Astronomy

Europe’s answer to GPS

When Galileo is fully functional in 2020, it will provide the most precise navigation ever, even at the North and South Poles.

The take-away

  • Europe’s €10 billion investment is paying off, even with strong US, Russian and Chinese competition.
  • Accurate to the nearest centimetre, Galileo will offer unprecedented opportunities not only for scientists but also for ordinary citizens.

Named for the famed 16th century Italian astronomer, Galileo Galilei, the constellation of 18 operational satellites is Europe’s stellar response to the ubiquitous US Global Positioning System (GPS). By 2020, the European version will consist of 24 operational satellites and a number of active spares – marking the completion of a 20-year, €10 billion journey to achieving sat-nav independence.

Since going live in December 2016, Galileo has amassed about 400 million users around the world, though this figure is likely increase to billions as people replace their smart phones. The latest iPhones and Samsung devices, and all new cars sold in Europe, are Galileo compatible. And Qualcomm has been incorporating Galileo receivers in all its wireless products since the end of 2016 – approximately 800 million units every year.

But with the American system and Russia’s GLONASS already providing similar services, and China’s BeiDou coming along in 2020, why do we need Galileo?

A different focus

For one thing, Galileo is a strictly civilian affair, created in partnership between the European Space Agency (ESA) and the European Commission. “The other systems were designed for military purposes,” explains Paul Verhoef, ESA’s Director of Navigation. “Of course, that gives a different focus.” Thousands of scientists, engineers and technicians working with major European industrial partners like Thales, Airbus, SSTL, OHB, GMV Arianespace and many others have collaborated to bring Galileo into being.

One tangible benefit of this non-military approach is that Galileo satellites follow orbits that cover the North and South Poles – something those behind GPS didn’t need to consider given the unlikelihood of deploying military forces at the Poles. This means that almost anyone anywhere will always be in sight of at least four Galileo satellites (see box).

“Another advantage is that we started later,” says Verhoef. Alongside a more advanced signal structure that increases tracking capabilities while counteracting interference, Galileo uses more accurate clocks. In fact, each satellite is equipped with four atomic clocks – two passive hydrogen masers and two rubidium clocks – that are more stable than the caesium clocks ticking in GPS and GLONASS satellites.

Better clocks and better signals mean better navigation, so that even running at reduced capacity right now the system performs about three times as well as GPS. “As a new entrant into the market this is a very good start,” says Verhoef. When fully operational in 2020, Galileo promises location accuracy down to just 1–1.5 m, vs. 3–4 m for GPS. In addition, Galileo is planning an ever better service for professional users that would offer some 20 cm accuracy.

Galileo satellite Europe GPS fullwidth - Europe’s answer to GPS

Galileo’s satellites

By 2020, Europe’s answer to GPS will consist of 24 operational satellites and a number of active spares.

Testing relativity

For scientists, a fully operational Galileo will be a boon. Roboticists will use Galileo to control swarming robots, oceanographers will monitor ocean currents precisely, meteorologists will make better weather forecasts, and climate scientists will have better data to predict how the planet is changing. Perhaps the most surprising scientific application of Galileo though is in fundamental physics – and it came about from a mishap.

In 2014 two satellites were fired into the wrong orbit due to a mechanical failure. The resulting highly elliptical orbits – instead of their intended near-circular orbits – meant the satellites lost and then gained 8,000 km in altitude as they revolved around the Earth. Although this jeopardised the two satellites’ ability to ever form part of the Galileo constellation, scientists soon realised that it presented them with an ideal opportunity to test Einstein’s theory of general relativity.

By comparing the atomic clocks aboard the satellites at their furthest and closest approach to Earth, scientists could measure “gravitational redshift” to see if it matched Einstein’s predictions. “Since 2015, we’ve been analysing the signals broadcast by both satellites in the framework of a project named RELAGAL – test of RELAtivity theory with GALileo satellites,” explains Technical University of Munich lecturer Gabriele Giorgi. Fortunately, Galileo gave Einstein no reason to turn in his grave. “Preliminary results confirm the predictions of general relativity,” says Giorgi.

More applications

While these benefits are impressive, equally profound effects are likely to be felt by society. More accurate navigation will allow companies to provide better information about nearby businesses and services through smartphones, while also helping blind people navigate cities. In emergency situations, Galileo-enabled devices will send signals that allow rapid search and rescue. Galileo’s accurate positioning will be a cornerstone technology in driverless cars. And a raft of other benefits will be felt by farmers, fishermen, civil engineers and traffic managers. In addition, says Kristian Pedersen, a Technical University of Denmark researcher, “Galileo is expected to enhance the infrastructure in the Arctic region and provide better navigation for air traffic and ships as well as support for construction and precision farming.”

Rather than being in competition, the European and American systems will complement each other. A concrete example is finding your location in areas surrounded by high-rise buildings. In urban canyons it is rare to have four satellites in direct line of sight, making navigation difficult. “Our calculations show that in a city with a few high-rise buildings your line-of-sight availability with GPS is about 45%,” says Verhoef. “But if you combine it with Galileo, the availability goes up to 95%, and obviously adding GLONASS and BeiDou will make it even higher.”

Because of this and other advantages, most devices are now being made to support multiple systems. As a result, the US is about to approve the use of Galileo for the first time, allowing users in their country to reap the same benefits of combined devices that Europeans already enjoy – and showing how technology cooperation can provide truly global benefits.

How does it work?

Cyril Botteron of the École Polytechnique Fédérale de Lausanne explains:

A Global Navigation Satellite System (GNSS) is composed of three segments: a space segment, a control segment and a user segment. The space segment is a constellation of satellites (typically more than 24) orbiting around the Earth at an altitude between 20,000 and 24,000 km, and broadcasting positioning signals towards the user segment, that is towards the GNSS receivers. The control segment monitors and controls the space segment.

Because a signal moves at the speed of light, the time it takes to reach the GNSS receiver can be used to calculate the distance from the satellite, and in turn to estimate its position in a process called multiteration that combines the measured distances from four or more satellites. The satellite’s clocks must be very accurate at the nanosecond scale (1 ns of travel-time error corresponds to about 30 cm of range error), which is why they rely on highly accurate atomic clocks.

Key dates

2003: The European Commission and the European Space Agency (ESA) agree to create the Galileo program.

2005 and 2008: Test satellites GIOVE-A and -B are launched, securing the frequencies reserved for Galileo, testing its atomic clocks in orbit and gathering environmental data.

2010 and 2011: Four Galileo in-orbit validation satellites are launched in pairs. They achieve navigational fixes and confirm the system design.

2014-2020: The remainder of the Galileo system gradually takes shape as fully operational satellites are added to the constellation. Just four more satellites are needed to complete the full 30-satellite Galileo system. The network is designed so that four satellites will always provide a signal from any place in the world.

2016: Galileo becomes operational. Products with Galileo-enabled receivers, chipsets, devices and modules immediately begin to provide global positioning, navigation and timing information.

Galileo, Global Positioning System, GLONASS, BeiDou, RELAGAL, Paul Verhoef (ESA Director of Navigation), Gabriele Giorgi (researcher at the Institute of Communications and Navigation, DLR), Kristian Pedersen (director of the National Space Institute DTU SPACE), Cyril Botteron (GNSS lecturer, EPFL)