Apollo 12 - Experiences, Odds & Ends

Miriam

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I've decided to take a look at AP12 and take some notes along the way. Maybe it helps you guys.

Boost: nothing out of the ordinary there.
LEO: again, nothing out of the ordinary there. Even sunset and sunrise occur to the minute as the flightplan says.
TLI: well, it goes quite of in yaw, but according to the launch ops checklist, this seemed to be normal, so I just let the good old LVDC do it's thing. The values for BT, dVc and Vi RTCC MFD gives are little bit off. It overburned about 6 s or about 80 fps dVc, but as Vi seemed about right I didn't bother.
TD&E: to only thing off was that both sep and extraction attitudes seemed to be some degrees off from the PAD values in roll. No biggie, one little nudge on the roll thrusters during final approach and that was it.
PTC: once you understand how RTCC MFD handles all those REFSMMATs internally (what's this G00 stuff for, anyway?), no problem. Earth and Moon appear in the side windows as one is used to it. Had to initialize it the Collins way though. It's still Colossus 55, sure enough.
MCC-1 & 2: I'm not there yet, but RTCC gives me 56.8 fps for MCC-1 and 67.4 fps for MCC-2, which seems right, at least for MCC-2 (flightplan says 68.8). I'm digging around in my collection, but I can't find my AP12 mission rules. Maybe somebody here knows the rule when to burn it and when not.
 

indy91

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TLI: well, it goes quite of in yaw, but according to the launch ops checklist, this seemed to be normal, so I just let the good old LVDC do it's thing. The values for BT, dVc and Vi RTCC MFD gives are little bit off. It overburned about 6 s or about 80 fps dVc, but as Vi seemed about right I didn't bother.

Yeah some missions needed to do a larger plane change during TLI, especially Apollo 8 and 12, so you get a large yaw angle at cutoff.

The burn time difference seems large, but the DVC error seems like a usual value. The TLI PAD in the RTCC MFD uses an outdated "simulation" of the TLI burn. The MCC for Apollo 8, 10 and 11 on the other hand already uses a newer, better method and therefore can calculate a better DVC. But it's quite complicated to implement in the MFD, in a way that doesn't require lots of extra steps. The MFD will get this newer calculation method eventually though.

TD&E: to only thing off was that both sep and extraction attitudes seemed to be some degrees off from the PAD values in roll. No biggie, one little nudge on the roll thrusters during final approach and that was it.

This is something I have looked into and I am very confused. The roll angle we usually get seems to be very close to the roll angle on the actual TLI PADs. Not only that, from the MOCR audio I know what the FIDO commanded the RTCC to calculate for this and I also have RTCC documentation that has the relevant calculation methods. So on the RTCC side I think everything works as intended?! Can you confirm that your TLI PAD roll angle is close to what the TLI PAD on the actual Apollo 12 mission had?

So maybe it's the LVDC side, but I have also evidence against that (sadly only for Apollo 8). The roll angle is always 180° in the LVDC presettings and seems to be inertial roll. There is a difference between inertial roll and LVLH roll, the reference for this basically changes when there is a large plane change during TLI (which of course is the case for Apollo 12 as I said earlier). And if RTCC is calculating using LVLH roll and the LVDC uses inertial (gimbal angle) roll then there will be a difference.

So either: 1. This discrepancy between RTCC and LVDC is something that existed during the actual missions and I just never found a reference to it in mission reports or debriefings. That would be quite odd. Or 2. After Apollo 8 they changed how the LVDC applied the roll angle and then it matched the PADs. Would also be a bit odd. Well maybe the RTCC calculation is still off, but I don't really see how...

PTC: once you understand how RTCC MFD handles all those REFSMMATs internally (what's this G00 stuff for, anyway?), no problem. Earth and Moon appear in the side windows as one is used to it. Had to initialize it the Collins way though. It's still Colossus 55, sure enough.

Sure is that same CMC version as Apollo 11, no Verb 79 yet. The reconstruction project for Comache 67 has stalled, no estimate when we will be able to use that.

The real RTCC didn't just have one (current) REFSMMAT saved but for both CSM and LM it had a number of REFSMMAT slots. There was always a current (CUR), a previous current (PCR), which just saved the old CUR matrix when it gets changed, and a number of others. For example if you wanted a LVLH REFSMMAT (the RTCC acronym was LCV) then it didn't immediately overwrite the CUR REFSMMAT, but only saved it in LCV. Then you could uplink it, the crew does P52 and then you want to sync the RTCC to the actual REFSMMAT in the AGC. That is what the Manual Entry Device (MED) code G00 was for. "CSM/LEM REFSMMAT LOCKER MOVEMENT", so it just moves a REFSMMAT from one slot to another. There was also a telemetry slot (TLM), so saving the TLM matrix and then moving it to CUR was also a common operation.

In our RTCC MFD this system isn't consistently being used yet. In almost all cases a REFSMMAT that is being calculated directly ends up in CUR. Eventually I'll do some revisions to the REFSMMAT section and then I might change it to require REFSMMATs being moved between the different slots.

MCC-1 & 2: I'm not there yet, but RTCC gives me 56.8 fps for MCC-1 and 67.4 fps for MCC-2, which seems right, at least for MCC-2 (flightplan says 68.8). I'm digging around in my collection, but I can't find my AP12 mission rules. Maybe somebody here knows the rule when to burn it and when not.

MCC-2 and MCC-4 are preferred points for any course correction during translunar coast. Even the mission techniques document doesn't really give a good decision logic. It just says "Is MCC-2 DV minus MCC-1 DV less than * FPS?" And the * means "Real-time decision which depends on SPS reserves".

In the consumables analysis done for each mission I have often seen the value of 120 ft/s budgeted for translunar coast. So I guess if MCC-2 was more than 120 ft/s they would think about doing MCC-1? Unless MCC-2 is a lot more than planned then you would probably always skip MCC-1.
 

Miriam

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Just dug out the .scn and flew TD&E again:
RTCC MFD gives (R/P/Y) 356/092/332 as sep and 304/272/028 as extraction attitudes.
The real TLI PAD had 356/092/332 as sep and 300 (sic!)/272/028 as extraction attitudes -which makes sense, as the checklist says that you've to substract 56 degrees from the sep roll angle to come to the extraction roll angle. So IMHO RTCC isn't right there.
Btw. the SIVB steers to 000 in roll, just to add to the confusion...
Edit: final att after docking is 300/272/028.
 
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indy91

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Hmm, I'm not sure why it is 56°, because I am fairly sure the LM is rotated 60° in the SLA. Maybe there is a tolerance and Apollo 11 and 12 both simply had 56°? From Apollo 13 on the procedure to calculate the extraction attitude is R22 (roll for Noun 22) = 300° -R20. In the separation attitude. So that is 60° in roll between the separation attitude and extraction attitude.

It's interesting that it works out exactly so that the roll angle in extraction attitude becomes correct with 56°. With the way our LVDC do the calculations right now the roll angle at separation is 0°, not 356° like the RTCC says. So that difference already exists there, not just for the exctraction attitude.

The CSM IMU and LV IMU alignments are nearly the same at launch, but the way it works out is 0° roll angle in the CSM is 180° in the LV IMU. And yeah, it does steer to 0° (in the CSM) for separation already... I guess what I should try to find out is how they got to 56° difference between sep and extraction and why from Apollo 13 on the calculation in the Launch Checklist has a 60° difference.

EDIT: The "OPERATIONAL SPACECRAFT ATTITUDE SEQUENCE FOR APOLLO 12" document has:

Separation: 356.0/92.0/331.7
Extraction: 304.0/272.0/28.3

That doesn't help with the confusion either...
 

rcflyinghokie

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Apollo 11 LOC had 56 for the roll angle as well I noticed.

Are we sure all LMs had the same orientation in the SLA?
 

indy91

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Are we sure all LMs had the same orientation in the SLA?

I am not sure yet, no. Changing the value from 60 to 56° in the RTCC only would give us a correct extraction roll, but separation would still be off. Changing the way our LM is actually rotated in the SLA as well would give us yet again 4° error in both sep and extraction roll.
 

Miriam

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Another oddity: waste water dumps now take (literally) hours. I've started mine at 11:30:00 at about 75% and now at 13:10:00 I'm still sitting at 30%. From what I read in the transcripts, that should take not more then half an hour.
 

n72.75

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Another oddity: waste water dumps now take (literally) hours. I've started mine at 11:30:00 at about 75% and now at 13:10:00 I'm still sitting at 30%. From what I read in the transcripts, that should take not more then half an hour.
This one's probably my fault. I think it started around the time that I changed how vapor pressure worked in our tanks.

Was this flown from a fresh, -4 hour, launch scenario? I flew 10 recently and dont recall having this issue so I may have to look into why there would possibly be a difference.
 

Max-Q

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waste water dumps now take (literally) hours. I've started mine at 11:30:00 at about 75% and now at 13:10:00 I'm still sitting at 30%. From what I read in the transcripts, that should take not more then half an hour.
I have noticed this same problem in 7-11. All from T-4h launch scenarios.
 

n72.75

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Okay. I know what the problem is.

What I changed in the systems code, improved how vapor pressure and enthalpy of vaporization were calculated making them much more realistic. This has the effect of sucking a bit more of heat out of the waste water tank as the dump is proceeding, which in turn lowers the vapor pressure drastically.

Our valves are defined by a size parameter which controls the flow-rate through them in l/Pa/sec

I already had a fix for this: increase the dump valve size from 0.001 to 0.050. But because I only changed it my scenarios, and never pushed the update, and because it took so long to finish the mission, I completely forgot that the issue wasn't fixed.

Anyway. The update is in the works now.
 

Miriam

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So...I don't have to start over again, but just need to change a value in the scn? If so: which?

Edit: just burned MCC-2. Nothing unusual from the CMC/SPS side, that incredible thing just nailed the burn with 0 residuals in either axis.:oops:
But: now I get a dV for MCC-4 of about 36 fps. That's not good, right?
Edit2: Disregard. I forgot to store MCC-2 to the SFP and switch to SFP-2 for calculating MCC-3 and -4.?‍♀️ Now I get 1.4 fps for MCC-3 and 5.0 for MCC-4. However, are those 5 fps worth burning, anyway?
 
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n72.75

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So...I don't have to start over again, but just need to change a value in the scn? If so: which?
Find the line:

Code:
     <TANK>  WASTEH2OTANK 25.400000 1 0 0 0 0.00100000 0.00100000 0.00100000 0.00100000

and replace it with:

Code:
     <TANK>  WASTEH2OTANK 25.400000 1 0 0 0 0.05000000 0.05000000 0.05000000 0.05000000
 

Miriam

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Jupp, that's a lot better. (y)

Some questions regarding the infamous mission plan table:
  • what's DVREM? I'd figure dV remaining, but that can't be right. If I hack in the maneuver sequence (MCC-4, LOI-1, LOI-2) I get a negative DVREM at LOI-2. Or does that just mean that I'm 'below the curve' in terms of dV budget?
  • how does the PDI button work? For me it just creates a nonsense maneuver which I can't delete anymore...:cautious:
 

indy91

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  • what's DVREM? I'd figure dV remaining, but that can't be right. If I hack in the maneuver sequence (MCC-4, LOI-1, LOI-2) I get a negative DVREM at LOI-2. Or does that just mean that I'm 'below the curve' in terms of dV budget?

The propellant masses are probably not exactly correct. Those masses are stored in the MPT, but they are separate from the total spacecraft masses and are not taken into account for any trajectory calculation. And most importantly they are not updated automatically together with the other masses on the init page, so they will just be some default numbers I came up with. I need to add an input page just for the propellant masses I guess. For now there is a button with the MED input for it, M49 on the MPT page. But you would need to figure out the current (in this case) SPS propellant in pounds for it to update to the correct numbers. Then the DVREM should be the actual DV remaining using the SPS. For each maneuver the DVREM uses the engine involved in the burn for that calculation.

  • how does the PDI button work? For me it just creates a nonsense maneuver which I can't delete anymore...

Hmm, that is unfortunate. I don't know if you can get out of that one without some light scenario editing. The PDI button of course adds the PDI maneuver to the MPT. What it needs is a fully initialized LM MPT and if you are still pre DOI the DOI maneuver on the MPT as well. Also the MPT keeps track of the vehicle configuration and if you are still docked to the CSM it might try to perform PDI (and/or DOI) with CSM+LM docked. I usually let the init page automatically generate the vehicle configuration and masses, but then I change the configuration from CL to L before sending the numbers to the MPT with the M55 and M50 buttons. That way you don't need to add a separate undocking maneuver just for changing CL to L in the LM MPT.

So there is a lot of things that have to be set up correctly for the PDI maneuver to get onto the MPT, and I probably need to add several more error conditions that prevent any issues like you got...
 

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Okay, so don't give too much on DVREM.
Also the MPT keeps track of the vehicle configuration and if you are still docked to the CSM it might try to perform PDI (and/or DOI) with CSM+LM docked.
Yeah, that came to my mind, too. Doesn't matter, I just wanted to figure out how much dV it costs me not to burn this 5 fps MCC-4. Turns out: 14 fps. I think I can live with that...
Btw.: is there a way to delete a maneuver without losing the following ones? E.g. I set up MCC-4, LOI-1, LOI-2 and want to scrub MCC-4. M62,CSM,1,D deletes all maneuvers, which isn't hard to recover from, but still a little bit inconvenient.
 

indy91

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Yeah, that came to my mind, too. Doesn't matter, I just wanted to figure out how much dV it costs me not to burn this 5 fps MCC-4. Turns out: 14 fps. I think I can live with that...
Btw.: is there a way to delete a maneuver without losing the following ones? E.g. I set up MCC-4, LOI-1, LOI-2 and want to scrub MCC-4. M62,CSM,1,D deletes all maneuvers, which isn't hard to recover from, but still a little bit inconvenient.

Are you sure that is something you want to do? TIG and DV of your LOI-1 maneuver will be different if you do MCC-4 or not. So the resulting orbit of a LOI-1 maneuver that was calculated with MCC-4 taken into account will be different if the trajectory suddenly has no MCC-4 maneuver. What gets stored on the MPT is basically the TIG and DV, and not the desired, final orbit of LOI-1, so it can't automatically adjust the LOI-1 burn to compensate for no MCC-4.

If you really want to try it, there is no direct way to remove a maneuver in between other maneuvers from the MPT, but you can do a direct input maneuver (INP button on MPT page) and specify a maneuver to be replaced. Just replace MCC-4 with a CSM RCS maneuver with 0 DV. I haven't tested that much, might not work, but that's how they could have accomplished that in the real RTCC.
 

Miriam

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Well, everything turned out well in the end (without MCC-4, that is), I'm in a nice 60 NM orbit now, DOI time will be 23 s later then the flight plan and it did indeed cost me 14 fps, just as predicted. I'm okay with that.
But this DOI button still won't work. I've both vehicles in undocked mode now, updated both masses and config successfully, the DOI maneuver is on the table. However, it still creates this nonsense-maneuver. Anything I'm missing?
 

indy91

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If the initial configuration in the LM MPT is "L" and not "CL" then I am out of ideas. Maybe something Apollo 12 specific. I can take a look at the scenario.
 

Miriam

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Got it. Forgot to update the LM SV on the VPS. It was still pre-LOI-1; that can't work.?‍♀️
Btw.: how does mask 1590 work? I do know how to get the DC SV, but how do I get the CMC SV, for example?
 
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