Eagle undocks, Apollo 11, July 20, 1969


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An evening pause: In honor of the fiftieth anniversary of Apollo 11, today’s evening pause shows the moment when the lunar module Eagle undocked from the command module Columbia. Though this video includes communications with mission control at the start, the actual undocking occurred on the back side of the moon, when the astronauts were out of touch with the Earth.

Near the end of the video, after they have reacquired communications with the ground, you can hear a recitation of a long string of numbers. This is mission control providing the astronauts the numbers that had to be uploaded into their onboard computer so that it could correctly fire the spacecraft engines at the right time and for the right duration.

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7 comments

  • Alex

    Beautiful.
    Sailors.
    So incredibly far beyond the horse latitudes.

    Sailors of The Sea. The Sea.

  • wayne

    Alex–
    see: The Doors, “Horse Latitude’s”

    slightly ahead of the mission, but some great James Burke stuff!

    James Burke Apollo 11 moon landing
    1979 retrospective
    https://youtu.be/8XuJj1zXkDw
    7:45 (excerpt)

  • Andi

    “you can hear a recitation of a long string of numbers. This is mission control providing the astronauts the numbers that had to be uploaded into their onboard computer so that it could correctly fire the spacecraft engines at the right time and for the right duration.”

    Just think about that for a minute. They had to READ numbers ALOUD to the astronauts so that the numbers could be MANUALLY loaded into the computer. Shades of the BBC reading codes to the underground during WW2.

    It’s absolutely amazing what they accomplished with the limited technology of the time!

  • Edward

    Andi,
    These numbers were the result of computations by the big computers on the ground. They gave instruction to the small on-board computer (one each in the command module and the lunar ascent module) for making the next maneuver. By separating these processes, the on-board computers could be small and light weight.

    There were back-up procedures for getting home safely in case communications between the spacecraft and Earth were lost, but most of the computing power was on the ground.

    This system also allowed for a small operating system in the on-board computer, which helped when the 1201 and 1202 alarms occurred during Eagle’s landing. The computer rebooted due to these alarms, but it was able to reboot quickly and so didn’t miss a beat during the landing.

    There is a book, “How Apollo Flew to the Moon,” that describes many of the systems and much of the equipment that were used in going to the Moon. It also explains the numbers that were entered for a few of the maneuvers. I would have loved to have had such a book back in the 1970s.

  • wayne

    Edward–
    Thanks for bringing that up.

    related– you might enjoy this:

    Behind the Apollo 11 on-board computer
    NASA programmer Don Eyles
    July 15, 2019
    https://youtu.be/z4cn93H6sM0
    7:17
    “Perhaps the most dramatic moment of Apollo 11’s mission to the moon was when the Eagle began its final descent to the lunar surface and the Apollo Guidance Computer became overloaded. Few were more nervous than the young computer programmer who had written the code for the landing…”

  • wayne

    Weaving software into core memory by hand
    “Rope Memory”
    https://youtu.be/P12r8DKHsak
    2:02

  • wayne

    ah… here we go:

    MIT Science Reporter—
    “Computer for Apollo” (1965)
    https://youtu.be/ndvmFlg1WmE
    29:20

    “This 1965 MIT Science Reporter television program features the Apollo guidance computer and navigation equipment, which involve less than 60 lbs of microcircuits and memory cores. Scientists and engineers Eldon Hall, Ramon Alonzo and Albert Hopkins (of the MIT Instrumentation Laboratory) and Jack Poundstone (Raytheon Space Division in Waltham MA) explain and demonstrate key features of the instruments, and detail project challenges such as controlling the trajectory of the spacecraft, the operation of the onboard telescope, and the computer construction and its memory.”

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