DORIS-class oscillator under radiations: the Jason family of satellites

The Jason family of satellites, which were launched in 2001, 2008 and 2016, embarked an ultra-stable-oscillator (USO) as the on-board frequency reference (short-term stability of a few 10(-13) at 10-100 seconds) for the Doppler Orbitography and Radiopositioning Integrated on Satellite (DORIS) tracking system. All three satellites shared the same orbit (circular, 66 degrees, 1335 km) and platform (PROTEUS) which is 3-axes stabilized. And all three oscillators have been perturbed by repetitive radiation exposures above the so-called South Atlantic Area, which implied deleterious frequency variations of various levels roughly from 10(-1)2 to 10(-11). The primarily objective of this work is to compare the frequency response of these USOs to radiations. On the assumption that all environmental parameters (proton flux from the SAA, position, orientation of the platform, etc.) are identical, we demonstrate that the oscillators present the same behavior with a pseudo-periodic frequency variation at 59 days whilst enhancing a different sensitivity. From all the perturbation sources, a dedicated exposure to radiations is identified due to a very particular situation - platform and attitude law, orbit, satellite anisotropy.