On the Use of Short Arcs in Orbit Determination.

At the IAF Congress in Stockholm in 1960, J. Kowalevsky urged that osculating elements of satellite orbits be determined for individual station passages. This implied determinations from short arcs. The present investigation shows that, with the ex ception of the semi-major axis, the elements of the orbit of Echo I can indeed be determined from a rcs with a half-arc length of lh.4 to 4h to the same accuracy as from conventional 1-day arcs. Several such determinations over an interval as short as 30 hours reveal deviations from gravitational behavior. Using 1-day arcs, such deviations can be readily found only from determinations spanning a longer interval.