Apollo 12 Ascent Planning w/RTCC

Wedge313

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Hello. I need some help with the RTCC procedures for the Apollo 12 ascent. This is my first attempt using the RTCC for calculating CSI, CDH etc. I tried to figure this out on my own, but I must be doing something wrong.

I've been able to figure out the TPI time (144:35:16 for me), and then using the LLT came up with a liftoff time of 142:00:50, CSI 142:59:38, and CDH 143:57:45. I'm able to generate the Ascent PAD.

After insertion I'm in a 45.6 x 9.9 orbit. I start P20, then P32, and wait for ten marks. But after V32, I get a 00604 alarm, "CDH to TPI time < 10 min or TIG CDH > TIG TPI"

I've run through the ascent three times, and keep getting the 00604 alarm. So obviously I'm doing something incorrectly.

I'd appreciate a walk-through for the RTCC procedures for this type of ascent and rendezvous. Thanks!
 

rcflyinghokie

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Did you verify your times in P32 for N11 and N37? Also what did you use for N55?

One cause might be using the LLT instead of LLW for a coelliptic rendezvous.

The RTCC input manual has a brief procedure for these as well:

T3, ASCENT (Concentric) TPI Times: Apollo 14 & earlier: Sunrise-23min, Apollo 15+: Sunrise-16min

- TAR, LLW, INI, TAR, VLH: +5535.6, VLV: +32.0 - TAR, LLW, THT: Desired TPI Time, CSI: 50

- CLC solution - TAR, ASC, LTO: Desired LLW sol. GET, CLC - Go back to LLW and CLC again

See if that gives you better results to enter in P32.
 

Wedge313

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Did you verify your times in P32 for N11 and N37? Also what did you use for N55?
The first time N11 shows up, it's all zeros. If I hit PRO it seems to populate with the apoapsis time. I've been manually entering my calculated CSI TIG. N55 is already populated, R1 +15105, R2 -00310, R3 +00000. I'm not sure what these numbers mean! The LM Handbook refers to them as N and E, but that doesn't help me. So I've left those alone out of ignorance, which may be the start of my problem. N37 (TPI TIG) comes up as a seemingly unrealistic time, 474:51:57.62. At this point I figure I've done something wrong, but I manually enter my calculated TPI TIG and press on.
The RTCC input manual has a brief procedure for these as well:
Yes, I've been trying to follow these guidelines, apparently not too well.
One cause might be using the LLT instead of LLW for a coelliptic rendezvous.
I've been using the LLW, not the LLT (which we use for the direct ascent method).

Thanks.
 

rcflyinghokie

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The first time N11 shows up, it's all zeros. If I hit PRO it seems to populate with the apoapsis time. I've been manually entering my calculated CSI TIG. N55 is already populated, R1 +15105, R2 -00310, R3 +00000. I'm not sure what these numbers mean! The LM Handbook refers to them as N and E, but that doesn't help me. So I've left those alone out of ignorance, which may be the start of my problem. N37 (TPI TIG) comes up as a seemingly unrealistic time, 474:51:57.62. At this point I figure I've done something wrong, but I manually enter my calculated TPI TIG and press on.

Yes, I've been trying to follow these guidelines, apparently not too well.

I've been using the LLW, not the LLT (which we use for the direct ascent method).

Thanks.
You mentioned LLT so I was just checking :)

So for P32 you need to enter all the values for N11 N55 and N37. You cant leave those as they are since you haven't begun any rendezvous computations yet. You also need the correct N55 values of +00000 +00001 +02660 and +13000 (apsis crossings, elevation angle, central angle) so it knows what solution to hunt for in computing rendezvous.

When you do it again, get your CSI time you computed in N11, the values above (also found in the data card book) for N55, and the TPI time you computed for N37. Those give your initial guesses so it can further refine them with RR marks.
 
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Wedge313

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You mentioned LLT so I was just checking
Yep, I miss-typed I guess, sorry for the confusion. I must be suffering from AOS (Acronym Overload Syndrome).

So I've made some progress, I've moved from the 00604 alarm to a 00605 alarm "No solution in 15 tries". I've been re-doing this so many time that I'm probably working from a bad save point, my geometry's all wrong. I'll need to go back before launch and re-do the whole ascent planning process.

Question about the F 06 55 entry: looking at the LM G&N Dictionary and LM Operational Handbook I was expecting the R3 entry to be a 0000X number, some code where X would be 0, 1, or 2. Is the +13000 entry satisfying the "CDH at CSI + multiple of 180 deg specified by R1" parameter? There's so much I don't understand here.

Anyway, thanks for the help. I'm heading back to the surface to start re-doing the ascent plan again. Fourth time's the charm!
 

rcflyinghokie

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1663678885765.png

From 12's G&N, you can see R1 is the number of crossings here. Same in the AOH:
1663679122507.png


I think you are just misreading what it's asking. because it has the ability to compute these values based on R1's entry. P32 allows certain things to be left blank so it can solve for them like leaving R3 as zero (blank.) If you leave the central angle zeroed, it will use the R1 value to compute CDH based on apsis crossings. If you load a value in R3, it will use that angle and compute CDH for 180 degrees from CSI (It's early I think I have that correct.)

I can see where its confusing as the procedure outlined has just 00000 under the N55 section not an angle, but I believe that's if you need to solve a rendezvous for a nonstandard case.

For your rendezvous, it seems something isn't in the correct position if its giving you those errors. I can check a scenario if you like, but yeah recomputing the liftoff again making sure you have the parameters correct should resolve the issue assuming the CSM is where it's supposed to be and you updated your landing site.
 

Wedge313

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You also need the correct N55 values of +00000 +02660 and +13000 (apsis crossings, elevation angle, central angle) so it knows what solution to hunt for in computing rendezvous.
I ran through the ascent again and when running P32 got the 00605 alarm again. But looking closer at the LM Data Card Book you sent me I noticed they had N55 R1 as +00001.

N55.PNG


So I tried that, and that gave me a solution that looks ok, I haven't burned yet but it looks like I'm in the ballpark.

We'll see where I am after the burn, but thanks for helping me get this far.
 

rcflyinghokie

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I ran through the ascent again and when running P32 got the 00605 alarm again. But looking closer at the LM Data Card Book you sent me I noticed they had N55 R1 as +00001.

View attachment 30454

So I tried that, and that gave me a solution that looks ok, I haven't burned yet but it looks like I'm in the ballpark.

We'll see where I am after the burn, but thanks for helping me get this far.
Oh I fat fingered that! Yes that should be a 1 not a zero!

I cant believe I didnt catch that typo....but at least I showed you where to correct my mistake :p
 

Wedge313

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Oh I fat fingered that! Yes that should be a 1 not a zero!

I cant believe I didnt catch that typo....but at least I showed you where to correct my mistake :p

Ha! Well, I'm the guy that was originally ok with +15105. And until the coffee kicked in and I put on my readers, I thought the Data Book did say +00000.

And since you've guided me through all six of these landings and answered hundreds of my questions, I guess we can let one tiny typo slide (y).

Anyway, I conducted the CSI burn, and it doesn't look great. The insertion had me in a 46.3 x 9.9 orbit. The CSI burn was 48.1 fps and resulted in a 49.8 x 43.9 orbit, I was hoping for something closer to 45 x 45 ish? I think I'd like to press on anyway and see if I can still achieve a rendezvous. P33 is giving me a CDH time of 143:56:19 which is close to my originally calculated CDH of 143:57:45 and a dH CDH of 12.9, so maybe I'm ok? Let's find out.

Again, thanks for all your help.

EDIT: Well, it seems to have worked out. I'm station keeping with the CSM. But something was not right, my dV for CDH was higher than planned and the whole TPI-TPF time seemed to slide by about 20 minutes. But the beauty of a simulation is I can go back and try again!
 
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rcflyinghokie

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Your CSI and CDH numbers look pretty good. Remember the orbits will be slightly different from what you see and what they computed because of the frame of reference (LS vs mean lunar radius, orbiters moon vs real moon, our lack of mascons etc)

This is also a function of where your CSM orbit is currently which is also impacted by the above differences, so I would say those are in the ballpark.

Curious about what you mean about the TPI-TPF time sliding?
 

Wedge313

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Curious about what you mean about the TPI-TPF time sliding?
Just that when I did the original calculations the TPI was at 144:35. After CSI and CDH the TPI burn ended up at 144:52, so actually about 17 minutes later than planned. And so I hit the braking gates and started station keeping a little later than planned, but it all worked out.
 

rcflyinghokie

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Just that when I did the original calculations the TPI was at 144:35. After CSI and CDH the TPI burn ended up at 144:52, so actually about 17 minutes later than planned. And so I hit the braking gates and started station keeping a little later than planned, but it all worked out.
That does seem like a bit of a slip, but that would be due to the accuracy of your RR marking on board and state vectors as well as how well you performed the CSI/CDH burns.

In the grand scheme though its not bad, the only concern in reality would be lighting at time of docking :)
 
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