AN ENSEMBLE OF ULTRA-STABLE QUARTZ OSCILLATORS TO IMPROVE SPACECRAFT ONBOARD FREQUENCY STABILITY

摘要

In the past years, we have reported on continuous improvement in the capability of our Time and Frequency Laboratory at the Johns Hopkins University Applied Physics Laboratory and its contribution to the TAI. We have discussed our ensemble of hydrogen maser and cesium beam atomic clocks into a timescale that enables UTC (APL) to be steered within ± 20 nanoseconds per month of UTC. A significant element to the control of UTC (APL) has been the use of our autonomous timescale algorithm, reported in 2005 at the combined PTTI and IEEE FCS.In our laboratory report this year, we will discuss experimentation using this timescale algorithm to investigate the timekeeping capability of an ensemble of three quartz ultra-stable oscillators (USO). This experimental ensemble could represent the frequency references of a system of spacecraft, similar to those proposed in deep space missions of long duration. Although these spacecraft would likely be in regular communication with the ground segment controllers, it may be necessary that they operate autonomously for periods of time ranging from a few days to several weeks. To make this possible, we are considering improvement in the frequency stability of the onboard timing reference that will act as a fly-wheel when frequency corrections from mission controllers have been temporarily interrupted. We present experimental data and examine the compliance of the ensemble of three USOs to a frequency stability of better than ± 1 × 10~(-11) per week.