Famous reverse-engineer Ken Shirriff has as soon as once more turned his consideration to a chunk of spacefaring historical past, uncovering the aim behind an odd gadget from the Apollo program dubbed the Up-Information Hyperlink Confidence Check Set.
“Again in 2021, a collector pal of ours was visiting a dusty warehouse in the hunt for Apollo-era communications tools,” Shirriff explains. “A field with NASA-style lights caught his eye — the ‘AGC Affirm’ mild urged a reference to the Apollo Steerage Pc. Disappointingly, the field was simply an empty chassis and the circuit boards have been all lacking. He continued to poke across the warehouse when, to his shock, he discovered a bag on the opposite aspect of the warehouse that contained the lacking boards!”
A comparatively easy diagram, painstakingly puzzled out: meet the Apollo Up-Information Hyperlink Confidence Check Set. (📷: Ken Shirriff)
With the chassis and its boards reunited, it was potential to determine what the gadget did — aided in no small half by the presence of a label on the rear, figuring out the machine because the “Up-Information Hyperlink Confidence Check Set” from Motorola. This, Shirriff and mates surmised, was designed for use on the bottom to check the Up-Information Hyperlink (UDL) system — designed to ship digitized instructions from the bottom to an orbiting spacecraft.
Documentation, nevertheless, proved sparse. “Mike [Stewart] discovered one NASA doc that talked about the Check Set,” Shirriff remembers, “however the doc was remarkably uninformative. Sadly, this was not very useful because the diagram merely exhibits the Check Set as a rectangle with one wire in and one wire out.”
A scarcity of documentation is one factor, however the machine as-recovered was additionally lacking key elements — leaving Shirriff with extra of a puzzle than traditional. Inspecting every of the gadget’s 25 particular person circuit boards, a block diagram was produced — with extra puzzling required to determine precisely what was occurring with Motorola-branded modules, constructed from discrete elements however absolutely encapsulated like a extra fashionable built-in circuit. This, Shirriff explains, required an X-ray machine to look on the components inside.
“As soon as I discovered the circuitry on every board, the subsequent drawback was figuring out how the boards have been related,” Shirriff writes. “I quickly realized that manually tracing the wiring was impractically gradual: with 25 boards and 47 connections per board, brute-force testing of each pair of connections would require a whole lot of 1000’s of checks. To automate the beeping-out of connections, I constructed a system that I name Beep-o-matic. The thought behind Beep-o-matic is to mechanically discover all of the connections between two motherboard slots by plugging two particular boards into the slots.”
A specific problem got here in tracing the backplane wiring — for which Shirriff designed an automated software, the Beep-o-matic. (📷: Ken Shirriff)
With that, Shirriff and mates have been in a position to full the reverse-engineering and restore the check field to purposeful standing — not solely with the ability to use its built-in paper-tape reader however actively use it to generate alerts to be used with different recovered Apollo {hardware}, together with an S-band communications system. “We have not transmitted these alerts to the Moon,” Shirriff admits, “however we’ve got transmitted alerts between antennas just a few toes aside, receiving them with a field referred to as the S-band Transponder.”
The total write-up is accessible on Shirriff’s web site; design recordsdata and supply code for the Beep-o-matic have been launched on GitHub underneath an unspecified license, although Shirriff warns “that is unlikely to be helpful to anybody else.”
