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Old 08-14-2019, 12:28 PM   #1
kneecaps
Orbinaut
Default A11 and the first P52 - maneuvers?

The first P52 for A11 around GET 00:50:00, to date I've only done this with whatever stars I could find....however I noticed that historically was done with stars 30 and 37.

Curiously I've repeatedly found that I cannot sight these stars without using the SIVB to manuver to sight these stars without exceeding allowed trunnion angles. (The trunnion angles exceed 90 degrees in the time frame of the P52 which is not permitted by P52 for sightings).

I also don't notice in the flight journal or mission reports any mention of SIVB maneuvers (Buzz mentions only SIVB at orb rate).

I don't see from the sources I've checked that any kind of clear mention of crew controlled attitude changes of the SIVB in parking orbit prior to TLI. The only thing I've found is a mention at
002:04:12 "Guidance to IU".

This could imply that the switch was sent to CMC (implying crew control over attitude) or it could just be calling out a check.

Before I scour the MCC audio loops does anybody have any thoughts how the historical stars would have been usable for P52 at this time without maneuvers? If maneuvers were in fact performed, if Orbiter is something 'out' with regards to this.
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Old 08-14-2019, 04:26 PM   #2
indy91
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I very much doubt that they went to CMC control for the P52. Maybe you just have the timing a bit wrong, the mission report says the P52 was done at 0:48h GET, but in the transcript it is even a bit earlier, maybe 0:45. So if Collins let the computer decide which stars to use it probably was around 0:45. At that time stars 30 and 37 should be available.
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Old 08-14-2019, 04:28 PM   #3
MrFickles
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According to AFJ transcripts, Apollo 11 peformed their P52 starting at approximately MET 00:44.

Looks to me that they acquired star 30 at ~00:45:02, and star 37 at ~00:46:45.

Using the historical times, and starting my P52 at MET 00:44, CMC was able to automatically acquire both star 30 and 37. I can also confirm that performing P52 at MET 00:50 as per the NASSP checklist puts both stars just out of range.

On a side note: I say the crew acquired stars 30 and 37 but according to the transcripts, it seems to me like they were absolutely winging it.
Collins reported being able to see Menkent through the telescope but not the sextant. He also couldn't tell whether he was looking at Nunki through the telescope, but there was a star in the sextant, so he just marked it. Despite that, they managed to get a star angle difference of 0.01.

Last edited by MrFickles; 08-14-2019 at 04:33 PM.
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Old 08-14-2019, 05:50 PM   #4
Thymo
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Honestly it doesn't really matter if you use the historical stars. I always let the CMC pick a pair and align to that.
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Old 08-15-2019, 02:44 AM   #5
kneecaps
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Quote:
Originally Posted by Thymo View Post
 Honestly it doesn't really matter if you use the historical stars. I always let the CMC pick a pair and align to that.
Exactly what I have always done...except for the first time when I tried historical stars, to my surprise I couldn't actually sight on them without manuvering with the SIVB ... As Indy points out, this looks to be a VERY tight timing issue.

The P52 is earlier then timelined in reality and Collins looks to be REALLY fast with his work. Judging by the timestamps on the audio he seems to site on both stars in a little over 60 seconds. I suspect with the optics joystick, physical switches and a real DSKY in reach you can be really fast. It's pretty impressive considering the Orb Rate rotation...I find chasing the moving star a challenge and have never done better than 00001 when the stars are moving :D

---------- Post added at 02:44 AM ---------- Previous post was at 02:40 AM ----------

Quote:
Originally Posted by MrFickles View Post
 According to AFJ transcripts, Apollo 11 peformed their P52 starting at approximately MET 00:44.

Looks to me that they acquired star 30 at ~00:45:02, and star 37 at ~00:46:45.

Using the historical times, and starting my P52 at MET 00:44, CMC was able to automatically acquire both star 30 and 37. I can also confirm that performing P52 at MET 00:50 as per the NASSP checklist puts both stars just out of range.

On a side note: I say the crew acquired stars 30 and 37 but according to the transcripts, it seems to me like they were absolutely winging it.
Collins reported being able to see Menkent through the telescope but not the sextant. He also couldn't tell whether he was looking at Nunki through the telescope, but there was a star in the sextant, so he just marked it. Despite that, they managed to get a star angle difference of 0.01.
Great input thanks.. Yes, in my case in reality I'm probably going the P52 always a little after 50..closer to 53. 30 and 37 are way out of reach by then it seems, 7 minutes later than historical.

I see now my notion that they may have maneuvered was a faulty first assumption. They clearly used whatever stars they could find at the time.

"Mystery" solved :D
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