Tracking the Earth Satellite, and Data Transmission, by Radio

The next round of problems created by an earth satellite after it is placed in its orbit are those associated with proving that the satellite is in fact orbiting, and the measurement of its orbit. The magnitude of these problems for optical methods is discussed, and the Minitrack system developed by the Naval Research Laboratory for acquisition and tracking of the satellite by radio techniques is described. A sub-miniature radio transmitter operating continuously for at least two weeks will be provided within the satellite to illuminate antennas at ground tracking stations. By phase-comparison techniques, these ground stations will measure the angular position of the satellite as it passes through the antenna beam, recording its "signature" automatically without the need for initial tracking information. Analysis of this signature will provide the complete angular history of the satellite passage in the form of direction cosines and time. These data will be transmitted immediately to a central computing facility for the computation and publication of ephemerides. Specific ephemerides will be transmitted to each principal optical tracking station to provide acquisition data to them. The probable tracking accuracies and the major problems associated with the Minitrack System are described.