Characterization of an ultra stable quartz oscillator thanks to Time Transfer by Laser Link (T2L2, Jason-2)

Abstract

The T2L2 experiment (Time Transfer by Laser Link), on-board Jason-2, with an orbit at 1335 km, since June 2008 allows the clock synchronization between ground clock (generally H-maser) and space clock (quartz Ultra Stable Oscillator (USO) DORIS) with a stability of a few picoseconds over 100 seconds. In common view, when two laser stations see T2L2, the time transfer stability is less than 10 picosecondes over few seconds. In order to perform non-common view time transfer for synchronizing distant ground clocks, it is important to precisely characterize the on-board oscillator at least on 10,000 seconds (maximal flight time between two distant stations). The key is to study the space environment on the Jason-2 orbit, to separate deterministic and stochastic behaviors of the USO (shift and drift). We show that T2L2 is able to provide accurate frequencies, which are deduced from the ground to space time transfer over each laser station (few 10−13). Since 2008, these time transfers helped us to create an on-board frequency data base. The major contributors to these frequency variations on 10,000 seconds are temperature and space radiation especially due to the South Atlantic Anomaly (SAA) (in which Jason-2 pass through). Aging can be considered as a linear drift during 10,000 seconds and the effect of radiation like a very small shift over each SAA overflight. The effect of the temperature is drived by the on-board temperature measurement. A model is realized to represent these effects on USO with a RMS of few 10−13 over 10,000 seconds. Space phenomena are also playing an important role in long term. Actually, if we consider both accumulation dose received by radiation and aging, we can explain 99.9 % of the global frequency variation of the USO since the beginning of the T2L2 mission.