an expanded coverage area, became known as LORAN-C. It was designated by the Department of Transportation as the sole government-provided radionavigation system for civil marine use in U.S. coastal and estuary areas. Usage, particularly in the civil sector as receiver costs plummeted and land navigation and timing applications emerged, grew steadily from the mid 1970s to the early 1990s. About 28 LORAN-C chains exist worldwide, including six that cover most of the continental U.S. In 1990, there were estimated to be 450,000 civil maritime users, and 76,000 civil aviation users worldwide, as well as about 700 DOD platforms. In the early 1980s, the emergence of GPS, with its promise of precise worldwide three-dimensional position, velocity and time, began to affect any plans for potential LORAN-C expansion, and eventually even threaten its very existence. For example, the U.S. Navy's Electronic Navigation's Policy document stated in 1985: "LORAN-C will be phased out after GPS becomes operational and has been demonstrated as suitable for all . . .The phase-out period is planned for 1988-1994." The current Federal Radionavigation Plan of 1996 issued in July 1997 states: "Current use of the LORAN-C system appears to be leveling off and will most likely decrease as GPS fills the market place. The U.S. will terminate operation of the LORAN-C system by December 31, 2000." However, as reported in the previous ION Newsletter (Volume 7, Number 4), a search is underway, centered in the Department of Transportation (DOT), to find a backup system for GPS. In the FY 1998 Department of Transportation Appropriation Bill, Congress funded a review of LORAN-C capabilities, including a study of the viability of extending the lifetime of the system. DOT commissioned Booz Allen & Hamilton to conduct that study; a draft report was completed in early May. Subsequent to the aforementioned 1946 article on LORAN appearing Volume 1 Number 1, there have been 71 articles published in the ION Quarterly on the subject, including perhaps a prophetic one by the next President of the ION, Dr. Frank van Graas in 1988 (Volume 35 No. 2) entitled, "Sole Means Navigation Through Hybrid Loran-C and GPS." One thing history teaches us, and it apparently is particularly relevant to LORAN-C, is that: "It ain't over 'til its over." |
Corporate Profile WR systems, Incorporated: Incorporated in 1983, W R Systems, Ltd. (WRS) is a rapidly-expanding provider of technical and engineering services to a broad government and commercial customer base. WRS is headquartered in Fairfax, Va., and operates offices in Norfolk, Va., Dahlgren, Va., and New York City. WRS has established a proven track record of success in software development and navigation systems engineering support. Their Engineering Services Division (ESD) in Norfolk is staffed by a highly versatile team of 70 engineers, systems analysts, technicians, logisticians, and technical writers. Their clients include the U.S. Navy, U.S. Coast Guard, U.S. Air Force, and U.S.-supported foreign military fleets. WRS ESD specializes in providing a wide range of technical support for inertial and gyrocompass navigation systems and Global Positioning System (GPS) technology. Their services include shipboard navigation system performance evaluation, diagnosis, and problem correction; system installation, maintenance, troubleshooting, and repair; engineering design; circuit card fault isolation and repair; software development; integrated logistics support; training and documentation; and field support. As a result of their demonstrated expertise with navigation systems, WRS ESD is authorized by the U.S. Navy to perform shipboard navigation certifications and is approved to install a variety of navigation system field changes and engineering changes in the fleet. WRS ESD is also playing an integral role in introduction of the Navy's newest inertial navigation system to the fleet. WRS ESD operates state-of-the-art facilities cleared to the secret level that include 19,500 square feet of consolidated office, laboratory, warehouse, and shipping and receiving spaces. Their staff operates in-house microminiature and screen and repair facilities to test, troubleshoot and repair sensitive navigation system instruments down to the component level. Additionally, courses of instruction in the screen and repair of navigation system inertial measuring units are periodically provided to active duty and civilian Department of Defense personnel and other contractor personnel. |
New Corporate Members The ION extends a warm welcome to the following new Corporate Members:
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Calendar July 1998 9-10: GPS Symposium 98 in Tokyo, The 2nd Asia Pacific RIM Meeting; International Information Subcommittee (IISC), Civil GPS Service Interface Committee (CGSIC); Waseda University, Tokyo; Contact: Japan GPS Council, Tel: 81-3-3839-6844, Fax: 81-3-3839-2166, E-mail: jgpsc@da2.so-net.or.jp September 1998 13-15: Civil GPS Service Interface Committee (CGSIC) 32nd Meeting; Nashville, TN; Contact: Rebecca Casswell, USCG Navigation Center, Tel: 703-313-5930, Fax: 703-313-5805, E-mail: cgsic@smtp.navcen.uscg.mil 15-18: ION GPS 98, The Satellite Division of The Institute of Navigation 11th International Technical Meeting, Nashville, TN; Contact: Tel: 703-683-7101, Fax: 703-683-7105, Web Site: www.ion.org 30-2 Oct: RTCA 98 Symposium; Operations, Certification and Standards, and Cornerstones for the Future; Sheraton Premiere Hotel, Tysons Corner, VA; Contact: Dee Clarke, Tel: 202-833-9339 October 1998 11-15: International Loran Association (ILA) Annual Technical Convention and Symposium 1998; Ferncroft Conference Resort, Danvers, MA; Contact: Bill Roland, Tel: 617-275-2010, E-mail: broland@megapulse.com 20-23: GNSS 98; EUGIN/Institut Francais de Navigation; Contact: Tel: 33 1 44 381 043; Fax: 33 1 40 619 319, E-mail: infranav@micronet.fr November 1998 22-24: ISIS 98 International Symposium Information on Ships; Kiel, Germany; Contact: The German Institute of Navigation (DGON), Tel: 49 (0) 228-201 970, Fax: 49 (0) 228-201 9719, E-mail: dgon.bonn@t-online.de 30-4 Dec: International Symposium on Marine Positioning (INSMAP 98); Florida Institute of Technology, Melbourne, FL; Contact: Professor George A. Maul, Florida Institute of Technology, Tel: 407-674-7453, Fax: 407-674-7212, E-mail: gmaul@marine.fit.edu December 1998 9-11: NAV 98; Royal Institute of Navigation; Contact: Tel: 44 (0) 171 589 5021, Fax: 44 (0) 171 823 8671, E-mail: rindir@atlas.co.uk January 1999 25-27: ION National Technical Meeting, ION CIGTF; Catamaran Hotel, San Diego, CA; Contact: ION, Tel: 703-683-7101, Fax: 703-683-7105, Web Site: www.ion.org May 1999 24-26: 6th St. Petersburg International Conference on Integrated Navigation Systems; St. Petersburg, Russia; Contact: Dr. George Schmidt, Draper Laboratory, Tel: 617-258-3841, Fax: 617-258-3355, Web Site: www.draper.com |
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