Restoring the Apollo Lunar Module Guidance Computer...
Posted: Mon May 29, 2023 1:15 pm
So close on bingo fuel...
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- Commander, David R. Scott Apollo 15Among his other achievements, Apollo 14 brought Eyles a special notoriety — including an invitation to the White House. Less than four hours prior to the planned descent from lunar orbit, the bright red Abort button on the LM's instrument panel illuminated and began sending a spurious signal to the computer that would have aborted Alan Shepard and Edgar Mitchell's landing at the moment the descent engine was ignited. Eyles had written the code that monitored that signal. At 1:00 in the morning he was called on to attempt to write a workaround for the problem, with no allowance for error. In less than two hours, not only did he write the workaround, but it was verified in simulators at both MIT and Houston, and then read up to the crew. That clever workaround simply changed a few registers, first to fool the abort monitor into thinking that an abort was already in progress, and then to clean up afterward so that the landing could continue unaffected. The procedure required inserting 61 precise and sequential keystrokes on the computer keyboard (the DSKY) under severe time pressure. Mitchell executed the procedure flawlessly and it worked perfectly. Apollo 14 landed at its target point on time, and the Apollo program once again proceeded without a major setback. An Apollo 14 failure, coming after the near-tragic failure of Apollo 13, would very likely have doomed my mission, Apollo 15, to a paper exercise. (Apollos 16 and 17 were already facing cancellation.) Eyles solved that problem — and thank goodness he did.
Eyles, Don. Sunburst and Luminary: An Apollo Memoir . Fort Point Press. Kindle Edition.Margaret Hamilton's role: Hamilton in 2016 received the Medal of Freedom from President Obama with a citation stating that she "led the team that created the on-board flight software for NASA's Apollo command modules and lunar modules." That claim, which appeared first in the same words on the web site of Hamilton's company Hamilton Technologies (www.htius.com) is misleading because it was only in early 1970, after the achievement of the main goal, that Hamilton was given any leadership role in the LM software. (The organization chart of the Apollo effort at the MIT Instrumentation Laboratory, dated Feb. 1, 1969, available at www.doneyles.com/LM/ORG [MITApolloOrg] snapshots the leadership structure of the Apollo effort at MIT during 1969.) Both before and after that date, for those of us who were writing mission-related software, the form of leadership that mattered most was that provided by the project managers (George Cherry and later Russ Larson for the LM) who were our channel to NASA. Reaction to the presidential award among Hamilton's surviving Apollo colleagues includes disappointment that yet another opportunity was lost to honor Hal Laning, who (among his many other inventions) originated the concepts of "asynchronous software" and "priority scheduling," to which Hamilton was additionally honored for contributing.