Galileo clocks keeping good time

Stephen Withers
Tuesday, 22 May 2007 08:44

Science - Space

The rubidium clocks carried by the Galileo project's GIOVE-A satellite are operating largely as expected after their first year in orbit.

Galileo is Europe's answer to the US Global Positioning System, and accurate timekeeping is essential for a satellite-based system to provide precise fixes on the Earth's surface.

Signals from GIOVE-A, together with those from GPS satellites, are combined with ground-based laser ranging of GIOVE-A to determine the accuracy of the clocks allowing for delays introduced by the Earth's atmosphere and the receiving equipment.

According to ESA officials, "The precision of the calculations is so great that even the tiny orbit disturbances caused by the pressure of sunlight shining on the satellites is taken into account."

No unexpected ageing or degradation has been observed, and the clocks are expected to exceed the required 12-year operational lifespan. As with other rubidium clocks, changes in frequency have been observed and the Galileo team is ground testing some design changes to reduce their occurrence.