The operational Galileo satellites will carry two types of clocks – passive hydrogen masers and rubidium atomic frequency standards. Each satellite will be equipped with two hydrogen masers, one of which will be the primary reference for generating the navigation signals, with the other as a cold (non-operating) spare.
Every operational satellite will also carry two rubidium clocks, one of which will be a hot (permanently running) backup for the operational hydrogen maser, instantly taking over should the maser fail and allowing signal generation to continue uninterrupted. The second rubidium clock will act as a cold spare.
GIOVE-A, the Galileo in-orbit verification satellite that is currently in service, carries two rubidium clocks – one operational and one cold spare. GIOVE-B, which is projected to enter service later this year, will carry one hydrogen maser and two rubidium clocks, one hot and one cold spare. The GIOVE-A2 satellite, which will be ready for launch in the second half of 2008, will carry a similar timekeeping payload to GIOVE-A, but will transmit additional navigation signals.
The Galileo passive hydrogen masers will keep time with an accuracy of around one nanosecond (one one-thousand-millionth of a second) in 24 hours – equivalent to losing or gaining a second in 2.7 million years. The rubidium clocks are accurate to 10 nanoseconds per day. In comparison, an ordinary digital wristwatch has an accuracy of about one second per day.
Galileo’s passive hydrogen maser clocks will be around one thousand million times more accurate than a digital wristwatch.
The need for accuracy
Conceptually, Galileo users will determine their position by measuring how much time radio waves transmitted by satellites in the Galileo constellation take to reach them. Radio waves travel at about 300 million metres per second, so they cover a distance of around 0.3 metres in one nanosecond. In order to offer navigation accuracies of the order of a metre, Galileo time measurements must therefore be performed with a precision in the nanosecond range.
As a by-product of satellite navigation’s need for accurate timekeeping, Galileo will also be able to offer precision time services to be used, for example, in the time stamping of financial transactions.
Galileo is a joint initiative between ESA and the European Commission. When fully deployed in the early years of the next decade, it will be the first civilian positioning system to offer global coverage.
Dominique Detain | alfa
NIST's antenna evaluation method could help boost 5G network capacity and cut costs
11.12.2018 | National Institute of Standards and Technology (NIST)
ETRI exchanged quantum information on daylight in a free-space quantum key distribution
10.12.2018 | National Research Council of Science & Technology
Over the last decade, there has been much excitement about the discovery, recognised by the Nobel Prize in Physics only two years ago, that there are two types...
What if a sensor sensing a thing could be part of the thing itself? Rice University engineers believe they have a two-dimensional solution to do just that.
Rice engineers led by materials scientists Pulickel Ajayan and Jun Lou have developed a method to make atom-flat sensors that seamlessly integrate with devices...
Scientists at the University of Stuttgart and the Karlsruhe Institute of Technology (KIT) succeed in important further development on the way to quantum Computers.
Quantum computers one day should be able to solve certain computing problems much faster than a classical computer. One of the most promising approaches is...
New Project SNAPSTER: Novel luminescent materials by encapsulating phosphorescent metal clusters with organic liquid crystals
Nowadays energy conversion in lighting and optoelectronic devices requires the use of rare earth oxides.
Scientists have discovered the first synthetic material that becomes thicker - at the molecular level - as it is stretched.
Researchers led by Dr Devesh Mistry from the University of Leeds discovered a new non-porous material that has unique and inherent "auxetic" stretching...
10.12.2018 | Event News
06.12.2018 | Event News
03.12.2018 | Event News
11.12.2018 | Physics and Astronomy
11.12.2018 | Materials Sciences
11.12.2018 | Information Technology