The System - November 2007

November 1, 2007 By: GPS World Staff GPS World

Go Faster, More, Cheaper on GPS III

Two leading GPS experts recommended key and fundamental changes in the GPS III program to the National Space-Based PNT Advisory Board. They urged the Department of Defense and the Air Force to focus on faster, more, cheaper: a commitment to early delivery of the modernized system; a constellation of 30+ satellites; and cutting modules not necessary to primary mission.

Brad Parkinson of Stanford University and Martin Faga, former CEO, MITRE Corporation, made the chief points that:

The five big goals for GPS must be prioritized: assured availability; resistance to interference; accuracy; bounded inaccuracy; and integrity.
Three of the top four goals are driven by the number of satellites; to fulfill the goals requires at least 30 satellites, while more is better.
Place GPS III quickly under contract with early delivery.
Formally commit to current level of service.
Enable service without brownouts (too many satellites off-line).
Place GPS signal and availability under a true national committee, not just the current players.
A 30+x constellation is more important and a higher priority than spot beams and wideband cross-links; GPS constellation should be specified as 30 satellites plus adequate spares, not the current definition of 24.
The Air Force should launch two GPS satellites at a time; the smaller payload enabled by dropping the extra features would enable such dual launches.

Presentation slides are viewable.

IIR-17(M) Launches

The fourth IIR-M satellite rose from Cape Canaveral, Florida, on October 17. GPS IIR-17(M), built by Lockheed Martin, provides increased signal power, improved accuracy, enhanced encryption, and anti-jamming capabilities. The launch was the first to be conducted with the new Launch and Early Orbit, Anomaly Resolution, and Disposal Operations (LADO) system. LADO will enable cradle-to-grave operations under 2SOPS and relieve the GPS program of dependence on the Command and Control System for spinning satellite operations. It will also support the 31 GPS satellites on orbit, and be responsible for all on-orbit GPS test and check-out operations and exchange data with the new Architecture Evolution Plan Master Control Station. IIR-17(M) is destined for Plane F, Slot 2 occupied by GPS 2A-14, launched in July 1992 with a seven-year design life. The new satellite, to be designated PRN 15/SVN 55, is expected to be set healthy for use in early November.

GNSS All Over the World

At the 47th Civil Global Positioning System Service Interface Committee (CGSIC) meeting, just prior to the ION GNSS Conference in Texas, attendees received these updates from around the globe.

GLONASS. Sergey Revnivykh of the Russian Space Agency stated that GLONASS has nine healthy functioning satellites “today.” He promised two launches of three GLONASS-M satellites each in 2007, in October and on Christmas Day, as is traditional.As the U.S. State Department had announced the day prior, the Russians propose a third civil signal at L3 and new interoperable signals at L1 and L5, the latter two to be CDMA structure rather than FDMA, as other GLONASS signals have been. Revnivykh held out the possibility of 18 satellites by the end of 2009. A new geodesy reference in GLONASS was implemented on September 20.

Revnivykh predicted an orbit accuracy improvement effort for the system, with its next step a clock accuracy improvement. He spoke of the necessity to coordinate activity between GNSS system providers during system development and modernization, and the need for both compatibility and interoperability to benefit users. Russia has ongoing agreements and satellite development and launch efforts underway with India.

Galileo. Marco Falcone of the European Space Agency (ESA) provided updates on both the EGNOS satellite-based augmentation service for GPS signals and the Galileo autonomous satnav system. EGNOS accuracy, integrity, and availability all show good figures, within performance spec, and the system is on course for completion of initial operational phase and system qualification review, and system certification and full provision of services.

Coverage will evolve to include Eastern Europe, Africa, and the Middle East, with possible regional extension modules. Standard evolution will include SBAS, Galileo safety-of-life standards, and a multi-constellation, multi-frequency regional system.

Developers aim to provide integrity on a global scale, augmenting both Galileo and modernized GPS.

Galileo is now in System Testbed v2 Phase, with one satellite in orbit. GIOVE-B is scheduled to launch “in early 2008.” Galileo Industries is still given as the prime for four in-orbit validation satellites to follow. Septentrio receivers are in the ground control stations, with plans to install NovAtel receivers also.

Falcone stated that “All Galileo signals perform significantly better than GPS C/A,” based on analysis of signals broadcast by the one experimental satellite, GIOVE-A. The L1-BOC(1,1) is the “worst” signal, while E5-AltBOC is the “best“ signal, as had been expected.

The first valid navigation messages were generated in May. Automated daily upload of navigation message files are operational since August. Navigation-message performance showed a radial error of less than one meter after 5 hours, and fit interval after 4 hours. Computed clock timing transmitted in nav data versus estimate showed peak-to-peak error under 5 nanoseconds over one day.

The GIOVE-B test satellite arrived at the ESA test center on September 6 and is undergoing final tests. A problem with the Soyuz launch vehicle has postponed launch from December 29 into February or March 2008. It will carry aloft alternative clock technology.

From a user point of view, “You see the first IOV satellites coming in 2009 . . . to really build the system.” Meanwhile designers proceed with implementation of the Galileo Control Center on two sites. Falcone alluded to “critical” elements in the budget.Galileo signal-in-space design is on track as confirmed by field measurement. Onboard clock performance spec appears feasible, with margin.

QZSS and MSAS. Satoshi Kogure of the Japan Aerospace Exploration Agency (JAXA) said that development of the first QZSS satellite, QZS-1, started in November 2006 on a purely governmental basis, after withdrawal of private communications companies. JAXA released the revised draft of the Interface Specification for QZSS in June 2007. Manufacture of the nav payload started at that same time.

Preliminary design review was completed in August 2007 and the critical design phase commenced. Design calls for at least one of three eventual satellites to be visible above the Japanese territory at a 60-degree angle at all times. Nine monitoring stations worldwide are envisioned, as well as GPS and Galileo interoperability, with several meetings and joint statements to those effects.

The third draft of the IS-QZSS is in preparation, to be released in November. The first satellite launch will take place in Japanese fiscal year 2009.

The first MSAS satellite launched in February 2005 and the second in February 2006. Certification has been completed and the initial operational capability (IOC) for enroute and NA was to be commissioned on September 27.

Beidou. As the Chinese delegation withdrew at a late date, Grace Xingxin Gao of Stanford University presented her work on decoding Compass codes.

The new system will include 30 MEO satellites and five GEO satellites for a global positioning service, with one-way communication. The Stanford Lab aimed its 1.8-meter parabolic dish at the one satellite aloft and has analyzed the signal. Several frequency bands overlap with Galileo bands and some GPS bands. This introduces an interoperability problem.

Gao collected Compass data, decoded M-1 broadcast codes in all three frequency bands, derived PRN code generators, and verified the codes and the generators by using them to acquire and track the broadcast Compass codes. The modulated signal is the product of a carrier, a PRN code, and a secondary code. The code length presents challenges for receivers.

In deriving the E2/E5b code generator, it turns out the E2 and E5b codes are identical, the same primary and secondary codes. The code sequence is actually a Gold code. The E6 code generator is much higher. It can be generated by a 13-stage Gold code. It has two parts, a head part and a tail part, that share the code generator polynomials.

We Call Him Sir Richard Now

The Institute of Navigation’s (ION) Satellite Division awarded Richard Langley its Johannes Kepler lifetime achievement award on September 28 at the ION GNSS 2007 con-ference in Fort Worth, Texas. The Kepler Award honors an individual during his or her lifetime for sustained and significant contributions to the development of satellite navigation.

Langley received the 2007 award for his sustained research in the general area of navigation and for the education of scientists, engineers, students, and the general public in the principles of GNSS. The Innovation column that he edits each month in GPS World (since 1990) constitutes a key — and the most far-reaching — part of his educational endeavor. We are honored to be associated with him.

During his acceptance Langley stated, “I could never have achieved this distinction without the support and contributions of the UNB GPS research team over the years, particularly the hard-working graduate students, as well as that of my colleagues in academia, industry, and government in Canada, the United States,and elsewhere. And I would be remiss if I did not thank my wife, Marg, for giving me a reduced load of domestic duties, so that I could spend more time on my many GPS-related activities.”

Langley has been involved in GNSS for many years as well as teaching and conducting research at Canada’s University of New Brunswick (UNB) since 1981. Langley’s research team in UNB’s Department of Geodesy and Geomatics Engineering has made significant contributions to GPS positioning and navigation, including understanding atmospheric effects on satellite signal propagation. Virtually every GPS receiver sold today contains a code module based on UNB atmospheric research.

Langley’s research team is working on a number of GNSS-related projects, including its continuing study of atmospheric effects, space-based augmentation systems, error mitigation techniques, and the development of applications for space-borne GNSS.He has supervised numerous masters and Ph.D. students, many of whom have gone on to their own distinguished careers in the general field of GPS and navigation.

Langley has received numerous other awards, and was recently named a Fellow of the Royal Institute of Navigation (UK).

Bookmark it: digg propeller del.icio.us technorati yahoo facebook

Add Comment