High Reliability PCM Telemeter System for Lunar Orbiter Spacecraft

Abstract

The PCM Telemeter System described in this paper was designed and developed specifically for the Lunar Orbiter Spacecraft (LOS). Its functional capabilities are those of a good general-purpose PCM Telemeter. Reliability of the PCM System was the most important design consideration. The system reliability of Ps 0.986 for a 30-day mission was endeavored to be met through the use of Hi-Rel piece - parts qualified to existing Minuteman/Gemini/Apollo/LEM high reliability specifications. The Reliability Program was based on NPC 250-1. In operation, the PCM Telemeter accepts three types of input signals, (1) high level analog, (2) parallel digital (bilevel), and (3) serial digital data. The analog signals are multiplexed and encoded with an accuracy of 0.2% including over-all linearity of 0.1%. Digital data is interlaced into the output word format by the system as it is received. System timing is normally synchronized with an external clock. However, if the external clock fails, timing is automatically switched to an internal clock source and thus the PCM System will continue to function. The basic output bit rate for the PCM System is 50 bits per second. The PCM Telemeter supplies "read-in" pulses to other external equipment as timing commands for reading serial digital data into the PCM. The PCM also provides a 50 PPS shift pulse to an external 26-bit serial digital channel register. The PCM Telemeter can be divided, for purposes of exolanation, into six subunits: •Analog Multiplexer •Analog-to-Digital Converter •Digital Multiplexer •Programmer •Output Shift Register & Formatter •Power Supply.