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Swiss clocks set for key role in space

RAFS rubidium clock used by ESA in its Galileo positioning project. Temex Neuchâtel Time

Atomic clocks made by a small Neuchâtel company are to provide pinpoint precision for one of Europe's future space challenges.

The Temex Neuchâtel Time (TNT) clocks will play a vital role for the Galileo global navigation satellite system.

An initiative of the European Union and the European Space Agency, the system will be a competitor of the United States’ Global Positioning System and is due to become operational by 2008.

Satellite navigation users in Europe today have no alternative other than to take their positions from GPS or Russian GLONASS satellites.

However, the military operators of both systems give no guarantees to maintain an uninterrupted system, a situation that has led Europe to want its independence.

Satellite system

TNT, which employs ten people in its space division, is supplying four clocks for each of the 30 satellites that will be deployed.

“We plan to put two types of clock on board the satellites. The first is a rubidium clock in which we use rubidium atoms. That is a common technology,” Fabien Droz, the company’s head of space, told swissinfo.

“And we’ll use a more accurate technology which is based on hydrogen maser. This type of clock is better in terms of accuracy but is larger and heavier,” he added.

The hydrogen maser clock is accurate to within 0.000000001 second per day.

Maser – an acronym for microwave amplification by stimulated emission of radiation – might be more accurate but it does have a drawback apart from size.

Complex technology

“Maser is three to five times more accurate than the rubidium clocks but they’re much more complex, so for reliability reasons we will use also rubidium clocks on board,” Droz said.

“In case of failure of the hydrogen maser we can switch on the rubidium clocks,” he added.

Satellite radio navigation is an advanced technology based on the emission from satellites of signals indicating the time extremely precisely.

It is essential to have the most accurate time possible because it is a determining factor for positioning: accurate time means accurate position

“To evaluate the distance between the satellite and the user on Earth we need a very accurate time to be accurate in terms of position,” explained Droz.

“Any error in time estimation will produce an error in term of position.”

With an accuracy of better than one billionth of a second, the clocks on the Galileo satellites will allow the user to locate any position on the Earth’s surface to within 45 centimetres, according to clock expert and navigation engineer Franco Emma at ESA’s technical centre in the Netherlands.

The Galileo system, which is being developed with a 12-year lifespan in mind, is set to support a broad range of applications, including control of road, rail and sea traffic, as well as synchronised data transmission between computers.

swissinfo, Robert Brookes

Galileo, a competitor of the US Global Positioning System, is planned to become operational by 2008.
The total investment cost for Galileo is €3.2 billion (SFr4.93 billion).
As a member of ESA, Switzerland will contribute SFr35 million to the project.
The Galileo system will be built around 30 satellites (27 operational and 3 reserve craft) occupying three circular earth orbits, inclined at 56° to the Equator, at an altitude of 23,616 kms.

Temex Neuchâtel Time will provide the atomic clocks used for the Galileo global navigation satellite system.

TNT plans to install two rubidium clocks and two hydrogen maser clocks on each of the 30 satellites.

The clocks have an accuracy of better than a billionth of a second.

TNT will also supply equipment for Galileo’s ground systems.

Atomic clocks are not radioactive.

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