A Miniaturized OCXO for Space Application with Low Radiation Sensitivity

The CNES engaged in 1996 a program of development of miniature OCXO for space applications. In an objective of costs reduction, it was decided to use (COTS) which were qualified by the methods of the aggravated tests . The first oscillator developed is a DIL 14 case OCXO called EWOS-513 which flies already on the Rosetta space probe and which is embarked on all micro-satellite Myriade space bus of the CNES. This oscillator exhibits a typical short term stability of a few 10-11 over Is, with a thermal sensitivity of 10^-9 /degC and an aging of a few 10^-10 per day. However this first generation of oscillators had an important radiation sensitivity, of electronic origin, which led to a fast and important degradation of its short term stability. The TES company decided to realized some studies in order to reduce this sensitivity and their results were so encouraging that we have developed a second generation of oscillator, the EWOS-513/B. The qualification campaign by aggravated tests has been just completed by tests in irradiations with low dose rate up to 100 kRad. The results obtained are very favorable : The short term stability degradation observed on the preceding generation of oscillator have completely disappeared and the oscillators preserve its performances up to 100 kRad. But beyond this first conclusion, it arises from these measurements a strong homogeneity of the behaviors, a low dose sensitivity and a relative insensitivity to fragmented irradiations. This contrast with all that was observed until now, more especially when we know that the resonators used are not swept. This paper, after a rapid presentation of the EWOS-513/B oscillator, will describe the conditions of tests and the results obtained. In conclusion, it will try to make proposals to go further in the comprehension of this problem.