Space Environment Effect on the Onboard Clock Behavior

A. V. Saltsberg, E. V. Timoshenkova, K. G. Shupen

Transactions of IAA RAS, issue 52, 57–62 (2020)

DOI: 10.32876/ApplAstron.52.57-62

Keywords: GNSS, space environment, solar activity, geomagnetic activity, onboard frequency standards, time scales, satellite clock time offset

Abstract

Space clocks play an important role in the successful achievement of mission objectives for various space programs. Thus, the task of estimating critical effects of space environment on the behavior of the satellite onboard clock is of particular importance. The main effects are successfully modelled and integrated into the design of precision clocks. However, the accuracy characteristics of the atomic frequency standards used as a part of GNSS onboard clocks are continuously improving. It necessitates identification and correct registration of experimental developmental effects, non-reproducible at ground, wich originate from the effect of the space environment on a satellite. The aim of the research is to overview the individual factors of the space environment that are proved to definitely affect the space clock, are still under consideration or are supposed to be interdependent. It is the influence of these factors on the space clock rate but not the effects appearing in radiotechnical (or optical) path that is the object of this review. The effects of the signal path are offset by using a combination of the measurements at several frequencies (ionosphere) or producing high-accuracy a priori models, and other methods. The first order effects are successfully simulated and considered in developing the precision clock. However, due to the constant improvement of accuracy characteristics of the quantum frequency generators used in the onboard clock GNSS there is a need for identifying and accurately registering the small order effects which cannot be reproduced on the ground, arising as they are from the impact of space environment on a satellite, thus being easily overlooked during the process of model construction. Since there are numerous factors connected with space environment, as well as systems involved involved in achieving the satellite mission, it is next to impossible to monitor all the possible correlations between them. The present study examines the impact of a number of solar and geomagnetic activity factors on the performance of onboard clock. This paper offers an overview of the results of studies in the field of the effect of space environment on the onboard clocks based on various physical principles. The analysis of correlations between the parameters of solar and geomagnetic activities and the behavior of GLONASS and GPS onboard clock time scales is carried out on the basis of the measurement data.

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