The Value of Photographic Observations in Improving the Accuracy of Satellite Orbits

摘要

With the great majority of close Earth satellites (99.5%), orbit determinations normally have to rely on radar and visual observations of accuracy about 200 m. When there are also camera observations, of accuracy about 10 m if the height is about 1000 km, the orbital accuracy can be considerably improved; but the degree of improvement has been difficult to predict. Large numbers of observations from the Russian AFU-75 cameras in the years 1971-1973 have recently become available, particularly of the balloon-satellite Explorer 19, from the observing stations at Riga, Helwan, Khartoum and Fort Lamy. These, together with observations from the Hewitt camera at Edinburgh, have been added to improve three orbits of Explorer 19 in October 1972 already well determined from radar, visual and kinetheodolite observations. The addition of the camera observations improves the accuracy of some of the orbital elements by factors of up to 11, while other orbital elements benefit much less. The reasons for the differences are identified, the most important being the number of camera plates and the spread of the stations in latitude. As a by-product of the work, the cross-track residuals of 12 visual observers were evaluated: their mean was 0.02. (Author)