Progress in the determination of some astronomical constants from radiometric observations of planets and spacecraft
Modern radiometric observations of planets, beginning in 1961, make it possible to determine and improve a broad set of astronomical constants from the value of the astronomical unit (AU) to parameters of PPN formalism. Three main factors that influence the progress in the determination of astronomical constants - 1) reductions of the observational data, 2) dynamical models of planet motion, 3) observational data themselves - are demonstrated in this paper. The reduction of the measurements included all relevant corrections, including the modeling of the topography of Mercury and Venus which reduced the rms residuals for observations by 14.5% and 23% correspondingly. The formal standard deviations of the solution elements of the planets and the AU are improved by 30-50% using the DE405 or EPM2000 ephemerides constructed in IAA (Russia) instead of DE200. It was shown that including the measurements of the Viking and Pathfinder landers, being free from the uncertainties due to planetary topography, into the observational data reduces the uncertainties of adjusted parameters by 1-2 orders. The astronomical constants obtained in the fitting process of the DE405 and EPM2000 ephemerides to data totaling more 80 000 radiometric observations of planets and spacecraft are given.