Antenna Mechanical and R. F. Systems Measurements and Alignment Using ALSEP

A valuable spin-off asset of the lunar exploration program has been the use of the Apollo Lunar Surface Experiments Package (ALSEP) transmitter systems for angular alignment as well as RF systems checks and alignment of AFETR large aperture telemetry antennas.Accurately known ALSEP antenna coordinates on the lunar surface, together with those of a telemetry antenna on the earth f s surface, makes possible accurate computation of antenna look angles versus time. In order to refine the accuracy of these angles, it was necessary to include the effects of nutations of the earth and librations of the moon. The resulting accuracy of computed antenna look angles is one or two orders of magnitude greater than that of techniques commonly used such as that using the sun's radio frequency noise emission. The use of Cassiopeia A is restricted due to the low level of flux density emitted by this star. Only high gain antennas are suitable for tracking Cassiopeia A, therefore it is impossible to make alignment comparisons with lower gain antennas.The ALSEP is a very practical tool which enables real time problem analysis and possible correction of alignment of antenna systems readout devices in almost real time.The availability of information on the performance of the ALSEP transmitter makes possible simple and accurate assessment of RF systems performance quality. In addition, the tracking availability of about 12 hours each day makes it an extremely valuable training aid for antenna system operators.The possibility of using the ALSEP angular data to navigate surface ships, which have accurate S-band tracking antennas and associated on-board digital computers, warrants investigation.