ACES microwave link requirements

摘要

Atomic Clock Ensemble in Space (ACES) is a project of the EuropeannSpace Agency on-board the future International Space Station (ISS). Thenpayload consists mainly of two atomic frequency standards, one spacenhydrogen maser (SHM) prepared by the Observatoire de Neuchateln(Switzerland), and one cold atom caesium clock called PHARAO prepared bynthe CNES (France), with the participation of the BNM-LPTF, the ENS-LKB,nand the CNRS-LHA. Because of the anticipated performances of thesenclocks on-board the ISS, the requirements of the links between thenpayload and the clocks on the Earth are at the limits of the knownnpotential of the optical or microwave techniques. The microwave linkn(MWL) requirements are described in this paper. Taking into account thencharacteristics of the ISS orbit, and fixing an arbitrary limit to thenadditional noise brought to the clock readings by the MWL, thencomputation of the required stability leads to two kinds ofnrequirements: the first one at the subpicosecond level over each singlencontinuous pass of the ISS above any Earth station, and the second onenat the level of one part in 1016 and below over a one day ornmore averaging period. Moreover, the ISS orbit parameters should lead tona knowledge of the ACES clock position at the m level, and of the ACESnclock speed at the mm/s level