Cannot update AGS from PNGS

ggalfi

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Hi all,

I'm flying the nominal Apollo 13 mission, and now I'm at GET135 hours where - to prepare the LM for ascent - the AGS should be updated from the LGC. The problem is that when I do first V47 then set up the new time bias to 130:00:00, call 414+10000 on AGS, and press PRO, then nothing happens in AGS. I mean 414 never changes to 0, and also reading out 440 (Rdot) is inconsistent with what I see on V83. I tried to turn on and off AGS, cycle telemetry HI/LO switch, etc. but nothing helped. I've printed the LGC telemetry downlink, and during V47 it provides the AGS update list (ID:77776) as it supposed to, so something on AGS's side causes the problem. The only solution I could come up with was to copy the AGS state (section between AEA_START and AEA_END) from an earlier phase of the same mission. It made V47 working, but certainly it is just a nasty hacking. I'm rather looking for a within-simulation solution - however there isn't any hint within the checklists how the AGS could be "reseted" or "restarted". Also I have no clue how I've messed up the AGS state. I tried to do every steps according to the LM Lunar Surface Checklist to power down and later power up AGS. If anyone who knows the guts of AGS has any advice on this topic, I'd greatly appreciate it.

I've attached a scenario right before pressing PRO in V47 to begin the update.
 

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  • Apollo 13 GET+135.00.00 0001 0001.zip
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rcflyinghokie

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Can you link the specific procedures you used? I want to make sure there isn't anything that could be specific to FP7 for instance since our 13 runs FP8.
 

ggalfi

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@rcflyinghokie:
Hi, thanks for looking into this. I was using mostly the documents on this page: https://history.nasa.gov/afj/ap13fj/a13-documents.html . For the LM I've used the Activation Checklist, Timeline book and the G&N checklist. I wasn't able to find the Lunar Surface Checklist for Apollo 13, so I used the one for 14 (https://www.hq.nasa.gov/alsj/a14/a14LMLnrSurfChklst.pdf) combined with 13's flight plan. Lunar Surface Checklist contains the power up-down steps after landing and before ascent, but I can't see in it any peculiar item regarding AGS. In the specific of V47 I've used the standard procedure (but that is confirmed by the A13 LM G&N checklist as well): 1. V47, 2. Set time bias, 3. Prepare AGS for the downlinked data (414+1), 4. PRO. It worked flawlessly before PDI every time I attempted.
 
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indy91

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I think I remember now, it has to do with address 411. In FP6 and FP7 this is the engine selection, RCS/DPS vs. APS to account for the APS cant angle. In FP8 this is the command for the AGS to look for RR data in the PGNS downlink. The Apollo 13 and 14 procedures probably set 411 to 1 for ascent. That might be the cause of the problem, it's looking for RR data instead of state vectors. I can give you a more precise answer this evening. Maybe we should re-evaluate using FP8 for Apollo 13 and 14, maybe FP6 is closer to FP7 after all.

EDIT: I think doing 411+0 and then 563+0 to reset the downlink search and then 414+1 again fixes the issue. Then V47 works for me.
 
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ggalfi

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Wow, that was bullseye :) In the attached scenario if I read out 411 it displays +10000, and your procedure also smoothed this problem for me. I cannot find any step in the Surface Activity Checklist which touches 411, but it could happen that during one of the previous V47s I typed accidentally 411+1 instead of 414+1, and I wasn't aware of what harm I've caused.
On FP6 vs FP8: in the Apollo 13 LM G&N Dictionary confirms what you say, 411 is specified as a switch between APS and DPS so at least in this regard Apollo 13's version is closer to FP6.
 

rcflyinghokie

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Wow, that was bullseye :) In the attached scenario if I read out 411 it displays +10000, and your procedure also smoothed this problem for me. I cannot find any step in the Surface Activity Checklist which touches 411, but it could happen that during one of the previous V47s I typed accidentally 411+1 instead of 414+1, and I wasn't aware of what harm I've caused.
On FP6 vs FP8: in the Apollo 13 LM G&N Dictionary confirms what you say, 411 is specified as a switch between APS and DPS so at least in this regard Apollo 13's version is closer to FP6.
If you were using 14's surface checklist, 411+1 is set in the AGS powerup which on FP7 would be correct
1673400735141.png
 
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