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    Re: Neat video about LEM stellar alignment scope
    From: Paul Dolkas
    Date: 2016 Jun 9, 21:27 -0700

    I love the fact that the backup timer for firing the ascent engine was their wristwatch. That’s why the watches also had to include stopwatches, so they knew when to turn the engine off. As I recall, the Omega Speedmaster gains or loses something like 5 seconds a day, which is horrible by today’s standards, especially considering the split-second accuracy normally demanded by orbital mechanics. I wonder if they knew what each watches’ daily gain/lost rate was in case they couldn’t reset them using the ground clock.

     

    By the way, this backup was so important, that Armstrong chose to leave his watch behind in the Lunar Module during his moonwalk – he didn’t want to risk losing it. (Can you imagine running around trying to find it someplace in the lunar dirt outside?)

     

    Paul Dolkas

     

    From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Frank Reed
    Sent: Thursday, June 09, 2016 12:54 PM
    To: paul{at}dolkas.net
    Subject: [NavList] Re: Neat video about LEM stellar alignment scope

     

    Brad Morris, you wrote:
    "Which implies a measurement good to +/-0.1°."

    Yes, I would say that's spot on. Given the other uncertainties involved in firing the ascent engine, a pointing accuracy around a tenth of a degree was good enough for a backup mode.

    Frank Reed

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