Long-term behavior of rubidium clocks in space

The generic, very long duration performance of rubidium (Rb) atomic clocks in space has implications ranging from deep-space missions to the outer planets to global-navigation satellite systems like Galileo and GPS. Here, using telemetry and frequency tuning data collected from spacecraft clocks that have been in operation continuously for anywhere from 2 to 11 years, we consider the performance and viability of Rb atomic clocks for very long duration space missions. While the results that we present are general in nature, and in no way system specific, they are nonetheless important and rarely available for space-mission planners.