Analysis of multi-station technique for noise reduction in Deep Space Doppler tracking

Precision measurements of spacecraft range-rate enabled by two-way microwave links are used in navigation and in radio science experiments as planetary geodesy. The final accuracies in the observables depend almost linearly on the Doppler noise in the link. Among all the types of noise that enter a Doppler measurement, the most important are thermal noise, spacecraft antenna buffeting and ground antenna mechanical noise. Several effects at different time scales are responsible for the antenna mechanical noise, such as wind loading, bulk motion due to irregularities in the supporting azimuth ring, unmodeled subreflector motion and long-term differential thermal expansion. Therefore, it is not always simple to prevent and relieve this source of noise. The following thesis is aimed at improve the Doppler measurements exploiting a noise-cancellation technique proposed by John W. Armstrong et al. and elaborated by Virginia Notaro et al. from the mechanical and aerospace engineering department at the Sapienza University. The Time-Delay Mechanical Noise Cancellation (TDMC) technique consists in a combination of Doppler measurements given by a two-way antenna and an additional one which should be stiffer, smaller and placed in a site with good tropospheric conditions. The antenna considered for the two-way link is the DSS 25 in Goldstone, CA from NASA; for the three-way antenna has been taken the 12-m Atacama Pathfinder Experiment (APEX) in Chajnantor, Chile. The simulation is performed for a 1000 s integration time.