Not quite that accurate. Apparently it’s more like 3 seconds per million years for a rubidium atomic clock, and 1 second per 3 million years for a hydrogen mase

Not quite that accurate. Apparently it’s more like 3 seconds per million years for a rubidium atomic clock, and 1 second per 3 million years for a hydrogen maser. (Caesium atomic clocks are somewhere in between) ESA use both types onboard Galileo satellites: https://www.esa.int/Applications/Satellite_navigation/How_the_Galileo_atomic_clocks_work https://www.esa.int/Applications/Satellite_navigation/How_th...