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.
In the photo above, deployment of the solar wings on the latest Galileo satellite is being checked at the European Space Agency’s technical hub in the Netherlands. The navigation satellite’s pair of 1 x 5-meter solar wings, carrying more than 2,500 gallium arsenide solar cells, will power the satellite during its 12-year working life.
With the first four Galileo In-Orbit Validation satellites already in orbit, this is the first of the rest of Europe’s satnav constellation.
A counterweighted rig supports the deployment; otherwise the delicate fold-out wings — designed for the weightlessness of space — would crumple under the pull of Earth gravity.
These Full Operational Capability satellites provide the same operational services as their predecessors, but they are built by a new industrial team: OHB in Bremen, Germany, built the satellites with Surrey Satellite Technology Ltd. in Guildford, UK, contributing the navigation payloads.
This satellite is the first of 22 ordered from OHB. It arrived at ESA’s ESTEC research and technical centre in Noordwijk in May to begin a rigorous campaign of testing in simulated launch and space conditions, guaranteeing its readiness for launch.
The first test performed on the satellite once it came out of its container was a System Compatibility Test Campaign, linking it up with the Galileo Control Centres in Germany and Italy and ground user receivers as if it was already in orbit.
Galileo’s wings with 30%-efficient solar cells were fitted at the end of June, supplied by Dutch Space in nearby Leiden. Future satellites will have their wings fitted at OHB before coming to ESTEC, but this first satellite offered an opportunity for Dutch Space engineers to train their OHB counterparts in the procedure.
“The 22 Galileo FOC satellites are being produced and tested on a batch production basis, which is a new way of working for ESA,” explained Jean-Claude Chiarini, overseeing FOC satellite procurement for the Agency. “The concept is really to set up a steady flow of satellites from OHB to ESTEC and then Kourou for launch over the next few years.
“The first four will undergo full validation testing, checking the underlying design is correct, in order to support the formal ground qualification of the design, with subsequent FOC satellites then going through acceptance testing, concentrating on checking workmanship,” Chiarini said.
The FOC satellites, while resembling their predecessors, are designed with this production concept in mind. Hinged modules offer easy access to internal subsystems for rapid repair or potential replacement of units.
The next satellite is due to arrive around the start of August. The battery of simulations includes vibration and acoustic testing, as well as thermal-vacuum testing — submitting them to the airlessness and temperature extremes of space for weeks at a time.
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.
The European Space Agency (ESA) has released detailed views of the next batch of Galileo satellites, the first of which cuurently performs under simulated space conditions at the ESTEC technical center in Noordwijk, the Netherlands.
The first Galileo Full Operational Capability (FOC) satellite is functionally identical to the four Galileo In-Orbit Validation satellites already in orbit, but has been built by a separate industrial team. All 22 FOC satellites so far procured by ESA have as prime contractor OHB in Bremen, Germany; Surrey Satellite Technology Ltd. in Guildford, UK, produces the navigation payloads. The photos shown here were taken at OHB.
The satellite’s body measures 2.5 x 1.2 x 1.1 meters (8.2 x 3.9 x 3.6 feet), and it weighs approximately 733 kilos (1,616 pounds). Atop it in these photographs (although on the underside when orbiting Earth) is the circular L-band antenna that will continuously broadcast navigation messages.
The smaller, hexagonal antenna beside it will pick up emergency messages from vessels in distress and relay location and other information to search and rescue authorities, contributing to the international Cospas–Sarsat system.
A second Galileo FOC satellite is due to also travel to ESTEC this summer, preparing for a launch later this year.
L-Band antenna of the FOC satellite. Photo: ESAemergency signal antenna of the FOC satellite. Photo: ESA
L2, L5 CNAV Testing
The U.S. Air Force Space Command began testing civil navigation (CNAV)capabilities on the GPS L2 and L5 signals on June 15 and was scheduled to continue until June 29. Civil users and manufacturers were invited to participate.
According to the GPS Directorate, the CNAV live-sky testing program will span several years and will evolve to support GPS enterprise and modernized civil navigation performance objectives. Objectives include:
◾ Verify and validate the CNAV requirements specified IS-GPS-200F and IS-GPS-705B.
◾ Facilitate the development of robust IS-compliant L2C and L5 civil receivers.
More information about the testing is available in a 52-page PDF, including sections on test strategy, event conditions and constraints, operational environment, test support resources and data collection, evaluation methodology, risk assessment, and reporting.
The L2 CNAV data is an upgraded version of the original NAV navigation message. It contains higher precision representation and nominally more accurate data than the NAV data. Two out of every four packets are ephemeris data and at least one of every four packets will include clock data, but the design allows for a wide variety of packets to be transmitted. Only a fraction of the available packet types have been defined; this enables the system to grow and incorporate advances.
One packet contains a GPS-to-GNSS time offset, enabling interoperability with other global time-transfer systems such as Galileo and GLONASS, both of which are supported. The extra bandwidth enables the inclusion of a packet for differential correction. Every packet contains an alert flag, to be set if the satellite data cannot be trusted. Users will know within six seconds if a satellite is no longer usable, important data for safety-of-life applications such as aviation.
The system is designed to support 63 satellites, compared with 32 in the L1 NAV message.
Possible New GPS Launch Option
The U.S. Air Force Space and Missile Systems Center (SMC) has signed a Cooperative Research and Development Agreement with Space Exploration Technologies Corp., better known as SpaceX, as part of the company’s effort to certify its Falcon 9 v1.1 Launch System for National Security Space (NSS) missions.
SMC and SpaceX will look at the Falcon’s flight history, vehicle design, reliability, safety systems, and other aspects. Once the evaluation is complete, the SMC commander will determine whether SpaceX has the capability to successfully launch NSS missions using the Falcon 9 v1.1.
Currently, United Launch Alliance’s Delta IV and Atlas V are the only certified launch vehicles capable of lifting NSS payloads — such as the GPS satellites — into orbit. The addition of multiple certified launch vehicles provides more options to place needed capabilities on orbit. While certification does not guarantee a contract award, it does enable a company to compete for launch contracts. Those contracts could be awarded as early as Fiscal Year 2015 with launch services provided as early as FY 2017.
GPS III Funds Cut, GPS IV on Horizon?
According to a U.S. Department of Defense (DoD) spending plan released on June 1, space programs were relatively protected in an environment of across-the-board budget cuts known as sequestration. Specifically, although the budget for GPS III has been reduced for both 2013 and 2014, the reductions still allow the proposed program to stay on course. The cuts amount to about $58 million from GPS III and its associated ground system.
Congressional lawmakers proposed spending $77 million less next year for the GPS III satellite and ground systems than proposed by the Air Force, which asked for nearly $1.1 billion.
Currently, the Air Force has eight GPS III satellites contracted with Lockheed Martin Space Systems, and current plans call for the purchase of 12 further satellites with improved capabilities.
GPS IV. Gen. William Shelton, commander of Air Force Space Command, floated the possibility of a new look for the constellation on Capitol Hill. In an April 25 House hearing, Shelton said the Air Force will study this fall whether to buy another 12 GPS III craft or move on to a new generation of satellites.
“Would it be better to continue [GPS III] as opposed to starting a whole new fourth generation?” asked Representative Doug Lamborn of Colorado. “That’s the decision we will have to make in the fall,” replied Shelton. “It seems like the answer would be ‘yes’ but we will study that.”
A key aspect of the next-next gen satellite would have to be dual-launch capability. The reduction in expense this would furnish is in higher and higher demand as time goes by. Both Lockheed and Boeing are reportedly in talks with the Air Force regarding IV.
System Briefs
GLONASS Embezzle Imbroglio. The Russian Federal Security Service is investigating the embezzlement of billions of rubles from the construction of the GLONASS center in Korolyov, a town outside Moscow, as reported by Izvestia.
Construction of the GLONASS control and support center began in June 2010 on the site used by TsNIImash, the head research company of Russia’s federal space agency. The center was supposed to hold equipment for collecting and processing the data supplied by the GLONASS global network.
The construction was financed by a federal program, with 1.050 billion ($33.22 million) allocated for the project. By the end of 2010, it came to light that construction costs had been overstated, Izvestia reports. An expert appraisal revealed that the contractor had rigged the costs. The government did not allocate additional funds, so construction was suspended in December 2011 when the Federal GLONASS Program for 2002-–2011 ended. The construction of the building has never been completed.
In November 2012, the general designer of GLONASS, Yuri Urlichich, was dismissed from his post as a result of the scandal.
IRNSS Nav Center, July Launch. The Indian Space Research Organization (ISRO) Navigation Centre for the Indian Regional Navigation Satellite System (IRNSS) was inaugurated May 28, at the Deep Space Network complex at Byalalu, near Bangalore, India.
IRNSS, an independent navigation satellite system being developed by India, will have a constellation of seven satellites in geostationary and inclined geosynchronous orbits. IRNSS coverage will extend over India and the southeast Asia region. The ISRO Navigation Centre (INC) is responsible for providing the time reference, generation of navigation messages, and monitoring and control of ground facilities including ranging stations of IRNSS. IRNSS will establish a network of 21 ranging stations geographically distributed primarily across India to provide data for the orbit determination of IRNSS satellites and monitoring of the navigation signals.
On June 15, India’s Economic Times reported that a new launch date (postponed from previously announced June 11) was set for IRNSS-R1A or 1A, the first IRNSS satellite: July 1 at 18:13 UTC.
Beidou Jammed. A Beidou satellite is now believed to have experienced interference from a complex electromagnetic environment, which cut off signal transmissions in 2007, China’s People’s Daily reported. A team of scientists was able to overcome the interference issue in less than three months by 2008.
Wang Feixue, a scientist specializing in the Beidou navigation system and a senior colonel in the People’s Liberation Army said, “Had they not been able to recover the signal within three months, future satellite launches would have been indefinitely delayed. And satellites already launched would have been put out of operation.”
EGNOS Contract. A new European Geostationary Navigation Overlay Service (EGNOS) service provision contract was signed June 26 at the European Commission Vice President Antonio Tajani’s office in Brussels. The contractee is again the European Satellite Services Provider (ESSP), founded in 2001and in 2008 transformed into ESSP SAS and moved from Brussels to Toulouse.
Its shareholders are seven European air navigation service providers: Aeropuertos Espanoles y Navegacion Aerea (Spain), Deutsche Flugsicherung GmbH (Germany), Direction générale de l’Aviation civile (France), Ente Nazionale Di Assistenza Al Volo (Italy), National Air Traffic Services (UK), Navegação Aérea de Portugal, and Skyguide (Switzerland).
QinetiQ and Septentrio jointly announced today that a milestone in the Galileo European Navigation Satellite System’s development and deployment program has been achieved. On March 12, staff at the European Space Agency at ESTEC, Noordwijk, The Netherlands, achieved the first navigation solution using only the encrypted Galileo Public Regulated Service (PRS) signals broadcast by the four Galileo In-Orbit Validation (IOV) satellites launched in 2011 and 2012. Septentrio and QinetiQ, working in close partnership, developed one of the two PRS test user receivers used in this historic first test.
PRS positioning was achieved using the Galileo PRS Test User Receiver (TUR-P) jointly developed by Septentrio and QinetiQ under an ESA contract. For the reception test, the receiver was installed in the PRS test facility in ESTEC and operated by technical experts from ESA. Positioning accuracy of ~10 meters was achieved, excellent for a first test so early in the system’s deployment. The TUR-P now continues to be used as part of the campaigns running during the Galileo In Orbit Validation Phase.
This milestone builds on a number of previous major Septentrio/QinetiQ achievements including:
First laboratory demonstration of the PRS signal acquisition and tracking in QinetiQ (Malvern, UK, 2006).
Successful RF compatibility test between a Galileo payload and the TUR-P (Portsmouth, UK, 2010).
Successful Galileo end-to-end system test including the Galileo Ground Mission Segment (GMS) and its key management facilities, satellite and TUR- P (Rome, Italy, 2011).
First successful reception and processing of the PRS signal from space (Fucino, Italy, 2012).
As key, long-term contributors to the Galileo program, Septentrio and QinetiQ have worked closely with ESA, the European GNSS Agency (GSA) and European industrial partners since 2003.
“Following last year’s first successful reception and processing of PRS signals from Galileo satellites, I am very pleased to see the program moving forward successfully,” said Leo Quinn, CEO of QinetiQ. “Achieving a first PRS-only Galileo navigation solution is a major achievement. With positioning, navigation and timing services increasingly critical to the safety, security and economic activity of UK and our European neighbours QinetiQ are very proud to be contributing to the development of Europe’s first secured satellite navigation services.
“This milestone is another important step towards the launch of operational Galileo services and will continue to build confidence in both prospective users and the industrial supply base. It showcases QinetiQ’s capabilities in this field and signals the way towards the production of exciting new solutions for critical navigation and timing applications.”
“Today, together with our partners, we take another decisive step in the early availability of commercial PRS receivers and Septentrio is extremely proud of this historic milestone for the Galileo program,” commented Peter Grognard, Septentrio’s founder and CEO. “This builds on a list of major achievements for Septentrio since the reception of the first Galileo signal from space in 2006. We are delighted to continue the excellent collaboration with ESA and to contribute to this ambitious European project.”
Averna, developer of test solutions and services for communications and electronics device makers worldwide, announced today that the European Space Agency (ESA) has selected Averna’s Record & Playback solution for signal analysis and monitoring of Galileo satellites.
The R&P platform selected by ESA features the RP-5300, a compact 2-channel wideband RF recorder designed to record live RF signals in the field, and the URT-2200 RF Player for GNSS. Averna’s R&P solution is powered by RF Studio, a high-performance RF recorder and playback software specifically designed for RF designers and researchers, to facilitate recording, analysis and storage of RF signals.
The Averna RP-5300 RF Recorder is specifically adapted for all GNSS applications, including Galileo, GPS, GLONASS, and Compass (BeiDou-2). The system has two 50-MHz wide channels that can be tuned on any frequencies from 330 MHz to 2500 MHz. To address the many synchronization and coherency challenges of GNSS testing, Averna has developed a proprietary software/hardware architecture that allows control and tight synchronization between multiple recording channels and systems under the 1 nanosecond (ns) level.
“Averna’s RP-5300 is the leading commercial product offering two 50-MHz wide channels that can capture such a wide range of real-world RF signals, complete with the interference and general degradation that end-users will experience. Two units can even be interconnected to enable a 4-channel, phase-coherent synchronized recorder,” commented Brendan Wolfe, director of Market Development for Averna. “The ESA is using the latest technology available and we are thrilled that our products have been chosen for this important undertaking.”
“Averna’s advanced record-and-playback systems support our pressing needs for long and extensive data-collection campaigns in the field,” said M. Crisci, Head of the Radio Navigation Systems and Techniques Section at the European Space Agency. “Averna’s R&P solution enables us to record multiple wideband signals at the same time, over a wide frequency range, and then replay the signals repeatedly. As receivers become more and more sophisticated, it is imperative that real-world signals and conditions be recreated for thorough validation and testing.”
Galileo is Europe’s program for a global navigation satellite system (GNSS), providing a highly accurate, guaranteed global positioning service, interoperable with the U.S. GPS and Russian GLONASS systems. It currently has four satellites in service and upon completion it will consist of 30 satellites and ground infrastructure. The Galileo system is a collaboration between the European Union and the ESA.
Recently released views of the next two Galileo satellites in the European Space Agency’s testing lab, along with dual-launch rumblings from the U.S. Air Force and Lockheed Martin, occasion this story about two birds with one drone. That is, an unmanned autonomous vehicle bound for the exosphere. The rest of the GNSS world is on board with this topic; isn’t it about time GPS caught up?
The first two Galileo Full Operational Capability (FOC) satellites will launch as a pair, earlier advertised as a September blast, now possibly delayed until December; a second dynamic duo will follow sometime thereafter. Then two again, and two, and two, until the Ariane 5 rocket launches four at once. Four!
The latest official U.S. Air Force plans say that by the ninth GPS III satellite (SV-09), the program plans to initiate programmatic and hardware changes to allow for the first-ever GPS dual launch. The motive, of course, is cost savings. The GPS program (probably) has no need to hurry, as other GNSSes do, in order to have a full constellation operative broadcasting — previous predictions about constellation gaps notwithstanding.
Even with dual launch, according to Lockheed Martin Navigation Systems vice president Keoki Jackson (and here I am drawing from Don Jewell’s Space Symposium column), from SV-09 forward the savings will only amount to about $70 million per launch, because it will require a larger launch vehicle.
Only $70 million. Well, to quote Senator Everett Dirksen, adjusting for inflation, “$70 million here, $70 million there, pretty soon, you’re talking real money.”
Take this all in the context of GPS III having reached the point that it will cost nearly $450 million to place a single GPS space vehicle and payload in orbit.
Rising costs and the possibility to combat them with dual launches constitute at least one of the driving forces behind the NavSat or NibbleSat drawing-board concept: a small GPS satellite, without the burden of other non-nav payloads.
Coincidentally, an initiative underway seeks to evaluate “new launch entrants,” according to General Willie Shelton, commander, Air Force Space Command. “If a new entrant can come in and provide a cost-effective launch capability for several launches, then we will look seriously at them as well,” he told Don Jewell in an interview nearly a year ago.
Jewell: “Why don’t we move into the arena of trying to pin down a vehicle or set of vehicles for dual launch? You and I once discussed GPS III vehicles 7-8 for that honor, and you mentioned at the time that it was a moving target. Where do we stand today?
General Shelton: Don, I think we are now probably talking about GPS III vehicles 9-10. We are still in the study phase on this issue with Lockheed Martin and United Launch Alliance. We are still trying to figure out how we would do dual launch and what kind of capabilities we need to develop. I think this is really the wave of the future…being able to put two up simultaneously will save us a lot in launch costs.”
In April of this year, John Frye, Lockheed Martin’s GPS III capability and affordability insertion manager, reiterated, in comments regarding the Delta Preliminary Design Review (dPDR) for the GPS III satellite, “The design modifications from this dPDR address ways to further reduce Air Force launch costs by $50 million per satellite through dual launch of two GPS III space vehicles on a single booster. This successful dPDR milestone sets the stage to proceed with SV09 design maturation.”
Rockets. Recently, the U.S. Air Force Space and Missile Systems Center (SMC) signed a Cooperative Research and Development Agreement (CRADA) with Space Exploration Technologies Corp., better known as SpaceX, as part of the company’s effort to certify its Falcon 9 v1.1 launch system for National Security Space (NSS) missions.
SMC and SpaceX will look at the Falcon’s flight history, vehicle design, reliability, safety systems, and other aspects. Once the evaluation is complete, the SMC commander will determine whether SpaceX has the capability to successfully launch NSS missions using the Falcon 9 v1.1.
Currently, United Launch Alliance’s Delta IV and Atlas V are the only certified launch vehicles capable of lifting NSS payloads — such as the GPS satellites — into orbit.
The Falcon CRADA may be a preliminary, tentative move towards dual-launch capability. Consider:
An earlier iteration, Falcon 9, can reportedly lift payloads of 4,850 kilograms (10,700 lb) to geostationary transfer orbit (GTO). The Falcon 9 v1.1— subject of the CRADA and scheduled for first flight in mid-2013—will use a longer first stage powered by nine Merlin 1D engines arranged in an octagonal pattern. Development testing of the v1.1 Falcon 9 first stage was just completed in June. These improvements will increase the payload capability by nearly 50 percent. The new first stage can also be used as side boosters on Falcon Heavy, which reportedly will have a capability of lifting 12,000 kg (26,000 lb) to GTO.
According to an Air Force fact sheet, the GPS III satellite has a launch weight of 8,115 lb.
The Atlas V 401 rocket, most recently used to launch the GPS IIF-4 satellite in May, has a GTO launch capability of 4,750 kg. (10,472 lb.) A steroid version of the Delta IV, the Delta IV Heavy, has a GTO launch capability of 13,130 kg (28,950 lb), more than any other currently available launch vehicle. It also carries a more substantial price tag.
To sum up these various vectors pointing largely in the same direction, GPS has a potential in the somewhat near-mid distant future of going to dual launch.
Meanwhile, this has been fait accompli for the other GNSSes.
Galileo
The first two in-orbit validation (IOV) satellites built by Astrium traveled aloft together in October 2011, as did the third and fourth IOV satellites in October 2012.
According Paul Flament, European Commission Programme Manager and Head of the EU Satellite Navigation Programme Unit, in an interview earlier this year with GPS World, “Satellites 5 and 6 will be launched in September of this year, aboard a Soyuz launcher from Kourou, and numbers 7 and 8 will follow in December.” These launches may since have been re-adjusted to later dates, respectively.
“Then, in 2013 we will see three Soyuz launches of two satellites each. We do not have the precise launch dates yet, but they are likely to be in April, June, and September. In December 2014, we expect to have the first launch using the Ariane 5 launcher, which is capable of deploying four satellites in one go. This means that by the end of 2014 Galileo will have deployed 18 satellites in orbit.
“In 2015, there will be two Ariane 5 launches, one in the middle of the year, one at the end, each carrying four satellites.”
GLONASS
Within days, perhaps, three GLONASS-M satellites will blast off together from Baikonur: GLONASS 48, 49, 50. This is only the latest of GLONASS triple launches.
As Richard Langley is my witness, the Russians accomplished a GLONASS hat-trick as long ago as September 1986! The first in a more recent series of triplets, in December 2010, failed rather spectacularly and cost Russia an estimate 5 billion roubles ($160 million), setting back GLONASS by six months. The system has since intermingled single- and triple-satellite launches.
Compass
China has demonstrated success with two dual launches of mid-Earth orbit satellites, among its constellation lodged at varied heights. Compass-M3 and Compass-M4 rose together in April 2012, as did M5 and M6 in September of that year.
The European Space Agency (ESA) has released a series of photos providing the first detailed views of the next batch of Galileo satellites, the first of which has already been delivered to ESA for rigorous testing in simulated space conditions. Scroll down to see the photos.
The first Galileo Full Operational Capability (FOC) satellite was delivered to ESA’s ESTEC technical centre in Noordwijk, the Netherlands, on May 15. It is being prepared for testing in the ESTEC Test Centre, a unique facility for Europe with all the facilities needed to validate a satellite for launch under one roof.
This initial FOC satellite is functionally identical to the first four Galileo In-Orbit Validation satellites already in orbit, the operational nucleus of the full Galileo constellation, but has been built by a separate industrial team.
Like all the other 21 FOC satellites so far procured by ESA, the satellite’s prime contractor is OHB in Bremen, Germany, and the navigation payload was produced by Surrey Satellite Technology Ltd. in Guildford, UK. The photos shown here were taken at OHB.
The satellite is approximately the size and shape of an old-fashioned telephone booth, dominated by its circular L-band antenna that will continuously broadcast navigation messages down to Earth.
The smaller, hexagonal antenna beside it will perform a no less vital task — picking up emergency messages from vessels in distress to relay to search and rescue authorities, contributing to the international Cospas–Sarsat system.
A second Galileo FOC satellite is due to join its predecessor at ESTEC later this summer, preparing for a launch scheduled for later this year.
Galileo FOC: These pictures give the first detailed views of the next batch of Galileo satellites, the first of which has already been delivered to ESA for rigorous testing in simulated space conditions. Credit: OHB
Galileo FOC main antenna: Galileo FOC is dominated by its circular L-band antenna that will continuously broadcast navigation messages down to Earth. Credit: OHB
The Galileo FOC satellite is approximately the size and shape of an old-fashioned telephone booth, similar to the preceding IOV design. Credit: OHB
Galileo FOC search and rescue antenna: Galileo’s smaller, hexagonal antenna beside its main navigation antenna is designed to pick up emergency messages from vessels in distress to relay to search and rescue authorities, contributing to the international Cospas–Sarsat system. Credit: OHB
Gaileo Full Operational Capability satellites in orbit – the second batch of Galileo satellites. These FOC satellites follow on from the initial four Galileo In-Orbit Validation satellites, the first two of which went into orbit on 21 October 2011 with the remaining two joining them on 12 October 2012. As prime contractor for the FOC satellites, OHB is responsible for developing the satellite platform and integrating the satellite with its payload – the part of the satellite that provides Galileo’s precision positioning measurements and services to users worldwide – developed at Surrey Satellite Technology Ltd in Guildford, UK (also providing assistance to OHB with final satellite assembly). Credit: OHB
Galileo FOC satellite does same work as the IOV predecessor. The ‘business end’ of the Galileo FOC satellite hosts the L-band navigation antenna and the smaller search and rescue antenna on the same face. This initial FOC satellite is functionally identical to the first four Galileo In-Orbit Validation satellites already in orbit, the operational nucleus of the full Galileo constellation, but has been built by a separate industrial team. Like all the other 21 FOC satellites so far procured by ESA, the satellite’s prime contractor is OHB in Bremen, Germany and the navigation payload was produced by Surrey Satellite Technology Ltd in Guildford, UK. Credit: OHB
Tallysman Wireless announces the TW4421 and TW1421 antennas, which offer a step forward in performance for small GNSS antennas, the company said.
The TW4421 is a low-cost dual-feed magnetic mount antenna covering the GPS L1, GLONASS L1, Galileo and SBAS (WAAS, EGNOS & MSAS) frequency band (1574 to 1606 MHz). The TW4421 features a 25-millimeter dual-feed wideband patch element that provides excellent multipath rejection with a more linear carrier phase response, by virtue of a low axial ratio across the full frequency bandwidth, Tallysman said. It is especially suitable for high accuracy applications, and also offers high out-of-band signal rejection.
The TW4421 is housed in a compact IP67 magnetic mount enclosure and is available with a wide range of connector options.
The TW1421 embedded antenna is lightweight (30 gm) and features a very small footprint (35 mm diameter x 7.25 mm). The TW1421 is suited for use in applications where performance and small size are of paramount importance, such as extreme-sport-wearable tracking devices and UAVs.
“Most small low-cost GPS/GLONASS/Galileo antennas are narrow-band devices with an elliptically polarized response at the GPS and GLONASS frequencies,” said Gyles Panther CEO of Tallysman Wireless. “The TW4421/1421 antennas feature a 40-percent wider bandwidth patch, with a dual-feed structure, which provides unparalleled multipath rejection previously only available in much larger, more expensive antennas.”
In the early hours of May 15, Galileo’s first full operational capability (FOC) satellite left manufacturer OHB System AG’s integration hall in Bremen, Germany, after successfully completing integration and system testing. Later that same day, it arrived by road at the European Space Agency’s (ESA’s) technical center at Noordwijk in the Netherlands for a rigorous set of tests to check its readiness for launch. The tests will simulate different aspects of launch and space environment. The comprehensive test program will validate the new design and all the FOC satellites to follow.
This first FOC satellite is functionally identical to the first four in-orbit validation (IOV) satellites already in orbit, but has been built by a separate industrial team. Like the other 21 FOC satellites so far procured by ESA, the satellite’s prime contractor is OHB System AG, and the navigation payload was produced by Surrey Satellite Technology Ltd. in Guildford, UK.
Thermal vacuum testing at the European Space Research and Technology Centre (ESTEC) will simulate temperature extremes the satellites must endure in the airlessness of space throughout their 12-year working lifetimes. Without any moderating atmosphere, temperatures can shift hundreds of degrees from sunlight to shadow.
Other activities on the schedule include shaker and acoustic noise testing — simulating the vibration and noise of launch — as well as electromagnetic compatibility and antenna testing, placing the satellite in chambers shielded from all external radio signals to reproduce infinite space and check that its various antennas and electrical systems are interoperable without harmful interference.
“The Galileo FOC satellites provide the same capabilities as the previous IOV satellites, but with improved performance, such as higher transmit power,” explained Giuliano Gatti, the head of the Galileo Space Segment Procurement Office. “They are to all intents a new design that requires a full checkout before getting the green light for launch.”
The second FOC flight model is due to arrive at ESTEC in early June, and the third in the middle of July. The first two satellites are to be placed in orbit on board a Soyuz launcher, with a scheduled lift-off from Kourou in French Guyana this fall, with two more due to follow by the end of the year.
The first four Galileo IOV satellites, launched in 2011 and 2012, were provided by EADS Astrium with Thales Alenia Space Italy responsible for integrating the satellites and Astrium in Portsmouth, UK, providing the navigation payloads. They provided their first navigation fix in March 2013.
The definition, development and in-orbit validation phases of the Galileo programme are being carried out by ESA and co-funded with the European Commission (EC).
The subsequent FOC phase is managed and funded by the EC. The commission has delegated the role of design and procurement agent to ESA for the FOC phase. At the same time as the satellites are being assembled on a production-line basis, ground stations are also being established on European territories around the globe.
Photo credit: Pat Corkery, United Launch Alliance.
GPS Leaves This Earth
A t 5:38 p.m. Eastern Daylight Time (21:38 UTC) on May 15, the fourth GPS IIF satellite, Space Vehicle Number (SVN) 66 built by Boeing, ascended towards orbit aboard a United Launch Alliance Atlas V rocket at from Cape Canaveral Air Force Station, Florida.
“The GPS constellation remains healthy and continues to meet and exceed the performance standards to which the satellites were built. Our goal is to deliver sustained, reliable GPS capabilities to America’s warfighters, our allies, and civil users around the world, and this is done by maintaining GPS performance, fielding new capabilities and developing more robust modernized capabilities for the future,” said Colonel Bernie Gruber, director of the U.S. Air Force Space and Missile Systems Center’s GPS Directorate.
The new capabilities of the IIF satellites will provide greater navigational accuracy through improvements in atomic clock technology; a more robust signal for commercial aviation and safety-of-life applications, known as the new third civil signal (L5); and a 12-year design life providing long-term service. These upgrades deliver improved anti-jam capabilities for warfighters and improved security for military and civil users around the world, the Air Force said in a statement.
The IIF-4 satellite is expected to complete testing in August, after which it will be utilized as a reserve or backup satellite. It becomes the fourth satellite in a 12-strong network of GPS IIF spacecraft manufactured by Boeing as lead contractor, the first of which was boosted into orbit in May 2010. The Air Force expects the first of the next-generation GPS IIIA satellites to enter service sometime in 2014.
System Briefs
GLONASS. The GLONASS 747 M-series satellite launched on April 26 has maneuvered into an orbital slot near GLONASS 728, the operational satellite in Plane 1, slot 2. 747 will presumably serve as a reserve until it replaces 728, unless another Plane 1 satellite expires first. The next Russian launch, a GLONASS-M trio, is scheduled for July 1. There are currently 24 operational GLONASS satellites.
IRNSS. The first Indian Regional Navigation Satellite System satellite is expected to rise at the end of June. The IRNSS plans to orbit of seven: three geostationary and four geosynchronous, providing regional coverage via navigation signals in the L5 and S bands.
The first four Galileo satellites used for in-orbit validation were launched in October 2011 and October 2012.They are now transmitting their signals on an operational basis. Thanks to the simultaneous use of these four satellites, the European Space Agency was able to compute the first autonomous Galileo-only fix using broadcast ephemerides in March 2013.
Using data from the real-time service of the International GNSS Service (as supported by the Multi-GNSS Experiment), real-time protocols and new high-precision multiple signal messages and a new generation multi-constellation network of GNSS stations, the Centre National d’Etudes Spatiales (CNES) has been able for the first time to compute decimeter-accuracy Galileo orbits in real time.
The networks used in this work include the CNES/Institut Géographique National REGINA (REseau Gnss pour l’Igs et la NAvigation) network and the Deutsches Zentrum für Luft- und Raumfahrt (DLR) and associated organizations CONGO (COoperative Network for GNSS Observation) network (real-time access courtesy of Oliver Montenbruck). The filter used for the multi-constellation real-time orbit determination is a CNES proprietary tool based on a Kalman filter.
The CNES orbits have been compared to an accurate reference orbit computed by Technical University München (TUM) as part of the MGEX project. The following figure shows the 3D orbit differences for the two solutions (for the ProtoFlight Model (PFM) and Flight Model 2 (FM2) satellites), over the 10 days of the experiment. Excluding the first day during which the filter converges, the 3D root-mean-square orbit difference is about 15 centimeters. This demonstrates the feasibility of accurate real-time Galileo solutions using currently available networks and software tools.
The fourth International Colloquium on Scientific and Fundamental Aspects of the Galileo Programme will be held in Prague, Czech Republic, December 4–6.
Since 2007, the worldwide scientific community has met every two years to discuss the possibilities for boosting the scientific use of Galileo and for contributing to the development of the GNSS.
The event is always organized in one of the 20 European Space Agency’s Member States, and makes an essential contribution to ESA’s implementation and definition of the evolution of the European GNSS. The gathering of major academic players provides a scientific reference for institutional executives and industry, as well as offering a unique platform for promoting innovative GNSS initiatives at large.
The colloquium focuses on four major areas of research:
Scientific applications in meteorology, geodesy, geophysics, space physics, oceanography, land surface and ecosystem studies, using either direct or reflected signals, differential measurements, phase measurements, radio occultation measurements, using receivers placed on the ground, in aircraft or on satellites.
Scientific developments in physics, dealing with future GNSS, particularly in testing fundamental laws in astronomy and in quantum communication. Relativistic reference frames and relativistic positioning will be addressed.
Aspects of metrology such as reference frames, onboard and ground clocks, and precise orbit determination.
Scientific aspects of satellite navigation and positioning such as signal propagation, tropospheric and ionospheric corrections and the means to model and mitigate multipath and interference.
The various possibilities to use navigation satellites such as Galileo for scientific purposes will be reviewed and the use of scientific applications to contribute to make the most of the present systems and define their evolution will be scrutinized.
The conference is being organized as a series of plenary talks and two parallel half-day sessions.
Online submission of abstracts is open until June 14 through the colloquium website, where other detailed information is also available.
QinetiQ
