Apollo 12: Post Landing P22 "Load MSFN Supplied Octal Acquisition Time"?

Wedge313

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Hi, Running through the Apollo 12 post-landing procedures, and not sure what to do with P22. Seems like I'm supposed to enter some octal time numbers that are supplied by mission control. I tried using the numbers that were used on the real flight (from the Lunar Surface Journal), but I'm not getting it to work as hoped. I'll have to run this procedure again a few hours before lift-off, so I need to learn how to do it. Any suggestions?
 

indy91

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The time you want to load is the acqusition time like during landmark tracking (T2). So when I flew Apollo 12 I switched to the CSM and calculated a landmark tracking PAD there and the T2 time was then what I input into the LGC.

For the conversion to octal, I am sure we can come up with a better way, but I used one of our padload worksheets (e.g. https://github.com/orbiternassp/pad...s/VAGC CSM Pad Load Worksheet Colossus237.xls) and looked for a double precision time in there, you can just use ATIGINC. And there I input the time in seconds I had gotten from the landmark tracking PAD and then to the right the two required octal values appear. Careful about the order, the right number is what you will have to input first on the DSKY. As a check, 120h GET would become 432000 seconds and that becomes 5114 and 27000 in octal.

I hope this helps!
 

Wedge313

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Thanks. Generating the tracking PAD is easy, now all I need to do is teach myself how to use an EXCEL spreadsheet. Just converting the seconds from decimal to octal gives me a number I can't enter into the LGC, thus the need to generate the double precision time? (You're thinking "How does anyone function in this world without knowing how to use EXCEL?" It was not a skill I ever needed...until now! Another learning opportunity.)
 

Wedge313

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So I've got EXCEL opened up. I've found the row where ATIGINC is (201). Column C looks like where I would enter the time in seconds (using your example I inputted 432000) but I'm not seeing anything that looks like 5114 and 27000. The spreadsheet generates values in columns E, F, and G but nothing even remotely looking like the numbers I want. Am I looking at the right spreadsheet? Thanks.

EXCEL.PNG
 

indy91

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It's not running the script to calculate the octal values. Was there no prompt to allow or disallow scripts when you opened the file? The numbers would appear where you see the #NAME?
 

Wedge313

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No, no prompts. Playing around with it I see it thinks there's some typo or other error. I've probably dug up some inferior/faulty EXCEL program, if it works for you it's got to be something I'm doing wrong. I'll look around and find something else to open the spreadsheet with.
 

indy91

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The worksheet is 15 years old, so I am pretty sure it works haha. If you are using Excel for the web, I think VBA macros (which this is) doesn't work in there.

Different method. Go here: https://coderstoolbox.net/number/

Put 432000 seconds in decimal, add two zeros because the AGC measures time in centiseconds. That gives you octal 244627000. Last five digits are the least significant word, 27000 (octal). That leaves you with octal 2446 which you have to multiply by two. In decimal that is 1318*2 = 2636 which becomes octal 5114. So your double precision octal value is 5114, 27000. Same procedure with your time.
 

Wedge313

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OK! That works for me. A few more steps than entering a number on a spreadsheet, but I only need to do it once or twice.

Thanks!
 

indy91

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In the real RTCC they had a feature to generate a custom uplink. And for that you could input numbers in engineering units, tell it what scaling and precision (single, double or even triple) you want and it would generate the data for an uplink. That would be quite helpful here I guess as it would show you the octals, even if you aren't actually uplinking it and they were just giving it to the crew by voice. I've had this feature planned for a while, it will definitely come. Including the ability to load some erasable memory programs from text files (like P99 on the later flights to deorbit the ascent stage).
 

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I did these flights in reverse order, but I find it interesting how the software seems to have improved through the flights. I used the built-in MCC feature for Apollo 11 so that flight was a lot of just inputting numbers, but then you helped me with the RTCC through 15 through 17 and then 14, which gave me a better appreciation for the whole process. I'm seeing so many procedural differences between 12 and the later flights. The LM LGC got a lot smarter with time!
 

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OK, P22 went well, thanks for the help.

New Question: I started to do my ascent planning. One of the first things I wanted to determine was the sunrise time. I want to get my sunrise time from MSK 1502. While in the CSM I went through the MPT initialization, and what I'm seeing is the CURRENT GMT time displayed on the VPS does not match my actual GMT (for example, the VPS GMT shows 156:50:12 while the actual GMT is 140:28:15). Also the CSM and LM anchor vector times are off (eg. CSM GMTAV shows 156:43:14 on the VPS, actual CSM GETAV was 140:21:13). MSK 1502 won't show SR/SS times unless I ask for times after 156:51.

The only way I could figure out to check the RTCC time was by looking at the Uplinks CMC Time Increment display 07 (MSK 340) which shows the correct GMT.

So I'm at a loss trying to figure out why the MPT VPS CURRENT GMT time is off by so large an amount, or what I can do do correct it.

Thanks.
 

indy91

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I think you are confusing GMT and GET. GMT in the RTCC is counting up from midnight Greenwich Mean Time of the launch day. The RTCC uses mainly this for time keeping, because it is an "absolute time" and doesn't depend on the liftoff time or even modified liftoff time like on Apollo 14, 16 and 17, when they changed the GET clocks to be closer to the flight plan. Apollo 12 launched at 16:22:00 GMT so that is the difference you are seeing. Note that the GMT in the RTCC is not going to zero at midnight but keeps going up. So the difference to Ground Elapsed Time (GET) is always the time of launch in GMT on the launch day.

And you can of course use the MPT with the correct displays to get the TPI time for the launch targeting. The easier way is to go to maneuver calculations, rendezvous, TPI time and calculate it there. That procedure needs no MPT and ephemeris so would be a bit easier.
 
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