Synchronization for space based ultra low frequency interferometry

Recently, there is a renewed interest in space based arrays for low frequency observations. Orbiting Low Frequency Antenna Array (OLFAR) is one such project which investigates the feasibility of a space based array of ≥ 10 satellites, observing the cosmos in the 0.3 - 30 MHz spectrum. The OLFAR cluster will be deployed far from Earth, with occasional communication with Earth, which presents new challenges in synchronization and localization of the satellites. In this paper, we present first order clock requirements for interferometry in general, by modeling the clock error as a polynomial in time. The bounds on the short term and long term clock requirements of the OLFAR satellite are defined in terms of jitter and Allan deviation respectively. Given a robust clock up to coherence requirements, it is shown that it suffices to assume the clock as a first order model. A list of commercially available clocks which meet OLFAR requirements are discussed and joint localization and synchronization solutions which cater to the needs of OLFAR are suggested.