A COMPUTING PROGRAM FOR THE DOPPLER TRACKING OF SILENT SATELLITES,

The purpose of the computing program is to use a single Doppler curve to estimate a rough orbit of a silent satellite for purposes of identification and prediction. This report contains the assumptions, theoretical equations, code, and preliminary tracking results of this initial computing program. To test the program, two sets of Doppler data, taken during two different passes of Explorer IV, were used to predict the Explorer IV orbit, and the resulting predicted orbits were compared with other orbit determinations. It was found that about forty minutes of computing time on the Univac 1103A were required to determine a predicted orbit from one set of Doppler data. The error in the predicted satellite position was found to range from less than twenty miles for an overhead pass to about 100 miles for a more distant pass. It is shown that this error is due mainly to the neglect of ionospheric refraction and second order force terms in the theoretical expression for the Doppler shift, factors which were neglected because of the requirement of keeping computing time to a minimum. Suggestions are made for future re-coding of the program which should materially reduce the tracking error without increasing the computing time. Author