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Galileo prepares to take off

Europe’s satellite navigation system enters the test phase.

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The launch of two satellites on October 20 means that Europe’s Galileo satellite navigation system is speeding up.
Credit: ESA – S. Corvaja, 2011

Galileo, the largest program ever launched by the European Space Agency (ESA), will enter its final phase with the launch of two navigation satellites on October 20. They will join two test satellites already in orbit, enabling the first tests of the Galileo network, a rival to the US Global Positioning System (GPS).

Scientists in Europe are closely monitoring the program’s progress, hoping that the satellite constellation will enable new or improved research. Nature exposes what the latest releases mean for Galileo and the scientific community.

How does satellite navigation work?

Everything is in time. Navigation satellites carry ultra-precise clocks that regularly transmit the time and their orbital positions to Earth. The signals travel at the speed of light, reaching the Earth’s surface after a very small delay. By comparing the arrival times of signals from different satellites, a receiver can determine how far away it is from each and deduce its own position on Earth.

Galileo is the European satellite navigation system. Costing more than €5 billion (US$6.93 billion), the network will eventually consist of up to 27 operational and three spare satellites in three orbital planes. The test satellites to be launched tomorrow will for the first time allow operators to test the system, including its ground stations.

How is Galileo different from existing systems such as GPS?

The short answer is that Galileo is not that different from GPS or the Russian GLONASS system. But he has a few tricks up his sleeve. Galileo will transmit over a wider range of frequencies than other systems, and the first satellites will carry clocks based on hydrogen masers, devices that exploit an ultrastable transition in hydrogen atoms to achieve accuracies up to five times better than the current GPS standard. .

How will scientists use Galileo?

Satellite navigation systems are of enormous importance to science, says Bertram Arbesser-Rastburg, head of ESA’s Electromagnetism and Space Environment Division. Researchers use GPS and GLONASS for everything from tracking wildlife to studying the movement of tectonic plates; Scientists around the world will use Galileo to make similar measurements.

In many fields, Galileo will strengthen existing measurements, says Seth Gutman, an atmospheric scientist at the US National Oceanic and Atmospheric Administration’s Earth System Research Laboratory in Boulder, Colorado. Signals from navigation satellites are often used to study the atmosphere, and the ability to monitor atmospheric changes “depends heavily on how many satellites are transmitting signals, where they are in space and time, and how many receivers are in the Earth tracking these signals. Gutman says. Galileo will augment GPS and GLONASS information.

Will Galileo be able to do something that GPS cannot?

For certain applications, Galileo stands out. For example, scientists are interested in using navigation satellites to measure features on the Earth’s surface. By looking at the reflected satellite signal shining off water or land, researchers can make specific measurements of things like sea level and soil moisture. Because Galileo operates over a wider bandwidth than GPS, it will provide more accurate reflection measurements.

What other scientific potential does Galileo have?

Galileo’s clocks will be able to test some alternative theories of gravity, according to Jorge Páramos, a physicist at the Lisbon Higher Technical Institute. Clocks many times more precise than those on today’s Galileo satellites would allow fundamental tests of Einstein’s predictions about how Earth’s mass warps space-time. However, it is unclear whether such precise clocks will ever be developed for Galileo, because they would have little commercial value.

Two more satellites will be launched in 2012, and by 2015 or so, enough satellites should be in orbit to provide some initial services. ESA aims to have the full constellation of 30 satellites in orbit by the end of the decade.

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Cite this article

Brumfiel, G. Galileo prepares to take off.
Nature (2011).

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