Look back with me at the five 2010 GNSS events that most affected surveying, mapping, engineering, construction, and natural resource users. Each one had, or could have had, a significant effect on you and your work. Taking it from the top:
GPS 24+3 Constellation. The most important event occurred a year ago, when the Air Force began implementing a new GPS 24+3 configuration. They had their military reasons, but the benefit for you and me is eliminating GPS brownouts — periods with fewer GPS satellites in view. When combined with obstructions such as terrain, trees, or buildings, they made GPS hard to use.
It’s especially an issue with real-time kinematic (RTK) high-precision users because RTK technology is satellite-hungry. It needs six or more satellites to provide a robust position solution.
The Air Force moved three satellites, SVNs 24, 26 and 30, from their original slots. SVNs 26 and 30 have already reached their destinations, and SVN 24 will do so this month.
Three other satellites are being shifted slightly. SVN 55 found its new slot in December, while SVNs 46 and 56 start this month and should have completed their journeys by May/June 2011.
By now, you should be seeing some improvements in GPS satellite visibility. Although you’ll see fewer peaks (high number of GPS satellites in view), you’ll also see fewer valleys (low number of GPS satellites in view). This should increase productivity for RTK users and those in obstructed environments such as tree canopy.
First GPS Block IIF. Although it doesn’t really help users at this point other than being another satellite to enter service, the Block IIF satellite launched in May is the first to broadcast the third civil signal. L5 marks the beginning of a new era in high-precision GPS positioning. The Block IIF launch was the catalyst for my June column “What Happen When High Accuracy is Cheap?”
This IIF is just a teaser though, and its fellows will launch at a snail’s pace. Remember though, it costs upwards of $200 million to launch a satellite and since there ares already 30+ operational GPS satellites in orbit, it’s hard for Congress and the Air Force to justify speeding up the launch schedule. The last target I heard was to have 24 satellites broadcasting L5 by 2019.
GLONASS Growth. Despite the recent catastrophe, the Russian Federation was still able to launch seven new satellites in 2010, including a new K1 satellite that will test a new CDMA signal for better compatibility with GPS.With 21 operational satellites and three more coming in March, a consistent and healthy number of GLONASS satellites in orbit has given receiver manufacturers more confidence to develop GPS/GLONASS receivers. This year, we’ve seen several manufacturers integrating GPS/GLONASS into handheld receivers as well as OEM board products.
User benefits are clear: more robust positioning and improved productivity due to decreased down-time.
Solar Activity. The big news is no news: the sun was eerily quiet in 2010. If your GPS receiver didn’t work at times this year, it wasn’t due to solar activity. But it may ramp up in 2011.
GAGAN, WAAS Failures. The Indian Space Research Organisation and the U.S. Federal Aviation Administration received a hard lesson in SBAS GEO management. In April, an Indian rocket launch failed, and one of the FAA WAAS satellites lost communication with its ground control.
If you’re an SBAS user, don’t let it bring you down. SBAS is here to stay, and likely you were not affected by either incident — unless you work in northwest Alaska. A new U.S. SBAS satellite came online, and India is regrouping for more launches.
Surplus fuel loaded in error onboard the launch rocket caused loss of three new GLONASS satellites on December 5. The mishap burdened the DM-3 booster rocket with an excess of 1.5 to 2 tons of fuel, causing it to deviate from its course after blast-off and dive into the Pacific Ocean instead of reaching orbit altitude — dashing hopes for an imminent, nearly full global operational GLONASS capability.
“The problem was not with the fuel service unit at the launching site, but with one of the sensors showing the fuel level,” said Gennady Raikunov, the head of the Central Scientific Research Institute of Machine Building. “We do not rule out the factor of human error,” he said, adding that the Russian corporation Energia may be linked to the incident.
News correspondent Peter de Selding, writing in the December 10 issue of Space News, reported that a new version of the Block DM upper rocket stage, which was used for the GLONASS launch, features larger propellant tanks than earlier versions. The DM stage is built by RSC Energia of Korolev, Russia.
“In what appears to have been a remarkable oversight,” de Selding wrote, “the personnel fueling the Block DM stage for the GLONASS launch did not account for the larger tanks. That led to loading between 1,000 and 2,000 kilograms more propellant on the Block DM stage than what had been planned for the mission. As a result of the excess propellant, the Proton’s third stage, suffering from the additional weight it was carrying, underperformed, placing the Block DM stage and the stack of GLONASS satellites into a lower-than-planned suborbital drop-off point.”
Get Back on That Horse. On December 12, the next-generation GLONASS-K1 satellite, serial number 11, was shipped to the Plesetsk Cosmodrome about 800 kilometers north of Moscow. According to manufacturer ISS Reshetnev, the satellite will transmit five navigation signals: two signals of normal and two of high precision in the L1 and L2 frequency bands, and a new code-division multiple-access (CDMA) civil signal in the L3 band (1205 MHz). The last is destined to shift the Russian constellation at least partly towards CDMA signal broadcast, in line with GPS and Galileo. It points towards possible and eventual interoperability of some kind between the systems.
Launch is scheduled for December 27 or 28 on a modernized Soyuz-2.1.b rocket equipped with a Fregat upper stage.
March FOC Vowed. Anatoly Perminov, the head of Roscosmos, the Russian Federal Space Agency, has stated that the setback is temporary and he plans to have a full 24-satellite constellation functioning by next March. He plans to accomplish this by repositioning one of the satellites now in maintenance and then bringing it back on line and by launching two more satellites over the next few months.
Galileo Supervisory Authority enroute to Prague
The Czech Republic has after an intensive multi-year lobbying effort landed a Galileo plum: the siting of the European GNSS Supervisory Authority (GSA) headquarters in its capital. The GSA has for the past three years worked out of Brussels, and longer prior to that, under the title Galileo Joint Undertaking.
An official with the GSA told GPS World informally, “I can confirm: the decision has been adopted today by the Competiveness Council. However the move might not be immediate. The Commission claimed (rightly) to be involved in the timing of the move to minimize disruption, to ensure continuation of the ongoing work, and to avoid the disruption of the progress towards the FOC of Galileo. The financial repercussions must also be assessed.”
In an interview on Czech television, Czech Prime Minister Petr Necas called the decision a success for the entire country. “This is very good news because this will bring the most advanced technologies to the Czech Republic and, accordingly, one of most technologically advanced systems in the European Union will be controlled from here, from the Czech Republic,” he said.
Necas’ statement was not entirely accurate, as the GSA does not actually control any technology. The Galileo constellation of current (two) and future (from four to 18) satellites remains firmly in the control of the European Space Agency (ESA), administratively based in Paris with many technical activities undertaken in Noordwijk, the Netherlands, and further under the thumb of the European Commission (EC), irrevocably grounded in Brussels.
Upcoming tasks faced by the GSA include most importantly the commercialization of Galileo — which may be seen as largely a marketing activity — and security accreditation and the operation of the Galileo security center.
Several countries vied to host the agency, and in the final days Prague was competing against Noordwijk itself for the post. The siting of the GSA outside the EU’s Western European core represents a nod to its pledge to include newer Eastern members in governing activities, specifically to give preference to new member states when looking for headquarters for its new agencies. Before the vote, the Czech Republic was one of four member states that joined the EU in 2004 that had not yet been chosen to host an EU agency or body. The X-37B, debriefing after its 220-day experimental mission.
Unmanned Spacecraft Returns Home
The U.S. Air Force’s first unmanned re-entry spacecraft landed at Vandenberg Air Force Base on December 3, after a 220-day maiden voyage, conducting on-orbit experiments. The X-37B, named Orbital Test Vehicle 1 (OTV-1), is a totally autonomous vehicle that depends a great deal upon GPS for
mission success.
GPS provided a significant contribution to the X-37B’s re-entry and landing — the first unmanned spacecraft that landed like an aircraft. It fired its orbital maneuver engine in low-Earth orbit to perform an autonomous reentry before landing.
The Air Force’s newest and most advanced re-entry spacecraft, X-37B performs risk reduction, experimentation, and concept of operations development for reusable space vehicle technologies.
The Air Force is preparing to launch the next X-37B, OTV-2, in spring 2011 aboard an Atlas V booster.
Overall, the program “has huge implications for the future of unmanned space flight and for the capabilities of the USAF and DoD missions in space. The GPS is a key component of this capability.”
“To go much farther,” an informed source told GPS World, “gets me into territory that I cannot discuss in this venue.”
Quoting industry sources, the Russian Federal Space Agency announced that the December 5 launch of three GLONASS-M satellites ended in failure when the Proton-M rocket’s Block DM upper stage and its three payloads crashed into the Pacific Ocean about 1,500 kilometers, or 932 miles, northwest of Honolulu. Although an investigation will look into the exact cause of the failure, early unconfirmed reports indicate a software error.
Apparently, the Proton carrier’s third stage deviated from its planned trajectory.
The three satellites were launched from the Baikonur cosmodrome in Kazakhstan. According to telemetry, the carrier rocket’s upper stage containing the satellites was launched into a “non-targeted orbit.” According to a BBC news report, the upper stage and GLONASS-M navigation satellite payload crashed into the Pacific Ocean near Hawaii. BBC news also reported that sources informed them that the launch rocket had deviated by eight degrees from its intended path after launch.
The Russian Federal Space Agency reported that a “special board has been established to find out the cause of the contingency and to define the next steps.”
According to the Russian News Agency RIA Novosti, incorrect calculations were loaded into the rocket’s onboard computer missiles. As a result, the rocket engine provided too much momentum, leading to the deviation of the vehicle from its planned trajectory.
RIA Novosti also reported that because of the accident, the pace of satellite launches will have to be accelerated. For example, the launch scheduled for September 2011 is likely to take place earlier.
The new generation GLONASS-K satellite is due to launch later this month from the northern Plesetsk cosmodrome.
Video of the pre-launch rocket delivery can be viewed here:
There are currently 20 operational GLONASS satellites, with another four undergoing maintenance and two reserved as spares.
JAVAD Receivers Track the First Truly Interoperable Signal
JAVAD GNSS engineers in Moscow have released plots of the C/A, L2C, L5, SAIF, and the new L1C signals broadcast by Japan’s QZSS Michibiki, the first satellite to transmit L1C.
The company stated that all of its current GNSS receivers can track QZSS signals with a software update that is available as an option to purchase.
A new civil signal, L1C is designed to be interoperable among GNSSs. Currently, agreements are in place between the U.S. GPS, Europe’s Galileo, and Japan’s QZSS systems regarding broadcast and use of L1C. The U.S. system is not destined to add the L1C signal until the GPS III block of satellites, still more than three years out.
The SAIF (Submeter-class Augmentation with Integrity Function) signal is a GPS augmentation with information on positioning correction and system health. The QZSS L1-C/A, L2C, L5, and L1C signals are GPS augmentation signals that can be operated reciprocally with positioning signals provided by GPS. The figures supplied by JAVAD GNSS show SNR (top) and code-minus-phase (bottom) plots for L1C.
Plot of QZSS L1C signal, SNR.
Plot of QZSS L1C signal, code minus phase (above).
Paul Verhoef, the European Commission’s program manager for European Union (EU) satellite navigation programs, discussed current issues at length with GPS World, in a conversation on November 10. He addressed aspects of interoperability with GPS and prospects for further development in that area, the need for an ongoing political commitment by the EU to Galileo, the challenges of financing, the prospects for an 18-satellite constellation (which he dismisses as unrealistic), military considerations for both Galileo and GPS, and the recent uncertainty around Galileo’s Public Regulated Service.
Interoperability. “We have seen in the process with the U.S. that first of all there has been a quite clear political commitment on both sides, at the highest levels, that interoperability was wanted. Secondly, in the implementation we’ve had a very good working relation with our U.S. colleagues in order to establish that. The advantage that I see is that we have been able at a very early stage to deliver on such an interoperability agreement, that this is clear to industry, it provides for predictability. It allows industry to monitor clearly how the two systems are evolving, and when this interoperability is actually going to be available in the marketplace, and it allows them to time their investments, their R&D, their production, and all the rest.” [ . . . . ]
Challenges. “It is time that Galileo delivers something concrete. We’ve had many years of discussion behind us on whether the system will come, and if it will come, and how it will come, and what it will look like, and all the rest. For my part, I’m very happy to see that in 2011, we plan to launch.
The first four satellites are on the way; they are almost ready. About half the ground infrastructure is currently under implementation, we have every couple of months the opening of another ground station around the world. With this, the system becomes a reality, and I think once the satellite launches will go across television screens in the whole world, people will see that the system is becoming a reality. And I think that is desperately needed in order to give it a sense that things are moving forward. I’m really looking forward to that. That is a piece of good progress we have achieved over the last couple of years.
Constellation. “There is a bit of a discussion for some reason in Europe, for some reason some people seem to think that we could do away with 18 satellites. Well, from me you will hear a solid ‘No.’
“The availability figures for an 18-satellite constellation are around 90 percent on average, which means that for an aggregate total of some six weeks a year you would not receive sufficient views, not have sufficient satellites in sight to actually determine a position. There are going to be sectors like aviation where this is completely unacceptable, and they would never invest in anything if that is what we’re going to do. So my sense is that we will always have a lot of upward pressure in terms of constellation size. Of course it needs to be offset against costs and other considerations, but I think the pressure is always going to be there. It is very premature for people to be trying to take a shortcut, to think, well, maybe we could do with less. Because in the end you would have a constellation with a technical performance which the marketplace is not interested in, and then you would have a real problem.”
The U.S. Air Force 2nd Space Operations Squadron is scheduled to release the next software upgrade for the GPS ground system in early December, as part of an ongoing effort to improve and maintain the GPS Operational Control Segment before the next-generation GPS Control Segment is deployed in 2015. The upgrade is expected to be completed in early January 2011. The upgrade does not change the navigation message and should be transparent to GPS users. Tests have shown that the navigation message produced by the new software is identical to that produced by the current ground software. While no anomalies are expected, civilians experiencing any anomalies should contact the Coast Guard Navigation Center at (703) 313-5900.
GLONASS Launch Fails
The Russian Federal Space Agency announced that the December 5 launch of three GLONASS-M satellites ended in failure when the Proton-M rocket’s Block DM upper stage and its three payloads crashed into the Pacific Ocean about 1,500 kilometers (932 miles) northwest of Honolulu. Although an investigation will look into the exact cause of the failure, early unconfirmed reports indicate a software error. According to the Russian News Agency RIA Novosti, incorrect calculations were loaded into the rocket’s onboard computers.
Compass Settles, Moves
The Beidou/Compass G4 satellite launched on October 31 achieved geostationary orbit by November 6. The satellite is positioned at about 160 degrees east longitude. G4 is the furthest east of the operational Beidou geostationary satellites. Meanwhile, the orbital location of the Beidou 1A satellite has been changed.
On or about October 27, as indicated by NORAD tracking data, the satellite underwent a significant delta-V, raising its orbit by about 200 kilometers. Its orbit had been slightly drifting for a few weeks before the maneuver, and there was speculation that the satellite had been placed in a disposal or graveyard orbit. However, on November 24 a second delta-V was observed that returned the satellite to the geostationary belt.
The two maneuvers placed the satellite at a new location at about 60 degrees east longitude — the furthest west of any of the Beidou satellites. The satellite may eventually end up at 58.75 degrees east, one of the Beidou orbital slots registered with the International Telecommunication Union.
The geostationary satellite, the first for the demonstration regional Beidou system or Beidou-1, was launched on October 30, 2000, and positioned at 140 degrees east longitude. Following several years of use, there were unofficial reports that the satellite was no longer functional. However, station-keeping was maintained, implying some usefulness of the satellite. It remains unclear how functional the satellite is and whether it is still useful for the Beidou-1 demonstration system.
At the Civil GPS Service Interface Committee meeting in Portland, Oregon, on September 20, Sergey Revnivykh, Deputy Director General of Roscosmos’s Central Research Institute of Machine Building, reported on the status and future of GLONASS.
He provided a number of details on the present constellation and how it will be augmented in the future, stressing that GLONASS is doing well and that a full constellation of 24 primary satellites will be in operation within months. The average signal-in-space range error has improved by a factor of five in the past three years and presently stands at about 1.8 meters (one sigma).
Figure 1. The GLONASS satellite generations through GLONASS-K2.
The present constellation consists of 20 healthy satellites with two reserve satellites, GLONASS 714 and 726. Revnivykh stated that GLONASS 726 had a failure of its navigation payload. It is known that the signal generator on the satellite is faulty and it had been set unhealthy since August 31, 2009. Nevertheless, it was placed in reserve status on March 19, 2010. GLONASS 714 is nominally healthy and could be brought back to service if needed. These initial reserve satellites are also being used to train the ground team to operate spare satellites in a full or nearly full constellation.
GLONASS 727, in orbital slot 3, which was taken out of service on September 8, has also had a failure of its navigation payload and may not be returning to service. The three new satellites launched on September 2 are expected to enter service in early October. About 11 more GLONASS-M satellites will be launched by the end of 2012.
Revnivykh announced that there will be two versions of the new GLONASS-K satellites: GLONASS-K1 and GLONASS-K2. GLONASS-K1 satellites will have a 10-year design life and a daily clock stability of 5 x 10-14.
The first GLONASS-K1 satellite will be launched this December from the Plesetsk Cosmodrome about 800 kilometers north of Moscow. This will be the first launch of a GLONASS satellite from other than the Baikonur Cosmodrome. Only one more GLONASS-K1 satellite will be built and launched after that. The K1 satellites will test an open service CDMA signal on the GLONASS L3 frequency in the 1205 MHz band. Although the launch of the first GLONASS-K1 satellite will occur in December, the design process for the CDMA signal structure is not yet finished, according to a subsequent e-mail message from Dr. Revnivykh. When the process is completed, the structure will be made public.
A completely new design, GLONASS-K2, will start launching in 2013. GLONASS-K2 satellites will have a 10-year design life and a daily clock stability of 1 3 10-14. Besides the CDMA signals on L3, CDMA signals will also be transmitted on L1 and L2. The GLONASS-K satellites will transmit the legacy FDMA satellites in addition to the CDMA signals.
A modernized GLONASS-K satellite, GLONASS-KM, for launch after 2015, is now under study. In addition to transmitting legacy FDMA signals on L1 and L2 and CDMA signals on L1, L2, and L3, CDMA signals may also be transmitted on the GPS L5 frequency at 1176.45 MHz. Also being studied is an alternative to the present three-plane, equally spaced satellite constellation. A different constellation design would be possible using CDMA signals. Such a move would require that the legacy FDMA signals be switched off. Revnivykh stated that any such move would require at least 10 years’ advance notice.
The signals that will be transmitted by the future generations of GLONASS satellites as well as those transmitted by the initial GLONASS satellites and the GLONASS-M satellites now on orbit are shown in Figure 2.
Figure 2. Signals transmitted by the different generations of GLONASS satellites. OF 5 open-access FDMA, SF 5 special (military) FDMA, OC 5 open-access CDMA, OCM 5 open-access CDMA modernized.
Revnivykh also spoke on the satellite-based augmentation system under development, System for Differential Correction and Monitoring (SDCM). Correction and integrity data will be transmitted by Luch geostationary communication satellites now under development. Luch 5A, to be launched in 2011 and positioned at 16°W longitude, and Luch 5B, to be launched in 2012 and positioned at 95°E longitude, will transmit signals on an L1 frequency. Luch 4, to be launched in 2013 and positioned at 167°E longitude, will transmit on two frequencies. The three satellites will provide almost global coverage. The satellite payloads are under development.
According to Revnivykh, the SDCM will make use of 12 monitor stations currently in operation in Russia and one in Antarctica at Russia’s Bellingshausen research station. However, the SDCM website indicates only 10 Russian stations currently in the test network. This anomaly might be explained by the fact that some locations have multiple monitor stations. Eight more monitor stations will be added in Russia and five more outside Russia. Revnivykh showed a map revealing the locations of the additional overseas stations as Cuba, Brazil, Vietnam, Australia, and an additional station in Antarctica. It is not intended, at least initially, that these stations would be used in generating the orbit and clock data broadcast by the GLONASS satellites themselves.
Finally, Revnivykh stated that a GLONASS performance document will be released in the 2012–2013 time frame. His full presentation is available on the U.S. Coast Guard Navigation Center website (www.navcen.uscg.gov).
Meanwhile, the three GLONASS-M satellites launched on September 2 have arrived at their designated orbital slots: GLONASS 736, plane 2, slot 9; 737, plane 2, slot 12; 738, plane 2, slot 16.
The operating frequencies are not yet fully known. GLONASS 736, in physical slot 09, is currently undergoing experimental tests. It is included in the broadcast almanac at slot 16 and is transmitting on frequency channel -6. Stations in the International GNSS Service ground network are tracking the satellite. According to the Roscosmos Information-Analytical Centre, when the tests are completed, GLONASS 736 will transmit on channel -2 and be identified as slot 09 in the almanac. It is unclear if GLONASS 736 will replace GLONASS 722 also currently in slot 9, with the latter becoming a spare, or if GLONASS 736 will become the spare as previously inferred.
GLONASS 737 and 738 have not started normal transmissions. Their assigned shared frequency channel is not yet known but -6 would be a likely candidate.
Future GPS Control Segment Advances
The Raytheon Company team developing the next-generation GPS Advanced Control Segment (OCX) successfully completed on schedule an integrated baseline review with the U.S. Air Force.
When completed, GPS OCX will deliver a control segment designed to provide secure, accurate, and reliable navigation and timing information to military, commercial, and civil users. Raytheon is the prime contractor on the $886 million program. The team includes ITT, The Boeing Company, Infinity Systems Engineering, Braxton Technologies, and NASA’s Jet Propulsion Laboratory.
Power Flex Positive
From September 7 to 12, the U.S. Air Force Space Command (AFSPC) activated the long-awaited Flex Power demonstration for GPS, a power increase on L1 and L2. The trial of a new capability designed for military use under special circumstances was deemed a success, essentially going off without a hitch, according to Colonel David Buckman, AFSPC Command Lead for PNT, and Colonel Bernie Gruber, GPS Wing Commander.
Officially, the flex power assessment ensured that the GPS control segment baseline (AEP 5.5) is properly integrated with the space segment with regard to command and control of High-Y Flex Power, a capability that increases the nominal transmit power of the desired signal by shifting power between signals (M-code and P(Y)) within a particular L-band. The net sum gain remains the same. High-Y Flex Power does not change total transmit power, does not affect phase stability between L1 and L2, is ICD-GPS-200E compliant, and does not affect the navigation message.
Only a handful of 10-year-old reference receivers may have been adversely affected, possibly due to an outdated algorithm. Many government, commercial, and civil agencies were involved in the test, and hundreds of GPS receivers were closely monitored. As far as impacts to the overwhelming majority of global users, it was a non-event. The 2nd Space Operations Squadron (2SOPS) was able, over the course of five days, to make power changes to several GPS satellites without causing a phase shift and without the majority of users even knowing what was happening, although various announcements and press releases had appeared to alert them of the fact.
All GPS satellites and signals have now returned to their normal power levels.
Air Force Fends off GAO Zinger
The U.S. Government Accountability Office has issued a follow-up to its alarming and much-criticized report, issued 16 months ago, on the health and prospects of the GPS constellation. Senior officers at the Air Force Space Command and Space and Missile Systems Center have characterized the new report as “overly pessimistic.”
The report’s principal findings — that the Air Force continues to face challenges in launching its satellites as scheduled, which could affect the availability of the baseline GPS constellation, that on-orbit performance of IIF satellites remains uncertain, that a disconnect exists between GPS III and OCX, and that a predicted possible delay in GPS III could affect GPS constellation performance — are discussed and rebutted in detail by GPS World defense editor Don Jewell, with further commentary (paraphrased) by Air Force Space Command, in his October column.
New Galileo ICD Embraced
European Commission (EC) officials held a briefing during ION-GNSS in Portland for industry representatives, to discuss the new Galileo Open Service Signal-in-Space Interface Control Document (OS SIS ICD). Hosts Paul Verhoef and Michel Bosco said they were pleased with what they characterized as positive feedback from U.S., European, and Japanese industry representatives regarding collaboration and consultation over changes made in the ICD. The updated version is available.
The EC grants free access to the technical information on the future Galileo open service signal: the specifications manufacturers and developers need to process data received from satellites. Anyone who wishes to use the intellectual property rights contained in the document simply needs to send an e-mail to [email protected] mentioning their request for a license agreement, which is without any exclusivity or geographic limitation.
FAA Green-Lights ADS-B
The U.S. Federal Aviation Administration (FAA) gave the go-ahead signal for full-scale, nationwide deployment of the satellite-based surveillance system called Automatic Dependent Surveillance – Broadcast (ADS-B) following its successful roll-out at four key sites. Air traffic controllers are now able to use the new technology to separate aircraft in areas with ADS-B coverage. Controller screens in those areas will show aircraft tracked by radar as well as aircraft equipped with ADS-B avionics, which broadcast their positions.
The new system tracks aircraft with greater accuracy, integrity, and reliability than the current radar-based system, the FAA said. ADS-B targets on controller screens update more frequently than radar and display information including aircraft type, call sign, heading, altitude, and speed.
Nationwide ADS-B coverage is scheduled to be complete in 2013. According to the FAA, every part of the country now covered by radar will have ADS-B coverage. More than 300 of the approximate 800 ADS-B ground stations that will comprise the entire network have been installed.
By 2020, aircraft flying in controlled airspace in the U.S. must be equipped with ADS-B avionics that broadcast their position.
At the Civil GPS Service Interface Committee meeting in Portland, Oregon, on Monday, Sergey Revnivykh, Deputy Director General of Roscosmos’s Central Research Institute of Machine Building reported on the status and future of GLONASS.
He provided a number of previously unpublished details on the present constellation and how it will be augmented in the future.
The present constellation officially has two reserve satellites, GLONASS 714 and 726. Revnivykh stated that neither of these satellites would ever be brought back to active service. 714 was a flight-test satellite, apparently, and 726 had a failure of its navigation payload. Rather than being possible replacement satellites, these vehicles are being used to train the ground team to operate spare satellites in a full or nearly full constellation.
GLONASS 727, in orbital slot 3, which was taken out of service on 8 September 2010 has also had a failure of its navigation payload and will not be returning to service. About 11 more GLONASS-M satellites will be launched by the end of 2012.
Revnivykh announced that there will be two versions of the new GLONASS-K satellites: GLONASS-K1 and GLONASS-K2. GLONASS-K1 satellites will have a 10-year design life and a daily clock stability of 5 ´ 10-14. The first GLONASS-K1 satellite will be launched this December from the Plesetsk Cosmodrome about 800 km north of Moscow. This will be the first launch of a GLONASS satellite from other than the Baikonur Cosmodrome. Only one more GLONASS-K1 satellite will be built and launched after that. The K1 satellites will test an open service CDMA signal on the GLONASS L3 frequency in the 1205 MHz band. When asked when the specific structure of the CDMA signal would be announced, Revnivykh said he didn’t know.
A completely new design, GLONASS-K2, will start launching in 2013. GLONASS-K2 satellites will have a 10-year design life and a clock stability of 1 ´ 10-14. Besides the CDMA signals on L3, CDMA signals will also be transmitted on L1 and L2. The GLONASS-K satellites will transmit the legacy FDMA satellites in addition to the CDMA signals.
A modernized GLONASS-K satellite, GLONASS-KM, for launch after 2015 is now under study. In addition to transmitting legacy FDMA signals on L1 and L2 and CDMA signals on L1, L2, and L3, CDMA signals may also be transmitted on the GPS L5 frequency at 1176.45 MHz. Also being studied is an alternative to the present three-plane, equally spaced satellite constellation. A different constellation design would be possible using CDMA signals. Such a move would require that the legacy FDMA signals be switched off. Revnivykh stated that any such move would require at least 10-years’ advance notice.
The design characteristics of the various generations of GLONASS satellites are shown in Figure 1, taken from Revnivykh’s presentation.
Figure 1. The GLONASS satellite generations through GLONASS-K2.
The signals that will be transmitted by the future generations of GLONASS satellites as well as those transmitted by the initial GLONASS satellites and the GLONASS-M satellites now on orbit are shown in Figure 2.
Figure 2. Signals transmitted by the different generations of GLONASS satellites. OF = open-access FDMA, SF = special (military) FDMA, OC = open-access CDMA, OCM = open-access CDMA modernized.
Revnivykh also spoke on the satellite-based augmentation system, SDCM (System for Differential Correction and Monitoring), under development. Correction and integrity data will be transmitted by Luch geostationary communication satellites now under development. Luch 5A, to be launched in 2011 and positioned at 16°W longitude and Luch 5B, to be launched in 2012 and positioned at 95°E longitude, will transmit signals on an L1 frequency. Luch 4, to be launched in 2013 and positioned at 167°E longitude, will transmit on two frequencies. The three satellites will provide almost global coverage. The satellite payloads are under development.
According to Revnivykh, the SDCM will make use of 12 monitor stations currently in operation in Russia and one in Antarctica at Russia’s Bellingshausen research station. However, the SDCM website indicates only 10 Russian stations currently in the test network. Eight more monitor stations will be added in Russia and five more outside Russia. Revnivykh showed a map revealing the locations of the additional overseas stations as Cuba, Brazil, Vietnam, Australia, and an additional station in Antarctica. It is not intended, at least initially, that these stations would be used in generating the orbit and clock data broadcast by the GLONASS satellites themselves.
And finally, Revnivykh stated that a GLONASS performance document will be released in the 2012-2013 time frame.
As this issue goes to press in late August, the first Japan Aerospace Exploration Agency Quasi-Zenith Satellite System (QZSS) space
vehicle, nicknamed Michibiki, holds steady for a September 11 launch.
QZSS will use multiple satellites in inclined orbits, placed so that one satellite always appears near zenith above Japan, well known for its high-rise cities. The design provides high-accuracy satellite positioning service covering almost all of the country, including urban canyons and mountainous terrain.
QZSS Phase One will validate technological enhancement of GPS availability, performance, and application. Phase Two will demonstrate full system capability using three QZSS satellites, including Michibiki.
The satellites will generate and transmit their own signals, compatible with modernized GPS signals. QZSS also transmits GPS corrections and availability data.
Michibiki Profile. Dual-box shape with wing-type solar-array paddles; overall dimensions, 2.9 x 3.1 x 6.2 meters, paddles extending 25.3 meters; weight approximately 4,000 kilograms; altitude approximately 32,000–40,000 kilometers; inclination approximately 40 degrees;
period, 23 hours 56 minutes.
Compass. In early August, the first Beidou/Compass inclined geosynchronous orbit (IGSO) satellite achieved near-geosynchronous orbit. The mean east longitude of the sub-satellite ground point is currently 117 degrees, 19 minutes (see figure 1). This is one of the first, if not the first, satellite to use such a highly inclined circular geosynchronous orbit.
Figure 1. Left, the orbit path of three QZSS satellites will eventually keep at least one of them directly over Japan at all times. Right, the inclined geosynchronous orbit of the fifth Compass satellite, launched in July, has a similar ground track and mission goal.
Multi-GNSS Campaign. An international collaboration is poised to take advantage of a coming proliferation of satellites, led by Compass and QZSS but also including GPS, GLONASS, and Galileo, over the Asia/Pacific region. The website www.multignss.asia/campaign.html states, “The Asia and Oceania region is a unique place where the number of usable modernized navigation satellites will increase much faster than other areas in the world. We will see great improvement of PNT capability and hence there is a great opportunity to try, test, and validate new receiver hardware, algorithms, and applications in order to address user requirements.”
The web page also carries an animation of the availability of more than 100 GNSS space vehicles that will operate over the region in the next decade. An initial campaign workshop in Bangkok, Thailand, in January drew 195 participants from 18 countries. A second workshop is scheduled for November 21–22 in Melbourne, Australia.
GLONASS September. Three GLONASS-M satellites to be launched on September 2 completed pre-launch testing and mating to the upper stage of the booster rocket at Baikonur Cosmodrome. Numbered 36, 37, and 38, the satellites will constitute the Block 42 triad.
GPS III Design: Done. The Lockheed Martin team developing GPS III has successfully completed the program’s Critical Design Review (CDR) phase, two months ahead of baseline schedule. CDR completion validates the detailed GPS III design to ensure it meets warfighter and civil requirements. It culminates many rigorous assembly, subsystem, element, space vehicle and system-level CDR events, validates the overall design maturity of the GPS III space vehicle, and allows Lockheed Martin to enter production phase. Col. Bernard J. Gruber, U.S. Air Force GPS Wing Commander, certified the completion. Lockheed Martin, ITT, and General Dynamics are working under a $3 billion development and production contract for up to 12 GPS IIIA satellites. The team is on track to launch the first GPS IIIA satellite in 2014.
GPS Interface Specs. New IS-GPS-200E, IS-GPS-705A, and IS-GPS-800A documents have been posted to www.gps.gov/technical.
SVN62 Rubidium Clock. The U.S. Naval Research Laboratory issued a preliminary report on the rubidium atomic clock currently in use on the SVN62 Block IIF satellite. While documenting excellent short-term performance, the report notes anomalous fluctuations in the clock signal with distinct 12-hour and 6-hour periodicities. The exact cause has not been identified although it is speculated that the fluctuations are of thermal origin like SVN-62’s L5 phase variance detected earlier. But note that the clock signal analysis relies only on L1 and L2 measurements.
GPS IIF Got Active. The 50th Space Wing’s 2nd Space Operations Squadron formally took over command and control of the first Block IIF satellite on August 26 from the GPS Wing, and the satellite was set healthy on August 27, making 31 healthy GPS satellites on orbit.
Advisory Board Update
GPS World Editorial Advisory Board member Art Gower has been elected a Lockheed Martin Fellow, an honor recognizing pre-eminent technical individual contributors in the company, delivering mission success and vision by undertaking the most difficult technical challenges facing the company and its customers. Art started his career with IBM Federal Systems Division (now part of Lockheed Martin Integrated Systems and Global Solutions) in 1983, developing displays and performing navigation upload and command and control system engineering for the GPS control segment, and becoming chief engineer for the GPS control segment in 1990. He has spent the majority of his career working on GPS, GNSS, and SBAS systems.
Multiple Constellation Processing in the International GNSS Service
By Tim Springer and Rolf Dach
Does combining GPS and GLONASS observations make a difference? The International GNSS Service (IGS) has been providing such data for several years. Representatives from two IGS analysis centers discuss the past, present, and future of IGS GNSS monitoring and product development.
INNOVATION INSIGHTS by Richard Langley
ARE WE THERE YET — at a multiple-constellation GNSS world? The European Galileo system only has two test satellites in orbit, with constellation completion not scheduled until 2014. The Chinese Beidou/Compass system has launched some test satellites, but global coverage is not promised until 2020. And the first Japanese Quasi-Zenith Satellite System space vehicle is scheduled for launch this year with the system not fully operational until 2013. So, does this mean GPS is still the only game in town? No, not by a long shot. We have overlooked Russia’s GLONASS.
Standing for Global’naya Navigatsionnaya Sputnikova Sistema, GLONASS was conceived by the former Soviet Ministry of Defence in the 1970s, perhaps as a response to the announced development of GPS. The first satellite was launched on October 12, 1982. But because of launch failures and the characteristically brief lives of the satellites, a further 70 satellites were launched before a fully populated constellation of 24 functioning satellites was achieved in early 1996. Unfortunately, the full constellation was short-lived. Russia’s economic difficulties following the dismantling of the Soviet Union hurt GLONASS. Funds were not available, and by 2002 the constellation had dropped to as few as seven satellites, with only six available during maintenance operations! But Russia’s fortunes turned around, and with support from the Russian hierarchy, GLONASS was reborn. Longer-lived satellites were launched, as many as six per year, and slowly but surely the constellation has grown to 21, with two in-orbit spares.
But are there any users outside Russia? Although dual-system GPS/GLONASS receivers have been around for at least a decade, manufacturers have taken notice of GLONASS’s recent phoenix-like rebirth. All of the high-end manufacturers now offer receivers with GLONASS capability. Does combining GPS and GLONASS observations make a difference? You bet — just ask any surveyor who uses both systems in the real-time kinematic (RTK) approach. Scientific applications requiring high-accuracy satellite orbit and clock data also benefit. The International GNSS Service (IGS) has been providing such data for several years, and in this month’s article representatives from two IGS analysis centers discuss the past, present, and future of IGS GNSS monitoring and product development.
So, getting back to our question, are we there yet? Many early adopters of GPS plus GLONASS data and products would reply with a resounding “yes.”
“Innovation” features discussions about advances in GPS technology, its applications, and the fundamentals of GPS positioning. The column is coordinated by Richard Langley, Department of Geodesy and Geomatics Engineering, University of New Brunswick.
In 2005, the International GPS Service (IGS) was renamed the International GNSS Service. With this change, the IGS governing board and the IGS community expressed their expectation to extend activities from the well-established GPS to other active and planned global navigation satellite systems such as GLONASS, Galileo, and Compass. Meanwhile, the GLONASS satellite constellation, as well as the IGS GNSS tracking network, have evolved significantly. Since 2003, the GLONASS satellite constellation has been improving steadily, leading to the current, May 2010, constellation with 21 operational satellites and two in-orbit spares. And starting in 2008, the GNSS capabilities of the IGS tracking network have been greatly enhanced giving rise to a truly global GNSS tracking system with more than 100 GNSS (GPS plus GLONASS) receivers. The almost-complete GLONASS satellite constellation, coupled with a readily available global tracking network with high-quality receivers, have greatly increased the interest in and need for GNSS products such as precise satellite orbit ephemerides. However, the IGS analysis center products are still mainly GPS-only. Only two analysis centers provide true multi-GNSS solutions. Two analysis centers provide GLONASS-only solutions (a GLONASS combined IGS product is available but without accurate clocks). No combined IGS GNSS product exists. In view of the large interest from the user community, this is a really disappointing situation. In particular, because experiences gathered with handling GPS plus GLONASS will make the incorporation of other GNSS such as Galileo, Compass, and the Quasi-Zenith Satellite System (QZSS) that much easier.
However, during a meeting of the IGS analysis centers in December 2009, it became clear that many of the centers had started to implement and enhance the GLONASS processing capabilities in their software. This was happening as a direct consequence of the improvements in the GLONASS constellation, the IGS GNSS tracking network, and increased user interest (if not demand). Throughout 2010 and 2011, we will therefore see a significant increase in the number of true GNSS solutions within the IGS. A very positive development for the GNSS world.
In this article, we give an overview of the recent developments in the area of multi-GNSS processing within the IGS in general, but with a focus on the activities of the two analysis centers in the IGS that are leading the GNSS efforts: the Center for Orbit Determination in Europe (CODE) and the European Space Operations Center (ESOC) of the European Space Agency.
Why GNSS?
Within the IGS, we are often confronted with the question: Why GNSS? Why should I go through the burden of adding GNSS capabilities to my software, having larger processing loads, and so on, for little or no benefit? Well, from an IGS analysis center point of view, this question is valid. The accuracies achieved with GPS alone are so good that there will be little visible benefit of including another system. Nevertheless, there are indeed benefits.
There is a large number of users worldwide who would see benefits of using GNSS products compared to GPS-only products. Clearly, all real-time users will benefit enormously from the increased number of satellites. Figure 1, showing the so-called position dilution of precision (PDOP), demonstrates this very clearly. The two panels in Figure 1 show the GPS-only PDOP and the GPS-plus-GLONASS PDOP using the satellite constellation of May 3, 2009.
FIGURE 1A. Effect of GLONASS on position dilution of precision.FIGURE 1B. Effect of GLONASS on position dilution of precision.
Figure 2 shows the PDOP improvement in percentage when comparing the GPS-only to the GPS-plus-GLONASS PDOP values. At high latitudes, that is, above 55 degrees, the improvement is at the 30 percent level. At mid-latitudes, the improvements are still well above 15 percent, demonstrating the significant improvements real-time GNSS users may expect compared to real-time GPS-only users.
Figure 2. Position dilution of precision improvement using GLONASS.
With the current GPS constellation, daily solutions are not limited by the number of available satellites, but rather by the analysis models (such as that for the troposphere), calibration uncertainties (such as models for antenna phase-center variation), and environmental effects (such as multipath). For these reasons, IGS-like processing strategies, in which data from reference stations are processed in 24-hour batches, will not show clear benefits from adding data from more satellites and other systems.
However, besides real-time users, users at high latitudes (including the whole of Canada and most of Europe) will see improvements. Recently, several researchers have noticed that for latitudes higher than 50 degrees, the addition of GLONASS brings benefit. This is, of course, thanks to the higher orbital inclination of the GLONASS satellites (about 64 degrees) compared to the inclination of the GPS satellites (about 55 degrees), which is also very nicely demonstrated in the PDOP (see Figure 1). So, from a service point of view — the “S” in IGS — there is a clear need to provide GNSS solutions to the user community. Besides offering significant benefits in terms of accuracy, the increased number of satellites will also make solutions more reliable and robust. The completely different repeat cycle of the GLONASS satellite orbits is especially important as it changes the sensitivity to multipath completely. Multipath effects in GPS-only data repeat almost perfectly from day to day with a 4-minute time shift giving rise to spurious, near yearly signals in GPS time series. Satellites from other constellations, such as GLONASS, introduce other system-related frequencies, which results in a general reduction of such GNSS-induced frequencies in a multi-GNSS solution.
Because of the constellation design, each GPS satellite follows its own ground track in each orbit cycle. That means that at a ground station, each GPS satellite is observed on one and the same track each day so that a systematic influence of a satellite (such as a mismodeling of the satellite antenna position with respect to the satellite’s center of mass) has a systematic effect on the obtained (daily) station positions. This systematic translation of satellite-related errors into station-related parameters doesn’t happen for any other GNSS constellation.
IGS GNSS Analysis Centers
A detailed description of the IGS is beyond the scope of this article; an excellent overview was provided in an earlier Innovation column. We simply point out here that it is important to know that the IGS serves as the reference in many GNSS applications by providing data and products of the highest possible quality. Very well known and widely used are the tracking data from the IGS station network — the raw pseudorange and carrier-phase measurements — and the orbit and clock products of the GPS satellites. The IGS generates these products by combining the orbit and clock solutions of the individual analysis centers that contribute to the IGS. For the GPS-only products, 10 different analysis centers contribute to three different product series called the ultra-rapid, rapid, and final products. The final products deliver the highest possible quality but have the longest delay, as they become available 12 days after the end of the observation week. The rapid products are roughly comparable in quality to the IGS final products, but they are delivered daily with a delay of only 17 hours after the end of the observation day. The ultra-rapid products are delivered four times per day 3 hours after the end of the last used observation. For example, at 03:00 UTC, an ultra-rapid product is delivered that used data up to 00:00 UTC. It consists of two parts: an estimated part and a predicted part that may be used for real-time purposes. The quality of the estimated part is very similar to that of the rapid products. The predicted part is, of course, significantly less accurate, although the orbits have an astonishing precision of well below 30 millimeters — much better than that of the orbits in the satellites’ broadcast navigation messages.
In addition to these GPS-only products, there is also a GLONASS product. However, contrary to the GPS side of things, for GLONASS, only a final product is generated. Four analysis centers provide products for the IGS GLONASS combination: the Bundesamt für Kartographie und Geodäsie (BKG), Frankfurt am Main, Germany; CODE, based at the Astronomical Institute of the University of Bern, Switzerland; ESOC, Darmstadt, Germany; and the Information-Analytical Center (IAC) of Roscosmos, Moscow, Russia.
The analysis centers BKG and IAC determine the GLONASS satellite orbits, introducing the information for the GPS satellites from the IGS solution without further estimation. The analysis center CODE provides, since May 2003, orbits for GPS and GLONASS based on a rigorously combined analysis of the data of both GNSS, that is, a true multi-GNSS solution. Since January 2008, ESOC follows this strategy as well. From these four analysis centers, only two, ESOC and IAC, provide satellite clock estimates for the GLONASS satellites. This situation prevents the IGS from making a robust and reliable combined GLONASS clock product. With four analysis centers contributing to the orbits, the IGS can and does make an excellent GLONASS combined orbit product.
In our definition of true multi-GNSS solutions, the measurements from each system contribute to all relevant parameters to the same extent. This can only be achieved by the rigorous combined processing of the data from all available GNSS. The two-step approach, introducing the GPS solution when solving for the GLONASS orbits and satellite clocks, is regarded as an extension of a GPS-only solution to GLONASS. As the contributions from BKG and IAC in the IGS GLONASS product demonstrate, this two-step procedure provides excellent results.
From a user point of view, a big disadvantage is the fact that the IGS does not provide a real GNSS product. The IGS provides a high-quality GPS product and a high-quality GLONASS orbit product, but there is no combined GNSS product. Also, the IGS is only capable of generating final GLONASS products because only two analysis centers, CODE and ESOC, submit GNSS products for the rapid and ultra–rapid products. IGS policy requires contributions from at least three analysis centers for a meaningful and robust combined product.
Users of GNSS orbits and/or clocks therefore have to use the products of one of the individual analysis centers or combine the GPS-only and GLONASS-only products from the IGS. Here, the GNSS products of the CODE and ESOC analysis centers are clearly preferable over those of the IGS and other analysis centers since these are the only two true GNSS products that guarantee the full consistency between the two GNSS.
GLONASS Tracking Network
Until 2003, the IGS had established a GLONASS tracking network of merely 20 stations. In 2003, this number grew rapidly from 20 to 30, but after 2003 the number of stations remained stable for quite a long time with a very inhomogeneous distribution. For example, there were only a few stations in the whole western hemisphere. In 2006/2007, a new generation of combined GPS/GLONASS receivers became available, produced by several well–known GPS receiver manufacturers. With this new equipment available, the number of GLONASS tracking stations in the IGS network started to increase steadily. In 2008, the increase rate went up significantly (see Figure 3) and, more importantly, the global distribution of the receivers improved as, finally, significant numbers of stations started to emerge in both North and South America. Orbits and clocks of the GLONASS satellites are, since ear
ly 2009, determined from the data of more than 100 globally well-distributed tracking stations in the IGS network (see Figure 4). A good global distribution of observing sites is extremely important for orbit determination and even more so for the clock determination. Until early in 2008, the GLONASS clock determination suffered from gaps in the global tracking network, which had severe impact on the clock estimates. If tracking gaps cause an interruption of the carrier-phase tracking of a GNSS satellite, the clock estimates are basically reset and a jump will occur. The size of the jump is delimited by the accuracy of the code (pseudorange) observations, that is, at the 1-meter level, or 3 nanoseconds in clock terms.
We may state that today orbit and clock determination for the GLONASS satellites may be based on a truly global tracking network of high-quality geodetic–type receivers. This significant improvement is due to the efforts of many IGS station managers and their institutions.
Figure 3. Number of sites in the IGS network providing GLONASS data, used for orbit determination at CODE.Figure 4. Current distribution of IGS combined GPS and GLONASS tracking stations.
GLONASS Constellation
After reaching a full orbit constellation of 24 satellites in early 1996, the GLONASS constellation degraded rapidly due to Russia’s economic difficulties following the break-up of the Soviet Union coupled with the short lifetime of the GLONASS satellites. Since 2002, the GLONASS constellation has slowly but surely been rebuilt (see Figure 5). Currently, there are 21 active modernized GLONASS (GLONASS-M) satellites, which have a significantly longer lifespan compared to the original satellites. Additionally, there are two reserve satellites on orbit.
Figure 5. Development of the GLONASS satellite constellation since 1982.
Russia intends to have a full 24-satellite constellation in place by the end of 2010. To achieve this goal, two more triple-satellite launches are planned, one in August and one in November. The November launch could include a new type of GLONASS satellite, GLONASS-K. The GLONASS-K version is a lighter, unpressurized spacecraft, with a design lifetime of 10 years. In addition to the legacy frequency-division-multiple-access signals, it will transmit code-division-multiple-access signals and use an additional frequency band overlapping with the GPS L5 band.
Orbit and Clock Accuracy
The developments of both the GLONASS tracking capabilities of the IGS station network as well as the steady increase in the number of GLONASS satellites has had a positive influence on the accuracy of the GLONASS orbits and clocks. It also has significantly increased the interest in the GLONASS system. The enhancement of the IGS GNSS tracking network from an almost purely European network to a truly global network between 2008 and now has had a significant impact on the quality of the GLONASS orbits and clocks. To show the effect on the quality of the GLONASS orbit estimates, we look at the difference between two independent consecutive solutions spanning 24 hours from 0 to 24 hours GPS Time. We compare the “midnight point” of both solutions, that is, the solution at the end of one day (or arc) and the beginning of the next day (or arc). This will give us a worst-case estimate for the orbit quality because typically the orbit is less accurate at the boundary of the orbital arc compared to the middle of the orbital arc. We have analyzed these orbit differences for all GPS and GLONASS satellites separately for four half-year time spans using the routine IGS GNSS solutions from ESOC. The differences are computed in three different satellite-orbit-related directions: radial, along-track, and cross-track. The times spans are:
January to June 2008 (6 months)
July to December 2008 (6 months)
January to June 2009 (6 months)
July to December 2009 (6 months)
The results are shown in Figure 6. For the GPS satellites, we cannot see any improvement over time. The quality of the GPS orbits is excellent at the 25- to 35-millimeter level for all three components.
Figure 6. Evolution of GPS and GLONASS orbit quality from January 2008 to December 2009.
Remember, we are looking at the worst-case differences here. For GLONASS, we can see a significant improvement over the four time spans. Early in 2008, the orbit quality was at the 120-millimeter level (cross-track), which has improved significantly to the 85-millimeter level. It is important to note that no processing changes were made during this time interval, and that the improvements are thanks to the improvements in the station tracking network and the GLONASS satellite constellation.
The clock quality is more difficult to assess, but over the timeframe of 2008 to 2009 we have noticed that the clock estimates of the GLONASS satellites have become complete. In 2008, with the still-far-from-global tracking network, there were many gaps in the tracking of the GLONASS satellites. This means that at some epochs no stations were tracking a GLONASS satellite. Such gaps cause jumps in the satellite clock estimates, because the carrier-phase observations become discontinuous, and these jumps are at the 1-meter (3-nanosecond) level. With the improvements of the IGS GNSS tracking network, the GLONASS tracking is now complete and clocks for all epochs are estimated. A comparison of the clocks of the two analysis centers that provide estimated clocks for the GLONASS satellites shows an agreement at the 80-picosecond level, which is only slightly worse than the agreement between the GPS clocks. Significant biases at the few-hundred-nanosecond level exist only in the GLONASS clocks because of receiver internal frequency-dependent delays. The ESOC GNSS orbit and clock products are, however, perfectly suited for precise point positioning using either GPS, GLONASS or, even better, both GNSS simultaneously. It should be noted that since February 2010, the ESOC IGS clock products are now sampled at 30 rather than 300 seconds, which further enhances their suitability.
Conclusions and Outlook
The IGS has promised to become a GNSS service by changing its name in 2005, more than four years ago. Meanwhile, the GLONASS satellite constellation as well as the IGS GNSS tracking network have matured and are practically complete. For the IGS to become a true GNSS service, a substantial number of the analysis centers should provide GNSS contributions to all IGS products: final, rapid, ultra-rapid, and real-time. These products should come from performing a rigorous combined analysis of the observations of all active GNSS satellites. It is expected that over the next two years, we will see a significant increase in the number of true GNSS solutions within the IGS, a very positive development for the GNSS world.
Within the IGS, the analysis centers CODE and ESOC are leading the GNSS efforts. CODE has provided fully consistent GPS/GLONASS products from a rigorously combined processing approach for all IGS products (final, rapid, and ultra-rapid) since May 2003, or for seven years. Since the beginning of 2008, ESOC has followed this good practice for its final products, and in February 2010 ESOC started to produce rapid and ultra-rapid GNSS products. A unique feature of the ESOC products is that they include the clocks for the GLONASS satellites, even with a sampling rate of 30 seconds for the final products. CODE will add GLONASS clocks to its IGS products very soon, during the fi
rst half of 2010. The GLONASS orbit and clock product quality has become comparable to that of the GPS products within the IGS. However, because GLONASS carrier-phase integer ambiguity resolution is difficult, the GLONASS products are and will remain somewhat less accurate than the GPS products.
The experiences gathered at CODE and ESOC by fully combining the observations from the GPS and GLONASS systems will pave the way for the integration of additional systems and signals within the IGS. Hence, IGS will retain its leading position in providing the reference, in the broadest sense of the word, for all GNSS. In the near future, this means the integration of QZSS and Galileo observations as well as the integration of the new triple-frequency signals from the latest generation of GPS satellites, Block IIF, the first of which was scheduled for launch last month.
The positive GNSS developments within the IGS will require an update of the IGS combination software to enable a true GNSS combination. The CODE and ESOC analysis centers have indicated that they are interested in taking on this important task of rewriting and enhancing the IGS orbit and clock combination software to make the IGS a true GNSS service.
Acknowledgments
CODE is a collaboration among the Astronomical Institute, University of Bern (Bern, Switzerland), the Swiss Federal Office for Topography (Wabern, Switzerland), the Bundesamt für Kartographie und Geodäsie (Frankfurt am Main, Germany), and the Institut für Astronomische und Physikalische Geodäsie of the Technische Universität München (Munich, Germany).
The authors are very grateful to the IGS and its numerous contributors for providing the global GNSS tracking data network.
TIM SPRINGER received his Ph.D. in physics from the Astronomical Institute of the University of Bern (AIUB) in 1999. He has been a key person in the development of the Center for Orbit Determination in Europe (CODE), one of the IGS analysis centers, located at AIUB. Since 2004, he has been working for the Navigation Support Office (OPS-GN) at the European Space Operations Centre (ESOC) of the European Space Agency (ESA) in Darmstadt, Germany. In this group, he has led the development of the new ESOC GNSS software, which is used for most GNSS activities at OPS-GN, including GIOVE-A and -B analyses.
ROLF DACH received his Ph.D. in geodesy at the Institut für Planetare Geodäsie of the University of Technology in Dresden, Germany. Since 1999, he has been working as a scientist at AIUB, where he is head of the GNSS research group. He oversees the development of the Bernese GPS Software, used at CODE for activities in the frame of the AIUB IGS analysis center and elsewhere.
“Renovated GLONASS: Improved Performances of GNSS Receivers” by A.E. Zinoviev, A.V. Veitsel, and D.A. Dolgin in Proceedings of ION GNSS 2009, the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation, Savannah, Georgia, September 22–25, 2009, pp. 3271–3277.
“Other Satellite Navigation Systems” by S. Feairheller and R. Clark, Chapter 11 in Understanding GPS: Principles and Applications, 2nd edition, edited by E.D. Kaplan and C.J. Hegarty, published by Artech House, Boston, 2006.
“GLONASS Performance, 1995–1997, and GPS-GLONASS Interoperability Issues” by G.L. Cook in Navigation, Vol. 44, No. 3, Fall 1997, pp. 291–300.
“GLONASS Review and Update” by R.B. Langley in GPS World, Vol. 8, No. 7, July 1997, pp. 46–51.
• The International GNSS Service
“The International GNSS Service in a Changing Landscape of Global Navigation Satellite Systems” by J.M. Dow, R.E. Neilan, and C. Rizos in Journal of Geodesy, Vol. 83, No. 3-4, March 2009, pp. 191–198, doi:10.1007/s00190-008-0300-3; erratum: Vol. 83, No. 7, July 2009, p. 689, doi: 10.1007/s00190-009-0315-4.
“GNSS Processing at CODE: Status Report” by R. Dach, E. Brockmann, S. Schaer, G. Beutler, M. Meindl, L. Prange, H. Bock, A. Jäggi, and L. Ostini in Journal of Geodesy, Vol. 83, No. 3-4, March 2009, pp. 353–365, doi:10.1007/s00190-008-0281-2.
IGS Central Bureau website. IGS FAQ, Site Guidelines, data and product access information, and network details are available: http://igscb.jpl.nasa.gov
• Benefits of Multi-GNSS
“The Benefits of Multi-constellation GNSS: Reaching up Even to Single Constellation GNSS Users” by B. Bonet, I. Alcantarilla, D. Flament, C. Rodriguez, and N. Zarraoa in Proceedings of ION GNSS 2009, the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation, Savannah, Georgia, September 22–25, 2009, pp. 1268–1280.
“Assessment of GPS/GLONASS RTK Under Various Operational Conditions” by R.B. Ong, M.G. Petovello, and G. Lachapelle in Proceedings of ION GNSS 2009, the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation, Savannah, Georgia, September 22–25, 2009, pp. 3297–3308.
“Anomalous Harmonics in the Spectra of GPS Position Estimates” by J. Ray, Z. Altamimi, X. Collilieux, and T. van Dam in GPS Solutions, Vol. 12, No. 1, January 2008, pp. 55–64, doi:10.1007/s10291-007-0067-7.
At press time, GPS spacecraft IIF-1 was set to be launched May 27 from Cape Canaveral Air Force Station in Florida. This first of a new generation of satellites will travel quickly — instead of taking several days to reach its orbital slot, the new satellite should make the journey in three-and-a-half hours.
The new IIFs will broadcast the operational civil L5 signal, intended for safety-of-life applications. It will be compatible with Galileo, GLONASS, and QZSS, with the goal to be interoperable as well. L5 will transmit at a higher power than current civil GPS signals, with wider bandwidth and lower frequency that may enhance indoor reception.
IIF-1 caught its breathless ride aboard a Delta 4 rocket from the United Launch Alliance, a joint venture of Lockheed Martin and Boeing, formed in late 2006.
Earlier GPS satellites rode on smaller Delta 2 rockets that, although reliable, did not possess the oomph to place space vehicles directly into the orbiting constellation, 11,000 miles high. Delta 2s put satellites into highly elliptical orbits looping from as low as 100 miles above Earth at perigee to the 11,000-mile apogee. At a strategic point, a solid-fuel kick motor attached to the satellites pushed them into position for circular orbit on high.
The more powerful Delta 4 will shoot the IIFs directly into their destination slots. Future IIF launches may also use similarly equipped Atlas 5 rockets. The next IIF satellite, GPS IIF-2, could rise aboard an Atlas 5 as early as November.
The IIF generation, manufactured by Boeing for the U.S. Air Force, is designed not only to broadcast the new civil L5 signal, but have a longer design life of 12 years and faster processors with more memory. “These next-generation satellites provide improved accuracy through advanced atomic clocks, a more jam-resistant military signal, and a new civil signal that benefits aviation safety and search-and-rescue efforts,” said Craig Cooning, vice president and general manager, Boeing Space and Intelligence Systems.
“GPS IIF will increase the signal power, precision, and capacity of the system, and form the core of the GPS constellation for years to come,” said Air Force Col. David Madden, GPS Wing commander.
A total of 12 IIF satellites will make their contribution to getting the new L2C and L5 signals closer to operational capability before the GPS III generation takes over, beginning with a 2014 launch.
As the first spacecraft in the GPS IIF series, GPS IIF-1 underwent stringent and comprehensive testing following shipment to the launch site in February. Tests included verification of key satellite functions as well as end-to-end system testing to verify operations between the satellite and the ground control segment at Schriever Air Force Base in Colorado.
Commands were sent from Schriever to GPS IIF-1 at Cape Canaveral to turn on payloads, reprogram processors, and verify interoperability with user receivers and equipment, both civil and military.
Launch of the satellite, originally scheduled for May 20, was delayed four times because of various technical problems.
Normally, my column following a webinar is dedicated to Q&A follow-up from the webinar. However, immediately following the April 22 webinar, I traveled to Phoenix, Arizona, to attend the ACSM/GITA conference, which I wrote about earlier this month.
This column is dedicated to answering questions I didn’t address during the webinar. Also, I always find the results from the polls I conduct during the webinar very interesting.
Poll #1: Have you or your work crews had to stop or alter your work pattern due to the lack of GPS satellites?
Total votes: 128, Yes: 73%, No: 27%
Gakstatter comment: This is consistent with other polls I’ve conducted regarding GPS satellite availability. The new GPS 24+3 configuration will help mitigate this problem. Read more about the new GPS 24+3 configuration in a three-part series I wrote earlier this year.
Poll #2: How often do you upgrade your GPS equipment?
Total votes: 113
Gakstatter comment: There’s no clear pattern here except to say that 46% of the users wait until at least 3 years before they consider upgrading their GPS equipment. That makes sense to me.
Poll #3: Does any of your GNSS equipment utilize GLONASS?
Total votes: 115, Yes: 39%, No: 61%
Gakstatter comment: When considering the result of this poll, keep in mind that there are very few “mapping-grade” receivers that are designed to utilize GLONASS. For example, there are very few, if any, sub-meter receivers that utilize GLONASS, primarily due to the lack of correction sources. SBAS doesn’t support GLONASS, DGPS (radiobeacon) doesn’t support GLONASS, and most CORS do not support GLONASS. Only recently did OmniSTAR begin supporting GLONASS. I think this trend will continue, although I doubt that SBAS or DGPS (radiobeacon) will support GLONASS in the foreseeable future.
Poll #4: Does any of your GNSS equipment utilize SBAS (WAAS/EGNOS/MSAS) as a primary source of corrections?
Total votes: 111, Yes: 60.5%, No: 39.5%
Gakstatter comment: This poll result doesn’t surprise me. Given that SBAS corrections are widely available, free of charge, reasonably accurate, and require no action by the user, it makes a lot of sense they are being used.
Following are some of the questions that were posed by the audience during the webinar:
Question #1: I am not sure, but when you say you’re “pushing” something out to us, it sounds like your trying to “push” something on us. Just a comment.
Gakstatter: I’m sorry about the webinar-speak. When I say “pushing the next slide,” that means I’m changing slides. I may change the way I say this. Thanks for your comment.
Question #2: Can you correct GLONASS signals with WAAS or other real-time technologies?
Gakstatter: WAAS (or any SBAS) doesn’t support GLONASS. Neither does DGPS (radiobeacon). This doesn’t mean that GLONASS measurement can’t be used, but you’ll be using uncorrected measurements to augment SBAS-corrected measurements. A case where it may be useful is when you’re mapping in an environment where there are a lot of trees. You might only have four GPS satellites visible that are being corrected via SBAS. In that scenario, there might be value in utilizing measurements from GLONASS satellites just to improve the PDOP, even though the GLONASS measurements are uncorrected.
Question #3: Do you feel manufacturers will begin to release lower-end mapping-grade GPS receivers with L2C and L5 functionality in the future?
Gakstatter: Yes, I do, but it will be a few years before there are enough satellites broadcasting an L5 signal. I think what you’ll end up seeing are inexpensive L1/L5 receivers (Galileo doesn’t support L2). They will not only be able to provide mapping-grade sub-meter, decimeter) but also RTK accuracies (cm-level). Since L2C and L5 are open civil signals, you won’t see the patent blocks that restrict competition for L1/L2 receivers like you do today.
I’m not saying L2C will not be supported at all. I think there will be L1/L2C/L5 receivers, but I think you’ll see L1/L5 on lower-end receivers.
Question #4: There is apparently some degradation of accuracy when using GPS and GLONASS for RTK. Have there been any rigorous studies quantifying this that you are aware of?
Gakstatter: I’m not sure I’d say I believe there is degradation in accuracy, but I wouldn’t count on GLONASS to improve accuracy. The value of GLONASS is improving productivity. Since it adds several satellite signals to the solution, it effectively eliminates GPS “brown-out” periods so RTK can be used 24/7. There was a rigorous study released by The Survey Association in the UK. The report focused on network RTK. They tested both GPS and GPS+GLONASS. You can download a copy of the report here.
Question #5: Does using GLONASS-capable receivers shorten the observation time required for fast-static points?
Gakstatter: My first thought is yes since generally more observables equates to shorter occupation time, but I would check with the manufacturer and follow their recommendations. Honestly, I’ve only used fast-static with GPS-only receivers so I don’t have any personal experience with your scenario.
Question #6: When is GLONASS-K launch scheduled? When can we receiver a valid CDMA signal?
Gakstatter: The first GLONASS-K satellite is scheduled for launch later this year. I haven’t seen a launch schedule beyond that. A representative from the Russian Space Agency is scheduled to present at the Institute of Navigation (ION) GNSS conference in September, so I’ll probably learn more at that point. However, it’s a lengthy process. It’s not just a matter of launching satellites. There are many other variables and unknowns such as the control segment and user equipment compatibility. I think it’s safe to say that we are a few years away from having a minimal GLONASS satellite constellation broadcasting CDMA.
Question #7: The visibility plots show one extra satellite in the “after” plots. Was that intentional? I would have expected there to be an improved number of satellites visible when one more was added to the plotted constellation.
Gakstatter: Good catch. In the “after” scenario, I set SVN-49 healthy, which it is currently not. The reason I did this was because SVN-49 is in an important slot in the 24+3 configuration. The status of SVN-49 is still undecided, but if they decide to not set it healthy they will move another satellite to take its place in the 24+3 configuration. If I would have kept it unhealthy in the “after” scenario, it would have only s
hown a 24+2 configuration. Clear as mud?
Question #8: Is 24+3 the solution to the blackout problem from now to 2014 stated by the GAO Report from last year?
Gakstatter: The definition of the 24+3 configuration had been around before the GAO Report. Personally, I don’t think the GAO Report had anything to do with 24+3. The 24+3 configuration just helps optimize the current satellites in orbit, whereas the GAO Report addresses the attrition of GPS satellites outpacing the addition of GPS satellites.
Question #9: Cellphone question: Is the move to 24+3 likely to degrade indoor GPS coverage – fewer peak sats => lower probability of seeing 4+ sats indoors?
Gakstatter: Interesting question. My first thought is probably so, although I think it would be a temporary problem. Assuming Galileo keeps pushing forward, that would be a big help for cellphone users, both indoors and outdoors.
Question #10: GPS Satellites are getting beyond the design life…is the USA behind schedule in satellite updates?
Gakstatter: GPS satellites have been unbelievably reliable. PRN-24, the oldest operational satellite, has been in operation since August 30, 1991. Since they have been so reliable, there hasn’t been as much pressure to launch GPS satellites. Prior to the 24+3 initiative, the minimum guaranteed constellation was 24 satellites. It costs $50-60 million to build each GPS satellite and another $150-200 million to launch it. With the GPS constellation hovering around 30 satellites these past few years, and government budgets tightening, I think it’s clear that the pressure to save money has resulted in a more relaxed launch schedule.
The delay in the Block IIF satellite (the first one being launched this week) was not a result of the above, but rather technical and program management mis-steps. The GAO Report was particularly critical of the IIF development.
Question #11: Do you see any future for ground-based free systems such as those broadcasting corrections in LF/MF radio, like the Coast Guard broadcasts?
Gakstatter: There is an interesting debate between DGPS (what you mention) and SBAS. The DGPS infrastructure has been in place and working reliably for mariners for better than a decade. Funding for DGPS seems solid for marine navigation, but less stable for inland-based applications (like the U.S. NDGPS system). I think the future of DGPS for mariners is solid for the next 10 years. Once there is a full constellation of satellites broadcasting GPS L5, the value of DGPS will be questioned.
Question #12: Will WAAS, EGNOS, etc. be needed after L1/L5 receivers can measure the iono effects themselves?
Gakstatter: I think it comes down to integrity. If the L1/L5 combo can deliver integrity that safety-of-life applications require (such as aviation), then one has to question the value of SBAS. My gut feeling is that the L1/L5 combo can’t and that some sort of augmentation will be needed to attain the integrity level required.
Question #13: What are your thoughts concerning Compass? Do you feel this will eventually be applicable for public use as part of a functioning GNSS?
Gakstatter: Compass is the GNSS wildcard. Since the Chinese aren’t particularly forthcoming with their plans, it’s hard to say. But I’m not sure that matters. With a full constellation of GPS, GLONASS (CDMA), and Galileo satellites in the future, that’s around an average of 25+ satellites in view at any one time during the day. If China doesn’t play well with others in a timely fashion, the user community won’t care what Compass brings to the table.
Question #14: If my current GPS receiver is not ready for L2C and L5, do I have to buy a new GPS or I can upgrade software/firmware later so that I can still use it?
Gakstatter: You’ll have to trade-in. Some might be upgradable to L2C, but L5 is a different story. It’s a completely different frequency. That affects the receiver as well as the antenna.
I wasn’t able to address all of the questions here, so look for more in the next newsletter. Particularly I’ll cover some discussion about reference frames, SBAS and L5.
Look for announcements in the next day or so about the Block IIF GPS satellite launch. It’s scheduled for Friday, May 21. It’s a new era with the first GPS satellite to broadcast an operational L5 signal.
“This is an event where one gets one’s goals for the next year.” Paul Verhoef, program director for satellite navigation programs of the European Commission, may have exaggerated for effect, and for the benefit of his audience and hosts at the Munich Satellite Navigation Summit in March. But not by much.
The conference, now in its eighth year, has assumed increasing importance on the international circuit of GNSS policymakers and communicators. Although with a decidedly European bent, it draws representatives from most if not all systems to mingle and present. A 16-member delegation from China’s Compass system furnished one of the liveliest topics of conversation — and speculation.
“When we started in 2003, there were many technical conferences on the one side, and we saw a niche for the institutional and political side of satellite navigation,” said Berned Eissfeller of the Institute of Geodesy and Navigation, German Federal Armed Forces University, conference director and host. You can watch video clips of Eissfeller and other speakers.
GNSS came in for a check-up, a sort of self-examination this time. The 2009 conference was titled “The GNSS Race,” but this year it was “GNSS — Quo Vadis?” The Latin phrase means “Where are you going?” Following program updates, sessions focused on safety-of-life, compatibility, legal/intellectual property, and privacy issues.
Galileo. Paul Verhoef continued his remarks that open this story. “I have been given [my goal]: Galileo must succeed.
“You know the world today is not what it was a year ago. It means obviously the financial crisis has had an impact on our economies, on public finance, and therefore I would not be surprised it may leave its mark on satellite navigation. The reason is simple: the systems that are either operating or being deployed are being publicly financed. Galileo is the only system that is financed from a purely civilian budget. All the systems need more than ever to demonstrate their public utility.
“I put it to you that this is an opportunity. As we’ve already heard, there is much to be gained in this market. After the PC, mobile communications, and Internet, satellite navigation is the next breakthrough technology. There are enormous revenues foreseen and already present in this market. There are many jobs possible for those who want to get it, and we think from the European side we have an enormous chance of capitalizing on this among other things by investing in this technology. Therefore, Galileo- and EGNOS-based innovation is certainly politically of interest.
“Obviously, it is not a path of roses. There will no doubt be many more critical questions during these days. However, from our side, we have set our goals. I think they are modest, but they are firm. We want to be the second system of choice. At least in the first instance, we will see where we will go after that. Obviously, this is going to cost a bit of time. I shall invite you, if you get impatient, if the public gets impatient, to look at the history of the other systems. Developing and deploying these other systems is costing time.
“We think that Galileo will meet its deadlines. I think one of the important messages this year, and you have seen it, we are putting things in place. There are contracts in place, there are satellites on order, there are launches on order, there are installations being built — Oberpfaffenhoffen, Fucino, there are others around the world — EGNOS is operational, we’re going to declare the safety-of-life of EGNOS later this year. So we are really moving forward at good speed at the moment.
“We need to win the hearts of the users, the application providers, and the service providers. At the downstream market is the real challenge for these systems. We need to help do that. We are addressing this among other things by providing a more and more reliable schedule for availability of Galileo and EGNOS services.”
Galileo ICD Soon. “We are about to publish in the next couple of weeks the so-called signal-in-space Open Service interface control document, which I know a number of you have waited for a long time.
“We need also to move forward at a political level. In this case, no GNSS system can be credible if it is not backed by a long-term political commitment particularly by its owner. So after the decision of the Parliament and the Council to deploy the system, these two institutions are now clearly called upon to provide us such political long-term commitment that is credible in the eyes of the users.”
GPS. Anthony Russo, director of the U.S. National Space-Based PNT Coordination Office, said “Keeping cards close to the chest in a competitive situation can well become a liability, creating a future need for a re-work or undoing if you paint yourself into a technological corner.” This appeared to refer to China and its Compass system; information has been singularly difficult to obtain on almost every aspect of this budding constellation.
Regarding the April 2009 U.S. General Accountability Office report that forecast gaps in constellation availability, Russo stated, “The GAO will revise its report somewhat. They were using a model that was a little too cautious, one used by the [GPS] Wing. But satellites on orbit have been performing past estimated life. Further, we can turn off secondary payloads to conserve energy onboard satellites [and thus extend life] if needed.”
The next morning, Lt. Col. Liz Roper, Air Force Space Command, gave a status and modernization briefing; the most eagerly awaited development is the launch of the first Block II-F satellite, scheduled for some time in May. She alluded to “a few setbacks” from the August 2009 launch of SVN49 with its well-documented signal problems, but emphasized the episode’s “positive aspects: the relationships we’ve been able to build in seeking solutions to that situation.”
GLONASS. Grigoriy Stupak, deputy general director and general designer on GLONASS systems, briefed the audience in fluent Russian. For a recent launch update, see story below.
Compass. Two of the Chinese delegates spoke in the opening session. Jiao Wenhai from China Satellite Navigation Office did elaborate the basic principles of the Beidou (Compass) system:
openness (“China will widely and thoroughly communicate with other countries on satellite navigation issues.”)
independence
compatibility (“China will pursue solutions to realize compatibility and interoperability with other satellite navigation systems.”)
the frequencies Compass will use: 1561.098, 1207.14, and 1268.52 Mhz in Phase II until 2012; and 1575.42, 1191.795, and 1268.52 in Phase III by 2020.
the general development plan: five geosynchronous, five inclined geosynchronous, and four mid-Earth orbit satellites providing a Chinese regional service using mainly Compass Phase II signals; then development of a global service broadcasting mainly Compass Phase III signals from five GEO, three IGSO, and 27 MEO satellites.
The Chinese speakers displayed a certain disingenuousness in giving verbally and in their slides the location of the January launch, Beidou G1 geostationary satellite, as 160 degrees East, somewhere over the open Pacific. When GPS World pointed out that NORAD satellite tracking shows G1 has been repositioned to a slot at 144.5 degrees East longitude, they huddled for several minutes before stating that yes, it had moved to that position and was undergoing in-orbit testing. That spot was previously occupied by Beidou 1D, apparently decommisioned about a year ago due to power problems. 1D currently orbits in graveyard above geostationary altitude.
A personage civilly associated with the U.S. Air Force confirmed the actual G1 location to the magazine, and could only speculate that it was more advantageous to Chinese ground control for monitoring and testing. As to why spokespersons misstated the location, that remains inscrutable.
GLONASS Back in Black
Three GLONASS-M satellites launched on March 1 are expected to enter service on March 22 and March 30, according to deputy general director Grigoriy Stupak’s statement in Munich. This would bring the constellation, according to his calculations, to 23 operational satellites, though two of those are held in reserve.
With 21 satellites broadcasting signals, the system claim 98.5 percent global availability. Block 42 (three more satellites) has an August 2010 launch date, and Block 43 one for November 2010. By December, Stupak predicted 24 active satellites on orbit, for 99.5 percent global availability.
The GLONASS-M satellites have a stated seven-year lifetime. CDMA signals will begin with next-generation GLONASS-K satellites, while FDMA signals continue in parallel. The Russians plan to “reach 5-meter accuracy by 2017, almost equal to accuracy of other GNSS,” and are “paying more attention to differential corrections for integrity monitoring.”
ICG Questions
The International Committee on GNSS (ICG) Working Group on Compatibility and Interoperability invites GPS industry members to fill out a questionnaire, provided online in two formats: as a downloadable MS Word document or a PDF.
The Industry and User Community Questionnaire is designed to obtain worldwide input from industry, academic institutions, and other representatives of the GNSS user community with technical expertise regarding GNSS signals and other system characteristics that aid or hinder the combined use of the signals in applications, equipment, or services. For instance, respondents are asked to grade certain signal characteristics as to their importance in overall interoperability considerations for a particular type of application.
Respondents are asked to e-mail completed questionnaires to the ICG by May 28.
The Russian space agency Roscosmos launched a venerable Proton rocket carrying three GLONASS-M satellites into orbit on December 14. Each 3,000-pound satellite is designed to last seven years. They join a constellation numbering 19 satellites, although only 16 are healthy.
Russian politicians and satnav system managers had hoped to launch six satellites between September and December, to attain a global service level, which requires 24 satellites, eight each in three orbital planes.
However, a payload glitch found aboard one recent satellite after its launch into space forced a return to the factory of three satellites scheduled for launch in September. The three put into orbit this week will now only bolster continuing GLONASS coverage of Russian sovereign territory, which requires 18 operating spacecraft.
The next GLONASS launch is now scheduled for a February 11–20, 2010, window.
The Block 41 GLONASS-M satellites (Nos. 30, 33, and 34) have been placed in Plane 1, which currently has only four healthy satellites. According to Roscosmos, communication has been established with all of the satellites and performance is nominal.
Next Up. Nikolay Testoedov, head of the Reshetnev satellite manufacturing company, said his enterprise plans to produce 17 more GLONASS-M satellites between now and 2013.
“The preproduction flight tests of new series of GLONASS satellites, GLONASS-K, will start in 2011,” said Andrei Buravin, vice head of Russian Institute of Space Device Engineering. The preproduction flight tests of GLONASS-K will be performed together with Reshetnev company.
It is still unclear whether the next-generation of GLONASS satellites will be launched via blocks of three satellites with Proton rockets from Baikonur, or via blocks of two satellites with Soyuz rockets from Plesetsk.
RTCM Supports Loran
It may be moot by the time you read this — the U.S. Coast Guard (USCG) could unplug Loran on January 4 — but the Radio Technical Commission for Maritime Services (RTCM) wrote to Secretary of Homeland Security Janet Napolitano in support of continuing and enhancing Loran service.
The letter asserts that it cannot be accurately certified that termination of the operation of the Loran-C signal will not adversely affect the safety of maritime navigation — counter to opinion issued by the USCG Commandant. The RTCM president states that the Loran-C infrastructure is needed to complete the eLoran system to serve as a backup to the U.S. Global Positioning System (GPS).
New Technique. Researchers have developed a technique to demonstrate a low-cost backward-compatible way to exploit eLoran to make GPS more robust. The method paves a way for the average GPS user to become a GPS+eLoran user. Go to env-gpsworld-integration.kinsta.cloud/loran for the letter and other Loran stories.
Galileo Contract Award Imminent
A contract award for at least eight of the in-orbit validation satellites had been promised for the end of this year by the European Commission (EC), but as this magazine goes to press on December 16, no official announcement has surfaced.
An unconfirmed report in early December claimed that the European Commission and European Space Agency had awarded a contract for eight Galileo satellites to underdog bidder OHB Technology of Germany. However, this report was privately denied and in fact refuted by an EC representative.
The OHB-led consortium includes small-satellite specialist Surrey Satellite Technology Ltd. of Britain, which built and continues to operate the GIOVE-A satellite, Galileo’s first launch. The competing Astrium-Thales Alenia consortium built the second Galileo satellite now in orbit, GIOVE-B.
The report, published on December 4 on the Space News website, asserted that “the European Commission has selected OHB Technology of Germany to build at least eight Galileo navigation and positioning satellites for about 350 million euros ($525 million) in a decision that postpones any award to competitor Astrium Satellites pending further negotiations with Astrium.” Reporter Peter de Selding cites industry officials as his sources.
An EC representative privately denied the report, asserting “it is not true.” An industry source said “It is not confirmed, we are waiting for the decision.”
The rumor created an uproar in the German state of Bavaria, a center for that country’s aerospace industry and government-aided research. Astrium had reportedly planned to perform much of its Galileo work in that region, and the Space News story holds out the expectation that “political pressure will be applied to reverse the ruling in the coming days.” The region is already home to the Galileo Control Center at a German Aerospace Agency (DLR) site.
Block Approach. The two consortia have been negotiating their bids on the contract with the commission and its technical adviser, the European Space Agency (ESA), for 15 months. Initially, the two European Union bodies set a contract ceiling of 840 million euros to build 28 Galileo satellites; un the past few months they revised the total order to 22 satellites and asked for bids for eight, 14, and 22 satellites. Reportedly, there are price ceilings for each of the three potential order sizes — around 400 million euros for eight satellites, 650 million euros for 14 satellites, and 840 million euros for all 22.
Repeatedly postponed throughout its conceptual phase, the Galileo system now — officially, at least — hopes to achieve initial operational capability by 2014.
Whether or not the Space News report is eventually substantiated, the central European government has already signaled in multiple ways its dissatisfaction with its various member states’ aerospace industry giants, whom it holds responsible for the protracted dysfunctionality of the now-abandoned public-private partnership to build Galileo. The EC has largely wrested control of the satellite award process away from its space agency, and indicated that it intends to maintain a firm grip on the purse strings.
Application Days: Galileo Application Days are set for March 3–5, 2010, in Brussels, Belgium, with live demonstrations of cutting-edge applications developed for GNSS under the European Union’s 7th Research Framework Programme (FP7), former ESNC Competitions, the ESA Technology Transfer Programme, and national and regional initiatives. See www.application-days.eu for details.
Roughly three years ago, the U.S. military conducted the first flex-power test on the L2 GPS codeless signal. Almost immediately, the civilian GPS community expressed concern that future changes to the L2P(Y) signal power levels might cause a signal phase shift; such a phase shift would be incompatible with equipment using the P(Y) signals in a codeless/semicodeless fashion for extremely accurate positioning applications.
Civilian users were naturally upset because they had invested millions of dollars in systems that might not be usable — even if the unusable periods were of a very short duration.
The National Positioning, Navigation, and Timing (PNT) Executive Committee responded by tasking the National PNT Engineering Forum (NPEF) to look at the problem. Within a few months, the NPEF announced a solution: flex power could be used in such a manner that it would not cause a phase shift. At the same time, the military reminded civilian users that the codeless use of L2P(Y), as accurate as it might be, was never intended and should not be a long-term solution.
An agreement was reached between the U.S. government and civilian users that the civilian users of this codeless/semicodeless technique would migrate from using the L2P(Y) carrier to using the new L2C signal to achieve not only the same, but better results. To codify this agreement, a Federal Register Notice was issued in 2008 identifying the terms of this agreement, which guaranteed the phase stability of the current L2P(Y) signal until 2020. This gives civilian users 12 years to figure out a migration plan and to obtain adequate use of the equipment they already have on hand.
In addition, 2020 is not a drop-dead date, but a date when the use of L2P(Y) codeless signals will no longer be guaranteed, though may well still work. Who knows what PNT advancements will take place between now and then? This could very well be a moot point by then, and in my opinion should be one now.
Problem Solved? Apparently not. A lag between the issuance of this national policy and analogous adjustments to interface specifications caused consternation within the civilian community. Misunderstandings added to this perceived impasse. Various solutions were identified to work around this looming quandary. However, given the national policy to support codeless/semicodeless use until 2020, the Air Force Space Command commitment to that policy, and the recommendations of the NPEF, these solutions seem wholly unnecessary to me.
The U.S. government has gone well beyond what is required to insure civilian codeless and semi-codeless users are accommodated.
For the foreseeable future, users will be able to employ L2P(Y) codeless/semicodeless techniques for very accurate position determination and will not have to worry about phase shifts disrupting their work.
— Don Jewell, GPS World Defense PNT Contributing Editor
Three GLONASS-M satellites launched on March 1 are expected to enter service on March 22 and March 30, according to deputy general director Grigoriy Stupak’s statement in Munich. This would bring the constellation, according to his calculations, to 23 operational satellites, though two of those are held in reserve.
However, a payload glitch found aboard one recent satellite after its launch into space forced a return to the factory of three satellites scheduled for launch in September. The three put into orbit this week will now only bolster continuing GLONASS coverage of Russian sovereign territory, which requires 18 operating spacecraft.
