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    Michael Collins and the sextant on Apollo 11
    From: Frank Reed
    Date: 2021 Apr 28, 14:05 -0700

    As you know Apollo 11 command module pilot Michael Collins passed away today. He was the guy who stayed in orbit while Neil and Buzz landed on the Moon. Although the sextant was already in a backup role for navigation (apart from the critical role of spacecraft orientation by stars which used the sextant as an astro-compass), Collins as CMP still had to fight with the sextant and work through various procedures that were part of the mission plan. In the Apollo 11 Technical Air-to-Ground transcript, you can follow along. Here's an example exchange, and again, CMP here is Michael Collins. The timestamps are days, hours, minutes, and seconds of mission elapsed time:

    "01 00 45 35 CMP

    It's really a fantastic sight through that sextant. A minute ago, during that AUTO maneuver, the reticle swept across the Mediterranean. You could see all of North Africa, absolutely clear; all of Portugal, Spain, southern France; all of Italy, absolutely clear. Just a beautiful sight.

    01 00 45 54 CC
    Roger. We all envy you the view up there.

    01 00 45 59 CMP
    But still no star.

    01 00 47 19 CC
    11, this is Houston. Over.

    01 00 47 23 CMP
    Roger. Go ahead, Bruce.

    01 00 47 25 CC
    On our ground computers we confirm the shaft and trunnion angle that you have as being pointed at the star. However, it looks as though that shaft and trunnion angle is also pointing into the structure of the LM, so that while you will be getting the Earth's horizon, the star ... is obscured by the LM. We recommend an AUTO maneuver to the attitudes pen-and-inked into the flight plan. Roll 1772, pitch 2982 and yaw 330.0. Over."

    You'll note the last comments from CC (Mission Control, Cap Com) mentions that the LM (lunar module) is getting in the way. This was a recurring problem with the Apollo spacecraft design. They had designed the command module with the sextant near the nose of the cone of the spacecraft and unfortunately on the way to the Moon, that's where the LM was docked. Even when it wasn't directly in the way, parts of it in direct sunlight often caused glare which made the sextant nearly impossible to use.

    To explore this transcript for navigation details, I recommend searching on the word "sextant" and also star names like "Vega" and "Deneb" (apparently those two were always paired). 

    In another portion of this official NASA transcript, we read that it is "impossible to say if the 1876 Cruelty to Animals Act would be violated unless and until the monster is found." Yep. Apollo 11 on the Moon... searching for monsters. :)

    Frank Reed

       
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