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Mercury ion space clock

At present atomic clocks fly on satellites in Earth orbit, but there are no atomic clocks in use on spacecraft exploring the solar system. Atomic clocks at DSN stations worldwide are the cornerstone for all deep-space navigation, since measured frequency differences between uplink and downlink are a direct measure of space-craft velocity through the Doppler effect. In complementary measurements, the pulsed round trip time from DSN station to spacecraft is timed to within 10 ns providing range measures to spacecraft accurate to 1 meter. We are developing a small, ultra-stable space-clock physics package suitable to maintain a few ns timing accuracy for many days and weeks.

space clock

Figure 1: Partially assembled Space Clock prototype

The clock physics package technical approach follows and parallels developments in other space vacuum tube technologies already used in deep space, for example, traveling wave tube amplifiers. In the physics tube now in fabrication, gas flow methods and moving parts used for evacuating the tube are eliminated. We have completed a carefully integrated physics package by use of materials to withstand high temperature thermal degassing. This allows the tube to be sealed while maintaining ultra-high vacuum sufficient for 10 or more years operational life. Ultra-violet optical system will be fabricated from UV grade sapphire to deliver much longer-lived source bulbs than fused silica currently used.

NEWS:Deep space GPS will benefit from the work done in our group. Read more news on the Deep Space Atomic Clock and the mission highlights at this NASA website.


  1.   John D. Prestage, Sang K. Chung, Robert J. Thompson and Paul MacNeal, V.S. Ilchenko and L. Maleki, “Progress on Small Mercury Ion Clock for Space Applications,”European Freq. & Time Forum ?Int. Freq.Control Symp 2009, Besancon, France. April 2009.
  2. John D. Prestage, Meirong Tu, Sang K. Chung, and Paul MacNeal, “Compact Microwave Mercury Ion Clock for Space Applications,”IEEE International Frequency Control Symp. Honolulu, Hawaii, May 2008