Optical Measurements on Telstar.

Abstract

The problem was to determine the orientation of the spin axis of the Telstar satellite as a function of time. Plane and fluted metal reflectors were fitted to Telstar, and for certain positions of the satellite in its orbit these mirrors reflected light from the sun to an observing station at Crawford's Hill, Xew Jersey. For any one mirror, the signal received was a short train of small pulses of light-one pulse per revolution of the satellite. A 12-in. aperture Cassegrainian telescope was set up on an M-33 radar mounting which could be driven so that the telescope was pointed continuously at the satellite. A pulse-operated camera was used with the telescope, or alternatively the light pulses could be made to fall on the cathode of a photomultiplier tube. The electronic equipment was triggered by the resulting pulses, and produced records of the time of occurrence of the pulses. From such data it was possible to show that soon after launch, the spin rate was about 3 rps and the axis of spin was oriented close to the perpendicular to the plane of the ecliptic. To obtain sufficient time resolution with the incoming signal, the photomultiplier output was continuously displayed on a cathode ray tube with a long persistence screen. Whenever a pulse was received of an amplitude sufficient to operate the triggering circuit, a drive pulse was passed to a camera which photographed the trace still persisting on the cathode ray tube screen.