The Lunar Orbiter Telecommunications Systems

The Lunar Orbiter is an unmanned lunar reconnaissance satellite which takes high-resolution photographs of large areas of the lunar surface to assist in selecting a landing site for Apollo. Because of various mission aspects and the fact that the Orbiter employs a film-type camera, the requirements placed on the telecommunications system are different from those of previous U. S. spacecraft. This paper describes the design of both the spacecraft and ground equipment of the Lunar Orbiter telecommunications system. Some of the unique features of the design include the use of vestigial sideband modulation for transmission of the picture data, a full-verification command system, a low-gain antenna system whose pattern approaches that of an isotropic radiator over a large portion of the radiation sphere, and a dual-power-level transmission system which does not use RF switching. Included in the paper is a link-design chart which shows the SNRs and performance margins obtained for all operating modes.