Space qualified 5 MHz ultra stable oscillators
New demanding targets have been specified for on board ultra-stable oscillators (USO) in the frame of new programs. The aim was to reach the highest feasible frequency stability performance over life-time, with the USO operating within all space environmental conditions. Immediate applications are dedicated to accurate orbitography (new DORIS equipment) and frequency metrology (PHARAO/ACES project); further ones will cover fine positioning equipment (navigation or localization ) and time-keeping systems. This paper summarizes: 1. Xtal qualification plan and test results; 2. USO qualification test plan; 3. qualification & flight models data. Main performance measured and validated on these USO models: a) aging slope better than 1.10<sup>-11</sup>/day at early stage operation, b) mid'term/TDEV lower than 3 ns over 24 hours, c) short-term stability/Allan standard deviation from 5 to 7.10<sup>-14</sup>/1 s to 10 s, (measured with a Sapphire reference), d) thermal stability better than 3.10<sup>-13</sup>/°C, e) irradiation sensitivity below 5.10<sup>-13</sup>/rad for on-board devices, f) magnetic field sensitivity below 5.10<sup>-13</sup>/gauss. USO mechanical robustness has been validated under vibration up to 30 grms (from 20 Hz to 2000 Hz), and shocks (200 g/0.5 ms). Space USO @ 5 MHz is now available with the same performance as the best CFPO-US1 ground base models with addition of all environmental conditions linked to Space applications.