Communications at megamile ranges

Megamile communications call for the fullest use of advanced modern technology. This paper surveys the design of a deep-space communication system. The basic constraints and capabilities of a low-noise ground receiving system are covered in detail, including antenna temperature contributions from galactic noise, tropospheric and ionospheric attenuation, and earth radiation through antenna side lobes. Low-noise preamplifiers, large high-gain antennas, and narrow-band phase-lock receivers are also considered. Digital biphase modulation, used in Pioneer V, is compared with more sophisticated bi-orthogonal coding systems. Both types of coding systems are compared with error rate as a parameter, with the ideal error-free Shannon limit. The design of Pioneer V and its record of achievement are described. Included are explanations of the coherent transponder within the spacecraft, and of the command transmitter and telemetry reception equipment at the ground stations.