Long‐period perturbations in starlette orbit and tide solution

Abstract

Continuous and dynamically consistent orbits have been computed using satellite laser ranging (SLR) data to Starlette for a one‐year period during 1976 and 1977 and the three‐year period from 1983 through 1985. A low degree and order ocean tide solution, consisting of a total of 66 tidal parameters from 14 tidal constituents, was obtained in a combined solution using both the one‐ and three‐year Starlette orbits. An enhanced model of the Schwiderski [1980] tide solution was used both as the a priori and the background tide model. The model contains 368 tidal coefficients from 21 tidal constituents. Yearly values for the second‐degree annual tides, Sa, which produce seasonal variations on the Starlette node, were obtained also. These variations were found to have year‐to‐year fluctuations of more than 25% about the mean value and produced significant long‐period perturbations in the Starlette orbit. The Starlette tide solution is in good agreement with the Schwiderski tide solutions and with other satellite solutions, including multi‐satellite tide solutions. The average uncertainties are approximately 0.1 cm for the estimated semidiurnal and diurnal tides and 0.4 cm for the long‐period tides. The discrepancies of effective k2 inferred from the Starlette tide solution and other tide solutions are less than 0.01. The tide solutions were evaluated using orbit fits of a three‐year LAGEOS and a one‐year Starlette long arc. The results indicate that the Starlette tide solution produces significantly improved orbit fits for both LAGEOS and Starlette. The uncertainties for the estimated tide model coefficients were used to predict tidal errors for the LAGEOS orbit and were found to be consistent with the apparent tidal errors present in this orbit. The computed secular change in the Moon's mean motion due to tidal dissipation is −24.8±0.8 arc second/century2, which is in good agreement with the results obtained from other investigations.