Radio science observations with Mars Global Surveyor: Orbit insertion through one Mars year in mapping orbit

Mars Global Surveyor (MGS) radio science comprises studies of the atmospher e and gravity of the planet. Perturbations of the 3.6-cm lambda radio path by the atmosphere during periods of atmospheric occultation provide the ver tical temperature-pressure structure T[p(r)] to accuracies at the surface o f DeltaT approximate to 0.4 K and Deltap approximate to 2 Pa, and similar t o 10 K and similar to0.6 Pa at altitudes of 40-50 km; the error in radius i s Deltar approximate to 1 m at all levels. Accurate knowledge of the radius permits fixing of the T-p structure to the geopotential and use of the gra dient wind equation to calculate components of the wind. Systematic samplin g of the atmosphere in combination with the accuracy of the MCS radio syste m supports studies of the large-scale dynamics of the atmosphere, including seasonal variations of the atmospheric fields and embedded waves such as K elvin and Rossby waves. Terminator region ionospheric electron density prof iles are obtained successfully much of the time but on occasion are undetec table with the MCS system. Two-way radio tracking of MGS with uncertainties in the line-of-sight velocity of several to tens of mum s(-1) and less sup ports solution for spherical harmonic models of the gravity field of order and degree in the range of 75x75, although the degree and order of meaningf ul terms is limited by the similar to 400 km spacecraft altitude to similar to 62x62, corresponding to a resolution of a few degrees of arc on the sur face. This resolution of gravity is sufficient to support geophysical studi es of the planet's interior structure and history. Additional radio science investigations include the search for gravitational radiation and observat ion of very low grazing angle forward scattering by the surface of Mars.