Delta IV, the current GPS launch vehicle, awaits a date with space at Cape Canaveral.
Launch Delays Ground GPS IIF and Galileo FOC
The scheduled October 23 launch of GPS IIF-5, the fifth in the current “follow-on” generation of GPS satellites, has been postponed in order to complete a review of an adjustment made to the rocket’s upper stage engine. A loss of thrust by a Delta IV rocket upper stage during a GPS launch last year worried the Air Force and the United Launch Alliance (ULA), though the satellite successfully reached its intended orbit.
A subsequent investigation identified a fuel leak in the engine system as the culprit. Two medium Delta IV rockets and one heavy version have launched since then, but ULA said further investigation had produced new information about the engine’s first start.
While no new launch date has been set, the ULA released a statement:
“The ongoing Phase II investigation has included extremely detailed characterization and reconstructions of the instrumentation signatures obtained from the October 2012 launch and these have recently resulted in some updated conclusions related to dynamic responses that occurred on the engine system during the first engine start event.
“The GPS IIF-5 Delta IV launch is being delayed to allow the technical team time to further assess these updated conclusions and improvements already implemented and determine whether additional changes are required prior to the next Delta IV launch.
“The Delta IV booster for the GPS IIF-5 mission has completed the standard processing and checkout on the launch pad and will be maintained in a ready state for spacecraft mate and launch pending completion of this assessment. A new launch date will be established when the assessment of the updated dynamic response information is completed in the coming weeks.”
A Soyuz rocket (right) will carry Galileo FOC satellites, but no sooner than June 2014.
Galileo. Continuing delays in ground testing of the first two fully operational Galileo satellites have postponed their launch to June 2014 at the earliest.
According to European officials, the European Space Research and Technology Centre (ESTEC) thermal vacuum chamber for testing satellites under orbit conditions was not ready for the two FOC satellites delivered by OHB in late summer.
The satellites thus cannot ship to the Guiana spaceport in South America in time for a planned 2013 launch on a Soyuz rocket. The Galileo schedule is also running into bottlenecks with scheduled launches by other satellite programs aboard Guiana Soyuzes.
A six-week test of the first Galileo satellite at ESTEC reportedly got under way in October.
Svalbard station on Spitsbergen in the Norwegian Arctic.
Ground Network Supports Galileo for SAR
Completion of a pair of European Space Agency dedicated ground stations at opposite ends of that continent has enabled Galileo satellites in orbit to participate in global testing of the Cospas–Sarsat search and rescue system.
The Maspalomas station, in mid-Atlantic Canary Islands, was activated in June. In September, the Svalbard site on Spitsbergen in the Norwegian Arctic activated. The two sites can now communicate and will soon undertake joint tests.
The International Cospas-Sarsat Programme is a satellite-based search and rescue (SAR) distress alert detection and information distribution system, established by Canada, France, Russia, and the United States, with participation by 33 other countries.
Activation of the two new stations enables participation of the latest two Galileo satellites in a worldwide test campaign for Cospas-Sarsat expansion.
The program is introducing a new medium-orbit SAR system to improve coverage and response times, with the Galileo satellites in the vanguard.
The second pair of Europe’s Galileo satellites — launched together in October 2012 — are the first of the constellation to host SAR payloads. These can pick up UHF signals from emergency beacons aboard ships or aircraft or carried by individuals, which are then relayed to ground stations. There, the source is pinpointed and automatically passed on to a control center, which then routes it to local authorities for rescue.
“The Galileo satellites, tested in combination with the same SAR payloads on Russian GLONASS satellites as well as compatible repeaters on a pair of U.S. GPS satellites, showed an ability to pinpoint simulated emergency beacons down to an accuracy of 2–5 kilometers in a matter of minutes,” explained Igor Stojkovic, ESA Galileo SAR engineer.
“Our in-orbit validation tests so far have been in line with expectation and beyond, giving us a lot of confidence in the performance of the final system, once completed. And using a combination of satellites is just how the upgraded system will operate in practice, in order to localize distress signals.”
Localization test performed from Maspalomas MEOLUT as part of Galileo’s SAR in-orbit validation. Beacon locations obtained with four satellites are shown in black, while those using three satellites are shown in grey. More than 93 percent of all beacon locations, after only a single beacon burst has been received, are within the required five kilometers from actual beacon position.
System Briefs
GLONASS Seeks UK Ground. According to the website of the Russian magazine GLONASS Messenger, the Russian Federal Space Agency communicated its proposals for specific areas in the United Kingdom (or, more likely, its territories) to accommodate stations of the GLONASS System for Differential Correction and Monitoring (SDCM). Apparently, an offer was made by the deputy head of Roscosmos, Oleg Frolov, in discussions with David Parker, the director of the British Space Agency. The desired locations for the stations will not be disclosed until the approval of their establishment by the British side, the website reported.
Head Rolls. After repeated satellite launch failures and rumblings about embezzlement and corruption within the Russian space program Roscosmos, Vladimir Popovkin was let go as director and replaced by Oleg Ostapenko, a colonel general in the Russian Military, deputy minister of Defence, and former commander of the Aerospace Defence Forces. The Russian government also announced formation of new agency, the United Rocket and Space Corporation, to manage satellite and rocket manufacturing facilities heretofore supervised by Roscosmos.
Russian scientists and engineers are at work on a new code-division multiple-access signal format to be broadcast on a new GLONASS L3 signal. Taking an approach similar to that implemented on the newly designed GPS L5 signal, this will, once implemented across the constellation by new satellite launches, facilitate interoperability with and even eventually interchangeability among other GNSS signals, including of course GPS.
An article in the November issue of GPS World, authored by Alexander Povalyaev, the deputy head of division in JSC Russian Space Systems and a professor at the Moscow Aviation Institute, will give an outline and provide some details on a new flexible navigation message format proposed for use in the GLONASS CDMA signal under development. The format allows for relatively easy upgrades in the navigation message, if required.
Navigation messages developed and broadcast so far, by both GPS and GLONASS, are fixed, regular structures including pages (frames), subframes (rows), and words. Despite their simplicity, “such structures are very conservative indeed,” says Professor Povalyaev. The only possibility to update such navigation messages is restricted to the use of previously allocated backup frames. Increasing numbers of such frames make for ineffective use of navigation message transmission capacity. Conversely, the relatively small number of backup frames restricts the potential for future navigation message upgrades.
Prof. Povalyaev states that a comparison of data transmission via GLONASS and GPS, respectively, reveals that the data transmission rate in GLONASS is 5 times greater than in GPS. This explained by the higher redundancy of the GPS navigation message. In addition to approximately 11 percent of its subframes in backup, the GPS signal reserves fields for transmission of 32 satellite almanacs. As a result, Povalyaev believes that the GPS navigation-message transmission channel used inefficiently.
For GLONASS, the situation is different, with fewer backup bits in the navigation message, and fields reserved for transmission of only 24 satellite almanacs. This increases transmission channel efficiency but creates problems when it comes to updating the system, particularly in maintaining backward compatibility for previously manufactured user equipment. From this point of view, he says, a large number if backup frames in preferable.
He proposes a GLONASS navigation message with flexible row structure, as was used for the first time in the design of the GPS L5 signal. In this structure, the navigation message is formed as a variable row flow of different types. Each row type has a unique structure and contains specified information type, for example, ephemeris, almanacs of specific satellites, parameters of Earth pole movement models, parameters of ionospheric delay models, and so on. He goes on to describe how signal-processing disruptions in legacy user equipment can be avoided.
A flexible row structure of the navigation provides more effective use of transmission channel capacity. The main advantage of the flexible row structure is the possibility of its evolutional upgrade, meeting the requirements of backward compatibility.
Currently GLONASS uses signals with frequency separation in L1 (1592.9 – 1610 MHz) and L2 (1237.8 – 1256.8 MHz). The foreseen upgrade, already underway with one recently launched GLONASS satellite transmitting an L3 signal, will permit, in the long term, signals with code separation in L1, L2, and L3 (1190.35 – 1212.23 MHz).
Look for further details in the November issue of GPS World magazine.
PCTEL, Inc. announced the launch of its next generation multi-band GNSS antennas for global timing and precision tracking applications at the ION GNSS Conference being held this week in Nashville, Tennessee.
The new antennas, which are designed for use with GPS, GLONASS, BeiDou, and Galileo systems, are being showcased along with other PCTEL antennas at the PCTEL booth in the Exhibit Hall, Booth 318/320. All models of the new antennas are available for sale.
Equipment providers for carrier network timing, precision agriculture, and global asset tracking applications need a single antenna solution for global deployment. PCTEL’s new GNSS1-TMG-26N and GPS-LB12GL-MAG antennas address global compatibility issues for two of the industry’s most crucial applications.
For critical timing applications for macro and small cell deployments, PCTEL has developed the GNSS1-TMG-26N antenna. The GNSS1-TMG-26N is a fixed mount network timing antenna covering GPS, GLONASS, Beidou, and Galileo system frequencies in one single unit, making it a true global solution.
PCTEL’s GPS-LB12GL-MAG antenna is designed for precision agriculture.
For global precision navigation applications, PCTEL has developed the GPS-LB12GL-MAG to cover GPS L1, GPS L2, GLONASS, and L-BAND constellations. The GPS-LB12GL-MAG’s multi-band coverage addresses the precision market in the USA as well as differential correction signals needed across Europe and Asia.
“PCTEL will meet the GNSS market requirements for our global customers while maintaining PCTEL’s high standards for quality and performance,” said Jeff Miller, president of PCTEL Connected Solutions. “We understand that our products need global compatibility to support our customers around the world. We are proud to showcase our design excellence in this highly technical area,” added Miller.
In the field, capture up to 200 MHz of multi-channel bandwidth and return to your lab with a rich library of GPS and GLONASS signals and impairments to accelerate RF product designs and research. Add a camera for a complete view and map of your recording environment.
Averna’s RF Studio software and suite of award-winning RF test instruments set the standard for portability, flexibility and repeatability, empowering you to efficiently record and play back all common radio, video, and GNSS signals in the highest fidelity to accelerate RF projects and reduce travel and testing costs.
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With the optional DriveView™ module, you can capture a complete visual record and map of where you made your recordings to aid analysis and troubleshooting. As well, RF Studio’s plug-in architecture supports additional hardware, channels, user inputs, remote triggering and a distributed control interface to ensure the widest possible application.
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Multi-Channel, 50 MHz and 20 MHz Compact RF Recorders
By Richard Langley, Steffen Thoelert, and Michael Meurer
The spectrum of signals from IRNSS-1A, the first satellite in the Indian Regional Navigation Satellite System, as recorded by German Aerospace Center researchers in late July, appears to be consistent with a combination of BPSK(1) and BOC(5,2) modulation.
Figure 1 shows that, centered at 1176.45 MHz, the signal has a single symmetrical main lobe and a number of side lobes characteristic of the signal structure that the Indian Space Research Organization (ISRO) announced would be used for IRNSS transmissions in the L-band. Figure 2 shows the corresponding IQ constellation diagram. Further analysis will be required to sleuth additional signal details as ISRO, so far, has not publicly released an IRNSS interface control document describing the signal structure in detail.
Figure 1. Spectrum of IRNSS-1A L5 signal.Figure 2. IQ constellation diagram of IRNSS-1A L5 signal.
The German scientists caution that “this is a very early snapshot of the current signal transmission and probably both the signal power and the signal quality will change and possibly improve during the in-orbit-testing phase of the satellite’s operation.
Extra Life for IIRs, IIR-Ms
U.S. Air Force engineers are testing on-orbit a technique to extend the life of the 19 GPS IIR and IIR-M satellites on orbit, roughly 60 percent of the current contellation.
A new charging method may reduce the rate of satellite battery degradation, thereby extending satellite operational life. If the technique passes the test, the initiative could add a combined 20 years to the life of the satellites — saving the Air Force tens of millions of dollars in the process.
Gen. William Shelton, commander of Air Force Space Command, credits Capt. Jacob Hempen of the Air Force’s 2nd Space Operations Squadron for the job. Capt. Hempen says in turn that Warren Hwang of the Aerospace Corporation originated the idea.
When satellite solar panels are directly exposed to the Sun, they charge satellite batteries while continuing to power other operations onboard the space vehicle. When the satellite passes into the Sun’s shadow behind the Earth, it runs on batteries. The batteries can be re- charged at variable rates. When some of the batteries are powered above a certain rate threshold, they can overheat, accelerating their natural rate of decay.
Lowering battery charging rates could still enable the satellites to perform well while minimizing the rate of degradation. Hitting the optimum number called for some finely-honed calculations.
The satellites were built by Lockheed Martin Space Systems, and the oldest still in operation was launched in 1997.
They had an intial design life of eight years, which many have now well outlasted. If the technique proves out and is carefully applied across the board, it could conceivably fill in replenishment gaps equivalent more than two additional spacecraft — conceivably as much hundreds of millions of dollars in build and launch costs, postponed. In today’s budget environment, a postponement can be construed as equivalent to outright savings.
System Briefs
GLONASS Partial Make-Good. Russia will launch two GLONASS satellites later this year to make up for the loss of three satellites in the July 2 Proton rocket explosion. The first is scheduled for the beginning of September, and the second at the end of October. Both will rise aboard Soyuz carrier rockets, which have proven more reliable than the Protons. A constellation of 29 GLONASS satellites is now in orbit, with 24 spacecraft in operation, three spares, one in maintenance, and one in test flight phase.
Meanwhile, plans to reduce GLONASS funding have alarmed at least some deputies of the Duma, the Russian state legislative body. Government officials have floated a plan to reduce funding of the space program in 2014 by 11.7 billion rubles ($355 million), by 13.5 billion rubles in 2015, and by 40 billion rubles in 2016. The federal space program of Russia for 2006-2015 already lacks 10.5 billion rubles funding, and this year there has been a 2.3-billion-ruble additional reduction in R&D. A Duma committee chairperson warned that this trend will “lead to the loss of confidence of the international community in the GLONASS system and, consequently, to a reduction in its use globally. Russia will lose a strategic global instrument of political and economic prestige.” The Duma has recommended that the government maintain funding of federal space programs.
Galileo Satellites’ Trial By Noise. The first Galileo Full Operational Capability (FOC) satellite successfully completed acoustic testing in July, part of a full-scale test campaign at ESA’s ESTEC Test Centre in Noordwijk, the Netherlands.
The satellite was placed in the Large European Acoustic Facility (LEAF), effectively the largest sound system in Europe. A quartet of noise horns embedded in a wall of the 11 x 9 x 16.4 meter test chamber generated an acoustic noise level of 140.7 decibels, about the same noise as standing 25 meters from a jet taking off, and intended to simulate the extreme environment experienced by a satellite atop a rocket about to fire itself off the launch pad.
A second FOC satellite arrived at ESTEC on 9 August from manufacturer OHB in Bremen, Germany. It will undergo a similar acoustic testing and then a System Compatibility Test Campaign will linking it with the Galileo Control Centres in Germany and Italy and ground user receivers as if it were already in orbit.
A total of 14 FOC satellites are being produced and then tested at ESTEC as an integral part of their path to orbit. A second work order of eight satellites has been given to OHB.
GPS III Pathfinder. On July 19, Lockheed Martin delivered a full-sized, functional prototype of the next-generation GPS satellite to Cape Canaveral Air Force Station to test facilities and pre-launch processes in advance of the arrival of the first GPS III flight satellite.
The GPS III Non-Flight Satellite Testbed (GNST) paves the way for the first flight GPS III satellite, expected to arrive at the Cape in 2014, ready for launch by in 2015.
An innovative investment by the Air Force under the original GPS III development contract, the GNST has helped to identify and resolve development issues prior to integration and test of the first GPS III flight space vehicle (SV-01).
Following the Air Force’s rigorous “back-to-basics” acquisition approach, the GNST has gone through the development, test and production process for the GPS III program first, significantly reducing risk for the flight vehicles, improving production predictability, increasing mission assurance and lowering overall program costs.
Lockheed Martin is currently under contract for production of the first four GPS III satellites (SV 01–04), and has received advanced procurement funding for long-lead components for the fifth, sixth, seventh and eighth satellites (SV 05–08).
GNSS Industry Survey. Here are the results of two questions asked about government and industry from the 2013 GNSS STATE OF THE INDUSTRY SURVEY.
Is government committed to private industry in a time of drastic budget cuts?Is industry actively making its concerns known to government?
The Indian Regional Navigation Satellite System (IRNSS) successfully launched its first satellite on July 1 from the Satish Dhawan Space Centre at Sriharikota spaceport on the Bay of Bengal. An Indian-built Polar Satellite Launch Vehicle PSLV-C22, XL version, carried the 1,425-kg satellite aloft.
IRNSS-1A is the first of seven satellites that will make up the new constellation: four satellites in geosynchronous orbits inclined at 29 degrees, with three more in geostationary orbit. IRNSS-1A is one of the geosynchronous satellites.
Following launch, the master control facility conducted five orbit maneuvers to position the satellite in its circular inclined geosynchronous orbit (IGSO) with an Equator crossing at 55 degrees east longitude. Reports indicate that orbit-raising maneuvers have been completed, and all the spacecraft subsystems have been evaluated and are functioning normally.
IRNSS-1A’s drift eastward from 47 degrees east longitude on July 10 was gradually slowed, and the satellite achieved its assigned inclined geosynchronous orbit, with a 55-degree East equator crossing, by July 18. The orbit inclination is 27.03 degrees.
Payloads. IRNSS-1A carries two types of payloads, navigation and ranging. The navigation payload will operate in L5 band (1176.45 MHz) and S band (2492.028 MHz), using a Rubidium atomic clock. The ranging payload consists of a C-band transponder that facilitates accurate determination of the range of the satellite. IRNSS-1A also carries corner-cube retro-reflectors for laser ranging. Its mission life is 10 years.
GLONASS Bellyflop
A Russian Proton-M rocket carrying three GLONASS navigation satellites crashed soon after liftoff on July 2 from Kazakhstan’s Baikonur cosmodrome. About 10 seconds after takeoff at 02:38 UTC, the rocket swerved, began to correct, but then veered in the opposite direction. It then flew horizontally and started to come apart with its engines in full thrust. Making an arc in the air, the rocket plummeted to Earth and exploded on impact close to another launch pad used for Proton commercial launches.
Despite the loss, GLONASS still has a full operating constellation of 24 satellites.
The crash was broadcast live across Russia. Fears of a possible toxic fuel leak immediately surfaced following the incident, but no such leak has been confirmed. The rocket was initially carrying more than 600 tons of toxic propellants. No casualties or damage to surroundings structures or the town of Baikonur have been reported.
The crashed Proton-M rocket employed a DM-03 booster, which was being used for the first time since December 2010, when another Proton-M rocket with the same booster failed to deliver another three GLONASS satellites into orbit, crashing into the Pacific Ocean 1,500 kilometers from Honolulu.
A Russian government investigation revealed that at least “three of six angular rate sensors [on the booster stage] were installed incorrectly,” to be specific, upside-down. Examination of the wreckage discovered traces of forced, incorrect installation on three sensors. Assembly-line testing at the factory failed to detect the faulty installation.
Several videos of the crash are viewable online (YouTube).
First Live Broadcast of GPS CNAV Messages
By Oliver Montenbruck, Richard B. Langley, and Peter Steigenberger
Over the past several years, some users of the GPS navigation system have already benefitted from the addition of various new signals in addition to the legacy C/A- and P(Y)-code. With the introduction of the Block IIR-M satellites in 2005, a new civil signal (L2C) was transmitted on the L2 frequency, and a new signal on a new frequency (L5) was introduced as a standard signal with the Block IIF satellites beginning in 2010. These new signals provide direct access to dual-frequency observations and thus enable improved ionospheric corrections for civil, including aeronautical, users. In addition, a new Civil Navigation (CNAV) broadcast message has been defined in the GPS Interface Specifications (IS-GPS-200 and IS-GPS-705).
This message will be transmitted jointly on the L2C and L5 signals and provides a variety of useful new parameters. Compared to the legacy L1 C/A-code navigation message, the CNAV message also offers an increased flexibility concerning the type, sequence, and repeat rate of specific messages.
CNAV messages have already been broadcast over the past two years by the Michibiki (QZS-1) satellite of the Japanese Quasi-Zenith Satellite System (QZSS), which shares many aspects of the GPS signal design. In contrast to this, Block IIR-M and IIF GPS satellites have only transmitted dummy messages so far and a fully operational CNAV transmission is only foreseen once the ongoing modernization of the GPS control segment has been completed.
Triggered by various interest groups, the Global Positioning Systems Directorate has just conducted a first test campaign with live CNAV transmissions on L2C and L5 over the two-week period from June 15 to 29 (see Global Positioning System Modernized Civil Navigation (CNAV) Live-Sky Broadcast Test Plan.) It served as a first opportunity for end users and receiver manufacturers to test the decoding and use of the new messages under a wide range of different configurations.
CNAV messages have a common length of 300 data bits and are identified by a message type number that signifies their contents. The messages presently defined for GPS are summarized in Table 1. For QZSS, complementary messages have been established, which enable, among other features, a rebroadcast of GPS-specific data to QZSS users.
Table 1. Summary of CNAV message types transmitted by space vehicles (SVs). Messages marked by an asterisk were transmitted during the recent CNAV test campaign.
Message
Type
CNAV Message Title
Function/Purpose
0*
Default
Default message (transmitted when no message data is available)
10*
Ephemeris 1
SV position parameters for the transmitting SV
11*
Ephemeris 2
SV position parameters for the transmitting SV
12*
ReducedAlmanac
Reduced almanac data packets for seven SVs
13
Clock Differential Correction
SV clock differential correction parameters
14
Ephemeris Differential Correction
SV ephemeris differential correction parameters
15*
Text
Text (29 eight-bit ASCII characters)
30*
Clock, Iono & Group Delay
SV clock correction parameters, ionospheric and group delay correction parameters (inter-signal correction parameters)
31
Clock & Reduced Almanac
SV clock correction parameters, reduced almanac data packets for four SVs
Other than the legacy L1 navigation message, which adheres to a fixed order of subframes, the sequence of CNAV messages can be varied widely to provide users with an optimized set of low latency information and parameters that change infrequently. As a baseline, the two ephemeris message types 10 and 11 are combined with any of the clock-and-auxiliary data messages (types 30 through 37) to provide users with the orbit and clock data of the received satellites. With a transmission duration of 12 seconds per CNAV message on L2C, a minimum of 36 seconds is required to transfer this information to the user if no other messages are transmitted. On L5, which operates at twice the data rate, a new frame is transmitted once every 6 seconds yielding a minimum of 18 seconds for the broadcast of ephemeris and clock data.
The recent test campaign started at 18:00 GPS Time on Saturday, June 15, 2013, with the transmission of message types 10, 11, 15, and 30 on a first space vehicle (PRN24) and included PRN12 from 18:42 onwards. Other space vehicles were sequentially phased in until all active IIR-M and IIF satellites (except for the recently launched IIF-4 satellite) transmitted CNAV on the supported signals. When the test ended exactly two weeks later (June 29, 18:00 GPST), all participating satellites were transmitting a complex master frame of 15 x 4 = 60 individual messages, which was repeated once every 12 minutes (on L2C). Each minor frame comprised the two ephemeris messages and at least one clock-data message (see Table 2).
Table 2. Sequence of message types in a CNAV master frame.
Message Types
10
11
15
30
10
11
32
33
10
11
12
35
10
11
12
30
10
11
12
33
10
11
12
35
10
11
12
30
10
11
32
33
10
11
15
35
10
11
32
30
10
11
12
33
10
11
12
35
10
11
12
30
10
11
12
33
10
11
12
35
Other messages included a reduced almanac (message type 12) and a text message (message type 15) with dummy content (“THIS IS A GPS TEST MESSAGE.”)
The CNAV data were recorded by selected multi-GNSS monitoring stations of the German Aerospace Establishment (Deutsches Zentrum für Luft- und Raumfahrt or DLR) and the University of New Brunswick (UNB), which were specifically configured to record raw GPS navigation frames in addition to the normal observation data. The stations are located at Singapore (SIN0); Sydney, Australia (UNX2); Maui, U.S.A. (MAO0); and Hartebeesthoek, South Africa (HRAG); as well as Fredericton, Canada (UNB) and are equipped with either Javad Delta-G2/G3TH or NovAtel OEM6 receivers. Following initial validation, the raw and decoded data from the CNAV test will be made available to interested users through the Multi-GNSS Experiment (MGEX) of the International GNSS Service (see http:/igs.org/mgex/) to facilitate the development of user software and suitable data formats (such as an extended RINEX navigation message format).
The CNAV orbit and clock data were updated once every two hours and offer a slightly higher bit resolution than their legacy counterparts. However, the accuracy of the ephemeris data has not yet been evaluated nor compared to that of the L1 C/A-code navigation data.
As indicated above, the CNAV data can also provide a particularly compact form of almanac data known as the reduced almanac. It does not offer clock information (that is not normally required for a signal search) and assumes a circular orbit, which reduces the overall accuracy. Still, it can be transmitted (and repeated) in a much shorter time interval than the legacy almanac, which requires a total of 12.5 minutes. Each reduced almanac message (message type 12) provides orbit information for a total of seven satellites and it takes a set of five such messages to convey information for a complete constellation. For the master frame layout described above, the full constellation reduced almanac is repeated twice within 12 minutes on L2C (and half this time on L5).
Novel types of CNAV data not covered by the legacy navigation message include the differential code biases (also known as inter-system corrections or ISCs), which are required for pseudorange-based positioning with signals other than the legacy P(Y)-code (in addition to the established Timing Group Delay parameter or TGD). An overview of TGD and ISC values broadcast by the various satellites participating in the CNAV test is given in Table 3.
Table 3. Differential code biases (in nanoseconds) of GPS Block IIR-M and IIF satellites broadcast during the test campaign as part of the message type 30 CNAV messages.
SV Type
SVN
PRN
TGO
ISC L1CA
ISC L2C
ISC L5I5
ISC L5Q5
IIR-M
48
07
-10.71
-0.84
6.52
IIR-M
50
05
-10.24
-0.32
5.41
IIR-M
52
31
-13.04
-0.55
7.36
IIR-M
53
17
-10.24
-0.84
6.17
IIR-M
55
15
-10.24
-0.47
5.62
IIR-M
57
29
-9.31
-0.76
5.06
IIR-M
58
12
-12.11
-0.76
6.64
IIF
62
25
5.59
-2.07
-5.24
-0.38
-0.87
IIF
63
01
8.38
-2.30
-7.57
0.38
2.15
IIF
65
24
2.79
-0.26
-2.27
2.27
3.70
Another important achievement is the provision of Earth orientation parameters (EOP) in message 32, which provides GPS users with access to the celestial reference frame. EOPs were transmitted during the second test week and updated on a daily basis (see Table 4). Knowledge of these parameters is of particular interest for GPS-based orbit determination and navigation of spacecraft (in low Earth orbit), which is preferably referred to an inertial rather than an Earth-fixed coordinate system.
Table 4. Daily Earth orientation parameters from the CNAV test campaign (pole coordinates and dUT1 (UT1-UTC) time differences and derivatives).
Epoch (GPST)
x_p
(arcseconds)
x_p_dot
(arcseconds per day)
y_p
(arcseconds)
y_p_dot
(arcseconds per day)
dUT1
(seconds)
dUT1_dot
(seconds per day)
June 22, 0:00
0.13517
0.00104
0.39657
-0.00054
0.06341
-0.00046
June 23, 0:00
0.13621
0.00102
0.39604
-0.00056
0.06295
-0.00049
June 24, 0:00
0.13740
0.00101
0.39535
-0.00058
0.06231
-0.00053
June 25, 0:00
0.13815
0.00099
0.39487
-0.00060
0.06164
-0.00063
June 26, 0:00
0.13846
0.00096
0.39443
-0.00062
0.06078
-0.00067
June 27, 0:00
0.13885
0.00094
0.39381
-0.00064
0.06004
-0.00067
June 28, 0:00
0.13947
0.00093
0.39310
-0.00066
0.05909
-0.00063
June 29, 0:00
0.13987
0.00090
0.39246
-0.00068
0.05842
-0.00053
Overall, CNAV offers exciting prospects for improved GPS utilization and users may look forward to the next test campaigns, which will tentatively be conducted once every six months.
As a side note, it should be mentioned that individual satellites could be observed to transmit various types of non-standard CNAV messages as well as CNAV messages with improper data (such as an invalid week count) after the end of the main test campaign. Various receivers in the MGEX network, which were processing the received CNAV messages internally and which put full confidence in their proper contents, were mislead by such information. During the actual test campaign, all data appeared fully valid and no problems were reported by the stations.
OLIVER MONTENBRUCK is the head of the GNSS Technology and Navigation Group at DLR’s German Space Operations Center in Oberpfaffenhofen, Germany.
RICHARD B. LANGLEY is a professor in the Department of Geodesy and Geomatics Engineering at the University of New Brunswick, Fredericton, New Brunswick, Canada.
PETER STEIGENBERGER is a staff member in the Institut für Astronomische und Physikalische Geodäsie of the Technische Universität München (TUM) in Munich, Germany.
Plans to reduce funding for GLONASS is causing concern among deputies of the State Duma. The government officials predict a loss of trust in the world by the Russian navigation system, according to a July 29 Roscosmos article.
Reduced funding of GLONASS will lead to a reduction of the orbital grouping system below acceptable levels, according to the first deputy chairman of the Committee on Industry, Vladimir Gutenev. The U.S. GPS system is functioning and both Europe and China are developing systems, Galileo and COMPASS respectively. This will “lead to the loss of confidence of the international community in the GLONASS system and, consequently, to a reduction in its use globally. Russia will lose a strategic global instrument of political and economic prestige,” Gutenev warned.
The proposal is to reduce budget funding of the state space program in 2014 by 11.7 billion rubles, in 2015 by 13.5 billion rubles, and in 2016 by 40 billion rubles, according to the ITAR-TASS news agency. In addition, the federal space program of Russia for 2006-2015 already lacks 10.5 billion rubles funding, and this year there has been a 2.3-billion-ruble additional reduction in R&D.The funding was in part intended to build and put into operation phase 1 of the Vostochny booster side building, which would use the Soyuz-2 space rocket system.
The State Duma, according to the ITAR-TASS news agency, has recommended that the government of the Russian Federation maintains funding of federal programs on space matters in the amount provided by an approved state program.
Ria Novosti reports that Russia will launch two GLONASS navigation satellites later this year to make up for the loss of three satellites in the recent Proton rocket explosion after launch from the Baikonur space center in Kazakhstan, according to a senior space industry official.
“We are planning to launch two satellites from the Plesetsk space center [in northern Russia] to replenish the GLONASS orbital grouping following the recent Proton-M accident,” said Nikolai Testoyedov, the head of the Information Satellite Systems (ISS) company, which manufactures satellites for the GLONASS project.
The first GLONASS is scheduled for launch in the beginning of September, and the second at the end of October, according to Testoyedov. The official added that both satellites will be launched on board the Soyuz carrier rockets, which has proven to be more reliable than ill-fated Protons.
A group of 29 GLONASS satellites is currently in orbit, with 24 spacecraft in operation, three spares, one in maintenance, and one in test flight phase, according to Russia’s space agency, Roscosmos.
Rohde & Schwarz provides developers of satellite-based navigation instruments with a global navigation satellite system (GNSS) simulator, which runs on the R&S SMBV100A vector signal generator. The new R&S SMBV-K101 option allows developers in the automotive and wireless communications industries, for example, to test GNSS receivers for specific effects such as obscuration and multipath propagation. Buildings, tunnels and bridges as well as reflections from concrete and glass surfaces affect the GNSS signal, regardless of whether the receiver is stationary or in motion. This option makes it easy to configure these kinds of scenarios.
If the GNSS receiver of a navigation instrument or smartphone is located inside a vehicle, testing must also take into account the obscuring effect of the vehicle’s metal body. The R&S SMBV-K102 option can simulate this obscuration and, if required, also the additional antenna pattern.
In addition to test scenarios for A-GPS, smartphone developers also have the Assisted Galileo (R&S SMBV-K67) and Assisted GLONASS (R&S SMBV-K95) options at their disposal. (Mobile radio networks transmit location-specific information to wireless devices via A-GNSS so that they can determine the current position faster.)
In many cases, navigation instruments handle signals of digital communications standards other than GNSS. As the first GNSS simulator of its kind on the market, the R&S SMBV100A also supports these standards. Now, manufacturers of mobile phones and car radios with integrated GNSS receivers need just one signal generator to test multiple functionalities. The R&S SMBV100A can also be used to perform interference tests on the DUT.
Users in the aerospace and defense industry can use the R&S SMBV-K103 option to simulate the relative position of a flying object as well as its rotation at a rotation rate of up to 400 Hz. This allows developers to perform lab tests to determine how a flying object’s different positions, the ground reflection of GNSS signals and rotary movements affect reception quality.
The GNSS simulator in the R&S SMBV100A uses up to 24 satellites to generate signals in realtime for GPS with civilian C/A code and military P code as well as for Glonass and Galileo in different constellations. In just a few steps, users can define their own scenarios for testing their GNSS receivers under various conditions. The R&S SMBV100A is the only GNSS simulator on the market that does not require an external PC. As a result, it is easier to automate, and test setup is simple.
The new options for the GNSS simulator in the R&S SMBV100A are now available from Rohde & Schwarz.
A Russian Proton-M rocket carrying three GLONASS navigation satellites crashed soon after liftoff today from Kazakhstan’s Baikonur cosmodrome, reports rt.com (Russia Today).
About 10 seconds after takeoff at 02:38 UTC, the rocket swerved, began to correct, but then veered in the opposite direction. It then flew horizontally and started to come apart with its engines in full thrust. Making an arc in the air, the rocket plummeted to Earth and exploded on impact close to another launch pad used for Proton commercial launches.
The crash was broadcast live across Russia. Fears of a possible toxic fuel leak immediately surfaced following the incident, but no such leak has been confirmed, rt.com reports. The rocket was initially carrying more than 600 tons of toxic propellants.
No casualties or damage to surroundings structures or the town of Baikonur have been reported.
As RT.com reports, the crashed Proton-M rocket employed a DM-03 booster, which was being used for the first time since December 2010, when another Proton-M rocket with the same booster failed to deliver another three GLONASS satellites into orbit, crashing into the Pacific Ocean 1,500 kilometers from Honolulu.
Photo: Russia Today
Photo: Russia Today
Photo: Russia Today
Photo: Russia Today
UPDATE: Russian Prime Minister Dmitry Medvedev has appointed a special government commission to investigate the causes of the crash and identify any officials who may have been responsible, reports the Christian Science Monitor. Medvedev also directed his government to prepare tougher oversight measures over the space industry to prevent such accidents in future, RIA-Novosti reported.
By Oliver Montenbruck, Chris Rizos, Robert Weber, Georg Weber, Ruth Neilan, and Urs Hugentobler
GPS IS ALMOST 40 YEARS OLD. While mass consumer use of GPS began only within the past decade or so, GPS was “born” during the Labor Day weekend of 1973, when about a dozen military officers and industry analysts under the leadership of Brad Parkinson met to consolidate the concept for a single satellite-based navigation system for the U.S. Department of Defense. Their proposal for NAVSTAR GPS was approved on December 22, 1973. The first satellite to be launched under the GPS program, on July 14, 1974, was the Naval Research Laboratory’s Navigation Technology Satellite (NTS) 1. NTS-2 followed, with a launch on June 23, 1977. These satellites carried payload components similar to those to be used on the subsequent GPS Block I or Navigation Technology Satellites. The first Block I satellite was launched on February 22, 1978, and was followed by nine others. With the launch of the Block II and IIA Operational Satellites and with 24 satellites on orbit, Initial Operational Capability was declared on December 8, 1993. Following testing, Full Operational Capability (FOC) was announced on July 17, 1995.
Whether in reaction to the development of GPS or simply to fulfill the requirement for a system with similar capabilities for its armed forces, the former Soviet Union developed the Global’naya Navigatsionnaya Sputnikovaya Sistema or GLONASS. The first GLONASS satellite was launched on October 12, 1982. By early 1996, a fully populated FOC constellation of 24 satellites was in orbit, but the number of operational satellites dwindled to a handful due to lack of financial support. Eventually the needed funds started flowing again and on December 8, 2011, FOC was again achieved and subsequently maintained.
With the announcement of FOC and the removal of the accuracy-limiting policy of Selective Availability on May 2, 2000, widespread consumer use of GPS took off.
And now GPS is approaching middle age. And like for some humans approaching that milestone desirous of change, a GPS renewal or modernization is under way. New civil and military signals are being transmitted by the Block IIR-M and IIF satellites along with the legacy signals pioneered by the Block I satellites. And new GNSS signals are now coming from the satellites orbited for the Chinese BeiDou Navigation Satellite System, the Japanese Quasi-Zenith Satellite System, and Europe’s Galileo, as well as those from satellite-based augmentation systems. Although it will be some years before full constellations will be transmitting these signals, scientists and engineers are already monitoring and analyzing the new signals to learn how best to use them and how to integrate subsets of them for a wide variety of applications in positioning, navigation, and timing.
In this month’s column, we learn the details of the effort established by the International GNSS Service to support the study of these new signals: the Multi-GNSS Experiment.
“Innovation” is a regular feature that discusses advances in GPS technology andits applications as well as the fundamentals of GPS positioning. The column is coordinated by Richard Langley of the Department of Geodesy and Geomatics Engineering, University of New Brunswick. He welcomes comments and topic ideas. To contact him, see the “Contributing Editors” section on page 4.
Over the past four decades, GPS has evolved from a primarily military navigation system into an indispensable tool not only for society at large, but also for geodetic research and global monitoring of the Earth. And within the past decade, the world of satellite navigation has experienced dramatic changes. With GLONASS, a second GNSS has achieved full operational status; GPS is introducing modernized civil and encrypted navigation signals; and a variety of new navigation constellations are being built up in Asia and Europe.
As of early 2013, Europe has successfully launched a total of four Galileo In-Orbit Validation (IOV) satellites, which are undergoing testing in parallel to the build up and verification of the ground segment. The satellites routinely transmit signals at four frequencies (E1, E5a, E5b, and E6) and offer a variety of publicly accessible pilot and data signals. As a unique feature, Galileo enables tracking of the alternative binary-offset-carrier (AltBOC) signal in the combined E5a+E5b band, which offers superior noise and multipath performance.
Meanwhile, the Chinese BeiDou Satellite Navigation System (BDS; formerly known as Compass) has completed the first stage of its system deployment and declared a regional navigation service for the Asia-Pacific region operational. A total of 14 functioning satellites have been launched so far, which includes five satellites in geostationary orbit (GEO), five satellites in inclined geosynchronous orbit (IGSO), and four in medium-altitude Earth orbit (MEO). These satellites transmit signals in three frequency bands (B1, B2, B3), and tracking of the corresponding open service (OS) signals is already supported by a variety of GNSS receivers. With the release of a B1 OS Interface Control Document (ICD) at the end of 2012, the BeiDou navigation message has become publicly accessible, and users throughout the Asia-Pacific region can now benefit from BeiDou as a supplementary or stand-alone navigation system.
The Japanese Quasi-Zenith Satellite System (QZSS) has, so far, only launched a single satellite but recent political decisions have paved the way for the build up of a mini-constellation of IGSO and GEO satellites. Aside from a high level of compatibility with GPS, QZSS has introduced new signals such as the modernized L1 Civil (L1C) signal and the L-band Experiment (LEX) signal (also known as L6) for high-precision point positioning in the E6 band. Along with this unique set of navigation signals, QZSS provides innovative service features such as the L1 Sub-meter-class Augmentation with Integrity Function (L1-SAIF or L1S) message. Also, QZSS precedes GPS in offering the new Civil Navigation (CNAV) message on L2C and L5, as well as the CNAV2 message on L1C. Long before their planned use in GPS, these messages are now broadcast on a routine basis and contain novel information such as inter-frequency corrections and Earth-orientation parameters.
Last, but not least, GPS has now a total of four Block IIF satellites in orbit that transmit an operational L5 signal for aviation users (and others) and which fly a new generation of highly stable rubidium clocks. While neither L2C nor L5 are transmitted by a full constellation, users and investigators can gradually familiarize themselves with these new signals that will enable encryption-free dual-frequency navigation services for aeronautical and other civil applications.
Within the International GNSS Service (IGS), more than 200 worldwide agencies have, for many years, pooled resources and permanent GNSS station data to generate precise GNSS products in support of Earth science research, multidisciplinary applications, and education. So far, this service has been restricted to two systems — namely, GPS and GLONASS. In recognition of the rapidly evolving GNSS landscape, the IGS has set up the Multi-GNSS Experiment (MGEX) to explore and promote the use of new navigation signals and constellations. It will enable an early familiarization with new GNSS, identify and overcome relevant challenges, and prepare use of emerging navigation systems in routine IGS products. MGEX comprises the build-up of a new network of sensor stations, the characterization of the user equipment and space segment, the development of new concepts and data processing tools, and the generation of early data products for Galileo, QZSS, and BeiDou. MGEX is coordinated by the IGS Multi-GNSS Working Group (MGWG), which interacts closely with other IGS entities, such as the RINEX WG, the Antenna WG, the Data Center WG, and the Infra-structure Committee.
The article starts out with a description of the MGEX network that formed the starting point and initial focus of the overall MGEX project. Following a description of system characterization activities, the current status of multi-GNSS data products and ongoing efforts for the development of new standards for multi-GNSS-related work within the IGS are presented.
Network
Following a call-for-participation released in the summer of 2011, the build up of a new international network of multi-GNSS sensor stations was initiated and has grown substantionally in a short time. By the end of 2012, the MGEX network had comprised approximately 50 stations supporting at least one of the new navigation systems (Galileo, BeiDou, and QZSS) in addition to the legacy GPS, GLONASS, and SBAS systems. At last count, the network now includes 75 stations.
The bulk of the stations is provided by IGS partners such as Bundesamt für Kartographie und Geodäsie (BKG), Centre National d’Etudes Spatiales (CNES), Deutsches GeoForschungsZentrum (GFZ), Deutsches Zentrum für Luft- und Raumfahrt (DLR), Geoscience Australia (GA), the Geospatial Information Authority of Japan (GSI), Institut National de l’Information Géographique et Forestière (IGN), and the Swedish National Land Survey (Lantmaeteriverket, LMV), that have upgraded existing sites with new, multi-GNSS-capable receivers and antennas or started to deploy new multi-GNSS networks (such as the COperative Network for GNSS Observation (CONGO) or CNES’s REseau GNSS pour l’IGS et la Navigation (REGINA) network).
As shown in FIGURE 1, the present set of MGEX stations exhibits almost global coverage, even though a concentration in Europe and a reduced coverage in the Americas and the western Pacific are obvious. However, this situation is expected to improve soon with announced contributions from Geoscience Australia, the Multi-GNSS Monitoring Network (MGM-net) of the Japan Aerospace Exploration Agency (JAXA), and other stations. While most MGEX sites support tracking of Galileo satellites, only a subset of stations provides data for QZSS and BeiDou. In particular, the regional BeiDou constellation (that is, the GEO and IGSO) satellites are not well covered by the current network.
Figure 1. Distribution of MGEX stations supporting tracking of QZSS (blue), Galileo (red), and BeiDou (yellow) as of June 2013.
Further MGEX sites are encouraged and the nomination of sites is still possible through the MGEX submission form under the provision of relevant improvements to the capabilities, coverage, and homogeneity of the overall network.
In terms of equipment, five basic receiver types and seven basic antenna types are employed at the MGEX stations (see TABLES 1 and 2). Observation types provided by the individual receivers have been compiled from summary reports generated by the Astronomical Institute of the University of Bern (AIUB) as part of their routine monitoring of RINEX 3 observation files from MGEX stations.
Table 1. Receiver types in use within the MGEX network (status as of June 2013). Observation types for Galileo (E), BeiDou (C), and QZSS (J) are based on RINEX 3 observation codes as reported in the submitted data files (frequency bands: 1=L1/E1, 2=L2/B1, 5=L5/E5a, 6=E6/B3, 7=E5b/B2, 8=E5ab; signals: C = C/A-code, I = data, Q = pilot, X = data+pilot). They do not necessarily indicate the full tracking capabilities supported by the receivers but rather the observations made available to MGEX users from the respective stations.Table 2. Antenna types employed within the MGEX network (as of June 2013).
Note that no common standard has yet evolved in terms of supported signals and observation types. This causes certain restrictions for data analysis and product generation. As an example, Galileo orbit and clock products will (at least initially) be based on E1/E5a observations due to a limited coverage of E5b and E5ab tracking.
Selected sites (such as UNB and USNO) offer multiple receivers in short- or zero-baseline configurations to facilitate equipment characterization. Further such installations will be added to the MGEX network at the time of the proposed extensions.
While all stations contribute data to offline archives hosted by the Crustal Dynamics Data Information Service (CDDIS), IGN, and BKG for the MGEX project, a selected subset also supports real-time analyses (see FIGURE 2). All real-time streams utilize the Networked Transport of RTCM via Internet Protocol (NTRIP), which has emerged as a standard for real-time GNSS data exchange. A dedicated MGEX caster is hosted by BKG in Frankfurt, where native raw data streams received from the individual sites are converted and encoded in the RTCM3 Multiple-Signal-Message (MSM) format.
Figure 2. Distribution of MGEX real-time stations supporting tracking of QZSS (blue), Galileo (red), and BeiDou (yellow) as of June 2013.
RTCM3-MSM will enable a harmonized framework for multi-GNSS real-time operations and ensure a seamless conversion to the RINEX3 offline data format. The new MGEX NTRIP caster provides a basis to gain early experience with the new MSM format and facilitates a timely adaptation of user software. This is further supported through freeware software modules for data conversion provided by BKG.
System Characterization
While a systematic quality control of the MGEX data has not yet started, first performance assessments of both the ground and space segment have been reported in the literature (see Further Reading). Overall, the measurement quality of the employed multi-GNSS receivers is found to be comparable or even superior to established GPS reference stations. A high performance is, in particular, obtained for unencrypted signals with high chipping rates and bandwidths such as the GPS/QZSS L5 and Galileo AltBOC.
By way of example, FIGURE 3 illustrates the elevation-angle-dependency of pseudorange errors for BeiDou tracking with a Trimble NetR9 receiver as used at numerous MGEX stations. Aside from the expected variation of receiver noise, the analysis reveals a systematic code bias that varies by 0.4-0.6 meters from horizon to zenith and can best be attributed to spacecraft internal multipath.
Figure 3. Code noise and elevation-dependent biases for BeiDou tracking.
An interesting opportunity for system characterization is provided by triple-frequency observations (GPS+QZSS L1/L2/L5, BeiDou B1/B2/B3, Galileo E1/E5a/E5b) made available by a subset of the MGEX network. A thermal variation of inter-frequency biases has earlier been identified for the GPS Block IIF satellites, but a high level of consistency is demonstrated for QZSS, BeiDou, and Galileo (see FIGURE 4).
Figure 4. Triple-frequency combination of Galileo IOV-3 observations.
Products
While the newly established MGEX network forms a mandatory prerequisite for multi-GNSS work within the IGS, the MGEX campaign supports a wider range of activities, which are now being established. Foremost, the generation of orbit and clock products for the new constellations is promoted in coordination with new and established IGS analysis centers.
Initial Galileo IOV products have been provided by CNES/CLS, CODE, and GFZ since mid-2012, and a combined Galileo+QZSS product has been added by Technische Universität München (TUM). Aside from the MGEX network, some of these solutions make complementary use of proprietary multi-GNSS networks to compensate existing coverage limitations and achieve an improved product quality.
TABLE 3 compares selected MGEX orbit products for the Galileo IOV satellites, while FIGURE 5 shows a time series of the difference between the TUM and CODE orbit products for IOV-1 (E11).
Table 3. Inter-comparison of selected MGEX orbit products for the Galileo IOV satellites. (IOV-1 (E11), DOY 323-329, 2012). Orbit differences (mean ± standard deviation) in radial (R), along-track (T) and cross-track (N) directions are provided in the upper right cells, 3D RMS position differences in the lower left. All values are in units of meters.Figure 5. Difference of MGEX Galileo IOV-1 (E11) orbit products from TUM and CODE for DOY 232-239, 2012 (R: radial direction, T: along-track direction, N: cross-track direction).
TABLE 4 shows the residuals of Galileo IOV-1/2 satellite laser ranging measurements (mean ± standard deviation) relative to the GNSS-based orbit products (days of year (DOY) 323-329, 2012).
Table 4. Satellite laser ranging residuals (mean ± standard deviation) for Galileo IOV-1/2 orbit products (DOY 323-329, 2012). Units are centimeters.
FIGURE 6 shows a time series of the differences between TUM orbit products for QZS-1 and precise ephemerides computed by the Japan Aerospace Exploration Agency (JAXA) for DOY 027-033, 2013. It demonstrates consistency at the 0.5-meter level, which already represents an important accomplishment, given the sparse subset of QZSS-capable MGEX stations available at the time. Further improvements are expected as the MGEX network continues to grow.
Figure 6. Comparison of TUM MGEX orbit products of QZS-1 with precise ephemerides of JAXA for DOY 027-033, 2013.
Concerning the Chinese BeiDou system, which has now reached initial operational capability for a regional service, early orbit and clock determination results have been reported by various Chinese and European researchers using data from dedicated regional sensor station networks. An effort will be made to promote the extension of the BeiDou tracking capabilities within the MGEX network and to make MGEX-only or mixed network-based orbit and clock products for BeiDou accessible to a wider user community through the MGEX data centers.
Given the late public availability of Galileo and BeiDou broadcast navigation messages, the MGEX orbit and clock products constitute a significant promotion for the early use of all available navigation systems. Aside from initial positioning experiments, they provide a basis for the in-depth characterization of both the space and user segment, and, it is hoped, will facilitate an improved interaction with system providers. Early applications of MGEX multi-GNSS products and observations have, for example, been reported at conferences and in journals (see Further Reading).
Standardization
In support of MGEX, the Multi-GNSS WG interacts closely with other IGS working groups to coordinate data formats, processing standards, and applicable models for use in multi-GNSS work. Examples include necessary RINEX 3 and RTCM3 extensions for full support of new GNSS signals and tracking modes as well as the rapidly growing set of diverse broadcast navigation data.
Another focus of current work addresses the proper modeling of antenna offsets and phase patterns for receiver and satellite antennas, along with documentation of constellation-specific spacecraft coordinate systems and attitude modes. This work is performed in close coordination with the IGS Antenna WG. Among others, conventional antenna phase center offsets (see TABLE 5) have been agreed upon, which will enable consistent processing of MGEX observations until the release of official information by the Galileo and BeiDou program offices.
Table 5. Conventional antenna offsets from the spacecraft center of mass for processing Galileo IOV and BeiDou observations. All values refer to the spacecraft coordinate system. Units are meters.
Public Outreach
As a central point for exchange of MGEX-related information with the user community, a dedicated website has been established at the IGS Central Bureau (see FIGURE 7). The new website provides an overview of available MGEX data and products with direct links to the respective archives at IGS data and product centers. Furthermore, users are provided with up-to-date information on the status of the emerging navigation satellite systems as well as recommended parameters (such as antenna offsets) for harmonized and consistent processing of MGEX observations.
Figure 7. Homepage of the IGS Multi-GNSS Experiment at http://igs.org/mgex.
Through individual members, the Multi-GNSS WG is represented on other boards and bodies such as the International Committee on GNSS, the International Association of Geodesy, and the Multi-GNSS Asia project.
Summary and Conclusions
As part of its continued effort to provide the highest quality data and products for all satellite navigation systems, the IGS has initiated the Multi-GNSS Experiment. MGEX supports early work with new signals and constellations. It enables a timely preparation of IGS analysis centers as well as the user community to expand from GPS/GLONASS towards full multi-GNSS processing.
Within the first year of MGEX, substantial progress has already been made. In particular, a global network of multi-GNSS receivers has been established in parallel with the existing core IGS network and by upgrading existing sites with new multi-GNSS equipment. The MGEX network forms the backbone for all other activities, such as system characterization and product generation. Aside from offline data provisions, a substantial fraction of MGEX stations are already offering real-time data streams, which paves the way for a rapid extension of the upcoming IGS real-time pilot service to Galileo and possibly other constellations. A limited number of analysis centers have already started to provide orbit and clock products for Galileo and/or QZSS as a basis for precise positioning applications. In addition to initial positioning experiments, they will provide a basis for the in-depth characterization of both the space and user segment, and help facilitate an improved interaction with system providers.
Upcoming activities will focus on the systematic incorporation of the BeiDou navigation satellite system. While BeiDou is the third constellation to reach an operational system status after GPS and GLONASS, it is not well covered by the current MGEX tracking network. Along with the targeted incorporation of BeiDou-capable reference stations (particularly in the Asia-Pacific region), the generation and provision of related orbit and clock products will be promoted to facilitate a timely use of BeiDou by the geodetic community.
Subject to active participation by a sufficient number of analysis centers, the MGEX project will eventually transition into an IGS pilot project offering operational data products of Galileo, QZSS, and BeiDou within the next few years.
OLIVER MONTENBRUCK is the head of the GNSS Technology and Navigation Group at DLR’s German Space Operations Center. He chairs the IGS Multi-GNSS Working Group and coordinates the MGEX Multi-GNSS Experiment.
CHRIS RIZOS is a professor at the University of New South Wales, Sydney, Australia; president of the International Association of Geodesy; co-chair of the Multi-GNSS Asia Steering Committee; and a member of the executive and governing board of the IGS.
ROBERT WEBER is an associate professor at the Department of Geodesy and Geoinformation, TU Vienna, and former chair of the IGS GNSS Working Group.
GEORG WEBER is the scientific director in the Department of Geodesy at the German Federal Agency for Cartography and Geodesy (BKG). He is a member of the IGS Real-time Working Group and the Radio Technical Commission for Maritime (RTCM) Services Special Committee (SC) 104 on Differential Global Navigation Satellite Systems (DGNSS).
RUTH NEILAN is the director of the Central Bureau of the IGS, vice-chair of the Global Geodetic Observing System Coordinating Board, and co-chair of Working Group D, Reference Frames, Timing and Applications, of the United Nation’s International Committee on GNSS.
URS HUGENTOBLER is a professor at the Institute of Astronomical and Physical Geodesy, TUM, Munich. He is the chair of the IGS Governing Board.
FURTHER READING
• The IGS MGEX Campaign
“The IGS MGEX Experiment as a Milestone for a Comprehensive Multi-GNSS Service” by C. Rizos, O. Montenbruck, R. Weber, G. Weber, R. Neilan, and U. Hugentobler in Proceedings of The Institute of Navigation 2013 Pacific PNT Meeting, Honolulu, Hawaii, April 23 –25, 2013, pp. 289–295.
“Multi–GNSS Working Group” by O. Montenbruck in International GNSS Service Technical Report 2012, edited by R. Dach and Y. Jean and published by the IGS Central Bureau, April 2013. Pp. 163–170.
“IGS M-GEX – The IGS Multi-GNSS Global Experiment” by R. Weber, U. Hugentobler, and R. Neilan in Proceedings of the 3rd International Colloquium on Scientific and Fundamental Aspects of the Galileo Programme, Copenhagen, 31 August – 2 September, 2011.
“Initial Assessment of the COMPASS/BeiDou-2 Regional Navigation Satellite System” by O. Montenbruck, A. Hauschild, P. Steigenberger, U. Hugentobler, P. Teunissen, and S. Nakamura in GPS Solutions, Vol. 17, No. 2, April 2013, pp. 211–222, doi: 10.1007/s10291-012-0272-x.
“Orbit and Clock Determination of QZS-1 Based on the CONGO Network” by P. Steigenberger, A. Hauschild, O. Montenbruck, C. Rodriguez-Solano, and U. Hugentobler in Navigation – Journal of The Institute of Navigation, Vol. 60, No. 1, Spring 2013, pp. 31–40.
• RTCM and NTRIP Formats
Differential GNSS (Global Navigation Satellite Systems) Services, Version 3, RTCM 10403.2, published by Radio Technical Commission for Maritime Services, Arlington, Virginia, February 1, 2013.
“The RTCM Multiple Signal Messages: A New Step in GNSS Data Standardization” by A. Boriskin, D. Kozlov, and G. Zyryanov in Proceedings of ION GNSS 2012, the 25th International Technical Meeting of The Satellite Division of the Institute of Navigation, Nashville, Tennessee, September 17–21, 2012, pp. 2947–2955.
“Networked Transport of RTCM via Internet Protocol (Ntrip) – IP-Streaming for Real-time GNSS Applications” by G. Weber, D. Dettmering, H. Gebhard, and R. Kalafus in Proceedings of ION GPS 2005, the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation, Long Beach, California, September 13–16, 2005, pp. 2243–2247.
GLONASS satellites 48, 49, and 50 are expected to launch at 02:38 UTC on July 2. Live launch coverage will be provided by TsENKI, the Center (for Operation) of Ground-based Space Infrastructure, starting at 01:00 UTC. Also, launch updates are available here.
