SpectraTime’s atomic clocks in Galileo
Founded in 1995 under the name Tekelec Neuchatel Time, SpectraTime, now a subsidiary of the Orolia Group, is developing space qualified atomic clocks (Rubidium Atomic Frequency Standard - Rb AFS and Passive Hydrogen Maser - PHM) from basic technology first developed at the Observatory of Neuchatel.Space qualified atomic frequency standards (AFS) are used primarily in navigation satellites but are also found in specialized communication satellites and have been used for one planetary mission. AFSs have lower drift rate and inherent insensitivity to radiation when compared to conventional crystal oscillators. Therefore, atomic clocks have been recognized as critical equipment for the satellite navigation system. That is because the principle of navigation by satellite is based on the transmission to the users of signals coming from at least four satellites. To get one-meter-level positioning and navigation data, these signals must be synchronized to a billionth of a second.
Rb AFS and PHM are at present the baseline clock technologies for the Galileo navigation payload. Galileo is a joint initiative of the European Commission and the European Space Agency (ESA) for a state-of-the-art global navigation satellite system, providing a highly accurate, guaranteed global positioning service under civilian control.
According to the present baseline, the 30 satellites of Galileo will embark two Rb AFSs and two PHMs. The adoption of a dual technology for the on-board clocks is dictated by the need to insure a sufficient degree of reliability and to comply with the Galileo lifetime requirement of 12 years. Both developments are based on early studies performed at the Observatory of Neuchâtel from the end of the 1980s and SpectraTime since 1995. These studies have been continuously supported by Switzerland within ESA technological programs.India and China choose Swiss clocks
In December 2005, an experimental satellite, GIOVE A, was launched and a second satellite ( GIOVE B) was launched in April 2008 to test some of the critical technologies, such as the atomic clocks, among other things. GIOVE A was supplied by Surrey Satellite Technologies Ltd., with two Rubidium AFSs supplied by SpectraTime. The first signals from GIOVE A were transmitted on January 12, 2006.
One PHM physics package manufactured by SpectraTime and integrated by Selex Galieo and two Rb AFS on board the satellite (GIOVE B) supplied by SpectraTime were launched in April 2008. The PHM not only improve by a factor 10 or more the autonomy of the system but also greatly improve its accuracy.
After the successful tests validating the world most stable atomic clocks in orbit SpectraTime signed an 11 million euros contract with Selex Galileo to provide the core elements of the PHM for the first 14 satellites of Galileo. Another contract to supply the Rb AFS is about to be signed. Meanwhile, China’s Beidou (a.k.a. Compass) satellite positioning system are equipped with both Chinese Rubidium clocks and Swiss clocks purchased from SpectraTime. The Compass constellation is planned to have 27 satellites in medium earth orbit, five in geostationary earth orbit, and three in inclined geosynchronous orbits. Also the Indian Regional Navigation Satellite System (IRNSS), planned to have three satellites in geostationary orbit and four in geosynchronous orbit, will have a payload of 3 Rubidium clocks. This redundant clocks ensemble is manufactured by Astrium GmbH using SpectraTime AFS.
En français dans le texte
Horloges suisses pour GPS
Spin-off de l’Observatoire de Neuchâtel, SpectraTime équipera en horloges atomiques précises au milliardième de seconde le système européen de positionnement par satellites Galileo. L’entreprise vient de signer un contrat pour livrer les masers à hydrogène passif des premiers 14 satellites du système. En parallèle, sa technologie d’oscillateurs au rubidium a déjà été adoptée par les systèmes indiens et chinois.