Long-term frequency aging rate for unpowered space-class oscillators

The presented data will provide empirical evidence that may be used to estimate the performance of backup, unpowered oscillators for long term space missions, as well as an aid in validating the worst case analyses that are routinely performed on these oscillators. An essential component of any space vehicle is the onboard master oscillator and the proper operation of the entire payload is dependent on the performance of the master oscillator or the onboard clock. For instance, phase-locked loops and receivers operate within limited frequency ranges; hence, the master oscillator for these systems must be tunable within these limits over mission life. For maximum reliability the onboard clock is often provided as a dual or triple redundant ensemble, with one active oscillator. The backup oscillators are usually powered off. The mission life of most space vehicles is typically 10 to 15 years and the primary clock may at times experience a failure or an anomaly resulting in the activation of one of the backup oscillators. The backup oscillator may have been off for a significant period of time but it would have to perform as well as the replaced primary clock. A significant parameter of importance for oscillator performance is the aging rate. Various papers have been presented on the aging performance of active oscillators in space, but very little data exists regarding the long term aging performance of oscillators in the non-operating mode. The aging rate data is extremely important for predicting the expected performance of these backup oscillators after 10 or 15 years in space. In this paper we will present performance data derived from TCXOs, VCXOs and OCXOs that have been dormant for significant amounts of years. In fact, all oscillators were manufactured between 1968 to 1985 and after initial testing no power have been applied until recently when tested in late 2007 and early 2008. The TCXOs and VCXOs were constructed with cold-weld AT-cut, and FC-cut 3rd overtone crystals. The VCXOs were manufactured with SC-cut, 5th overtone, cold-weld quartz resonators. An estimate of radiation effects in space will also be presented.