P23 Questions

ADT187

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Couple of quick questions on P23 if I may...

When you are initially asked to mark the horizon using fixed line of sight, are you expected to manouevre the spacecraft using RCS so its exact?

Or is somewhere near the correct side of the earth close enough?

Secondly, on one or two of the sightings the star concerned is actually obscured by the LM structure.... making an accurate sighting somewhat challenging!!

Just to make sure my CMC had good data I did an IMU alignment and also a manual SV update before trying again, and same results. Other stars work fine.

Any clue as to what might be going on?

Thanks,

Alex

PS: I am 25 hrs into Apollo 11, so sighting stars 01/02/44/45 EFH/ENH
 

Thespacer

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Regarding the LM obscuring the stars, this is at least true to the real thing. From the post-flight debrief:

Ground-supplied gimbal angles were used rather than those from the onboard computer. This technique was devised because computer solutions are unconstrained about the optics shaft axis; therefore, the computer is unable to predict if lunar module structure might block the line of sight to the star. The ground-supplied angles prevented lunar module structure from occulting the star, but were not accurate in locating the precise substellar point, as evidenced by the fact that the sextant reticle pattern was not parallel to the horizon. Additional manoeuvres were required to achieve a parallel reticle pattern near the point of horizon-star superposition.
 

ADT187

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OK thanks. Guess you just have to bypass the mark when this happens!

Cheers,

Alex
 

rcflyinghokie

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OK thanks. Guess you just have to bypass the mark when this happens!

Cheers,

Alex
You just need to choose a different star. What mission are you flying? There is also a chance you could have an incorrect REFSMMAT or have selected a bad star.
 

thermocalc

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Hi Alex,
I am also doing A11 currently and I remember to have experienced a similar problem ... I checked my notes and I saw that when I had to mark star 44 the 1st time at 25h it was "slightly" hidden by the LM structure, so I just select manually another star nearby ... the 2nd time instead at 25h 10m (for me 25h 13m as I got some delays) star 44 was just outside the LM structure so it could be observed and marked.....I thought that was "maybe" the reason why in the FP it was mentioned to acquire it twice at 25h and 25h 10m so I didn't bother to investigate further ... but normally you can always use the option to mark another star (not historically correct maybe but even in real life the possibility was there so for the sake of realism we may "assume" we didn't see or recognize the CMC star and we chose another one that we could see/recognize ;))...
 

ADT187

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Ah brill, glad I'm not the only one! I'll try manually selecting another star then (y)

Thank you!
 
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