The value of photographic observations in improving the accuracy of satellite orbits

Orbit determinations normally rely on radar and visual observations. Camera observations are shown to improve orbital accuracy considerably. Observations from the Russian AFU-75 cameras onboard the balloon-satellite Explorer 19 together with observations from the Hewitt camera at Edinburgh were used to improve three orbits of the Explorer 19 Satellite in October 1972. The camera observations improve the accuracy of the orbital elements by a factor 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 deg.