By David Ord
……………. So, where are we with SAT NAV?
A couple of years ago, it was reported that the divorce rate in the United States had fallen to its lowest rate for almost 40 years. The wide adoption of GPS technology has been accredited with removing one of the irreconcilable differences between couples. The dulcet tones of an automaton ensured that journeys to new destinations were no longer a source of contention. But, all is not well with the next generation of Global Navigation Satellite System (GNSS).
The Earth currently has two fully operational global systems, both of which were developed for the military. The American GPS and the Russian GLONASS are now both available for civilian applications. Coming on stream is the Chinese ‘BeiDou’, which is also within the control of the military. The first of the exclusively civilian driven GNSS is the European Union’s Galileo system, which is expected to be fully functional in 2018. The launch of the final 4 satellites this year will complete the constellation.
The problem with the military link to GNSS is that there is a danger it can be switched off or degraded for political reasons during times of extreme tensions or during military conflict. All of the original American satellites used for GPS had an option called Selective Availability. This was employed to downgrade the accuracy of the system to civilian users compared to the military. In 2000, President Clinton announced that the use of this option would be phased out completely by 2006, thereby proving a 10-fold increase in civilian GPS and reduced the time for the first accurate position reading from minutes to under 30 seconds. However, should a military need prove necessary, then Selective Availability could be re-invoked.
The GNSS on which the American GPS is based had some limitations in any case with regard to accuracy, which was typically within the 25-50 meter range. GNSS receivers triangulate their position using their distance from at least four GNSS satellites. Because they measure this distance based on the time it takes a satellite signal to reach them, even the slightest errors – down to a few billionths of a second – can negatively impact accuracy. Errors in satellite orbit position can lead to around 2.5 meters’ loss of accuracy. Satellites clock errors can add another 1.5 meters. And perturbations in the troposphere and the ionosphere can add another one and five meters respectively – even more if the satellite is close to the horizon or during periods of intense solar activity.
The American GNSS for GPS
By far the largest error is caused by multipath effects, in which satellite signals reach the receiver on multiple or indirect trajectories, for example by bouncing off building walls in urban areas. In best conditions, standard accuracy GNSS receivers are accurate to within about two meters, typically though several meters more.
The accuracy of GNSS can be improved by adding a second transmitting signal from each satellite at a different frequency. Combining multiple signals from multiple satellites should mitigate any atmospheric perturbations and some signal bouncing. Tracking the satellites for drift can be improved by fitting laser retro-reflectors which will allow a laser beam to be bounced back to Earth for the most accurate satellite position.
One way to improve the data involves monitoring GNSS signals from base stations at known locations. Deviations from the base station’s position are observed and sent to a rover – a manned or unmanned vehicle equipped with a GNSS receiver – allowing it to obtain a more accurate position reading. In favorable conditions, this approach can be used to achieve centimeter-level accuracy. In effect, a calibration factor can be encoded into the transmitted signal of the satellite. This could also be charged for at a premium rate compared to the ‘standard accuracy’.
So, it was with much of the above in mind that the European Union embarked upon its Galileo GNSS project. The justification was that Galileo would not be subject to the needs of a foreign military and in addition, the satellites would carry transponder receivers which could be used to pick up distress signals from aircraft or shipping which could then be relayed to the monitoring base stations. On all new cars from April 2018, in the event of a major accident an eCall facility will dial the emergency services (112) and give the precise location of the vehicle.
Galileo would be a high precision GNSS with autonomous driving applications, drone flight control and potentially autonomous shipping in mind. At the outset, it was believed that the project would be predominantly funded by industry. However, the Americans announced that they would upgrade their GPS to improve accuracy, robustness of signal and remove the Selective Availability option which had allowed them to degrade the signal to civilian applications. European Industry could not be persuaded to stump up the funds in the face of the upgraded American GPS – which would remain free to use. And so, it was decided in early 2000s to fund Galileo through European tax payers.
A GNSS Satellite in the Galileo Constellation
The UK took on the lion’s share of Galileo funding at almost 20% of the bill, with major contributions from Germany and Holland. A plan for public financing was put together by the unelected Brussels officials behind closed doors, without debate and in such a complex way (it also included the diversion of EU farm subsidies) that budget monitoring and control would be almost impossible. The plan was approved by the EU in November 2007.
In 2008, a British parliamentary committee were not convinced. They said the decision to proceed had been “pressed through in an unacceptable manner“, and “the Galileo program provides a textbook example of how not to run large-scale infrastructure projects“.
In a damning report, the UK MPs went on to say “The process for reaching a decision on the future of Galileo and its funding is impenetrably complex. We fear that this complexity… is creating an unstoppable momentum for a very expensive decision that is not supported by any robust evidence…”.
The committee accepted that it had no suggestions as to how the UK Government could in anyway stop or impose changes to the project. Only the EU at large could alter the program and the UK had demonstrated little influence over the larger body.
Contracts placed to implement the project are roughly in line with the proportion of the source of funding. So, UK companies should benefit to the tune of about 20% of project budget. In other words, all the UK can do is try to grab back as much of its own money as it can and try to make sure that the system is as good as it possibly can be.
Meanwhile, the EU also agreed to the combined use of both the American GPS and the Russian GLONASS with Galileo to create the most comprehensive and accurate system available. Base stations for calibrating the signals included the UK territories of the Falkland Islands and Ascension Island. Airbus in the UK won the bid to control the satellite constellation and Surrey Satellites Technology assembled the satellites.
Precise timing is at the core of all satellite-navigation systems. Atomic clocks generate the time code that is continuously transmitted to users on the ground to help them fix a position. Each Galileo satellite is equipped with 2 passive hydrogen maser clocks – a maser is a laser working in the microwave frequency of the electromagnetic spectrum. The clocks are determined to be accurate to one billionth of a second per day, or one second in three million years. In addition to the hydrogen masers, each satellite also carries 2 Rubidium atomic clocks as secondary standards.
To date, 22 satellites are in orbit about 24,000 Km above Earth. The final number will reach 30, which will include 6 spares. But, no one can claim that the Galileo project is anything but tortuous. Two of the satellites were launched into the wrong orbit by a failure of a Russian second stage rocket. Then, the clocks began to fail.
Currently, nine clocks in total – 6 hydrogen maser and 3 rubidium atomic clocks have stopped. One of the satellites has a lost both a maser and a rubidium clock. All the clocks naturally came from a Swiss supplier.
The cost of Galileo has escalated from 3 billion to 9 billion Euros, with the UK contribution to almost 1.5 billion euros. And we may not be able to use it!
Since Brexit, the European Commission has suggested that the UK may not be trusted with European Union’s most sensitive security information aspect of Galileo. The UK’s armed forces were planning to use Galileo to supplement their use of the US GPS system, but press reports suggest they will now be blocked from doing so. The US retains the more accurate and robust GPS signals for its own armed forces.
An EU discussion has taken place to exclude the UK from any further industrial participation in the program.
The UK has responded that they do not accept the European Commission’s position and have called for a 3 month freeze on procurement of the next batch of satellites. The UK Business Secretary stated that, if the European commission prevails, the UK will seek legal redress for the return of its funding to date. In addition, the use of the British base stations in the Ascension Islands and the Falklands would not be allowed.
Meanwhile, the seriousness of the tiff has escalated to the commissioning of a feasibility study by the UK Space Agency to launch the UK’s own GNSS. Most of the technology inherent in Galileo, its operation and satellite assembly are British. The Chief Executive of Airbus (UK) has stated that his company has all the skills and expertise to lead the development of a totally British GNSS and for substantially less than the cost of Galileo.
By 2022, it is estimated that the satellite navigation services market will be worth $290 billion. Well worth an argument or two.