Accession Number : AD0707333

Title :   A REAL-TIME DATA COMPRESSION SYSTEM FOR APOLLO PCM TELEMETRY.

Descriptive Note : Technical memo.,

Corporate Author : JOHNS HOPKINS UNIV SILVER SPRING MD APPLIED PHYSICS LAB

Personal Author(s) : Carlton,A. George ; Zink,Harry D. ; Appel,Robert L. ; Gafke,Gary P.

Report Date : DEC 1969

Pagination or Media Count : 181

Abstract : The Johns Hopkins University Applied Physics Laboratory (APL) has developed a method of applying data compression to the pulse coded modulation (PCM) telemetry bit stream from Apollo spacecraft. The compression could be applied to the data transmission on the link between the Manned Space Flight Network (MSFN) sites and Goddard Space Flight Center (GSFC) to give a savings in realized telephone cable capacity and to transmit more information to Mission Control. The method of data transmission developed permits all the data in the 51.2 kbps bit stream from the Command Service Module (CSM) or the Lunar Module (LM) to be sent in real time over two 2.4-kbps voice-data-quality telephone lines. Very basically, the system uses a zero order predictor with a variable window to screen out redundant data; run length encoding is used to encode the location sequence, and '2-9' encoding is used to encode the data values. Combining these two coding schemes results in 88 bits per frame, on the average. This technique requires modification of the present computer software only; it does not require any hardware changes. (Author)

Descriptors :   (*MANNED SPACECRAFT, TELEMETER SYSTEMS), (*DATA TRANSMISSION SYSTEMS, TELEMETERING DATA), MULTIPLEXING, CODING, REAL TIME, PULSE CODE MODULATION, DIGITAL COMPUTERS, COMPUTER LOGIC, CONTROL SEQUENCES, COMPUTERS, SHIFT REGISTERS, COMPUTER PROGRAMS

Subject Categories : Computer Programming and Software
      Computer Hardware
      Manned Spacecraft

Distribution Statement : APPROVED FOR PUBLIC RELEASE