Design factors for atomic clocks for space

There are very strong differences between the designs of clocks for space applications and those used on Earth. This paper discusses the performance impacts from differences in mechanical design, thermal design, radiation hardness, and control. The design changes necessary to survive launch and operate in space go beyond the expected issues of mechanical strength and remote control. There are a number of design trade-offs that can affect clock performance. For example, the added structural members needed to secure a microwave cavity may result in poor thermal control due to heat loss along the structure or de-tuning due to new stresses on the cavity structure. Reliability and radiation hardening drive performance less directly by limiting the availability of critical electronic component types. On the positive side, the lack of gravity, fluctuations in air temperature, and mechanical perturbations sometimes lead to space clocks running better than similar ground units. The differences between clocks for short-term space experiments and production space vehicles are examined.