High accuracy time and frequency from space

Accurate time and frequency are fundamental components of modern metrology. The potential now exists to provide global access to a primary time and frequency laboratory operating aboard an orbiting space platform. Such a laboratory could provide primary time and frequency, in terms of the internationally agreed definition of the second, with unprecedented accuracy. Operated in space, a frequency standard based on freely drifting atoms could provide accuracy approaching 1 part in 10 ¹⁶ higher than is currently available. This capability, in turn, would enable a globally shared basis for the unit of length in terms of the definition of the meter. This paper reviews the concept of such a frequency standard and the availability of components and systems for its operation. We discuss the possibility of highly precise time and frequency transfer, based on previously developed and tested microwave and pulsed laser technology, along with the corrections required to account for effects of general relativity