Doppler tracking of spacecraft with multi-frequency links

Abstract

We discuss the use of multi-frequency microwave links in Doppler tracking of interplanetary spacecraft for scientific purposes, especially in relation to the measurement and the elimination of the contribution due to the plasma in the solar wind and the ionosphere. We show how the two contributions in the up- and the down-link can be separately measured with a five links scheme; for the ordinary case in which we have two carriers in the down-link, but only one in the up-link, (for which the plasma contribution can be directly measured only for the former) we find the optimum algorism for computing the latter contribution. We also discuss in detail Doppler measurements near opposition, which can provide information on the dynamics of the turbulence in the solar wind and, in particular, study the dispersion of its modes. Finally, we discuss the use of multi-frequency links in experiments near solar conjunction.