Concepts for high precision time and frequency transfer between Earth and space clocks

Operation of new space fountain clocks now provides levels of accuracy and frequency stability approaching one part in 10/sup 16/. We offer some ideas for providing access to this accuracy and stability with Doppler cancelling microwave techniques that employ coherent carrier phase. Corrections for relativistic effects will require continuous tracking of position and velocity at levels of precision that are now realistically expected from Global Positioning System which also provides time transfer capability to enable high precision orbit-to-orbit recovery of phase in the Doppler canceling system.