Apollo 12 Powered Descent/LR Issue

Max-Q

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So powered descent is nominal up until pitchover & P64, then shortly after I get a flashing altitude light and the LGC never seems to accept the LR data. The velocity light remains out, and when I switched the Alt/Alt Rate tapemeter to LR to troubleshoot, it continued to show valid data so I know the LR is locked on. There were no program alarms or other odd LGC behavior, and it happens regardless of what I do with the LR antenna switch (Auto vs Hover).
If I let things continue anyway, I end up hovering at 2000 ft, horizontal velocity nulled, descent rate zero until I run out of DPS fuel.
As far as I know, I did all the activation and checkout stuff in the flightplan.
Another thing, at pitchover I didn't recognize anything on the surface, I'm not even sure I'm in the right place. Or maybe I just don't know what the landing site is supposed to look like... My PDI TIG was real close to the flightplan TIG.
Also, when I pressed Abort Stage nothing happened even with master arm on. I was able to stage with the switch, but couldn't light the APS and the LGC never went to P71.
Needless to say, things didn't end well for this particular LM.
Attached are a few scenarios.

Side question, totally unrelated and not important:
I noticed the the SHe pressure is and has been right on the line, around 1320psi, from the time I started LM power-up. It kept climbing to above 1340 before DOI, then after DOI it cam back down a bit. Shouldn't it not start to rise until the DPS is fired for the first time? Basically, why would it be at 1314psi during LM activation?
Tangent question on that, is the SHe burst disc & blowdown functionality implemented in NASSP?

Thanks in advance!
 

Attachments

  • Before P63.scn
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  • PDI -9m.scn
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  • PDI -60s.scn
    251.2 KB · Views: 70
  • Before Pitchover.scn
    253.7 KB · Views: 77

rcflyinghokie

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So powered descent is nominal up until pitchover & P64, then shortly after I get a flashing altitude light and the LGC never seems to accept the LR data. The velocity light remains out, and when I switched the Alt/Alt Rate tapemeter to LR to troubleshoot, it continued to show valid data so I know the LR is locked on. There were no program alarms or other odd LGC behavior, and it happens regardless of what I do with the LR antenna switch (Auto vs Hover).
If I let things continue anyway, I end up hovering at 2000 ft, horizontal velocity nulled, descent rate zero until I run out of DPS fuel.
As far as I know, I did all the activation and checkout stuff in the flightplan.
Another thing, at pitchover I didn't recognize anything on the surface, I'm not even sure I'm in the right place. Or maybe I just don't know what the landing site is supposed to look like... My PDI TIG was real close to the flightplan TIG.
Also, when I pressed Abort Stage nothing happened even with master arm on. I was able to stage with the switch, but couldn't light the APS and the LGC never went to P71.
Needless to say, things didn't end well for this particular LM.
Attached are a few scenarios.
I will check some of your saves later, but did you do things like updating the descent target and TLAND?

What did your PDI pad look like?

Did you set your NORRMON flag after the self tests during activation?


Side question, totally unrelated and not important:
I noticed the the SHe pressure is and has been right on the line, around 1320psi, from the time I started LM power-up. It kept climbing to above 1340 before DOI, then after DOI it cam back down a bit. Shouldn't it not start to rise until the DPS is fired for the first time? Basically, why would it be at 1314psi during LM activation?
Tangent question on that, is the SHe burst disc & blowdown functionality implemented in NASSP?
Simple answer SHe is hardcoded and isnt currently implemented as it would be in the actual LM yet.
 

indy91

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I just landed your T-60s scenario. It worked so accurately that it auto landed directly in the Surveyor crater. Somehow I couldn't get any LPD commands in though, not sure why. Maybe you never allowed LR data to go in? On Apollo 12 this procedure is a bit different. You do V57, which puts up 06 68 and then you have to PRO to allow LR data and then PRO again to get back to 06 63. That's all you have to do, but it's different to Apollo 11 and also different to later missions.

Which procedures were you following? The LM Timeline Book is missing a few pages. In the scenario I noticed that the Abort Stage and AELD circuit breakers aren't closed, those are needed for abort staging and firing the APS. The staging will usually only happen with an APS ignition signal present.

And for the SHe, the only thing that is simulate is a slow increase of temperature over time. Mass is fixed and doesn't go down when opening valves, temperature increases, so pressure also increases. Not sure what could make the pressure decrease at the moment, there is a lot to be done to simulate this properly...
 

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You do V57, which puts up 06 68 and then you have to PRO to allow LR data and then PRO again to get back to 06 63.
I did the V57, just didn't PRO twice. That would do it...
Landed successfully - On the side of surveyor crater, almost on top of surveyor itself! I didn't really care about my landing point this time, I just wanted to check out the LPD commands. Will refly and try to hit the historical landing site.

Somehow I couldn't get any LPD commands in though, not sure why.
Huh. They seemed to work fine for me when I retried it just now. :unsure:

Which procedures were you following? The LM Timeline Book is missing a few pages. In the scenario I noticed that the Abort Stage and AELD circuit breakers aren't closed, those are needed for abort staging and firing the APS. The staging will usually only happen with an APS ignition signal present.
Where can I get the LM timeline book?
I'm following three things: The Apollo 12 flightplan, NASSP's generic checklists, and my memory about how lunar missions are flown from all my runs through Apollos 10 and 11. Obviously not ideal, and I'm sure I'm missing some stuff (like the Abort Stage and AELD CBs).

Thanks so much to both of you for all the help! :)
 

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Max-Q

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That really helps! Especially the Lunar Surface Checklist.
Now I'll know that I don't leave a CB closed that shouldn't be and drain the batteries by accident...
Any idea what pages are missing in the timeline book? Especially in the ascent & rendezvous phase.
 

rcflyinghokie

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That really helps! Especially the Lunar Surface Checklist.
Now I'll know that I don't leave a CB closed that shouldn't be and drain the batteries by accident...
Any idea what pages are missing in the timeline book? Especially in the ascent & rendezvous phase.
3 and 4 are missing from Apollo 12's which basically covers separation through PDI.
 

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Crew is back in the CSM, LM is jettisoned.
For the LM deorbit burn, I ran P30 before undocking & closeout, then I run P42 for the burn. Here is where the issues start.
The P42 automaneuver points the engine the wrong way, and at TIG I get the 99 40 as expected, PRO, Ullage, and... no APS ignition. For the next attempt, I closed all the STAB/CONT breakers and set ENG ARM - ASC. Got ignition, but definitely pointed the wrong way, it ended up in something like a 200x60 orbit.
What is going on here? I also tried setting it to PNGS ATT HOLD and bypassing the automaneuver, but then the APS burns to depletion.
 

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rcflyinghokie

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Crew is back in the CSM, LM is jettisoned.
For the LM deorbit burn, I ran P30 before undocking & closeout, then I run P42 for the burn. Here is where the issues start.
The P42 automaneuver points the engine the wrong way, and at TIG I get the 99 40 as expected, PRO, Ullage, and... no APS ignition. For the next attempt, I closed all the STAB/CONT breakers and set ENG ARM - ASC. Got ignition, but definitely pointed the wrong way, it ended up in something like a 200x60 orbit.
What is going on here? I also tried setting it to PNGS ATT HOLD and bypassing the automaneuver, but then the APS burns to depletion.
First of all you shouldnt be automaneuvering, whatever you computed for your deorbit burn attitude should have been your undocking attitude as well.

For the burn, you arent burning the APS, you are letting P42 ullage until the desired dV is reached then commanding "enter" to terminate.

They did kind of a work around using uplinks here, so they tricked P42 into just commanding ullage while holding attitude until the dV was reached then they uplinked "enter" to terminate ullage. Of course later missions used EMP 99 to better facilitate the RCS deorbit burn.
 

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First of all you shouldnt be automaneuvering, whatever you computed for your deorbit burn attitude should have been your undocking attitude as well.

For the burn, you arent burning the APS, you are letting P42 ullage until the desired dV is reached then commanding "enter" to terminate.

They did kind of a work around using uplinks here, so they tricked P42 into just commanding ullage while holding attitude until the dV was reached then they uplinked "enter" to terminate ullage.
I see. A bit confusing! P42 used to... not fire the APS!
Doing it this way, it worked great. Looks like my impact point is very hear the landing site as desired for the ALSEP seismic experiment.

Of course later missions used EMP 99 to better facilitate the RCS deorbit burn.
I think a nominal Apollo 13 may be next for me, How do I simulate this? Call it advance planning...

Also, for the rendezvous in 13+, what parameters do I load for TPI at 06 55 in P32? For this run at 12 I used the same parameters as 11 (+00001, +02660, +13000) and it worked fine, but I just wondered where I get this data.
 

rcflyinghokie

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I see. A bit confusing! P42 used to... not fire the APS!
Doing it this way, it worked great. Looks like my impact point is very hear the landing site as desired for the ALSEP seismic experiment.
Great! And yeah P42 is called "APS Thrusting" so it being listed as that might have been confusing since you, well, aren't firing the APS.
I think a nominal Apollo 13 may be next for me, How do I simulate this? Call it advance planning...

Also, for the rendezvous in 13+, what parameters do I load for TPI at 06 55 in P32? For this run at 12 I used the same parameters as 11 (+00001, +02660, +13000) and it worked fine, but I just wondered where I get this data.
You will fly 13 much like 12, the major difference being you will have a DOI burn as your LOI-2. Rendezvous however will be almost identical to 12's with respect to a coelliptic rendezvous.

The TPI values should be the same as 11 and 12 (+00000 +02660 +13000) and the data can be found in Apollo 13's data cards.

As far as the P99, you can uplink EMP99 with the RTCC MFD and uplink to it with the LM TM client for realism or you can simply type the commands into the DSKY.

You can use this doc as a good reference for how P99 works and how it was used http://www.ibiblio.org/apollo/Documents/LUM168-RC_text.pdf
 

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Looking through the docs on the Apollo Flight Journal, it appears that the lunar surface checklist for 13 isn't there. I found this one, but it appears to be checklists for just the EVAs. Can I substitute 12's surface checklists since they are both H missions with similar surface ops or is it available somewhere else? I found the LM timeline book, as well as the activation checklist.
 

rcflyinghokie

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Looking through the docs on the Apollo Flight Journal, it appears that the lunar surface checklist for 13 isn't there. I found this one, but it appears to be checklists for just the EVAs. Can I substitute 12's surface checklists since they are both H missions with similar surface ops or is it available somewhere else? I found the LM timeline book, as well as the activation checklist.
This is where it gets tricky, 14's timeline book would be much closer to the planned one of 13, however there are a few changes you have to be aware of, most notably the fact that 13/14 AGS used Flight Program 7 (which we do not have) so some of the DEDA commands are incorrect for our use of FP8 on 13.
I think we are going to revert to using FP6 on 13 but we havent pushed that change just yet to the 13 scenario file.
 

rcflyinghokie

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So then I'd use the surface checklists from 15 for the AGS stuff and 14's for everything else?
I would say the values from 14's should be close enough, you just need to pay attention to the addresses. The big one to watch out for is 411, for FP8 this enables a radar updating and prevents AGS downlinks, and for FP7/FP6 it is the engine selector logic.

What I would do is have 13 and 15's G&N dictionarys open and just cross reference the DEDA addresses in 14s surface checklist and make sure you are putting the correct values in the correct addresses. Again most are exactly the same, just a few "gotchas" that can cause problems!
 

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That doesn't sound too bad. Good thing I have more than one screen to put PDFs up on for reference...
However, makes me wonder if I could just switch 13 to FP6 via the mission config file, or will this cause a bunch of odd problems?
 

rcflyinghokie

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That doesn't sound too bad. Good thing I have more than one screen to put PDFs up on for reference...
However, makes me wonder if I could just switch 13 to FP6 via the mission config file, or will this cause a bunch of odd problems?
Hmm I think it's done in code. @indy91 could this change of FP8 to FP6 be done pretty easily?
 

indy91

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It's not hardcoded, the mission files (Missions\ProjectApollo) have the flight program for each mission. If no line with FP6 or FP8 is present it defaults to FP8. I think a lot of the padload in the launch scenario would need to be changed for this, too.

The main disadvantage of using FP6 for Apollo 13 and 14 would be the loss of the second descent abort phase. Somewhere after PDI the PGNS and AGS switch to a different rendezvous profile if you abort. They added that to the PGNS on Apollo 12, with an awkward procedure for the AGS because FP6 didn't have this second abort phase yet. So that would be a problem. I think that was the main reason to use FP8 as early as possible. It has all the capabilities that FP7 for Apollo 13 and 14 also had. There are just a bunch of procedural issues (like the 411 entries) you have to be careful to avoid when using Apollo 13/14 checklists.
 

rcflyinghokie

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Ahh I didnt know about that feature, I think the slight address changes is a reasonable price to pay to have that in there.

So @Max-Q just use my previous advice and pay attention to the addresses :)
 

Max-Q

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Understood. Seems easy enough and the extra feature makes sense.
Just out of curiosity, is there any chance a copy of FP7 still exists in some archive somewhere or could it be reconstructed? Obviously a massive project, just curious.

However...
I think the slight address changes is a reasonable price to pay to have that in there.
What are these "Abort" things you speak of? I don't stop powered descent for anything... :sneaky:
 
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