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WG3K > ANS 03.12.24 20:07z 20 Lines 4200 Bytes #42 (0) @ AMSAT
BID : ANS336.1
Read: GUEST
Subj: AMSAT OSCAR-7 50th Anniversary: CodeStore Breaking New Groun
Path: SR1BSZ<EA2RCF<LU9DCE<VA3TOK<VE3CGR<KA1VSC<WG3K
Sent: 241203/1952Z 10487@WG3K.#SMD.MD.USA.NOAM LinBPQ6.0.24
There has always been a fascination among radio amateurs in digital modes of communications. In thinking about where this spacecraft sits in electronic history, it is all too easy to forget that it was designed at least three years before the appearance of the first 8-bit microprocessor. The notion of packet communications was still nearly 10 years into the future. The team wanted to demonstrate that they could store data at-will on a spacecraft in transit across the sky and then download it at another location. They wanted to demonstrate non-real-time digital communications to themselves and to the world.
Jan King, W3GEY, AMSAT OSCAR-7 Project Manager explains, “Thinking in retrospect, that experiment wasnt the best it could have been. However, it was simple and it proved our resolve. The entry in 1972 on AO-6 and, then again, in 1974 on-board AO-7 was a demonstration experiment we called CodeStore. And, it did lead to far more ambitious packetized, store-and-forward data satellites in our future.
“It probably wasnt the best choice at the time, but we chose the command frequency for the uplink. This meant we didnt have to implement yet another receiver. However, this made the experiment far less accessible to hams than it could have. AMSAT did not want to share the knowledge of the command frequency and codes with anyone who didnt have a need to know them. Thus, CodeStore was not an experiment that was shared with everyone as were the communications transponders. It could realistically only be used by authorized command stations. We had hoped for a universal store-and-forward demonstration, but what was in fact created was a broadcast tool and in that regard CodeStore was very successful.”
CodeStore was the brainchild of and was designed and fabricated by John Goode, W5CAY. In one small module, he housed an AFSK decoding system, which allowed uplink data to be clocked into a “long” shift register containing 896 bits. This was done with the memory IC's of the day. What one could manage then was 14 IC's each containing 64 bits of serial data storage. The contents of the shift register was sequentially downlinked first-in-first-out (FIFO) to the selected beacon when CodeStore was commanded to the RUN mode.
This number of bits is divisible by 8 so one might have expected that a downlinked message of 112 8-bit words. No, this was 1974 so Morse Code messages were downlinked. The idea was more individuals can copy a broadcast message if they dont need specialized decoding equipment. King adds, “No one can deny that we could have made a better go of it if the notion of a remote terminal digital communications goal had remained pure. It did not.”
“Ultimately, its highest value was discovered to be to store the spacecrafts NORAD TLEs as well as any critical AO-7 operating schedule modifications, which might be of importance to the users. CodeStore was already available for use on AO-6. So, users were already expecting this feature, which appeared regularly on the beacons.”
While CodeStore was used on both AO-6 and AO-7 to demonstrate non-real-time communications via satellite, it was never used by independent remotely located stations to demonstrate two-way communications in that way. The memory facilities required on-board and the lack of any firmware that even approached the capabilities of a file handling system did not exist in 1972-74. That would have to wait for another day when, once again, four AMSAT spacecraft in a small constellation would demonstrate a proper store-and-forward packet handling system. That was to occur in 1990.
CodeStore went into service as a broadcast device allowing users to receive, in Morse Code, the latest, (then) NORAD TLEs. CodeStore was a complete success. It saved command stations a tremendous amount of work, avoiding the need for a global network of operators who would otherwise be needed to relay the same data.
Persons wanting to read more about the life and history of AMSAT OSCAR-7 are invited to visit https://www.amsat.org/amsat-ao-7-a-fifty-year-anniversary/.
[ANS thanks Jan King, W3GEY, AMSAT OSCAR-7 Project Manager for the above information.]
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