Abstract :
The accuracy of position determination required for the various purpo for which earth satellites may be used is discussed briefly. The capabilities of optical tracking methods are indicated. The three principal radio methods are those using radar, Doppler fre quency shift and interferometer techniques. Although radar has already been used to some extent in satellite tracking, its main use is likely to be in connection with manned satellites and the arrangement for the U.S. project Mercury is described. The use of the Doppler frequency shift of the signals received from a moving satellite may be utilized in the determination of its orbit and, provided full use is made of the observed data and allowances made for ionospheric refraction, very precise orbital information can be obtained, as illustrated by the development of the Transit navigation system. The tracking system in most general use at the present time is the inter ferometer in which directional information is obtained from measure ments of the phase difference between the satellite signals received on a spaced aerial system. The U.S. Minitrack system is of this type and the construction, operation and performance of the station installed at the Radio Research Station Winkfield Field Station are described in detail. The paper concludes with a brief review of future trends in satellite tracking by radio.
