The different space weather phenomena. (Image: UK Department for Business Innovation & Skills)
A “Space Weather Preparedness Strategy” has been issued by the government of the United Kingdom. The document sets out the nature of the risk to the UK from severe space weather, as well as progress made to prepare for the risk and priorities for future work.
Responsibility for managing the risk passed from the Cabinet Office to the Department for Business, Innovation and Skills in 2015.
The strategy — produced for government and local responders to guide preparedness — has been shared with international, industry and academic stakeholders. It is an updated version of the “Space Weather Preparedness Strategy” produced in July 2014.
The UK approach to space weather preparedness is underpinned by three elements: designing mitigation into infrastructure where possible; developing the ability to provide alerts and warnings of space weather and its potential impacts; and having in place plans to respond to severe events.
“The main challenge we face is that awareness of the risk is low,” reads the report’s executive summary. “Much more needs to be done to encourage potentially vulnerable sectors to adopt measures to mitigate the likely impacts.”
Space weather, resulting from solar activity, can produce X-rays, high energy particles and coronal mass ejections of plasma. According to the executive summary, “Where such activity is directed towards Earth there is the potential to cause wide-ranging impacts. These include power loss, aviation disruption, communication loss, and disturbance to (or loss) of satellite systems. This includes GNSSs, on which a range of technologies depend for navigation or timing.”
GPS World reported on Richard Langley’s ionospheric research project in the March issue. Langley manages the CANSPACE Listserv, which includes frequent updates about ionospheric events.
The sun has an 11-year cycle of activity, with the current cycle peaking in early 2014. (Image: UK Department for Business Innovation & Skills)
Shortly after the Galileo satellite using the E24 PRN code started transmitting, its sibling began transmitting using code E30. Several stations participating in the International GNSS Service Multi-GNSS Experiment are tracking the new satellites.
Prof. René Warnant from the University of Liege has reported that as of 10 October, their PolaRx4 and PolaRxS receivers (but not yet NetR9 receivers) are tracking one of the new Galileo satellites using code E24.
Meanwhile, the latest BeiDou satellite, BeiDou I2-S, appears to have reached its orbital slot with a nominal nodal longitude of 95 degrees east.
All seven satellites of Indian Regional Navigation Satellite System (IRNSS) are expected to be in orbit by March 2016, reports New Delhi Television, citing Indian Space Research Organisation (ISRO) Chairman Kiran Kumar.
“We expect by March 2016 all the seven constellation of IRNSS to be in orbit,” Kumar said.
Four IRNSS satellites are now in orbit, with three remaining to complete the system. The next IRNSS satellite, 1E, is scheduled for launch in November, and 1F is set for launch in December.
Also, the GSAT-15 satellite, which has a GAGAN payload, will be launched on Nov. 10.
Kumar made his comments after inaugurating GNSS User Meet 2015 at the ISRO Satellite Centre (ISAC) in Bengaluru, India. The event was jointly organized by ISRO and Airports Authority of India (AAI).
Proposed GNSS Navigation Messages for Improved Performance
By Wentao Zhang and Yang Gao
INNOVATION INSIGHTS by Richard Langley
TIME-TO-FIRST-FIX, commonly known by the initialism TTFF, is the elapsed time between the powering on or starting up of a GNSS receiver and when it successfully computes either a two-dimensional (height constrained) or three-dimensional position fix and sets its clock to the correct time. A three-dimensional fix requires simultaneous receiver measurements on the signals from a minimum of four satellites along with the satellites’ positions (ephemerides) and the offsets between the individual satellite clocks and the GNSS system time.
TTFF depends crucially on the availability and timeliness of the satellite ephemerides and clock information when a receiver starts up and, accordingly, there are three types of start-up with correspondingly different TTFF.
A cold start (sometimes also called a factory start) occurs when the receiver has no knowledge of its current position, time or the positions of the satellites and their clock offsets. The receiver must do a blind search of the sky trying different possible Doppler frequency shifts and pseudorange delays for all the satellites in the constellation. Once satellites are found and tracked, the ephemerides and clock information must be collected. This is repeated in each satellite’s navigation message every 30 seconds. In addition, the information on the offset between GNSS system time and UTC must be collected along with the ionospheric delay correction parameters and the almanac (an approximate ephemeris for all active satellites in the constellation) to be used for faster subsequent signal acquisition. This data is only transmitted once in the 12.5-minute-long navigation message. Therefore, the TTFF for a cold start can take up to 12.5 minutes and even longer especially if the GNSS signals are hard to acquire such as in obstructed environments.
A warm start, or what we might call normal operation, occurs when the receiver has some a priori information on its position, the time and the approximate locations of the satellites. Typically, this means knowing the receiver position to within a few hundred kilometers, time to within 10 minutes or so, and a reasonably fresh almanac. Armed with that information, a receiver knows which satellites should be visible to it and can quickly acquire and track satellite signals and obtain the satellite ephemeris and clock information. Since that information is repeated every 30 seconds, TTFF for a warm start can be 30 seconds or less.
A hot start occurs when a receiver is powered on after being off and stationary for a short interval and it therefore has a very good estimate of its position and the current time and valid satellite ephemeris and clock data. TTFF for a hot start, therefore, is typically only a few seconds. This mode of receiver operation would also apply to scenarios where all signals are temporarily lost in road or rail tunnels or where a number of signals are momentarily blocked by obstructions causing a break in position fixing.
Fast first fixes were traditionally only possible when a receiver had a clear view of the sky and could readily acquire the navigation messages. Pseudorange measurements can be made, however, even if satellite signals are somewhat attenuated in strength to the point that navigation messages cannot be acquired. Position fixing in this case would be possible if the receiver could obtain the navigation information from elsewhere. Over the past decade or so, assisted GNSS techniques have been developed to provide frequently refreshed navigation information over cellular telephone networks, for example. But would there be a way to achieve fast first fixes autonomously without reliance on these assisted techniques? Not with the signals presently being transmitted by either the mature or nascent constellations, it seems, but in this month’s column, we look at proposed changes to the way navigation messages are formulated that could result in a future satellite navigation system providing faster fixes effectively giving receivers higher sensitivity and stronger performance.
“Innovation” is a regular feature that discusses advances in GPS technology and its 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. Email him at lang @ unb.ca.
Despite some differences in their structures, different GNSS broadcast navigation (NAV) messages usually consist of two parts: immediate (primarily ephemeris) and non-immediate (primarily almanac) data. The immediate data is repeated at a much shorter interval than the non-immediate data, and expires much sooner than the non-immediate data. Taking GPS as an example, the civilian navigation (CNAV) messages consist of five subframes with each lasting six seconds, as depicted in FIGURE 1. The first three subframes provide the ephemeris, with the content repeated every 30 seconds and updated every two hours, while the last two subframes provide the almanac for each satellite in 25 pages, with the content updated nominally every six days (according to the GPS Interface Specifications document), but updates are actually daily.
FIGURE 1. Frame structure of GPS CNAV messages.
Depending on the accuracy of receiver time and the availability of previously collected ephemerides (the immediate data) when powered on, GNSS user equipment (UE) might experience cold, warm or hot starts, among which the warm start is the most common case. In the widely accepted definition for warm start, no valid ephemeris is available, but the receiver time is roughly known at startup.
As depicted in FIGURE 2, the position fix sequence by a standalone GNSS UE normally consists of signal acquisition, tracking, bit synchronization, frame synchronization, ephemeris downloading, measurements taking and position computation. In performing a regular warm start, signal acquisition usually takes only a few hundred milliseconds for a GPS device in open-sky environments. However, under weak signal conditions, signal acquisition might take much longer (say a few tens of seconds). Once the signal is acquired, the tracking loop is activated, and immediately after the signal is pulled in the process of data-bit synchronization is started. This process takes a few hundred milliseconds to several seconds depending on signal strength and algorithm efficiency. In a stable tracking status, the navigation bits are collected sequentially one by one. Collecting a complete copy of a GPS ephemeris takes about 18 seconds in open-sky environments but may take minutes or even forever in weak signal environments due to an increased bit error rate (BER). As soon as the ephemeris downloading from three to four satellites is completed and the measurements are made, the user position fix usually can be obtained immediately. Therefore, in weak signal environments, the obstacles to fast time-to-first-fix (TTFF) are primarily signal acquisition and ephemeris downloading, and in open-sky environments the obstacle mainly lies in the time needed for ephemeris downloading.
FIGURE 2. Typical sequence of position fix process in standalone GPS user equipment (Msr=measurements).
For a GNSS UE in an open-sky environment on the Earth’s surface, the minimum received signal level for GPS L1 is around -130 dBm according to the interface specifications. For other GNSS signals, the nominal received signal levels are approximately the same.
However, in some extreme cases, such as urban canyon, foliage and indoor environments, the signals finally arriving at a receiver’s antenna could be heavily attenuated by 30 dB or even more. Working under such conditions requires GNSS UE to have high-sensitivity capability.
When the GNSS signal strength drops to a certain level, it causes immediate difficulties in the GNSS receiver tracking loop and for ephemeris downloading. Firstly, the parameters of the tracking loop, designed for normal signal strengths, are no longer optimum for either obtaining enough gain for signal detection or for maintaining signal tracking. Secondly, BER increases with decreasing signal strength. When the signal carrier-to-noise-density ratio drops below 27 dB-Hz, even if signal tracking is maintained, the increased BER would make it difficult for successful decoding of NAV messages.
Sensitivity improvements for a GNSS receiver can involve contributions from the antenna, the RF front end and baseband signal processing. In the signal processing, to obtain adequate processing gain in signal-to-noise ratio for signal detection, combined coherent and non-coherent integrations are needed. An approximate relationship for calculating such processing gain is given in Equation (1). Considering that non-coherent integration is subject to squaring loss, for a fixed total integration period (TI), increasing the coherent period (Tc) is more efficient for achieving higher processing gain. However, without knowing the navigation bits, the coherent integration is limited within a 1-bit period or 20 milliseconds for GPS signals.
(1)
To improve sensitivity to -160 dBm, coherent integration over multiple bits is desired. Therefore, valid navigation bits as well as the bit boundaries are needed for data wipe-off. For this purpose, previously collected navigation bits can be directly used if they are still valid or fresh navigation messages from different sources, including ephemeris and almanac, can be used to recover the navigation bits.
GNSS Assistance Technologies
The existing efforts for improving TTFF and sensitivity for GNSS UE include developing assistance systems and implementing new algorithms for UE. The concept of AGPS goes back to the late 1990s when lots of patents were filed and then granted in early 2000s. Seeing the challenges of TTFF and sensitivity for standalone GPS devices, the general idea from the patents is to provide assistance information to GNSS UE, such as time, rough location, a list of visible satellites, the Doppler shift of each satellite, ephemerides and so on, in a way to speed up each stage in the process of a position fix (Figure 2). With a series of AGPS specifications embodied in the 3GPP and Open Mobile Alliance standards since 2001, AGPS-enabled products have become quite popular in the GNSS marketplace.
The assistance data definitely brings enhanced performance in TTFF and sensitivity for GNSS UE, but it is a challenge when network connectivity is not available. A technology often referred to as ephemeris extension (EE) was introduced by Global Locate and SiRF, which enables fast TTFF and high sensitivity for GNSS UE even without network connectivity. According to the descriptions of the long-term orbit used by Broadcom and InstantFix used by CSR, both are based on orbit determination theory and provide alternative ephemerides with a validity period extending to a few days, rather than two hours for the regular GPS ephemerides. As of today, a variety of EE products are available from many companies and research institutes, and EE has become a standard feature for GNSS products in the market place.
Limitations of Existing GNSS Assistance Technologies
In spite of the benefits to TTFF and improved sensitivity, the assisted GNSS (AGNSS) and EE technologies have obvious limitations, as detailed in TABLE 1. Building and maintaining the AGNSS infrastructure require significant efforts and continuous cost. Any AGNSS-capable UE, unlike standalone GNSS UE, are tied to good signals from the subscriber cellular phone networks to get assistance data on time, which substantially limit their areas of operation. The EE technologies consist of server-based and client-based modes. Client-based EE is good for standalone UE, but the accuracy is subject to the validity of the embedded Earth orientation parameters (EOPs), and the quantity and quality of the local data collection. Server-based EE is able to provide better accuracy, but it also needs support from the global infrastructure for data collection and is subject to network connectivity. Table 1 clearly indicates that AGNSS and EE can only be beneficial under certain prerequisite conditions, such as with network connectivity and data availability. In other words, even with the above-described technologies, fast TTFF and high sensitivity may still not be obtainable when those prerequisite conditions are not met, which is not uncommon in practical use.
TABLE 1. Comparison of assisted GNSS (AGNSS) and extended ephemeris in improving time-to-fist-fix (TTFF) and sensitivity.
Suggested New GNSS NAV Messages
The fundamental cause of the problem related to TTFF and sensitivity, in our view, lies in the congenital weakness of the design of the existing GNSS NAV messages. Taking GPS as an example, the contents of GPS subframes 1–3 are updated every two hours, although the ephemeris is valid for up to four hours. It is challenging for standalone GPS UE working in weak signal environments to catch up with such frequent ephemeris updates. Working properly during the past two hours does not mean that the UE can work properly in the next two hours if ephemerides are not downloaded in time. The NAV messages received two hours ago cannot be used for data aiding in the subsequent two hours to improve tracking sensitivity. For startups under normal signal conditions, the UE, if missing the start of subframe 1, have to wait 30 seconds to get to the next subframe 1 to download a complete copy of the ephemeris. Successful startups four hours ago also do not help much to reduce the TTFF in the subsequent startups, as time is needed again for ephemeris downloading.
For other GNSSs, some specifications of their NAV messages are listed in TABLE 3. According to these specification, the downloading of Galileo ephemerides takes at least 30 seconds, and if the start of the first ephemeris page is missed, it will take at least 50 seconds to get a complete copy. So, from this perspective, the Galileo TTFF for standalone devices is expected to be longer than that for GPS. As to BeiDou, given the high degree of similarity between BeiDou D1 and GPS CNAV messages, it is expected that for standalone BeiDou UE, TTFF is also similar to standalone GPS UE. For GLONASS, the downloading takes just about10 seconds, and it will take about 30 seconds to get a complete copy of the ephemeris if the start of the first ephemeris string is missed. Therefore, in this regard, the GLONASS TTFF for standalone devices is expected to be the fastest among the GNSSs. It is worth noting that the GLONASS ephemeris, unlike that of other GNSSs, comprises Cartesian coordinates, velocity components and solar/lunar gravitational accelerations at the reference time, with the content valid over about 0.5 hours. Upon receiving the ephemeris, the UE is to calculate the satellite orbit by numerically integrating the motion equations that include the second zonal geopotential coefficients through a fourth-order Runge-Kutta method. Since the designed NAV messages for GPS, GLONASS, BeiDou and Galileo are all valid for only short periods (see Table 3), they are all subject to the aforementioned limitations.
TABLE 3. Comparison of the NAV messages for GPS/GLO/BD(D1)/GAL(F/NAV)/New GNSS.
The common weaknesses in the NAV messages of GPS, GLONASS, BeiDou and Galileo described above can be overcome and fast TTFF and high sensitivity can be facilitated through the design of new NAV messages, when the following guidelines are followed:
Update interval, as short as possible
Repeat interval, as high as possible
Length of ephemeris content, as short as possible
Ephemeris life expectancy, as long as possible
Let’s take a closer look at the GPS CNAV messages in terms of the above four guidelines. In the GPS CNAV messages, the primary content includes:
Satellite clock
Satellite ephemeris
Ionosphere information
UTC parameters
Almanac
Two types of atomic clocks, rubidium and cesium, with stabilities of 10-12 to 10-13 are used on the GPS satellites. Given such stabilities, it is possible to have the clock parameters updated at an interval much longer than two hours, without introducing significant errors in the pseudorange observations. For the Keplerian parameters in the GPS ephemerides, they are derived from the fitting of four-hour orbit curves. The orbit, represented by the Keplerian parameters plus perturbation corrections, gives the overall best fitting of the whole orbit segment. If fitting over a longer orbit curve, it would be harder for the fitted orbit to agree well with each small portion of the original orbit. A set of Keplerian orbital parameters can be a good approximation of a short orbit segment (say four hours), but can hardly be the case over a long period (say 24 hours). Frequent updating of the ephemeris content is therefore indispensable in order to guarantee the orbit accuracy using this approach. As a result, there is not much room for extending the ephemeris update interval or equivalently to lower the update frequency.
GPS CNAV messages include ionosphere information using the Klobuchar model, UTC parameters for relating GPS Time to UTC, and the almanac providing the rough orbits for all GPS satellites in service. According to the GPS Interface Specifications, all these messages will be updated at least once every six days, but they are typically updated on a daily basis.
Based on the above analysis, it can be concluded that, in GPS CNAV messages, the only part that changes frequently is the ephemeris (primarily the Keplerian parameters). To facilitate fast TTFF and high sensitivity, we should reduce the update frequency of the GPS CNAV message. For that, the key is to find a way to minimize the update frequency of the ephemerides.
Taking a close look at the satellite orbit may help us find a hint. For a satellite in space, given the initial conditions (position, r, velocity, , and so on) in Equation (2) at time t0 , the succeeding orbit, r(t), can be obtained by integrating the accelerations, , in Equation (3), as illustrated in Equation (4).
(2)
(3)
(4)
To ensure the accuracy of the derived orbit, r(t), the forces exerted on the satellites that result in the acceleration, (t), should be well modeled. The forces are both gravitational and non-gravitational.
Standard gravitational force models embedded in UE can be independently used for years without introducing significant accuracy loss. As to the force of solar radiation, it is related to the reflectivity and attitude of the solar panels of the satellite, which can also be well modeled by some slow-varying and satellite-dependent parameters. If a set of such solar radiation parameter(s) along with some satellite initial conditions (position and velocity) can be provided with a certain period (say one day), the satellite orbit can be derived in the UE through some embedded force models.
By now, we have found what we are looking for — namely, the solar radiation parameter(s) together with the satellite initial condition at a reference time, which can be the ideal content for our new ephemeris that can deliver a long orbit even if updated at a low frequency.
Consider that, at any epoch, the satellite position and velocity expressed in Cartesian form (r, ) can also be identically expressed in Keplerian form through the set of standard elements as is currently done with GPS.
The initial condition expressed in Keplerian form may give a better idea of what the orbit looks like and may have advantages for message encoding and sanity checks when it is adopted as the ephemeris content.
The above fundamental analysis leads us to propose the new GNSS NAV messages provided in TABLE 2, which comply with the previously mentioned guidelines and therefore should be able to inherently facilitate fast TTFF and provide UE with high sensitivity.
Note that the EOP data in the above table, used for relating coordinates in an Earth-centered Earth-fixed (ECEF) frame and those in an Earth-centered inertial (ECI) frame, are slowly varying parameters. The update interval for each part of the new NAV messages in Table 2 is one day, but for the almanac part, the update interval can be possibly extended to a few days similar to that currently used for GPS. In the ephemeris part, the proposed messages contain the six basic Keplerian elements and one solar radiation parameter for a selected reference time (t0). Once the ephemeris is downloaded, the six Keplerian elements can be immediately transformed to Cartesian position, r(t0), and velocity, (t0), in the ECEF frame, and further converted to the initial condition in the ECI frame to derive the entire orbit through Equation (4).
TABLE 2. Proposed content of new GNSS navigation messages.
Compared to the current GPS ephemeris, Table 2 contains many fewer parameters, so it is possible to have the new GNSS ephemeris and clock data packed in only two subframes, assuming that the data rate, word structure and subframe length are the same as for GPS CNAV messages. For the remaining parts listed in Table 2, they can be packed into multiple pages of 2 subframes in a similar way as the pages of subframes 4 and 5 in GPS CNAV messages. Therefore, we have the frame structure of the proposed new GNSS NAV messages as depicted in FIGURE 3. Considering that the contents of the first two subframes play a primary role in TTFF, the pages of subframes 3 and 4 are not further discussed here.
FIGURE 3. Frame structure of the new GNSS NAV messages.
Advantages of the New NAV Messages
The content of the new NAV messages have been proposed in the last section, but the detailed format design is beyond the scope of this article. In TABLE 3, a comparison of the new NAV messages to the current GPS, GLONASS (GLO), BeiDou (BD) and Galileo (GAL) messages is presented. For the convenience of comparisons, the same data rate (50 bits per second [bps]) and the same length of subframe (6 seconds) as for the GPS CNAV messages have been used for the new GNSS NAV messages.
Compared to other GNSS NAV messages, the new NAV messages have a smaller size, but the contained ephemeris has a longer life and, as a whole, the new NAV messages just need to be updated once every 24 hours. To help understand the advantages of the new NAV messages, we have made several comparisons.
Standalone UE, New GNSS vs. GPS. For any new GNSS that deploys the new NAV messages, the UE just need to download the ephemeris from the satellites once in a whole day, whereas current GPS UE need to do it 12 times. In each downloading, it takes about 18 seconds for current GPS UE compared to about 12 seconds for the new GNSS UE. So there is no doubt that, from the TTFF perspective, the new NAV messages have incomparable advantages over the current GPS ones. Once a complete copy of the new NAV messages is downloaded, it can be used for data aiding in tracking loops for the rest of the whole day, even without network connections in weak signal environments. However, for current standalone GPS UE, they have to be in a strong signal environment to acquire fresh NAV messages every two hours. Otherwise there could be no position fix available in the next two hours due to the stale NAV bits and expired ephemerides. So, from a sensitivity point of view, a GNSS with the new NAV messages (referred to as new GNSS below) will also have incomparable advantages over GPS.
Assisted UE, New GNSS vs. GPS. There are three purposes for assistance information for mobile devices: 1) to expedite signal acquisition; 2) to save time in ephemeris downloading; and 3) to have navigation bits for data aiding in the tracking loops. For assisted GPS UE and assisted GNSS UE with the new NAV messages, there is not much difference in the first aspect, as the assistance data, such as a satellite vehicle list, Doppler frequency, code phase, location and time, are common to both. For the second and third purposes, the assistance data sent from the assisting network to the UE are only needed once per day using the new NAV messages because they are updated only once per day. For assisted GPS UE, the assistance data are needed once every 2 hours, which means that GPS UE need frequent network connectivity and more network bandwidth for data transportation. In addition, as the size of a GPS frame is larger than the frame of the proposed new NAV messages, the time delay in transporting the assistance data will be longer in a GPS assistance network.
New GNSS, Standalone vs. Assisted. When the new GNSS NAV messages are deployed, as the messages are only needed to be downloaded once a day, the assisted UE mostly show advantage in sensitivity and the required time for signal acquisition. Since signal acquisition is difficult only when the signal becomes weaker than a certain level, the performance of standalone and assisted new GNSS UE is expected to be comparable under normal signal conditions. Under weak signal conditions, as long as the NAV messages are received once a day, the performance in tracking sensitivities for both standalone and assisted UE is also expected to be comparable.
Feasibility Considerations
Since the proposed update interval for the new NAV messages is 24 hours, a period much longer than that currently used by all constellations, some immediate concerns may arise, such as:
Is the orbit/clock derived from the ephemeris good enough for 24 hours?
Is the calculation load for deriving satellite orbits affordable for a UE?
The advancement in orbit determination and EE technologies can help relieve the worry on the first concern. For the JPL predicted orbit and clock states, it is claimed that the user range error (URE) of around one meter for one day and URE of less than 10 meters for seven-day predictions can be obtained.
For a future GNSS that deploys the proposed new NAV messages, an orbital determination center (ODC) on the ground should be able to provide orbit predictions better than or at least comparable to those already obtained. Every 24 hours, as the intermediate results of the orbit predictions are obtained in the ODC, the new ephemeris data can be extracted and packed as one part of the new NAV messages. Once uploaded to the satellites and broadcast to GNSS UE on the ground, they can be used in deriving satellite orbits. The accuracies of the orbits/clock finally derived by GNSS UE will be subject to the accuracy of ephemeris, clock coefficients, EOPs and force models embedded in UE.
The EOP data, describing the irregularities of the Earth’s rotation, are needed for coordinate transformations between ECEF and ECI, so the up-to-date EOP data carried in the new NAV messages ensures no accuracy loss in such transformations. For the force models embedded in GNSS UE, accuracy is not a problem as long as they are the same as that used by the ODC.
As to the satellite clock, it is desired that, even if the clock coefficients are updated once per day, the accuracy of the predicted clock is still sufficient for navigation. For the current spaceborne clocks on GPS satellites, they are primarily rubidium atomic clocks with stability not better than about 10-13. The advancement of atomic clock technologies is fast, especially in recent years, and the era of rubidium, cesium and hydrogen maser clocks is evolving to ytterbium and even optical atomic clocks. As of today, atomic clocks as stable as 10-18 have been operated in laboratory settings. A project called the Space Optical Clock aims to put a lattice optical clock with a stability of 10-16 on the International Space Station by 2020. So it is foreseeable that new GNSSs should be able to deploy atomic clocks with stability several orders better than those currently deployed. At the stability of 10-16, the clock will only introduce millimeter-level errors in ranging in a 24-hour period. With such a stable satellite clock, there should be no accuracy concerns with clock data being updated once per day.
Once the broadcast ephemeris is received by a UE, numerical integration can be started to derive the satellite orbit. During the numerical integration, the calculation load is primarily dependent on the following factors: 1) the length of numerical integration; 2) the numerical integration step size; 3) the order of the integrator; and 4) the complexity of local force models. Regarding the run-time necessary for orbital numerical integration on an embedded system, some published results indicate that a three-day prediction (numerical integration) takes only around 0.6 seconds on a 600-MHz processor with floating point unit. So a 12-hour integration would take only about 0.1 seconds on the same platform. As of 2014, for the popular high-end smartphones on the market, the speed of embedded processors ranges from 1.2 to 2.5 GHz with dual- or quad-cores. Considering the drastically growing computation power of mobile processors and the potential of further algorithm optimizations in orbital integration, the calculation load of numerical integration for a 12-hour interval is not at all an issue on a mobile device today, much less in the future.
The GPS system designers four decades ago might not have realized that GPS would become so popular in the 21st century. Fast TTFF and high sensitivity have become standard requirements. The growing power of the application processors has also been beyond the imagination of people 40 years ago. So in their design, fast TTFF and high sensitivity might not have been given too much attention. The GPS modernization program is an attempt to meet the growing expectation on the system performance in the applications for today and the near future. In view of this, there is no reason not to give special considerations to inherently support fast TTFF and high-sensitivity applications when investigating and designing a new GNSS. Certainly, such efforts can be found both in recently launched GPS (Block IIF) and Galileo satellites, such as the pilot channels, but navigation under weak signal conditions for future standalone GPS and Galileo devices is still susceptible to the frequent change of NAV messages (see Table 3).
Conclusions
In this article, we have analyzed the benefits and limitations of the existing technologies (AGNSS and EE) widely adopted to improve TTFF and sensitivity performance, and pointed out the weakness in current GNSSs. Instead of seeking solutions in the user terminal, this article proposes to deploy new NAV messages on future GNSSs, with the contents updated once a day, to inherently facilitate fast TTFF and high sensitivity in the standalone GNSS UE. A future GNSS that uses such new NAV messages will have significant advantages for both standalone and assisted UE.
Acknowledgment
This article is based, in part, on the paper “New GNSS Navigation Messages for Inherent Fast TTFF and High Sensitivity” presented at the 2015 Pacific PNT Meeting of The Institute of Navigation, held in Honolulu, Hawaii, April 20–23, 2015.
WENTAO ZHANG is a Ph.D. student in the Department of Geomatics Engineering at the University of Calgary. His research interest lies in different location technologies, and he is focusing his research on potential new GNSS navigation messages in an attempt to inherently improve time-to-first-fix and receiver sensitivity.
YANG GAO is a professor in the Department of Geomatics Engineering at the University of Calgary. His research expertise includes both theoretical aspects and practical applications of satellite-based positioning and navigation systems. His research focuses on high-precision GNSS positioning and multi-sensor integrated navigation systems.
FURTHER READING
Authors’ Conference Paper
“New GNSS Navigation Messages for Inherent Fast TTFF and High Sensitivity” by W. Zhang and Y. Gao in Proceedings of The Institute of Navigation 2015 Pacific PNT Meeting, Honolulu, Hawaii, April 20–23, 2015, pp. 131–141.
Assisted GNSS
A-GPS: Assisted GPS, GNSS, and SBAS by F. van Diggelen, published by Artech House, Boston and London, 2009.
“Assistance When There’s No Assistance — Long-Term Orbit Technology for Cell Phones, PDAs” by D. Lundgren and F. van Diggelen in GPS World, Vol. 16, No. 10, Oct. 2005, pp. 32–36.
“SiRF InstantFix II Technology” by W. Zhang, V. Venkatasubramanian, H. Liu, M. Phatak and S. Han in Proceedings of ION GNSS 2008, the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation, Savannah, Ga., Sept. 16–19, 2008, pp. 1840–1847.
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The U.S. Air Force released a final Request for Proposal (RFP) for GPS III Launch Services on Sept. 30. Launch services include launch vehicle production, mission integration and launch operations for a GPS III mission scheduled to launch in 2018. Proposals are due back to the Air Force no later than Nov. 16 in accordance with the solicitation instructions.
After evaluating proposals through a competitive, best-value source selection process, the Air Force will award a firm-fixed price contract that will provide the government with a total launch solution for the GPS III satellite. The Air Force’s acquisition strategy for this solicitation achieves a balance between mission success, meeting operational needs, lowering launch costs, and reintroducing competition for National Security Space missions, according to a statement by the Air Force.
“Through this competitive solicitation for GPS III launch services, we hope to reintroduce competition in order to promote innovation and reduce cost to the taxpayer while maintaining our steadfast laser focus on mission assurance and assured access to space,” said Lt. Gen. Samuel Greaves, Space and Missile Systems Center commander and Air Force Program Executive Officer for Space.
This will be a standalone contract for one GPS III launch, the Air Force said. This is the first of nine competitive launch services planned in the FY 2016 President’s Budget Request under the current Phase 1A procurement strategy, which covers awards with FY 2015-2017 funding. The next solicitation for launch services will be for a second GPS III mission.
The Phase 1A procurement strategy reintroduces competition for national security space launch services. Under the previous Phase 1 strategy, United Launch Alliance (ULA) was the only certified launch provider. In 2013, ULA was awarded a sole-source contract for launch services as part of an Air Force “block buy” of 36 rocket cores that resulted in significant savings for the government through FY 2017.
In May, Space Exploration Technologies (SpaceX) was certified for EELV launches resulting in two launch service providers that are qualified to design, produce, qualify and deliver a launch capability and provide the mission assurance support required to deliver national security space satellites to orbit.
“With the recent certification of SpaceX, we now have multiple launch service providers that can service critical NSS missions. Reintroducing competition into EELV will ultimately save taxpayer dollars and increase assured access to space. ” said Claire Leon, director of SMC’s Launch Enterprise Directorate.
“As part of this reintroduction of competition, we’ve been working with our industry partners to develop and finalize this RFP,” said Leon. “Their feedback has been critical to developing the criteria for this source selection and how we are innovating government processes to better match commercial processes as directed by OSD’s Better Buying Power 3.0. This is an exciting time in NSS launch acquisitions.”
GPS III is the next generation of GPS satellites that will introduce new capabilities to meet the higher demands of both military and civilian users. GPS III is expected to provide improved anti-jamming capabilities as well as improved accuracy for precision navigation and timing. It will incorporate the common L1C signal which is compatible with the European Space Agency’s Galileo global navigation satellite system and compliment current services with the addition of new civil and military signals.
The Air Force Space Command’s Space and Missile Systems Center, located at the Los Angeles Air Force Base, Calif., is the U.S. Air Force’s center of excellence for acquiring and developing military space systems. Its portfolio includes the Global Positioning System, military satellite communications, defense meteorological satellites, space launch and range systems, satellite control networks, space based infrared systems and space situational awareness capabilities.
Galileo’s latest pair of full operational capability (FOC) satellites now orbit proudly in space, “performing beautifully.” The first two FOC birds may soon shift their focus from navigation to gravity experiments instead.
Meanwhile, as the European Space Agency tries to fly, European industry seeks firmly grounded support in the form of an industrial policy and economic stimuli, expressing concern that the current situation “might jeopardize the achievement of the main objections of the European GNSS programmes.”
Alba and Oriana (aka Galileo satellites 9 and 10), launched on Sept. 11, are drifting towards their target orbital positions. Thruster firings will resume around the end of October to stop their drift and achieve fine positioning in orbit. Their control now rests in the electronic hands of the Galileo Control Centre in Oberpfaffenhofen, Germany.
Gravity Probe. The two satellites launched last September have not fared so well. Injected into the wrong orbit by a faulty Soyuz rocket, they were moved to a “usable” orbit in December 2014, reducing orbit eccentricity and avoiding the high radiation doses in the Van Allen belts, but still not high enough to function fully as navigation satellites. The European Commission (EC) and ESA remain convinced that Doresa and Milean (satellites 5 and 6) will be able to contribute in some limited fashion to Galileo’s PNT solutions, but they are also preparing alternate roles for the pair.
Together with Sytèmes de Référence Temps Espace (SYRTE, or Time-Space Reference Systems department) of the Observatoire de Paris and the Center of Applied Space Technology and Microgravity (ZARM) at the University of Bremen, ESA has explored taking advantage of the combination of Dorena’s and Milesa’s eccentricity (about 0.15 in the corrected orbits), the passive hydrogen maser (PHM) on-board clocks’ high accuracy-stability (~10−14 per day), and high orbital precision to perform a measurement of the gravitational redshift. The redshift or Einstein shift is a process by which electromagnetic radiation originating from a source that is in a gravitational field is reduced in frequency, or redshifted, when observed in a region of a weaker gravitational field. The three organizations believe that the two satellites can help measure this effect with a superior accuracy compared to today’s state of the art, based on Gravity Probe A, an experiment performed in 1976.
These tests are noted to have a high scientific relevance, as many alternative theories of gravitation predict violations of the Einstein Equivalence Principle at some level of accuracy. Two parallel research activities, with SYRTE and ZARM, will be launched by ESA to assess this potential in greater detail.
See What the Future Brings. Two further Galileo satellites are scheduled for launch by end of this year. Next year the deployment of the Galileo system will be boosted by the entry into operation of a specially customized Ariane 5 launcher that can double, from two to four, the number of satellites that can be placed into orbit by a single launch.
We Want What They Got. Earlier this month, the 29-company Galileo Services association, made up of European chipset and receiver suppliers and associated service providers, issued a position paper calling for “a coordinated industrial policy to support the European economy,” specifically that portion of the economy based on satellite positioning, navigation and timing. The companies jointly complain that in the United States, Russia, China and Japan, dedicated national strategies, including “massive funding” for both R&D and manufacturing, support GNSS downstream industries — but in Europe, no such backing exists. The un-level playing field imperils European commercial activity.
“As things stand, in a few years, it will be difficult or nearly impossible for European industry to survive in the highly competitive GNSS global market,” the position paper reads. “Unless an effective and long-term strategy is put in place during the Galileo early services exploitation phase (2016–2020), the window of opportunity for European industry to benefit from the current GNSS market boom will soon be closed.”
“Europe Must Succeed in the Global Navigation Market Race” (the full document is available here) calls upon European governments to devise and adopt a strategic plan to support Galileo’s downstream suppliers and manufacturers. The desired strategy connotes money and favorable regulations.
Europe governmental hands may be a bit tied by a U.S.-European agreement that neither will put up barriers discriminating against each other’s satnav systems. China and Russia have not signed the agreement and so are not bound by its restrictions; the two countries can freely make “massive procurements equivalent to several billions of euros from the public sector, as anchor customer, which radically boosts private investment,” according to the Galileo Services paper. Further, the United States can step around the agreement’s terms via military contracts to U.S. manufacturers, leveraging their commercial ventures.
Thirty-three or Bust. The report continues to reference the magic number 33 percent, the traditional European global market share in any high-tech sector. European industry partners estimate they hold 20 percent of the worldwide satnav currently, if even that, and, ominously, they see that share declining. They cast U.S. manufacturers in the dominant role: “80 percent of well-established market owners are of U.S. origin.” This is not the same as an 80 percent market share, but it still sounds scary to European ears. Meanwhile, “the size and growth of Chinese industry, which has already in just a few years outperformed European industry in the field of telecommunications, is particularly worrying” to satnav concerns.
Section Two of “Europe Must Succeed” defines the strategic plan that the industry partners would like to see:
quantitative objectives in terms of market share, revenue, and job creation;
clear support actions in terms of public procurement and regulations;
key performance indicators to assess progress towards set milestones.
Section Three lays out a series of recommended key support actions for public institutions to undertake, and Section Four proposes a Galileo Services Forum, a permanent and formal arena for discussions between the European Commission, the European GNSS Agency, and the European Space Agency on the one hand, and European GNSS downstream industry on the other.
Interestingly, while the report in an earlier section calls out a number of promising application and service markets — basically all the usual suspects, from connected vehicles to offshore infrastructure — it singles out one, “the leading position of Europe in GNSS security and resilience,” for particular attention. It “should be strengthened, as it is critical for today’s and tomorrow’s markets.”
The report also makes a pointed allusion to European industry’s “strong reputation for quality and reliability.” This note is not sounded elsewhere in the paper, suggesting a fear that price trumps quality in today’s marketplace. A well-founded fear.
Galileo Services represents more than 180 members. Its most active and representative GNSS players include: Airbus Defence & Space, Ansaldo STS, CGI, European Satellite Services Provider (ESSP), Eutelsat, France Developpement Conseil, Fugro, GMV, Guide, Hertz Systems, Honeywell, Indra, Ineco, JAVAD GNSS, Kayser-Threde, Kongsberg, M3 Systems, NavCert, NLR, NovAtel, Nottingham Scientific Limited, OHB, QinetiQ, Septentrio, Catapult, Sogei, Spirent, Thales and Veripos.
Rick Hamilton, CGSIC Executive Secretariat of the U.S. Coast Guard Navigation Center (NAVCEN) provided the following report on the Civil GPS Service Interface Committee (CGSIC) conference, which took place Sept. 14-15 in Tampa, Fla., before the Institute of Navigation’s ION GNSS+ conference.
All CGSIC:
On the 14th and 15th of September, the 55th meeting of the Civil GPS Service Interface Committee (CGSIC) conference was hosted by the U.S. Department of Transportation (DOT) and the U.S. Coast Guard Navigation Center (NAVCEN) at the Tampa Convention Center in Florida. DOT serves as the civil lead for GPS and chairs the CGSIC in this capacity. NAVCEN is assigned duties as Deputy Chair and Executive Secretariat for the CGSIC.
On September 14, the Timing, States and Local Government, International Information, and Surveying, Mapping, and Geosciences subcommittees of the CGSIC held their meetings. A summary of their subcommittee meetings was presented to the CGSIC Plenary on September 15th.
The Keynote speaker for this year’s CGSIC Plenary meeting was the Honorable Gregory Winfree, Assistant Secretary for Research and Technology, at the U.S. Department of Transportation. The agenda for the CGSIC Plenary meeting included presentations on the operational status and modernization of the GPS constellation of satellites, U.S. space-based PNT policy, GPS augmentation systems, and information related to international Global Navigation Satellite Systems.
Several new briefings were part of the Plenary session this year, including presentations from the 19th Space Operations Squadron that provides GPS Launch, Anomaly and Disposal Operations (LADO), from NASA on space missions and their success in using GPS side lobes for space navigation beyond Geostationary orbit, and from Airservices Australia detailing progress in providing a Global Tracking capability in the wake of the missing Air Malaysia MH370 aircraft in the Indian Ocean. The Department of Homeland Security also provided an informative briefing that included discussion of use of Space-Based PNT in Critical Infrastructure and strategies for managing PNT risk.
Many thanks to the 2015 CGSIC speakers for their excellent presentations which always make these meetings valuable and interesting, as well as great questions from the audience. This year, 220 attendees participated in the CGSIC meeting. All CGSIC presentations are available for viewing online via the GPS.gov website.
Next year’s 56th CGSIC meeting will be held at the Portland Convention Center, 12-13 September 2016 in conjunction with the ION GNSS+ 2016 meeting in Portland, Oregon. Additionally, the CGSIC States and Local Government Subcommittee will meet on November 19, 2015, in conjunction with a Field Technology for Data Collection in Forestry, Fisheries, and Natural Resources Conference in Portland, Oregon. This meeting will be webcast and details will be circulated prior to the event to foster maximum participation from around the country. The CGSIC International Information Subcommittee will meet on November 16, 2015, in conjunction with the International Symposium on GNSS in Kyoto, Japan.
As a reminder, CGSIC meetings are free and open to the public. Finally, GPS-related inquiries or reports of signal interference/degradation problems can be made to the U.S. Coast Guard Navigation Center or 703-313-5900.
V/R
Rick Hamilton
CGSIC Executive Secretariat
GPS Information Analysis Team Lead
U.S. Coast Guard Navigation Center
The 20th BeiDou satellite is launched, Sept. 30, 2015.
China launched a new-generation BeiDou satellite into orbit at 7:13 a.m. China Standard Time on Wednesday, Sept. 30, according to the Xinhua News Agency, the 20th satellite for the BeiDou Navigation Satellite System.
The satellite was launched from Xichang Satellite Launch Center in the southwestern province of Sichuan aboard a Long March-3B carrier rocket.
In a first for BeiDou, the new BeiDou satellite is equipped with a hydrogen maser atomic clock. A series of tests related to the clock and a new navigation-signal system will be undertaken, according to the center as reported by Xinhua.
China plans to expand the BeiDou services to most of the countries covered in its “Belt and Road” initiative by 2018, and offer global coverage by 2020.
Named after the Chinese term for the plough or the Big Dipper constellation, the BeiDou project was formally launched in 1994. The first BeiDou satellite was launched in 2000.
Two videos of the launch are available on the CCTV website.
Galileo satellites 9 and 10 are functioning perfectly, and the initial series of flight operations is continuing as part of the critical launch and early orbit phase, according to a European Space Agency Rocket Science blog by Daniel Scuka, senior editor for Spacecraft Operations at ESOC, ESA’s European Space Operations Centre, Darmstadt, Germany.
Galileo 9 and 10 lifted off together on Sept. 11 from Europe’s Spaceport in French Guiana atop a Soyuz launcher, bringing the total number of Galileo satellites in orbit to 10.
“The pair are being stepped through an intense series of check-outs, confirmations, mode changes, configurations and health verifications by the joint ESA/CNES mission team working around the clock at ESOC, Darmstadt, Germany,” according to the blog. “The team are now focusing on conducting a series of thruster burns designed to start the drift of the two satellites toward their target orbital positions.”
“Following the burns performed during the LEOP (launch and early orbit phase), the satellites will continue naturally drifting, ending up in their final desired operational orbits at about 23,222 km after another set of thruster burns, planned to achieve fine positioning in orbit, around the end of October,” said Liviu Stefanov, co-flight director from ESA.
With the excellent performance of the spacecraft and the ground teams, the LEOP is expected to wrap up soon.
All the Soyuz stages performed as planned during the September 11 launch, relieving anxieties tied to a faulty Soyuz launch in September of last year. The Fregat upper stage released the satellites into their target orbit close to 23,500 km altitude, around 3 hours and 48 minutes after liftoff.
“The deployment of Europe’s Galileo system is rapidly gathering pace,” said Jan Woerner, director general of the European Space Agency (ESA). “By steadily boosting the number of satellites in space, together with new stations on the ground across the world, Galileo will soon have a global reach. The day of Galileo’s full operational capability is approaching. It will be a great day for Europe.”
Two more Galileo satellites are scheduled for launch by end of this year. These satellites have completed testing at ESA’s ESTEC technical centre in Noordwijk, the Netherlands, with the next two satellites also undergoing their own test campaigns.
More Galileo satellites are being manufactured by OHB in Bremen, Germany, with navigation payloads coming from Surrey Satellite Technology Ltd in the UK, in turn utilizing elements sourced from all across Europe.
“Production of the satellites has attained a regular rhythm,” said Didier Faivre, ESA’s Director of Galileo and Navigation-related Activities. “At the same time, all Galileo testing performed up to now — including that of the ground segment — has been returning extremely positive results.
“And while the continuing deployment of Galileo remains our priority, along with exploitation of EGNOS — Europe’s already operational satellite navigation augmentation system — ESA is also looking farther ahead.
“With the European Commission, we are doing the technical work to ensure Galileo goes on forever — locking in continuity of Europe’s navigation services into the long term, to meet performance on a par with the other global satellite navigation systems.”
Next year Galileo deployment will be boosted by operation of a specially customized Ariane 5 launcher that can double, from two to four, the number of satellites that can be inserted into orbit with a single launch.
European SBAS Advances, Improves
After extensive ground and space testing, the SES-5 GEO satellite has entered into the European Geostationary Navigation Overlay Service (EGNOS) operational platform, broadcasting EGNOS Signal-In-Space (SIS). Replacing Inmarsat-4F2, SES-5 will ensure reliable EGNOS services until 2026, and will enable a range of performance improvements. In particular, EGNOS will offer even greater stability during periods of high ionospheric activity.
“SES-5 is the first step of the complete renewal of the EGNOS Space Segment, securing the EGNOS services for the next decade and the future transition to the dual-frequency multi-constellation services,” said Carlo des Dorides, European GNSS Agency executive director. “It will be completed by the introduction of the ASTRA-5B signals and the procurement of a new EGNOS payload which are both planned for 2016.”
SES-5, carrying EGNOS L1 and L5 band payloads, was launched in July 2012. The integration of a second EGNOS SBAS L1/L5 band payload on SES ASTRA-5B GEO satellite is currently ongoing. The introduction of the second SES GEO satellite for EGNOS is planned at the end of 2016.
GAO Report Spotlghts OCX Delays, Cost Increases
According to a report released by the U.S Government Accountability Office (GAO) on Sept. 9, titled “Actions Needed to Address Ground System Development Problems and User Equipment Production Readiness,” the Air Force has experienced significant difficulties developing the GPS next-generation operational control system (OCX). According to the report, completion of OCX will require $1.1 billion and four years more than planned to deliver OCX. The report Highlights section states, “The Air Force began OCX development in 2010,” and “accelerated OCX development in 2012 to meet optimistic GPS III satellite launch timeframes even as OCX development problems and costs grew, and then paused development in 2013 to address problems and resolve what it believed were root causes.
“However . . . OCX cost and schedule growth have persisted due in part to a high defect rate, which may result from systemic issues. Further, unrealistic cost and schedule estimates limit OSD visibility into and oversight over OCX progress. “ The full report may be read online.
During the course of development the Air Force made changes, updating the specifications for connections to other government systems and in the M-code signal requirements. Officials for Raytheon, the prime OCX contractor, estimated that, as a result of various modifications “nearly two-thirds of the requirements baseline as of [preliminary design review] had changed by mid-2012.” Subsequent software updates and modifications contributed to a high defect rate in the OCX software. “
If you have requirements change at the same time you’re developing the software, it’s more likely that you could have a higher amount of defects that you have to change after the fact,” said Matthew Gilligan, Raytheon’s vice president for navigation and environmental solutions.
Europe’s ninth and tenth Galileo satellites being fueled by technicians in protective SCAPE suits within the Guiana Space Centre’s 3SB preparation building on Aug. 24. (Photo:ESA)
It has been a good late summer for the European Galileo programme. The latest launch on the night of 10 and 11 September has got the number of orbiting satellites in the EU’s GNSS constellation into double figures at last, and one-third of the way towards the ultimate target of 30.
The European Space Agency’s (ESA) press releases around the launch were positively euphoric, and there were many pictures of smiling ESA launch teams. And so there should be. The two new satellites (the fifth and sixth fully operational capability (FOC) versions named Alba and Oriana) will now inch their way towards their operational orbits and will soon be joined by two more satellites to be launched in December.
However, as we already know, one of the in-orbit validation (IOV) satellites (Sif) is not very well, having suffered a power failure in late May, and the first two FOC satellites (Doresa and Milena) ended up in the wrong orbit. At the considerable expense of a significant part of their fuel payloads, these two craft are now established in a more useful orbit and are the current subject of testing to determine the exact contribution they can make to the Galileo services.
The Commission and ESA are convinced that the outcome will be positive, with Doresa and Milena able to contribute to the network — or at least not degrade the network’s navigation performance. A final decision on if and/or how these two satellites integrate into the system will be made sometime next year.
In any case, they will be used for the provision of Galileo’s Search and Rescue services. And they are also to be made available for scientific research. One possible science area that has been discussed is to ‘repurpose’ the satellites to measure the slow down of time due to the Earth’s gravitational field as predicted by Einstein’s theory of relativity.
However, more worryingly, there are rumours of various glitches and performance issues with other in-orbit members of the constellation. Hopefully, they are just rumours; only time will tell.
Position Paper
Not surprisingly, those wanting to use the system are getting a tad frustrated. On Sept. 1, Galileo Services, a non-profit organisation involving 180 members including most of the active players in the EU GNSS industry, published a position paper entitled “Europe Must Succeed in the Global Navigation Market Race.”
The organisation’s aim is to foster an end-to-end vision of the Galileo system that can fully respond to user and market needs. The paper looks at the options to strengthen the competitiveness of the European GNSS downstream sector in the global market and calls for better coordination between the public and private sectors to develop new technologies, applications, services and industries in Europe as a key factor for success.
In particular, the paper stresses the necessity to urgently establish a European strategic plan to enhance Europe’s GNSS downstream industry’s competitiveness and to foster the uptake of the European GNSS, Galileo and the European Geostationary Navigation Overlay Service (EGNOS), with the aim to corner 33 percent of the global GNSS downstream market for Europe by 2025.
Galileo Services argues that unless an effective and long-term strategy is in place during the Galileo early services exploitation phase — from 2016, the current official start date for services — the window of opportunity for European industry will be closed. Europe’s goal of achieving GNSS autonomy is also at risk. The paper warns that Galileo is just one of three new GNSS solutions, along with the Russian GLONASS and Chinese BeiDou, that are complementing the U.S.’s GPS — and most applications do not require four GNSS constellations.
The target of European autonomy will be achieved if and only if Galileo is widely used with equipment designed and manufactured in Europe, as well as applications and services developed in Europe, concludes the paper.
More R&D Support
Part of the strategy should be enhanced support for EU GNSS technologies and applications. The European GNSS Agency (GSA) has just launched a new research support channel for GNSS chipset and receiver technologies in Europe.
The Fundamental Elements programme has a projected budget of EUR 100 million over the period 2015 to 2020 and is part, says the GSA, of an overall strategy of market uptake initiatives in accordance with EU regulations. “For the first time, EU regulation provides a financing tool for the market uptake of European GNSS chipsets and receivers,” said GSA Executive Director Carlo des Dorides in launching the new programme.
The Fundamental Elements programme complements the EU’s current Horizon 2020 research programme that focuses on adoption of Galileo and EGNOS via content and application development.
Two types of financing will be available via the Fundamental Elements programme: grants and procurement. Grants will be provided to cover up to 70 percent of funding requirements for a project, and intellectual property rights will stay with the beneficiary under the condition that the developed product is actively commercialised.
Procurement (at 100 percent funding) will be used only in cases where keeping intellectual property rights allow for the better fulfilment of the programme’s overall objectives. For example, by licensing it to different potential manufacturers rather than creating a monopoly supplier.
Meanwhile, EGNOS Continues
Of course, one EU GNSS, EGNOS, is operational. The GSA proudly announced that after extensive testing, the latest space segment — the SES-5 GEO satellite — is now fully functional. This will ensure the long-term service of EGNOS until at least 2026 and enable a range of performance improvements, including greater stability during periods of high ionospheric activity.
The SES-5 is a first step in the complete renewal of the EGNOS Space Segment, including the transition to dual-frequency, multi-constellation services. The renewal will be completed by the introduction of the ASTRA-5B signals and the procurement of a new EGNOS payload, both planned for 2016.
In parallel, the GSA and ESA have met formally to launch activities to develop the system further following the signing of a working agreement for EGNOS in July. Under the agreement, ESA will be responsible for the development and procurement of future EGNOS evolutions, such as the forthcoming release (V2.4.2), and a new generation of the EGNOS system (V3).
One of the annual gatherings of the whole European GNSS value chain will take place in October in Berlin with the Satellite Masters conference and awards ceremony. We can be sure that comforting words will be spoken by persons from the Commission, the GSA and ESA about their future plans and present progress. But the real buzz of this event is from the showcase of new ideas and applications for Galileo and EGNOS from pretty much every corner of Europe and beyond.
Despite the uncertainties expressed by some big industrial players, and slow progress in establishing the actual infrastructure, there is still an entrepreneurial enthusiasm from the ‘small guys’ to get involved in this space-based business.
I have attended these events for a few years now. One of the most enthusiastic winners of recent years is JOHAN, a sports application named after renowned Dutch soccer player and now sport commentator Johan Cruyff.
The application is the brainchild of Dutch graduate Jelle Reichert, whom I first met when he won the 2013 European Satellite Navigation Competition with this innovative EGNOS-enhanced tracking idea. “We are now operational with our first four clients! And in a final testing phase we are making the system ready for a commercial launch at the beginning of 2016,” he tells me. “We also just have an investor on board, which allows us to hire personnel and take the final steps to become really commercially ready.”
In just 18 months, Jelle’s idea has been brought into life with support from GSA and ESA. The JOHAN sports tracker and application helps improve teams by monitoring on-field performance. The system’s small, lightweight trackers, or pebbles, use GNSS technology such as EGNOS to ensure reliability and precision.
The trackers are small and light so they can fit into training vests worn by players across a variety of field sports, though early adopters have all been football teams so far. The trackers measure location, speed, distance, acceleration and orientation statistics, which are then visualized in an online data platform for coaches and players. This allows coaches to monitor workload and performance, and get tactical information and event analysis and ensure players’ strengths are used to the whole team’s advantage. Players can spot weaknesses and improve their individual game over time.
“You can see who is training too hard and who has a higher chance of injury, as well as who is strong in which performance aspects, such as endurance, sprint, agility or recovery,” explains Jelle.
I look forward to hearing about lots more grassroots GNSS innovation in Berlin.
And Finally … An Out-of-This-World App?
Take me to the moon! And why not, indeed? It appears that Galileo could be a vital part of an interplanetary navigation system. Or at least it could help (with GPS) spacecraft to routinely navigate to the moon.
A paper in Acta Astronautica highlights the strict requirements in terms of performance, flexibility and cost for all the spacecraft subsystems required to navigate to the moon. GNSS could introduce an easier way to provide an autonomous orbit determination system using an on-board GNSS receiver. While GNSS receivers have already been used successfully to pilot craft in Low Earth Orbit (LEO), their use for very High Earth Orbit (HEO) up to and including the Moon is an active research area.
The study from researchers at the Swiss Federal Institute of Technology in Lausanne (EPFL) made use of the Spirent GSS8000 multi-GNSS constellation simulator, which supports simultaneously the GPS and Galileo systems with L1, L5, E1 and E5 frequency bands. It showed that GNSS signals can be tracked up to the Moon’s surface, but would need new, more sensitive GNSS receiver technology. The paper describes a possible navigation solution that uses a double constellation GPS-Galileo receiver aided by an on-board orbital filter system to improve the accuracy of the navigation solution and achieve the required sensitivity. Without the filter, position error below 700 metres is possible, but the orbital filter increases the position accuracy to within about 100 metres.
Vincenzo Capuano from the EPFL team tells me that a further paper on the use of an GPS L1 C/A based orbital filter for Moon transfer orbits will be published soon, which also shows an achievable accuracy of a few hundred meters. So who needs expensive tracking stations for a flight to the moon?
But the work also has a very practical down-to-Earth application. The EPFL team is developing more sensitive GNSS receivers to pick up these weak signals, and the new receivers could find applications on Earth where current receivers often struggle to get a location, such as inside buildings or in built-up areas, where signals are weak.
The Galileo Control Centre in Oberpfaffenhofen, Germany, monitors and controls the constellation with a high degree of automation. (Photo: ESA)
News courtesy of the European Space Agency
Europe’s latest pair of Galileo satellites has passed its initial check out in space, allowing control to be handed over to the main control centre and join the growing fleet.
“This was a beautifully smooth start to the mission,” said ESA mission director, Richard Lumb. “From liftoff through to handover to the constellation operator and beyond, this has been a textbook performance not only of the satellites but also for all the operations and manufacturer teams on the ground.”
Galileos 9 and 10 were launched on Sept. 11. Their individual lives began within four hours, as they separated from their rocket’s final stage, overseen from ESA’s ESOC operations centre in Darmstadt, Germany. Days of round-the-clock effort followed, to bring the satellites to life, beginning with closely monitoring the unfolding of their solar wings and their pointing towards the Sun.
The various satellite elements were methodically switched on, their health checked and readied for work. Liviu Stefanov, an ESA flight director, described the process as “one of the smoothest yet.” The satellites fired their thrusters to drift towards their target orbital positions at around 23,222 km altitude — helped along in this case by a near-perfect orbital injection to begin with.
Firings will resume around the end of October to stop the drift and achieve fine positioning in orbit, guided by ESOC’s specialist flight dynamics team.
The accuracy of the Galileo system relies on the orbital position of its satellites being fixed to a very high level of precision.
Once on their way, the satellites were handed over on 19 and 20 September, respectively, to the Galileo Control Centre in Oberpfaffenhofen, Germany managed by SpaceOpal.
The team of engineers from ESA and France’s CNES space agency are preparing for the next launch, scheduled for December. The early phase for Galileos 11 and 12 will be overseen from CNES in Toulouse, France, which alternates with ESOC as hosts.
The navigation payloads on Galileos 9 and 10 still need to undergo detailed testing, led from ESA’s Redu centre in Belgium with the support of both Oberpfaffenhofen and the second Galileo Control Centre in Fucino, Italy, which has oversight of Galileo’s navigation mission.
This phase ensures the latest satellites’ navigation and search and rescue payloads are operating normally, giving them a clean bill of health before they can join the Galileo constellation.
