Apollo 12 TLI results in large MCC-1?

Wedge313

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Hi,

I'm running the Apollo 12 mission, and just finished MCC-1 at T+11h 48m. It was a much larger burn than I hoped to see (65.7 fps, using about 1.6% of my SPS fuel). I used option #5 in the RTCC when calculating the MCC.

I had a question about the TLI burn. Starting the burn the yaw was 001. The burn looked normal for the first 1:40, then the spacecraft began to slowly yaw to the left, until at the end of the burn the yaw was 017. I don't remember seeing this much yawing on any of the other TLIs I've run (Apollo 8,11,15,16,17,14). Is this yaw unusual, or have I just not noticed it before?

Looking ahead to MCC-2 at T+30h 52m, my expected dV looks like 2 fps (again using option #5), so it appears I'm back on an ok course. But I'm curious about the TLI yaw. Is that normal or was something done incorrectly?

Thanks
 

rcflyinghokie

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This all looks normal to me. Remember Apollo 12 used a hybrid FRT and TLI targeted a high pericynthion of 280 miles, so an MCC2 of about 65 fps sounds expected to drop this back to 60. If you checked your MCC2 dV and MCC1 dV, the difference should have been small and you would choose the recommended burn point of MCC2.

The yaw is also completely normal to place you on the correct lunar plane for the landing site.

Actual mission commanded yaw at TLI ECO was 18 degrees, and actual MCC2 was 61.8.
 

Wedge313

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Thanks. I did look at what the MCC-2 values were, and like you said they were a couple fps less. But I was questioning the yaw and wanted to get back on a better trajectory. Just as long as I'm in the ballpark and not eating into my SPS budget too deeply.
 

indy91

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In the launch checklist you can find these tables, left side is nominal TLI and right side is manual TLI:


The greek letter psi is the yaw angle during the burn. And what you saw is probably close to the nominal TLI. During a manual TLI you simplify the procedure a bit and use a constant yaw angle, 8° in this case. That is slightly suboptimal and might need a bit more DV, but not much.

Don't worry about the SPS budget, the combined MCC-2 and LOI-1 would not very different (or even less!) if your TLI had targeted 60 NM pericynthion altitude. MCC-2 really is the preferred point and the flight plan is based on burning MCC-2 and not 1. Doing MCC-1 instead of 2 costs a bit less DV, but they wanted more hours of ground tracking, so MCC-1 would only be done if TLI was quite off-nominal.
 

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Jupp, I had that, too, when I flew 12. Just be careful with your RCS fuel, you'll have to do a lot a more maneuvering and tracking in lunar orbit then 11, so don't waste too much on those P23s and use the wide deadband for PTC. Or better turn off the jets completly. Yes, it will cone around a bit, but that's okay. And use 0.2 deg/s rate in the DAP when the LM is attached. 0.5 deg/s can be a real burner...
 

rcflyinghokie

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Jupp, I had that, too, when I flew 12. Just be careful with your RCS fuel, you'll have to do a lot a more maneuvering and tracking in lunar orbit then 11, so don't waste too much on those P23s and use the wide deadband for PTC. Or better turn off the jets completly. Yes, it will cone around a bit, but that's okay. And use 0.2 deg/s rate in the DAP when the LM is attached. 0.5 deg/s can be a real burner...
This is all outlined in the flight plan. Dap changes, disabling quads, changing deadbands etc are all there for a reason. There is plenty of margin for P23s and such.
 

Wedge313

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I need to get a better copy of the flight plan! I'm using what looks like the FAO's copy, and all the intro stuff is missing. And the DAP changes for 12 aren't in the main body of the flight plan like they are for other flights (usually in the top left of every page), so I need to get a more complete flight plan.

Thanks all for the info.
 

Wedge313

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Thanks for the flight plan. But I'm not seeing any info on what they wanted the DAP settings to be at different points throughout the flight. Where would I find that?
 

rcflyinghokie

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Thanks for the flight plan. But I'm not seeing any info on what they wanted the DAP settings to be at different points throughout the flight. Where would I find that?
They are shown as they are changed in the flight plan. Here are a few examples:
Screenshot 2022-08-20 080745.jpg
Screenshot 2022-08-20 080810.jpg
Screenshot 2022-08-20 081032.jpg
 

Wedge313

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OK, I saw the ones at 4h and 7h. But I'm at 61h now, and the last DAP change I saw was the one at 7h. It just seems like I changed the DAP more frequently than that on other flights.

EDIT: I'm missing something. At 7h they want us to widen the deadband to 30 deg (I guess using the procedure in the AOH 4.8.2.2?). Then nothing changes until LOI-2? I can understand the wide deadband for PTC, but seems like we'd tighten that for the MCC's and LOI-1?


Thanks for the help.

Unrelated question: At 56h they talk about uplinking a dH value if the P23 dH values were off by 5 km. What's going on here? Does uplinking a CSM SV take care of that? And why km instead of miles?
 
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Miriam

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It automatically thightens back to the N46 deadband when you do some things.
Out of memory:
  • THC-CW and back to neutral
  • SC CONT - SCS and back to CMC
  • V48
  • V37EXXE (yes, selecting P00 also collapses the deadband. For clearing the DSKY I usally do a V82E and leave it with PRO)
When I remember right the checklist calls for V48 when you terminate PTC, so that's taken care of.

This particular dH is the altitude above earth's horizont P23 thinks you are marking on. Even in Orbiter earth's horizont is a fuzzy thing, the real earth is even fuzzier. During training, every CMP sooner or later found his 'sweet spot' to mark on, and this value was fed in the CMC for flight. To refine this Houston would take the data from the P23s the CMP did during the first days of flight and come up with a new value for dH, if necessary. We can't replicate that, so there's nothing to do for you.
 

Wedge313

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Thanks for explaining.

I just came across your thread "Apollo 12 - Experiences, Odds & Ends". Good stuff, but reading through it I feel like I've mistakenly wandered into a NASSP honors class when I was supposed to be in the "NASSP for Dummies" intro course.
 

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😅 Well, I'm with NASSP since -uh, ten years? I hadn't even met my now-wife those days, so that should be about right. Anyway, you gain a lot of experience and knowledge over the course of time, so you can pester the developers with more complicated questions.😏
But good that you remind me -I really should bring the mission to an end. Now that both kids are finally in school I should have more time (so they say, at least).🤨
 

Wedge313

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Just finished LOI-2. Question about the whole LOI-1 and LOI-2 process: on my LOI-1 the flight plan expected the yaw for the burn to be 018, my PAD ended up at 356. Then for LOI-2 the flight plan expected the yaw to be 360, mine was 336. It's like they did the plane change with LOI-1, I did it on LOI-2? From the RTCC manual: "All plane change is accomplished with the first burn. A second burn (LOI-2 or DOI) adjusts the inplane orbital elements so that a specified orbit occurs at the landing site". My required dVs matched up sort of (LOI-1 flight plan 2889.9, mine 2899.2, LOI-2 FP 169.6 mine 136.7). Just eyeballing it with the MAP MFD the orbit looks ok in relation to the landing site. Just curious what I did wrong here with the RTCC?

Now that both kids are finally in school I should have more time (so they say, at least).
Ha! Well, I guess if you choose to prioritize family over NASSP it can be tough :LOL:.
 

rcflyinghokie

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Just finished LOI-2. Question about the whole LOI-1 and LOI-2 process: on my LOI-1 the flight plan expected the yaw for the burn to be 018, my PAD ended up at 356. Then for LOI-2 the flight plan expected the yaw to be 360, mine was 336. It's like they did the plane change with LOI-1, I did it on LOI-2? From the RTCC manual: "All plane change is accomplished with the first burn. A second burn (LOI-2 or DOI) adjusts the inplane orbital elements so that a specified orbit occurs at the landing site". My required dVs matched up sort of (LOI-1 flight plan 2889.9, mine 2899.2, LOI-2 FP 169.6 mine 136.7). Just eyeballing it with the MAP MFD the orbit looks ok in relation to the landing site. Just curious what I did wrong here with the RTCC?


Ha! Well, I guess if you choose to prioritize family over NASSP it can be tough :LOL:.
How did you compute your REFSMMAT?
 

Wedge313

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How did you compute your REFSMMAT?
I'm working from memory.....UTI>REFSMMAT>Landing Site. The planned landing time was already populated. Hit CLC and then went back and uplinked it as option 2 desired.
 

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Just finished LOI-2. Question about the whole LOI-1 and LOI-2 process: on my LOI-1 the flight plan expected the yaw for the burn to be 018, my PAD ended up at 356. Then for LOI-2 the flight plan expected the yaw to be 360, mine was 336. It's like they did the plane change with LOI-1, I did it on LOI-2? From the RTCC manual: "All plane change is accomplished with the first burn. A second burn (LOI-2 or DOI) adjusts the inplane orbital elements so that a specified orbit occurs at the landing site". My required dVs matched up sort of (LOI-1 flight plan 2889.9, mine 2899.2, LOI-2 FP 169.6 mine 136.7). Just eyeballing it with the MAP MFD the orbit looks ok in relation to the landing site. Just curious what I did wrong here with the RTCC?
I had exactly the same thing. It is a REFSMMAT issue, the actual orientation of the spacecraft is correct. I checked with Orbiter’s HUD and found that the yaw really was zero during LOI-2! Once in lunar orbit, I recalculated my landing site REFSMMAT and did a new P52 opt 1… sure enough, there was a big difference! Not sure why or what happened, but it worked.
 

Wedge313

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Well dang. After reading your post I re-did the landing site REFSMMAT and P52 opt1, pitch and roll stayed the same but the yaw changed by about 21 degrees.

Just so I understand, was this due to an error on my part when I did the first REFSMMAT, or some quirk in the RTCC?

Nothing that some Beeman's won't fix. "It was a GLITCH. It was a- a TECHNICAL MALFUNCTION. Why in hell won't anyone believe me?"
 

indy91

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I need to update the REFSMMAT section of the RTCC MFD manual...

The landing site REFSMMAT depends both on the CSM state vector (its orbital plane really) and the landing site coordinates. And that would be the CSM state vector at the time of landing, not some time before LOI. So there used to be a complicated process in the MFD to 1. calculate MCC-4, 2. calculate LOI-1 and then 3. calculate the LS REFSMMAT so that it can be uplinked even before MCC-4. There was no real other way to get a CSM state vector at the time of landing, which is required for this calculation.

I solved this by adding a separate REFSMMAT option, "LS during TLC". That option uses the nominal approach azimuth to the landing site, which is known long before LOI-1, instead of the CSM state vector in the calculation. So if a flight plan calls for uplinking a LS REFSMMAT before LOI-1, use the "LS during TLC" option. And then later, in lunar orbit, the REFSMMAT gets an update and you can use the normal landing site calculation option.

The LOI-1 performs a plane change and the difference in yaw angle you got is explained by that not being taken into account with the "wrong" REFSMMAT option.
 
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