The International Space Station is upgrading its timepiece. An atomic clock constructed by EADS Astrium will arrive at the ISS in 2014, providing the most accurate timekeeping to date in space, better synchronization of clocks on Earth, and the opportunity to learn a few things about time itself.
Cesium clocks, like the one the National Institute of Standards and Technology uses to keep the official time in the U.S., generally rely on the microwave signals that electrons emit when they change energy levels to keep highly precise, consistent measurements of time (it's estimated that the NIST's current clock won't gain or lose a second for more than 60 million years).
The cesium atoms are laser-cooled, then launched upward into a sensor cavity where instruments can tap into that microwave frequency that gives us our standard concept of the second, minute, hour, etc. A microgravity environment the atoms spend longer in the microwave chamber, and that should allow for better measurements of the microwaves emitted, making the Atomic Clock Ensemble in Space (ACES) 100 times more accurate as the clocks ticking away on satellites.
As a bonus, a single frame of reference in space could help atomic clocks back on the ground synchronize better, and it might even reveal if certain physical constants are as constant as physics says they are.
Would there be compensation for relativistic time differences?
I think not, since I imagine part of the point of having this clock is to get a better idea of the effect of relativistic time differences.
"As a bonus, a single frame of reference in space could help atomic clocks back on the ground synchronize better"
I figured that they would use it to study relativistic time differences, it is just interesting that they would use it as a single frame of reference when the difference is still being studied.
As an aside, is it posted anywhere what the ISS's speed is compared to us?
Go to nasa.gov/ station, then put Cartesian state vector in the search tab, because it's velocity is dependent on it's current altitude.