The Apollo VHF Ranging System

Abstract

Redundancy of functions on manned space flights has been an important concept for crew safety. However, a redundant system generally implies doubled weight - a luxury that can not easily be afforded on a spacecraft. The Apollo Command Module- Lunar Module rendezvous mission was performed with the rendezvous radar system. RCA developed a VHF Ranging System, which permitted the voice/telemetry radios to be adapted as a backup for the radar's ranging function at relatively low additional weight. The proven accuracy and reliability of the VHF Ranging System resulted in its selection as the sole rendezvous sensor for subsequent earth orbital manned missions. The constraints imposed by existing radios are discussed, the ranging options and selected implementation are described, and the system accuracy is reviewed.