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Galileo Light Show: First Laser Range Measurements to GIOVE-A

European researchers have obtained laser range measurements of 1.5-centimeter accuracy to GIOVE-A, the first element in the Galileo In-Orbit Validation phase. The observations were made through collaboration between the UK Space Geodesy Facility (SGF), Surrey Satellite Technology Limited (SSTL), and the European Space Agency (ESA). The SGF is operated by the UK Natural Environment Research Council, with support from the British National Space Centre and the Ministry of Defence.

European researchers have obtained laser range measurements of 1.5-centimeter accuracy to GIOVE-A, the first element in the Galileo In-Orbit Validation phase. The observations were made through collaboration between the UK Space Geodesy Facility (SGF), Surrey Satellite Technology Limited (SSTL), and the European Space Agency (ESA). The SGF is operated by the UK Natural Environment Research Council, with support from the British National Space Centre and the Ministry of Defence.

The SGF satellite laser ranging system at Herstmonceux, East Sussex, made the range measurements on April 8. The facility had been invited to attempt observations by SSTL, the prime contractor that built the GIOVE-A space vehicle launched from Kazakhstan’s Baikonur space center on December 25, 2005.

At the time of acquisition, GIOVE-A was more than 25,000 kilometers distant from the station, the furthest distance ranged by the facility. GIOVE-A orbits the Earth at a height of more than 23,000 kilometers, some 3,000 kilometers above the GPS and GLONASS satellites that SGF regularly observes.

In order to track the satellite from Herstmonceux, predictions of its path based upon its transmitted navigational signals were supplied to SGF by the GIOVE Processing Centre located at ESA ESTEC, The Netherlands. The predictions were sufficiently accurate for the sunlit image of the satellite to be detected at night by the system’s high intensity camera and allowed the observer to direct short laser pulses towards it.

Laser Ranging
The satellite laser ranging (SLR) technique uses small astronomical telescopes to emit short pulses of laser light towards specially equipped spacecraft and to detect those photons that are reflected back. The times of emission and reception are recorded to an accuracy of a few picoseconds such that the range to the satellite can be deduced from the measured time of flight to a precision of better than one centimeter. The satellites tracked by this technique are equipped with an array of quartz cube-corner reflectors that closely return to source the incoming laser pulses.

The technique is weather dependent as skies have to be fairly cloud-free, but measurements are carried out both during daytime and at night. The key to success in extracting signal from noise is narrow-band spectral filtering in the return optical path and spatial filtering through a range gate technique that arms the detector only a few tens of nanoseconds before the expected arrival time of returning photons.  During the satellite pass the time of flight inferred from every detected event is compared to the expected time of flight to the satellite and back.

A plot against time is built up of these observed-computed values, where true returns appear as a correlated track amongst the sky-noise events. Post processing extracts the real events, which are made available to the analysis community a few minutes after the end of the observations.

Unlike the microwave signals used by GNSS, the propagation time of laser light is not affected by the ionosphere; the tropospheric delay, amounting to a zenith range correction of two meters, can be estimated to millimeter accuracy using atmospheric mapping functions and local meteorological data. This lack of dependence of propagation delay on the variable effects of the ionosphere makes laser ranging a very strong technique for high-precision terrestrial reference frame (TRF) determination.

Laser range observations of a series of geodetic satellites, high-density small spheres encrusted with retro-reflectors and orbiting the Earth at heights of from 800 to 19,000 kilometers, are routinely used to monitor tiny changes in the location of the center of mass of the Earth, the origin of the TRF, that are driven by mass redistributions within the Earth system.

The technique is also used in precise orbit determination of Earth-observation altimeter and SAR satellites, complementing on-board tracking systems such as GPS and DORIS. This work and the operation of the worldwide network of SLR stations is coordinated by the International Laser Ranging Service (ILRS, http://ilrs.gsfc.nasa.gov/).

The GIOVE-A satellite is equipped with 76 quartz corner-cube retro-reflectors in an array to one side of its base, which is taken from the ESA document “Specification of GALILEO and GSTB-V2 Space Segment Properties Relevant for Satellite Laser Ranging, ESTEC, November 2005.”

During the design phase of the satellite, discussion took place among SSTL, ESTEC, and SGF in order to use SGF’s previous experience of ranging to the navigational satellites to help understand the difficulties and inform the choice of numbers of cubes to deploy, within available space and weight constraints, to enable a realistic link budget. For comparison, the two GPS satellites that are fitted with retro-reflectors have an array of only 32 cubes, and the newest GLONASS satellites have about 130 cubes.

The higher altitude of GIOVE-A reduces the return signal, which varies as the fourth power of the range, by some 55 percent relative to the signal from a GPS satellite; so, the greater number of cubes on GIOVE-A should ensure a return signal that is about 30 percent better than that from the GPS satellites, which from SGF’s Herstmonceux SLR facility are difficult targets.

SLR Results
Observations from Herstmonceux tend to support this analysis, with the Galileo laser return rate estimated at about 4 percent on average over the one-hour session; for the GPS satellites the rate is about 2 percent, and for GLONASS closer to 10 percent.

We can also use the laser range observations to estimate the accuracy of the predictions supplied by the GIOVE Processing Centre located at ESTEC. The differences between the observed and computed ranges imply that the predictions were accurate to about two or three kilometers, the major error being in the along-track direction.

Previous studies carried out by SGF and others have used laser range observations from the global network of ILRS stations to measure the quality of GPS and GLONASS orbits that are computed by the International GNSS Service (IGS, http://igscb.jpl.nasa.gov/). The laser ranging technique is a powerful, independent method of testing the accuracy of these orbits, which are determined from continuously transmitted navigational signals.

Given knowledge of the accurate location of the retro-reflector arrays on the satellites, SGF uses the laser range measurements to determine at a level of accuracy of better than one centimeter the radial distance to the satellite center of mass. The results suggest that the IGS orbits for GPS and GLONASS have an RMS radial accuracy of better than five centimeters and, interestingly, that there appears to be a radial bias in the IGS orbits of a few centimeters, in the sense that the IGS-determined orbits appear too big.

SGF and other researchers expect to use a similar technique to test the quality of any available precise orbital information derived from the GIOVE Processing Centre. In addition, once laser range data from the global network is available, it will be possible to determine SLR-only satellite orbits, which will further assist on-board clock characterisation in flight.

For figures, graphs, and images, please download the PDF of the article, above.

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By Alan Cameron
GPS III, Block IIF Programs Hit New Delays

GPS III, Block IIF Programs Hit New Delays

The GPS program appears to be struggling on several fronts recently.

GPS III, the next-generation modernization project for the space and ground segments, is facing renewed uncertainty and possible schedule delays. At the same time, anticipated first launch of the follow-on block of satellites (Block IIF) with the new civil L5 signal has been postponed.

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By Inside GNSS
Civil L1 Signals: Galileo ICD, GPS L1C, New MBOC

Civil L1 Signals: Galileo ICD, GPS L1C, New MBOC

Within weeks of a bilateral working group’s recommendation for a common civil GNSS signal design, the European Galileo and U.S. GPS programs have filed draft interface specifications (IS) or interface control documents (ICDs) for the new signals planned for the L1 frequency (around 1575 MHZ).

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By Inside GNSS
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Geodesy and Satellite Navigation
April 1, 2006

Geodesy and Satellite Navigation

There has always been a love-hate relationship between geodesy and satellite navigation. Indeed, satellite positioning started life as an extension of terrestrial geodesy. When the first satellite, Sputnik 1, started orbiting the Earth in 1957, geodesists in several countries realised that satellites offered substantial potential as a geodetic positioning and navigation tool.

There has always been a love-hate relationship between geodesy and satellite navigation. Indeed, satellite positioning started life as an extension of terrestrial geodesy. When the first satellite, Sputnik 1, started orbiting the Earth in 1957, geodesists in several countries realised that satellites offered substantial potential as a geodetic positioning and navigation tool.

The basic technologies of terrestrial geodesy of the day, notably triangulation, traversing, and precise leveling, were slow and cumbersome, mainly because of the effect of the curvature of the surface of the Earth, which limited the range of measurements to theodolite observations between points situated on hilltops, observation towers, and triangulation masts.

The advent of EDM (electronic distance measurement) in the 1960s helped terrestrial geodesy, but it, too, was affected by the same limitation, namely the shortness of observable EDM ranges due to the Earth’s curvature.

Earth orbiting satellites did not suffer from this drawback. They could be viewed simultaneously from several points on Earth, and therefore direction and range measurements made, provided that the space vehicles were not obscured by high natural features or tall man-made structures. This led to several new satellite geodesy positioning methodologies.

The first of these was satellite triangulation, which was used initially to supplement and strengthen terrestrial triangulation networks. Satellite triangulation consisted of geodetic direction measurements derived from high power photographs of satellite orbits made against a stellar background of stars, with known right ascension and declination.

A few years later, this was followed by range measurements to satellites, made from Earth-bound EDM equipment to corner cube reflectors placed on the early satellites. The methodology used thus far was an extension of geodetic astronomy, with little reference to physical geodesy.

This situation changed significantly when geodesists realized that they could use the Doppler shift on the signal broadcast from a satellite to obtain differential range measurements that, together with the known Keplerian orbit of the satellite, could lead to a relatively fast positioning, or navigation, method. The Keplerian orbital motion of satellites is primarily based on the Earth’s gravity field, a subject of expertise by practitioners of physical geodesy.

This technical advance gave birth to Transit-Doppler, the first satellite navigation technology. Transit-Doppler was used in the late 1970s and early 1980s not only for the positioning of naval ships and of submarines surfacing in the polar regions, but also for the strengthening and scaling of national and continental terrestrial triangulation networks.

However, practitioners soon realized that positioning by Transit-Doppler to a reasonable degree of accuracy took several minutes, and, therefore, precluding its use as a full navigation methodology, which requires quasi-instantaneous positioning.

Enter GPS
These were the early days of a new global satellite positioning, navigation, and timing system, first called the NAVSTAR Global Positioning System, a name later shortened to just GPS. The rest is history. The early decision to base GPS on a constellation of 24 medium-Earth orbit satellites was taken on the advice, as you would expect, of geodesists at the U.S. Naval Surface Weapons Center in Dalgren, Virginia.

The close relationship between the early GPS and geodesy was further demonstrated by the adoption of WGS84, the World Geodetic System 1984, as the basis of the 3-D coordinate system of GPS. As GPS was born during the Cold War, it was declared a US military navigation system, with full access to NATO but only restricted access and down-graded positioning accuracies for civilian users.

This so-called Selective Availability (SA) gave the green light to the civilian geodetic community to come up with new methodologies that could counter the effects of SA. As always, human ingenuity did not disappoint, and two new differential techniques were developed. The first was the differential GPS (DGPS) technique, which improved relative positioning accuracies of GPS by at one order of magnitude, down to a few meters. As a result, DGPS soon became the standard methodology for the offshore positioning of oil platforms, pipelines, etc.

The next advance in improving the accuracy of satellite positioning was made on the advice of radio-astronomers, who proposed replacing the standard GPS pseudorange measurements, which are based on timing the modulated signal from satellite to receiver.

Instead, they suggested making measurements on the basic carrier frequencies of these signals, just as they did with extra-galactic signals arriving at, say, two widely spaced radio telescopes in so-called very long baseline interferometry (VLBI), leading as a by-product to the Cartesian coordinate differences between the two telescopes. This was the beginning of centimetric positioning by the carrier phase GPS method, which was later developed further by geodesists into kinematic GPS and centimetric navigation.

GPS had now become the universal high precision quasi-instantaneous positioning and navigation tool, creating the basis for hundreds of new applications. Again, geodesists led the way, concentrating on high precision scientific and engineering applications. These included surveying and mapping, positioning in offshore engineering, the monitoring of local crustal dynamics and plate tectonics, the relative vertical movements of tide gauges, and the continuous 3-D movements of critical engineering structures, such as tall buildings, dams, reservoirs, and long suspension bridges.

All of these applications required very high relative positioning accuracies, but not quasi-instantaneously as in the safety-critical navigation and landing of civilian aircraft. This came much later.

Geodesy and Navigation
Initially, GPS was considered as a standard navigation tool for military vehicles on land, sea, and air, but not for safety-critical civilian transportation. This was because, unlike military positioning and navigation, safety-critical civilian transportation not only requires quasi-instantaneous and accurate positioning, but also so-called “high integrity and good coverage.”

Geodesists will immediately realize that “integrity” stands for the geodetic concept of “reliability,” whereas “coverage” refers to the availability of a sufficient number of satellites that can be sighted by a receiver continuously and are not obscured by natural or man-made obstructions, such as high mountains, tall buildings, and the wings of an aircraft.

On its own, GPS cannot meet these requirements to the level required in safety-critical civilian transportation. Military transportation, on the other hand, has relatively modest requirements, which can be met by GPS. Indeed, you do not become a NATO Air Force pilot if you want a safe life. Flying as a passenger in a commercial airline is something else all together.

The penetration of satellite navigation, and primarily GPS, into civil aviation involved yet again, as you would expect, geodesists. They had to develop jointly with the civil aviation community the necessary theoretical and practical tools, which could be used to establish and quantify their requirements of accuracy, integrity, and coverage.

This involved the use of existing geodetic tools, such as the covariance matrix, the analysis of least squares residuals, and the well-established geodetic reliability measures. New tools were also introduced, such as the concept of RAIM or receiver autonomous integrity monitoring, based on the analysis of the least squares residuals.

Persuading Non-Geodesists
These geodetic tools, which were highly beneficial to the civil aviation community, initiated a fruitful, long-term collaboration between the two communities. However, this has not always been a straightforward and smooth relationship, and it involved — especially at the beginning — a deep suspicion of these “academic” geo-scientists. Here are a few notable examples of this love-hate relationship.

As a general rule, the existing civil aviation horizontal coordinates were based on latitudes and longitudes, with no particular reference to a reference datum. Heights in civil aviation were and still are based on barometric altimetry, on the assumption that all that matters is “the relative heighting between airplanes,” which is not affected significantly by a change in barometric pressure.

This assumption disregards, of course, the fact that the heights of natural features on the ground, such as mountains, do not change with changing barometric pressure. The first challenge was to convince the international civil aviation community that their horizontal coordinates, that is, latitudes and longitudes, required a proper geodetic datum and, as GPS was being contemplated as a future navigation tool, it made sense to adopt the same reference datum, namely WGS84. It took a while to convince the community to accept that.

The adoption of WGS84 led to the resurveying of most airports, runways, and various en route and landing navigation aids in order to bring them into WGS84, in preparation for the introduction of GPS. This led to the discovery of some large discrepancies, at airports and among navaids in many countries, between the existing horizontal coordinate values and their new WGS84 equivalents. Geodesists will be familiar with such occurrences, whenever they start dealing with a new community, whether they are civil or offshore engineers, oceanographers or meteorologists.

The first GPS receivers did not lend themselves to mass market adoption. Geodesists of a certain age will also remember some of the earliest commercial GPS receivers, such as the TI 4100 receivers, made by Texas Instruments. These early receivers operated by measuring sequentially four pseudoranges to four different satellites. Consequently, the receivers were programmed to first check the geometry of the satellites in view and decide on the best four in terms of geometrical configuration.

However, later on, with the emergence of new receivers that could measure all the available pseudoranges quasi-simultaneously, there was no need to carry on with measurements only to the “best four” satellites. One could track all available satellite signals and process these measurements by least squares, rejecting those with relatively large residuals, if any. This standard processing of observations is bread-and-butter stuff to surveyors and geodesists.

However, this was not the case with a number of navigation experts, who persisted on recommending the use of only the “best four” satellites for quite sometime, before they finally abandoned the practice.

A New Era of GNSS
Satellite navigation and positioning has changed substantially and significantly over the last 5 to 10 years. With Galileo in its development and in-orbit validation phase, the future developments in GPS IIF and GPS III, renewed interest in GLONASS, and satellite navigation initiatives in Japan, China, India, Australia, and several other countries, GNSS or the Global Navigation Satellite System is moving from being a concept, largely based on GPS alone, to a full global reality. A comprehensive program of GPS modernization currently under way aims to deliver significant improvements to both military and civil users.

The earliest mass-market applications of GPS involved road vehicles and mobile phones. In both cases, the twin aims are navigation (where am I, and how do I go to my destination?) and tracking (where is he, she, or it?). In the case of road vehicle tracking, successful applications include fleet monitoring (taxis or road transport companies), theft recovery of private cars, “black box” incident recorders, and the transport of hazardous or valuable cargoes.

Typically, most of these applications share three common features, namely prior knowledge of the proposed route, the continuous tracking of position and velocity by GPS, and the trigger of an alarm by a significant deviation.

Similarly, a number of GPS tracking applications use mobile phone technology (GSM or GPRS), but these are not as developed and widespread as vehicle tracking. Typically, these involve vulnerable people, such as young children, the elderly, key workers in some risky environments (for instance, railways), individuals with a chronic or contagious disease, and even VIPs.

Person tracking with GPS+telematics could also involve judicial cases (ordered by a court of law), of suspected criminals or anti-social elements. Other proposed applications include environmental information, location-based security, and location-sensitive marketing.

On its own, a GPS-enabled phone offers location and communication. This may answer the questions “Where is she or he?” and “Where am I?” but nothing more. However, when position and communication are combined with an appropriate geographic information system (GIS) database and a direction sensor, the combined system could answer two other very important questions, namely “What’s around me?” and “What’s that building over there?”

This could be achieved by a GPS+compass device, providing positional and directional data, which the mobile phone or the PDA transmits to a remote server. The server calculates the user’s position and identifies the building along the measured azimuth, gets the relevant information from the database, and sends it back to the client.

This is clearly valuable for the public utilities (water, gas, electricity, TV), shopping and leisure (restaurant menus, theater tickets), house hunting (details of the property advertised for sale), and of course, for visitors and tourists (museums, notable buildings, archaeological sites).

Leaving mobile phones aside, satellite navigation can also be used for location-based- security. For example, a briefcase or a portable PC can be programmed to unlock safely only in a specified location and nowhere else. This would minimize the risk of sensitive military or commercial material falling into the wrong hands.

Some working prototype systems already exist. Other location-and-context-based applications under consideration include the marketing and selling of goods, the reception of pay-TV, credit card security, spectator sports, road user charging and many others.

Indeed, the qualification of “critical application” is no longer restricted to safety-critical transportation, but it also applies now to financial-critical, legal-critical, security-critical, and business-critical applications as well. This creates a problem with standard off-the-shelf autonomous GPS receivers, which cannot operate indoors, because of signal attenuation and multipath.

Over the last few years, GPS chip and receiver manufacturers have tried, with some success, to develop high sensitivity GPS (or HS-GPS). The latest HS-GPS receivers, which incorporate up to 200,000 correlators operating in parallel, make it relatively easy to identify true pseudoranges from among the many signal and multipath reflections. Several manufacturers in the United States, Japan, Korea, and Europe, already advertise HS-GPS chips, and many other companies use such chipsets in their receivers.

GNSS Evolution
Like nearly all the technologies that preceded it, satellite navigation and positioning is going through the standard stages of development from birth to maturity. Older surveyors and geodesists may well remember the advent of EDM, using microwaves or lightwaves in the late 1960s and the 1970s. When the first EDM instruments were introduced, the distances measured were also measured with tapes, just in case.

Then came the second phase, when surveyors became fully confident about EDM and used it routinely for fast and precise range measurements. It took a few years and several critical mistakes in local mapping and national triangulation, to realize that EDM instruments could go wrong and that they had to be calibrated regularly in order to determine their accuracy and systematic biases.

The development of satellite navigation and positioning is following practically the same stages as EDM did 40 years ago. Only now we can formalize these successive stages of development of a technology and give them names by using Gartner’s famous “Hype Cycle Curve,” which was invented about 10 years ago in conjunction with new information technology products.

Using a simplified version, these successive stages of technology development are now formally called “Technology Trigger,” followed by “Peak of Inflated Expectation,” leading to “Trough of Disillusionment”, happily followed by the “Slope of Enlightenment,” and hopefully leading to the “Plateau of Productivity.”

As I write this, the first Galileo satellite, GIOVE-A, has been launched and tested successfully, opening a new era in satellite navigation. Hopefully, this will lead to the development of a large number of new critical applications — and involve close collaboration with geodesy and several other related disciplines — for the benefit of business, government and society.

Here is one last example about the strange relationship between geodesy and GPS. The U.S. delegation to the International Telecommunications Union (ITU) recently proposed to abolish leap seconds, and thus cut the link between Solar Time and Coordinated Universal Time (UTC) and ipso facto GPS Time.

At present, whenever the difference between UTC and Solar Time approaches 0.7 second, a leap second correction is made in order to keep the difference between them under 0.9 second. This is done every few years on the recommendation of the International Earth Rotation and Reference Systems Service, which monitors continuously the difference between Solar Time and UTC.

This leap second correction, which has to be applied every few years to GPS Time, apparently causes software problems because it has to programmed in manually. However, considering the difficulties that this change would cause to other scientific communities, such as astronomers, and even to users of GPS time itself for some critical applications, the U.S. proposal has now been postponed for the time being.

In conclusion, I must declare a conflict of interest. Although all the work I do at present involves GNSS, my academic background is clearly in geodesy. However, a change is in the air now, as safety-critical transportation is no longer the only critical application that has to be catered to. It has now been joined by several other emerging critical applications, notably financial-critical, legal-critical, security-critical and business-critical applications, which will also require nearly the same level of accuracy, integrity and coverage as safety-critical transportation.

This is where geodesy could step in again and create some new statistical tools, which will differentiate between the navigation and positioning systems on offer, and assess their suitability for the specific critical application.

For figures, graphs, and images, please download the PDF of the article, above.

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Using Maps as Automotive Sensors

Using Maps as Automotive Sensors

Accurate real-time positioning is a necessary condition for many land transportation applications. But positioning alone cannot ensure successful and safer navigation, let alone higher-order driver assistance and awareness applications. The most common accessory to positioning is a map database — of more or less sophisticated design with greater or lesser data content and granularity.

Accurate real-time positioning is a necessary condition for many land transportation applications. But positioning alone cannot ensure successful and safer navigation, let alone higher-order driver assistance and awareness applications. The most common accessory to positioning is a map database — of more or less sophisticated design with greater or lesser data content and granularity.

Another resource and tool for navigation, route guidance, and advanced assistive systems is the application of geometrical principles to the positioning and mapbase data to anticipate or project upcoming conditions and events along a route.

This article introduces the map database as a sensor in driver assistance and awareness applications, which begin with a map-matched position and then look ahead from that position to determine the most likely driving path (MLP). From this calculation, we can support assistance and awareness applications such as curve speed warning, predictive adaptive front lighting systems, adaptive cruise control, and forward collision warning.

We will explore the role of MLP in these applications as well as its use in modifying route guidance instructions and map-matched positions. Finally, this article will also take up the question of map requirements and the navigation system interface needed for such applications.

Path Prediction
Adaptive cruise control (ACC) and forward collision warning (FCW) require systems that can determine the primary target in the host vehicle lane and then accurately estimate the geometry of the road between the host and the target vehicle. Curve speed warning (CSW) also requires knowing the geometry of the intended driving path to warn the driver of going too fast for the upcoming curve. Predictive adaptive front lighting can use the predicted road geometry to swivel the headlamps in the road curvature direction.

. . .

Driver Assistance, Awareness
Visteon has used GPS and map databases as sensors. In a road departure crash warning (RDCW) field operational test funded by the U.S. Department of Transportation (DoT) and completed last year, Visteon developed a CSW functionality using a commercial navigation system and map database. The CSW system warns the driver when the vehicle is traveling too fast for an upcoming curve by processing the map database geometric and attribute information.

. . .

Land Vehicle Navigation
Route guidance is an essential feature in current land navigation systems. In this navigation feature, a driver feeds the navigation system with the desired trip destination. The route guidance algorithm calculates the route for the driver to follow. The driver may make mistakes in following the intended (calculated) route, and the route guidance system will have to adjust its instruction to correct this mistake.

. . .

Map Database as a Sensor
Current commercial map databases are designed for navigation purposes. The accuracy of these maps is sufficient for navigation in a large variety of road scenarios. However, they sometime fail in such situations as service drive/highway, highway/exit ramp, fork, complex overpasses, and mountain area/single road. All of these scenarios could lead to placing the vehicle on the wrong road or off the road.

. . .

Conclusion
Map database can provide detailed information of the road segment at the vehicle position and the road segments ahead of the vehicle. This information when processed can be used for advanced driver assistance and awareness applications Moreover, these systems should incorporate a map corrective/updating capability due to the changing nature of the roads and associated driving restrictions.

Map database errors can arise in such road scenarios as merging, road connections (overpasses), divided/undivided roads, and mountains areas In order to optimally use the map database, such error sources should be defined and modeled. Furthermore, inclusion of additional information such as height or elevation could extend the usage of the map for other automotive applications.  From a commercialization perspective, it is recommended to standardize the navigation system interface.

For the complete story, including figures, graphs, and images, please download the PDF of the article, above.

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Builders Notes: Russian GLONASS at the Stage of Active Implementation

Builders Notes: Russian GLONASS at the Stage of Active Implementation

Modernized GLONASS-M satellite (left), A GLONASS-M satellite design (right)

On December 25, 2005, from the Baikonur Launch Site, there were three launched three navigation satellites belonging to the GLONASS system: one GLONASS satellite (the last of the first generation) and two new GLONASS-M satellites (see photo, above left).

This launch ensured the possibility of completing the flight tests for the modernized GLONASS system and performing the direct navigation determination using four GLONASS-M satellites simultaneously (two of these GLONASS-M satellites were launched earlier in 2003 and 2004).

On December 25, 2005, from the Baikonur Launch Site, there were three launched three navigation satellites belonging to the GLONASS system: one GLONASS satellite (the last of the first generation) and two new GLONASS-M satellites (see photo, above left).

This launch ensured the possibility of completing the flight tests for the modernized GLONASS system and performing the direct navigation determination using four GLONASS-M satellites simultaneously (two of these GLONASS-M satellites were launched earlier in 2003 and 2004).

Today, the orbital GLONASS constellation includes 16 satellites (12 GLONASS satellites and 4 GLONASS-M satellites). This article discusses the planned modernization of the GLONASS satellite navigation system with particular emphasis on the improved design of GLONASS-M satellites.

A New Commitment
The first satellite of the Russian navigation system GLONASS was launched on October 12, 1982, and the system was introduced into operation in 1993, being deployed to the complete constellation of 24 satellites in 1995. With 24 satellites in orbit, the GLONASS system can ensure the continuous global navigation for military and civil users by employing two types of signal: a signal of standard accuracy for civil users and a high-accuracy signal for military users.

When Russia faced new economical conditions in the 1990s, the financing for the space industry was reduced leading to the orbital GLONASS constellation reduction and decrease of its effectiveness.

Bearing in mind that the Space Navigation System GLONASS is a part of the national patrimony of Russia, in 2001 the president of Russian and the government of the Russian Federation ratified the policy directives setting out the intent to conclusively preserve and develop this navigation system. The Federal Target Program “Global navigation system” is one of these documents.

This program has been developed to be completed for the decade (from 2002 to 2011). During this period certain research and development activities shall be performed, including the ground experimental development for the prospective navigation spacecraft as well as flight and design tests; the ground control segment for the navigation system shall be modernized; the orbital constellation with the nominal number of satellites (24) shall be replenished.

GLONASS Modernization
The 10-year program of creation and operation of the modernized Russian Navigation System GLONASS space segment covers two stages: the current GLONASS-M satellites – at the first stage, and the proposed GLONASS-K satellites – at the second stage.

The GLONASS system is being modernized based on the following main conditions:

•     qualitative improvement of radio-navigation signal (introduction of the third frequency, increase in message rate, addition of new information into a navigation signal, etc), shift in the frequency bands keeping the possibility to work for the current existing users of the GLONASS system
•     improvement of the reliability and accuracy of the navigation support provided
•     increase of the satellite operation autonomy period and decrease of the level of the Ground Control Segment support needed to control the satellites
•     reduction of maintenance costs for satellite constellation as a result of increased satellite lifetime, reduced mass and resulted decrease of cost per satellite in-orbit
•     extension of the range of mission tasks to be performed.

With the preceding conditions implemented, there is kept the orbital configuration established earlier (three planes, with eight satellites in each plane), the orbital parameters (Н=19,400 km, i=64.8°, е=0) and the quantity of satellites in the nominal constellation (24 satellites). This enables the GLONASS operators to maintain the principles and methods of ballistic support of the satellite constellation and to provide the high-accuracy ephemeris.

New Generation Satellites
A GLONASS-М satellite, which is being developed at the first stage of the GLONASS Space navigation system modernization, has the following specific features as compared to a GLONASS satellite which is in use now:

1)     upgraded navigation radio signal
2)     implementation of intersatellite radiolinks to provide ranging measurements and data exchange between satellites located in the same plane and in different planes
3)     the stability of navigation signals increased up to 1·10-13 as a result of providing precision thermal stabilization of on board cesium frequency standards
4)     an improved dynamic model will decrease the level of unaccounted active forces impacting the satellite, mainly as result of increased accuracy of solar arrays pointing towards the Sun
5)     increased operational life of a satellite — up to seven years.

A GLONASS-М satellite can be injected into orbit by a cluster launch (three satellites by a single launch vehicle — see photo at the top of this article) from the Baikour Launch Site (using Proton LV and Breeze-M Booster) or by a single satellite launch from Plesetsk Launch Site using Soyuz-2 LV and Fregat Booster.

Spacecraft Design
A GLONASS-М satellite design (see Figure 1, above right) is based on a pressurized container inside which comfortable temperature conditions are maintained, ensuring the temperature range from 0 to 40°С, and local areas of temperature stabilization (near atom frequency standards) with ±1°С accuracy level. The temperature range is maintained by an active gas loop, shutter subsystem with electrical drivers and a set of controlled heaters. All dissipating mission equipment units are located outside the pressurized container on the antenna module in the areas not illuminated by the Sun.

Due to the fact that on board a GLONASS-M satellite there is a great amount of mission equipment units operating in the open space environment, the satellite design represents the intermediate stage between pressurized and non-pressurized design. In the nominal mode, the satellite longitudinal axis is continuously maintained pointed to the Earth, with accuracy of 0.5°, the satellite lateral axis is kept in the Sun-satellite-Earth plane with accuracy of ~0.5°, solar array axes are oriented towards the Sun with the accuracy of 2°. The orientation is provided by electrical wheels, periodically unloaded by electromagnets.

The propulsion subsystem being a single component thruster subsystem based on the catalytic thermal hydrazine separation method provides the possibility to form control torques within the initial orientation modes of the satellite, and to generate pulses for orbit correction. The orbit correction is performed after the satellite has been injected into orbit, while drifting to the designated orbital slot. High accuracy of the initial correction of orbital parameters allows keeping the satellite within the specified station limits (±5° latitude argument) without need for further corrections during the remaining lifetime.

An electric power subsystem based on nickel-hydrogen batteries and silicon solar arrays (30m2 area) provides electric power supply for onboard equipment of continuous stable voltage of 27+1-2 V and the power of up to 1400W, continuously in eclipse and illuminated orbit arcs. The onboard control subsystem based on an onboard digital computer provides data exchange between the equipment via MIL-STD-1553-B buses and performs the functions of control, diagnostic, intersatellite ranging data processing, calculation and generation of ephemeris time data.

For figures, graphs, and images, please download the PDF of the article, above.

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White House Defense Budget Proposes GPS Funds
March 2, 2006

White House Defense Budget Proposes GPS Funds

The Bush Administration’s Fiscal Year 2007 (FY07) budget proposal for the Department of Defense (DoD), announced in February, allocates $315,314,000 in advanced technology development for GPS, including work on the GPS III program. If approved by Congress, that would represent a sizable increase from the FY06 expenditures of more than $85 million and $33 million in FY05.

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March 1, 2006

Carrier Phase Ambiguity Resolution, GNSS Use In Cellular Telephone Systems, and New Antennas?

Q: Will I need a new antenna for the new GPS and Galileo signals? Will one antenna work for both systems?

A: To answer these questions, information will be presented on the GPS and Galileo signal formats, some antenna basic fundamentals with various user applications in mind, followed by some predicted performance assessment.

Q: Will I need a new antenna for the new GPS and Galileo signals? Will one antenna work for both systems?

A: To answer these questions, information will be presented on the GPS and Galileo signal formats, some antenna basic fundamentals with various user applications in mind, followed by some predicted performance assessment.

The well known “Basic GPS” signals are centered at L1 (1575.42 MHz) and L2 (1227.60 MHz), with the GPS Coarse/Acquisition (C/A) code, at a chipping rate of 1.023 Mcps (million chips per second) on L1. The Precise (P) code is transmitted with a chipping rate of 10.23 Mcps on L1 and L2; if encrypted, it is then called the P(Y) or Y-code when broadcast at the 10.23 Mcps rate.

For these binary phase shift key (BPSK) modulated signals we often use the null-to-null bandwidth (twice the chipping rate) to characterize the signal bandwidth, which is 2.046 MHz and 20.046 MHz for the C/A and P(Y) codes that are transmitted in phase quadrature, respectively. Note that for many high performance applications we often require additional signal bandwidth to include the power in the sidebands of the signal spectrum. This is a very important factor in considering antenna bandwidth for a particular application.

(For the rest of Dr. Chris Bartone’s answer to this question, please download the complete article using the PDF link above.)

Q: How will the new frequencies in GPS and Galileo affect carrier phase ambiguity resolution?

A: In the years to come, GNSS users will benefit from the availability of more satellites and signals with the coming of Galileo and the modernization of GPS. Galileo will consist of a brand new constellation of 30 satellites transmitting their signals on four frequencies. Four different navigation services will be offered, meaning that some of the signals and information is available for free to every user, but other services are either to be paid for or are only available to certain authorities.

The first milestone for GPS modernization is the availability of the L2C code for civil users. In the next phase, the L5 signal will also be available.

GNSS positioning will thus be possible with improved precision, reliability, availability and integrity. Still, for rapid and high precision positioning, carrier phase ambiguity resolution remains indispensable. Only with the ambiguities fixed to their correct integer values do the carrier phase observations start to act as very precise pseudorange observations. This implies that the probability of correct integer estimation, generally referred to as the success rate, should be very close to unity.

(For the rest of Sandra Verhagen’s answer to this question, please download the complete article using the PDF link above.)

Q: Aside from E-911 and E-112, how is GNSS used in cellular telephone systems?

A: While mobile positioning for E-911 and E-112 emergency services are becoming more pervasive, other important applications of GNSS exist that are less obvious. These fall into two main categories: namely, those associated with direct mobile user applications based on the mobile’s location and those associated with enhancing the performance of the overall cellular network.

A plethora of user applications based on mobile location are rapidly emerging including street map and direction finding, fleet position data logging and targeted advertising. No dominant “killer application” has emerged at this stage, but the steady accumulation of these minor location-sensitive services is rapidly making GNSS an indispensable component of cellular functionality and markets.

The other main application category of GNSS in cellular telephony is associated with the enhancement of the overall performance of the wireless network infrastructure from the perspective of network capacity and quality of service. First-generation cellular wireless systems were based on time division or frequency division multiplexing.

(For the rest of Dr. John Nielsen’s answer to this question, please download the complete article using the PDF link above.)

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Building Monitors

Building Monitors

Severe loading conditions such as strong winds and earthquakes acting on modern tall buildings and structures can cause significant loads and vibrations. Recent trends toward slender, flexible, and light-weight buildings have left a large number of buildings susceptible to wind-induced motion. Furthermore, human perception of building motion has become a critical consideration in modern building design.

Severe loading conditions such as strong winds and earthquakes acting on modern tall buildings and structures can cause significant loads and vibrations. Recent trends toward slender, flexible, and light-weight buildings have left a large number of buildings susceptible to wind-induced motion. Furthermore, human perception of building motion has become a critical consideration in modern building design.

More complex building shapes and structural systems further accentuate eccentricities between the mass center, the elastic center, and the instantaneous point of application of aerodynamic loads, and consequently will generate significant torsional effects.

Verifying dynamic structural analysis requires the development of direct dynamic measurement tools and techniques in order to determine the natural frequencies, damping characteristics, and mode shapes. Among these tools accelerometers have played the most important part in analyzing structural response due to severe loading conditions. However, they provide only a relative acceleration measurement. The displacement from acceleration measurement cannot be obtained directly by double integration.

In contrast to accelerometers, GPS can directly measure position coordinates, thereby providing an opportunity to monitor, in real-time and full scale, the dynamic characteristics of a structure. GPS used in the real-time kinematic mode (GPSRTK) offers direct displacement measurements for dynamic monitoring. Earlier studies by the authors and other researchers, referenced in the Additional Resources section at the end of this article, have shown the efficiency and feasibility of structural deformation monitoring by combining accelerometer and GPS-RTK.

However, GPS-RTK has its own limitations. For example, the measurement accuracy can be affected by multipath and depends strongly on satellite geometry. Moreover, the typical GPS-RTK 20Hz sampling rate will limit its capability in detecting certain high mode signals of some structures. The new 100Hz GPS-RTK systems need to be further tested in order to ensure the independence of the measurements.

In order to exploit the advantages of both GPS-RTK and accelerometers, two data processing strategies have typically been used, namely to convert GPS measured displacement to acceleration through double differentiation and compare it with the accelerometer measurements (what we refer to as forward transformation), or to convert the accelerometer measurements into displacement through double integration and compare it with GPS measured displacement (the reverse transformation).

The latter approach is much more challenging because we have to determine two integration constants in order to recover all the components of displacement (static, quasi-static and dynamic). If the structure to be monitored is subject to a quasi-static force, as in the case of a typhoon, this further complicates the analysis.

Although earlier research has proposed a lab-based threshold setting for accelerometers to deal with the quasi-static issue, we believe that avoiding this procedure and developing new ways to recover the false and missing measurements from GPS by acceleration transformation would provide a preferred approach.

This article discusses recent efforts to design such a system based on a new integration approach that employs the correlation signals directly detected from a GPS-RTK system and an accelerometer to transform one form of measurement to the other. The methodology consists of a Fast Fourier Transform (FFT) for correlated signal identification, a filtering technique, delay compensation, and velocity linear trend estimation from both GPS and accelerometer measurements. We also present results derived from its installation on structures in Japan that subsequently experienced the effects of an earthquake and typhoon.

(For the rest of this story, please download the complete article using the PDF link above.)

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GLONASS: The Once and Future GNSS
January 1, 2006

GLONASS: The Once and Future GNSS

Once widely written off as another victim of the economic and political disarray following the collapse of the USSR, Russia’s GLObal NAvigation Satellite System (GLONASS) has arguably demonstrated the most stability of the world’s three GNSS programs in recent years.

Once widely written off as another victim of the economic and political disarray following the collapse of the USSR, Russia’s GLObal NAvigation Satellite System (GLONASS) has arguably demonstrated the most stability of the world’s three GNSS programs in recent years.

GLONASS followed the Global Positioning System into space with its first satellite launch on October 12, 1982, 4½ years behind the first GPS satellite went up. After reaching a high point in 1996 with more than two dozen operating satellites in orbit, GLONASS dwindled over the next five years to a nadir of seven operational satellites.

Strapped for cash and expecting a greater role in Europe’s Galileo project, Russia allowed paying commercial payloads from foreign customers to get in line ahead of GLONASS at its launch facilities. A dispute with newly independent Kazakhstan over maintenance, operation, and funding of the Baikonur launch facility further complicated the picture. Meanwhile, the relatively short design life of the spacecraft (three years compared to 7½ years for GPS) contributed to a rapid decline in operational satellites.

In 2001, a new Russian government under President Vladimir Putin reassessed its commitment to space-based positioning, navigation, and timing (PNT), and refashioned its development timeline to more sustainable dimensions. An August 21, 2001, decision committed the government to a 2002-2011 program to rebuild and modernize GLONASS.

A schedule of annual launches since then has doubled the constellation to 13 operational satellites. As a result, since 2001 the gap in worldwide navigation with GLONASS declined from 14 to 2 hours as of November with coverage 98 percent of the time over Russia, according to Sergey Revnivykh, an official with Roscosmos’ Satellite Navigation Department at the Mission Control Center of the Central Research Institute of Machine Building.

Picking Up the Pace

On December 25, Russia placed three more spacecraft into orbit and brought the system within striking distance of an 18-satellite constellation, which should be in place late next year with all satellites in service by early 2008. Under the current plan, the frequency of launches would increase over the next two years to provide a 24-satellite constellation by 2010–11.

The day after the December 25 launch, however, Putin expressed support for accelerating the GLONASS effort. According to the Russian Information Agency Novosti, Putin told government members, “The GLONASS system should be created before 2008, as it was originally planned. We have the possibility. Let us see what can be done in 2006-2007.”

RIA Novosti subsequently quoted Anatoly Perminov, head the Russian Federal Space Agency, as saying a proposal for earlier completion of the system would go to Putin before January 15, 2006.

Modernized GLONASS spacecraft (GLONASS-M) with a 7-year design life have flown on the launches since 2003. Two more went up with the most recent launch. Not well known is the fact that these include a second open civil signal at L2.

The availability of a second full open signal provides little practical benefit, however, because of the lack of user equipment outside the GLONASS control segment that can process the GLONASS L2 civil signal. New 72-channel chips recently announced by Javad Navigation Systems (the GeNiuSS) and Topcon Positioning Systems (Paradigm – G3) employ a common technical design that can process the GLONASS L2 signals, both C/A-code and P-code, as well as the new Galileo signals. Topcon has launched a new line of surveying equipment based on the technology, with the first product to be released as the NET-G3 receiver for reference station installations.

Technology, Policy, and Budgets

Unlike the Global Positioning System and Galileo, in which each satellite broadcasts a distinct code on the same frequency, GLONASS broadcasts the same code on different frequencies. At the L1 frequency, for example, the GLONASS open signal is spread between 1598.0625 MHz to 1607.0625, in sub-bands with signal peaks separated by 0.5625 MHz. This RF strategy requires broader swaths of increasingly rare radio spectrum and, at one point, brought the Russian system under pressure from radioastronomers and satellite communication systems that wanted to operate at the upper end of its RF allocation.

An agreement in the late 1990s committed Russia to an “antipodal” signal strategy that halved the number of bands on which satellites transmit their signals by assigning the same frequency to spacecraft orbiting on opposite sides of the Earth. This ensured that GLONASS receivers would not see conflicting signals on the same frequency, while allowing the bandwidth that it required to be compressed toward the lower portion of its allocation.

A 1999 presidential decree formally established GLONASS as a dual-use (civil and military) system, as is GPS. An Interagency Coordination Board comprised of civil and military agencies provides inputs from user communities, similar to the U.S. Interagency GPS Executive Board and its successor, the Space-Based PNT Executive Committee. The Russian Ministry of Defense (MoD) maintains and controls the system’s ground and space assets, although Roscosmos – the Russian Space Agency – acts as the program coordinator.

GLONASS receives funding directly from the Russian federal budget through line items in the MoD and Roscosmos agency allocations. Until recently, however, getting the funds through the civil agency remained problematical, according to Russian sources. The run-up in oil prices over the past couple of years has benefited Russia substantially. The nation produces and sells on the world market large quantities from its central Asian petroleum fields. President Putin has primarily used the funds to pay down indebtedness to the International Monetary Fund. Military programs, however, have received higher levels of support, which has translated into more stable funding for GLONASS, too.

Closing the Performance Gap

Shorter satellite survival on orbit has exacerbated the difficulty of sustaining the GLONASS constellation. All of the current operational spacecraft have been launched since 2000, and the mean mission duration (actual operational lifespan) is 4.5 years – about half that of GPS satellites.

Moreover, GLONASS performance has lagged behind GPS. A March 2005 study by the Swiss Institute of Science Research and Engineering, cited in a Tokyo symposium in November, reported that the accuracy of GPS ephemerides (the orbital locations of satellites broadcast as part of the navigation message) averaged about one meter compared to postprocessed tracking data from monitoring stations. In contrast, GLONASS ephemerides averaged about seven to eight meters.

In part, that reflects the more difficult challenge of tuning multiple signal/frequency combinations and accounting for the different propagation effects of carrier waves with slightly varying lengths. But the quality of on-board atomic clocks and system timekeeping, as well as weaknesses in the satellite navigation payload software and ground monitoring network, also contributed to the problem.

Now Russia is implementing an accuracy improvement program with modernization of satellites and ground infrastructure. Beginning with the GLONASS-M, manufactured by Reshetnev Applied Mechanics Research and Production Association (NPO-PM) in Krasnoyarsk, on-board clock stability over 24 hours has improved from 5×10-13 to 1×10-13. An improved dynamic model in the satellite navigation software will produce a lower level of unpredicted accelerations.

GLONASS-M spacecraft use previously reserved bytes in the navigation message to provide additional information, including the divergence of GPS and GLONASS time scales, navigation frame authenticity (validity) flags, and age of data information. Moreover, improved filters have been installed to reduce out-of-band emissions.

On the ground, GLONASS will also gain 3 stations from military tracking facilities and 9 to 12 from the Roscosmos network, much as the United States has done by incorporating National Geospatial-Intelligence Agency monitoring sites into the GPS tracking network. Both the United States and Russia are evaluating the utility and security of adding facilities from the International GNSS Service, an extensive network coordinated by NASA’s Jet Propulsion Laboratory in California.

New system clocks with high stability and improved systemwide synchronization will further improve GLONASS timing. Definition of the GLONASS coordinate system will tie it to the International Terrestrial Reference System, an international standard. As a result of these modernization efforts, Russian officials predict that GLONASS performance will equal that of GPS by 2008.

A new generation of satellites — GLONASS-K — is planned for launch beginning in 2008. These satellites will have a 10-year design life and carry a third civil signal at L3 frequency band, with a couple of frequency schemes under consideration in the 1198 to 1208 MHz band. Current plans for GLONASS-K include providing GNSS integrity information in the third civil signal and global differential ephemeris and time corrections to enable sub-meter real-time accuracy for mobile users.

Renewed Initiative

The recent progress in rebuilding and modernizing GLONASS appears to have bolstered the confidence of Russian officials in promoting the system internally and internationally. Russian state policy enacted last June mandates that, beginning in 2006, federal GNSS users employ only GLONASS or combined GLONASS/GPS receivers on Russian territory for aerospace and transport vehicles as well as for geodesy and cadastral surveying. And even before Putin’s recent remarks, Russia had re-engaged in several initiatives

The most recent round of talks with the United States led to a joint statement in December 2004 confirming that direct user fees would be imposed on civil GLONASS or GPS services and committed the two nations to ensuring the compatibility and interoperability of the two systems, implementing search and rescue functions using GNSS positioning, and cooperating on GNSS issues at international organizations.

On December 6, Russia and India signed an intergovernmental pact on the protection of classified military technologies during long-term cooperation under an agreement reached a year earlier for the joint development and peaceful use of GLONASS. This includes cooperation in GNSS ground infrastructure development and launch of GLONASS-M satellites on India’s Geosynchronous Satellite Launch Vehicle (GSLV). The GSLV design incorporates Russian rocket engine technology.

Finally, consultations with the European Union continue on a prospective Galileo/GLONASS agreement, with a technical working group scheduled to submit a proposal in April on signal compatibility and interoperability at the GLONASS L3 and Galileo E5b bands. Russian rockets will help launch Galileo satellites, including a Soyuz-Fregat used in the successful first launch of GIOVE-A on December 28 (See article on page 16.), and laser retro-reflectors produced by NIIPP, the Russian Scientific-Research Institute of Precision Instrument-Making, will measure the altitude of both GIOVE spacecraft to within centimeters.

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Will Success Spoil GPS?

Will Success Spoil GPS?

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.

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The Perils (and Pearls) of Galileo

The Perils (and Pearls) of Galileo

Successful launch of the first Galileo satellite on December 28 marks the culmination of a process that began almost exactly 13 years earlier.

Successful launch of the first Galileo satellite on December 28 marks the culmination of a process that began almost exactly 13 years earlier.

On January 19 the European Space Agency and Galileo Industries GmbH, the European company steering a consortium of more than 100 subcontractors, signed a €950 million (US$1.15 billion) contract that will pave the way for the operational deployment of Galileo. The contract calls for a mini-constellation of four satellites backed by an extensive network of tracking and control stations that will validate the design of the Galileo space and ground infrastructure. Four satellites are the minimum required to generate three-dimensional positioning and precise timing over the selected showcase sites.

In December 1992, however, Galileo was just a glimmer in a few visionaries’ eyes. That was the month that two European Commission (EC) directorates-general — those for transport and science, research, and development – decided to fund a modest study of satellite navigation options for Europe. The intervening years produced a kind of programmatic version of “The Perils of Pauline,” the cliffhanger serial movie in which each installment ends with the title character – a perpetual damsel in distress – placed in a situation that threatens her imminent demise, only to be rescued at the beginning of the next episode.

Galileo’s most recent “peril” revolved around a dispute between Germany and other members of the European Union (EU) over the allocation of contracts and responsibilities that they would have during the deployment phase of the system. A December 5 agreement on sharing Galileo operational and control centers among five nations rescued Galileo from the months-long impasse.

The next (but probably not final) act of the “Perils of Galileo” remains to be played out: the signing of an agreement with a consortium of companies that will complete the development of the space and ground segments and operate the system for the next 20 years. Current estimates place that milestone in the latter half of 2006, reflecting delays that have dogged the program since its inception and finally pushed its timeline for completion to 2010 – two years beyond the date long proposed by the EC and its Galileo partner, the European Space Agency (ESA).

Nonetheless, the launch of GIOVE-A, the experimental Galileo spacecraft built by Surrey Satellite Technology Ltd., marks a major—and probably irrevocable—step forward for the European GNSS. The start of transmissions from GIOVE-A and a second testbed satellite, GIOVE-B, manufactured by Galileo Industries, will allow the system to lay claim to use of the radio frequencies allocated at World Radio Conferences in 2000 and reaffirmed in 2003.

They will also allow ESA to evaluate on-orbit performance of several new satellite components and technologies and, significantly, also enable GNSS receiver developers to work with real signals in space. For example, GIOVE-B will be launched in the first half of 2006 and will have a passive hydrogen-maser clock as an additional payload, the first such clock ever flown into space. Current spaceborne clocks are cesium and rubidium frequency standards. Galileo satellites will also have rubidium clocks on board.

Political Merry-Go-Round

Several aspects of the €3.8 billion (US$4.6 billion) Galileo program distinguish it from its U.S. and Russian counterparts, GPS and GLONASS: full civilian control, a so-called public-private partnership (PPP) in its deployment and operation, international participation, and a multitude of services, including some that will be fee-based with guaranteed delivery of service. Indeed, the political challenges have long eclipsed the technical ones.

Fusing the interests of 15 (later 25) EU member-states, three additional non-EU ESA participants, and their leading industrial factors into a single enterprise has required a sustained exercise in what’s sometimes called “concertation.” Galileo represents the first Europe-wide infrastructure project and, consequently, challenged the EU and ESA to achieve a new level of political capability — within themselves and between one another. After the original 1992 satnav study, it took nearly seven years before Galileo even got its name in a February 1999 EC document, “Involving Europe in a New Generation of Satellite Navigation Services.”

Until then the program had been known rather generically as GNSS 2, distinguishing it from GNSS 1, the European Geostationary Navigation Overlay Service (EGNOS), a satellite-based augmentation of GPS and GLONASS. In May 1999 the ESA Ministerial Council approved the GalileoSat program; in June 1999 the EU Transport Council endorsed a first resolution on Galileo.

A November 22, 2000, EC communication to the European Parliament and European Council laid out the financing, organization, R&D, and implementation plan. In November 2001 the ESA Ministerial Council approved the development of Galileo (Phase-C/D, with a budget of €550 million). In May 2002 the Council authorized a joint undertaking, an institutional entity envisioned under Article 171 of the European Community Treaty but only implemented once previously, which allows the EU to collaborate in a single enterprise with non-EU bodies.

ESA and the EC (on behalf of the EU) comprised the initial membership of the Galileo Joint Undertaking (GJU), which has as its primary task the completion of a concession contract. Subsequently, non-EU governmental organizations representing China and Israel signed on with the GJU. Other nations, including Ukraine and India, are expected to join soon. The concessionaire will complete deployment of the Galileo satellites and ground infrastructure and operate the system over the next 20 years, monitored by a Galileo Supervisory Authority.

Final action to deploy the system only came with European Council action on December 10, 2004. Along the way, however, the growing EU-ESA cooperation on Galileo led to a broader initiative on a common European space policy. Late in 2003 the two institutions issued a White Paper on Space and signed a “framework agreement” for cooperation in space activities. Under the agreement, “the EC and ESA will launch and fund joint projects, participate in each other’s schemes, create common management agencies, carry out studies and jointly organize conferences and training of scientists, exchange and share experts, equipment and materials, and access to facilities.”

The overall cost of the Galileo system was first estimated at €3.4 billion, with a public investment for the development and validation phase of €1.1 billion divided between the EC and ESA. This phase was re-evaluated in 2005 at €1.5 billion.

The Art of the Deal

Currently, a “grand coalition” of leading European aerospace, telecommunications, and banking interests is negotiating with the GJU in a formerly competitive process that saw the merger of the two leading consortia in March 2005. Last month’s agreement on Galileo’s operational and administrative direction saw Eurely — a grouping led by Alcatel, Finmeccanica, and Vinci Networks — and the iNavSat consortium headed by the European Aeronautic Defense and Space Company (EADS), Thales, and Inmarsat, joined by a new consortium of Munich, Germany–based companies. The latter group, TeleOp, includes the commercial arm of the German Space Agency (DLR), the LfA Förderbank Bayern, and subsidiaries of EADS and T-Systems.

But the agreement didn’t come easily. Multi-sided talks by representatives of eight companies and five governments (France, Germany, United Kingdom, Italy, and Spain) would reach tentative accords at one level or with one group of negotiators but then fall apart when brought to another forum. Coloring the dialog were national ambitions to be seen as leading the Galileo program and the sensitivity to geographic return — the practice of spreading contracts and revenues among program participants in a proportion close to the contributions made by the various nations.

“Finally, we realized we can’t keep on fighting over these assets without getting an agreement,” Martin Ripple, director of Galileo Program for EADS Space Services, told Inside GNSS. “So, EADS said let’s put the all industrial players in one room and get the five governmental players into the same room. And lock them in until they come out with something.”

What they came out of the room with was a plan that reallocated key components of Galileo operations among the five leading space nations in Europe. The headquarters of the Galileo concessionaire will be located in Toulouse, France, with administrative and market development responsibilities. Inmarsat will have overall management leadership of the operations company based in the United Kingdom and responsible for global network operations, including performance monitoring and operations security. The two control centers (for constellation and mission) will be located in Germany (near Munich in Bavaria) and Italy (Fucino space center in Abruzzo region) along with two performance evaluation centers supporting the concessionaire headquarters. Spain will host backup control centers as well as facilities related to Galileo safety-critical applications.

“It’s a major step toward a concession contract,” says Ripple.

The Same, Only Different

On the technical side of the program, Galileo has entered the in-orbit validation (IOV) and development phase using the two GIOVE experimental satellites to test out ESA’s spacecraft design and ground control. The IOV phase will conclude with the deployment of four operational satellites in 2008. According to the current schedule, an additional 26 satellites will then be launched over the following two years with full operational capability (FOC) declared in 2010.

Galileo operational satellites will transmit signals in a variety of bands clustered around the 1176-1207 MHz spectrum near the GPS L2 frequency, 1775.42 MHz centered at the GPS L1 frequency, and 1278.75 MHz. The latter band lies at some distance from the GPS L2 signals at 1227.6 MHz, but would fall within one of the bands that Russia is considering for the third civil GLONASS signal that will begin broadcasting with launch of its new satellites in 2008.

Galileo signal structures include a combination of biphase shift keying (BPSK) and binary offset carrier (BOC) designs. (Current GPS signals are BPSK variations, but future signals will also be BOC-based.) Recently, the Galileo Signal Task Force has proposed the addition of a composite binary coded symbols (CBCS) design that superposes BOC and a binary coded symbol waveform with the same chipping rate.

Galileo will offer five services: a free open service; a fee-based, encrypted commercial service offering higher accuracy and service guarantees; a safety of life service the includes signal authentication and integrity alerts (targeting, for example, commercial aviation); a search and rescue service operating in near-real time with a return communications link possible; and an encrypted governmental service known as the “public regulated service” or PRS, which will be used by public safety agencies and, conceivably, military forces. Certification for safety of life services is scheduled to occur within a year after FOC.

This final point and the liability issues that it raises probably is the largest complication for the final negotiations in the concession contract. Sizing and sharing the risk associated with service guarantees introduces a problematical element to the Galileo project not faced by its GPS and GLONASS counterparts. As one participant in the deliberations has posed the dilemma: What do you do if a hiker in the Rocky Mountains gets lost and sues Galileo in front of a U.S. judge? Once signed, the concession agreement will lead to the phasing out of the GJU and the advent of the Galileo Supervisory Authority’s role. The concession contract also represents the turning point of the public-private partnership that marks Galileo as a different kind of beast from publicly funded GPS and GLONASS. The framework for negotiating the concession contract assumes a two-thirds contribution from the private sector for the €2.2 billion deployment phase and all of the €220 million annual expense of operating and maintaining Galileo.

Given the past history of the European GNSS initiative persevering and escaping perils — including self-created ones, the Galileo project will probably manage to solve the PPP riddle and get on with the (comparatively) simple task of building and operating a system.

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