Passenger on board Jason-2
The T2L2 instrument (Time Transfer by Laser Link) was launched on board the Jason-2 satellite on 20 June. This CNES mission, conducted in collaboration with the Côte d’Azur Observatory, will use laser signals to synchronize clocks. It is already functioning with a network of 25 ground laser ranging stations and atomic clocks, out of the 50 such stations operating around the globe.
“The ground stations send laser pulses to Jason-2,” explains Philippe Guillemot, T2L2 Operations Project Leader at CNES. “T2L2 receives the signals, which are partially reflected back to the transmitting stations.”
“Each step is time-tagged very precisely to determine the time difference between the orbiting clock and clocks on the ground. Everything is then synchronized using complex algorithms.”
In September, it provided a 1st independent comparison with the DORIS instrument’s clock, which is not an atomic clock but an ultrastable quartz oscillator. This oscillator is a key component of DORIS, which helps to determine Jason-2’s orbit precisely and thus enhance altimetry mission performance.
Two new experiments
“The aim is to refine the instrument’s calibration, as we already know the result: there should be no difference between the two,” says Philippe Guillemot. For the 2nd experiment, in 2009, the Paris Observatory will conduct a series of laser firings to validate T2L2’s performance.
There are many immediate applications for atomic clock synchronization, including banking operations and geolocation systems like GPS. Ultimately, the experiment will also serve a wide range of science missions, particularly in fundamental physics. And one day it may even be used to test some of the principles of Einstein’s theory of relativity.