Planned on a similar scale to (the US) GPS, the network (due to be operational in 2017) will have 24 satellites (the minimal number for global coverage) with six more as backups. Galileo’s main difference from GPS is an orbital altitude 3,000 kilometers (1,864 miles) higher, which in turn points the satellites at a sharper angle back toward Earth: 56 degrees instead of 52. This will yield two benefits, project director Marco Falcone says: better coverage in “urban canyons,” where surrounding buildings can interfere with the GPS signal, and in the polar regions that European and other companies will increasingly be tapping for oil and other resources.
Galileo also aims to improve on GPS with a new kind of onboard clock powered by hydrogen laser technology. Very reliable clocks are essential: A deviation of one nanosecond—one-billionth of a second—per day translates to a 30-centimeter (12-inch) mistake in location, Falcone says. Galileo’s new clock will make the system more accurate than the current generation of GPS, which has a “worst case” margin of error of 7.8 meters (compared with Galileo’s four).
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