Apollo 15: Lunar Ascent Preparation and RTCC Procedures?

Wedge313

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Hello, After a nice long stay on the lunar surface it's time to head home, and I'm (again) looking for guidance on using the RTCC to generate the necessary uplinks and PADs to get me from A to B. I have looked through the RTCC manual and the RTCC MFD Input Reference Guide and I'm still not sure where to begin.

First, pretty sure I need to have the CSM perform a plane change before the LM lifts off, but not sure how to get that info from the RTCC. Is this a General Purpose Maneuver? Or do I play with the LOI processor somehow? Also, what about the REFSMMAT? Do we use a P30 REFSMMAT here?

Second, looking at the RTCC Input Reference Guide for the ascent, I've gone through this a few times but it seems to me I'm missing the big picture. There's a sequence of events that's unclear to me. For instance, it looks like I need to know my lift off time to begin using the Lunar Ascent Processor. But where do I get that? The CSM's orbit is going to dictate that, so until I complete the plane change will these different processors (LLW, LLT) generate any solutions? And am I looking at the "T3, Ascent (Concentric)" section, the "Direct Ascent & Tweak" section, or both? Lots of questions and I don't know where to begin.

As always any guidance will be greatly appreciated. Thanks.
 

rcflyinghokie

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Ah you are on your way to the most challenging aspect! Lets see if we can get you going...

First, pretty sure I need to have the CSM perform a plane change before the LM lifts off, but not sure how to get that info from the RTCC. Is this a General Purpose Maneuver? Or do I play with the LOI processor somehow? Also, what about the REFSMMAT? Do we use a P30 REFSMMAT here?
Yeah you will see the plane change on the flight plan as well. Which gives you a good idea of the target time. You will be using the descent processor with the new RLS here so first update your RLS (Utilities->landing site, select target as the LM and hit CLC).

Then move to the descent processor and select the CSM Prelaunch Plane Change with the MOD button. Use the TIG-1h as TH1 and your predicted liftoff time as TH2 (you can use the flight plan for this for now.)

You then calculate the burn as you have with others in the RTCC and after you can generate a P30 REFSMMAT heads up.

Second, looking at the RTCC Input Reference Guide for the ascent, I've gone through this a few times but it seems to me I'm missing the big picture. There's a sequence of events that's unclear to me. For instance, it looks like I need to know my lift off time to begin using the Lunar Ascent Processor. But where do I get that? The CSM's orbit is going to dictate that, so until I complete the plane change will these different processors (LLW, LLT) generate any solutions? And am I looking at the "T3, Ascent (Concentric)" section, the "Direct Ascent & Tweak" section, or both? Lots of questions and I don't know where to begin.
You can, if you wish, put the CSM plane change into the MPT and then proceed to compute your ascent before you burn it if you wish, or you can burn PC and then compute the ascent without the MPT, your call but I encourage the MPT so you can get other data.

In any case, since you are running a direct ascent profile (Apollo 14+), you will be using the Lunar Launch Targeting Table (LLT) to compute the ascent. You will need to do some "working backwards" timings here.

First, you need to compute your expected TPI time. This is going to be sunrise -16 minutes on the orbit after lift off. I use the SR/SS table (MSK 1502) to find that orbit's sunrise and then subtract 16 minutes for my TPI time.

You then can use the LLT, set your target to your CSM, TTH to your estimated liftoff time (you can use what you used for the CSM plane change here), and your DT (time from insertion to TPI) to 45 minutes, and RDO to 32 fps. Then try calculating a solution.
Next we do a little iteration to fine tune the actual liftoff time, you will go back to the ascent processor and CLC, this should give you a slightly different TIG, and then back to the LLT and CLC again. Here you want to make sure your TPI time didnt change on the LLT page, if it has, adjust your DT to get your TPI time you computed previously. Do this a few times until your liftoff time and TPI time remains constant. I would encourage writing the liftoff and TPI times down for reference as well at this point.

Then we want to determine the insertion time. You use the checkout monitor with your ascent maneuver on the MPT here and you can get your insertion time (should be the GET in the top left) which you need for the tweak burn.

Since you cannot compute the dV's yet, we will just get the table ready to compute quickly since the tweak is just a few minutes after insertion. TAR->REN->TI->OPT->Both Fixed. Set T1 to your insertion time +3 minutes, and set T2 as your computed TPI time. Then set up the parameters OFF: P51,15,1.7,26.6,130;

Before disabling the MPT, you can use the plane change and ascent you have on there to uplink time tagged state vectors per the flight plan. After, make sure the MPT is inactive after this. You should then be able to compute the ascent pad, have the updated tig for the alignment and P12.

After insertion you quickly will compute the tweak burn with the following: TAR->REN->TI->DIS->CLC->MPT->CLC, read tweak-burn DV’s which you will burn with a V47 at your cutoff attitude.


I know this was a lot, so if you have specific questions within let us know!
 

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Wow. Nice walkthrough, thank you. It looks about as complicated as I first thought, but your input makes it a little less daunting.

Let's see how this goes! Thanks.
 

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Didn't take me long to hit a roadblock.

RTCC Mask 1502, CLC asks for an entry "Format: U08,GET or REV,Time or Rev number;". I've tried a number of times to get this entry correct but no luck.

There seems to be three fields, first "U08", not sure what to do here so I'm entering "U08".
Second field "GET or REV", I've tried both. Let's say I pick "REV".
Third field "Time or Rev number;" If I picked REV in field two I enter "47"

So my entry looks like "U08,REV,47;" which is obviously wrong because it doesn't work. Can you straighten me out? Thanks.

BTW Happy New Year
 

rcflyinghokie

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Didn't take me long to hit a roadblock.

RTCC Mask 1502, CLC asks for an entry "Format: U08,GET or REV,Time or Rev number;". I've tried a number of times to get this entry correct but no luck.

There seems to be three fields, first "U08", not sure what to do here so I'm entering "U08".
Second field "GET or REV", I've tried both. Let's say I pick "REV".
Third field "Time or Rev number;" If I picked REV in field two I enter "47"

So my entry looks like "U08,REV,47;" which is obviously wrong because it doesn't work. Can you straighten me out? Thanks.

BTW Happy New Year
You are going to use GET in this case, revs will not work. Also, I believe you need to do it in the CSM since it's in orbit.

I need to try it myself to remember but give GET a try in the CSM.

Happy new year!
 

Wedge313

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Wow, I think I'm even more stupid in 2022 than I was in 2021.

I've tried numerous variations of inputs, tried different formats, I give up. Mask 1502 and I don't get along.

From the flight plan I can tell sunrise should be around 172:46. Their TPI burn was about 172:30.

I'd like to get my "real numbers", and do this correctly. But I cant figure out the Mask 1502 format.
 

rcflyinghokie

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Wow, I think I'm even more stupid in 2022 than I was in 2021.

I've tried numerous variations of inputs, tried different formats, I give up. Mask 1502 and I don't get along.

From the flight plan I can tell sunrise should be around 172:46. Their TPI burn was about 172:30.

I'd like to get my "real numbers", and do this correctly. But I cant figure out the Mask 1502 format.
Is your MPT active with a current anchor vector? It's working fine for me U08,GET,XXX:XX:XX

Use a GET before liftoff I usually round to the hour before for simplicity.
 
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Wedge313

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Is your MPT active with a current anchor vector?
Once again a learning opportunity.

Until now the only time I've seen the acronym "MPT" is when it refers to one of the buttons on the RTCC I have to push when computing a burn, as in the plane change I just computed (but haven't executed yet), it's where I select the engine or RCS I want to use for the burn, then it generates DVX,DVY,DVZ.

But I think what you're talking about is the MPT you get with Mask 0047? I've never seen that or used that. And the section in the RTCC manual that addresses it has not been written yet.

Yet another gap in my knowledge. How do I learn how to use that?
 

rcflyinghokie

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Oh yes! So this is the feature that lets you compute burns and then compute other things based on the burn's completion. You use the MISSION PLAN TABLE button on the RTCC main page.

You will need to use this ideally for ascent as I mentioned in my other reply so you can compute the insertion time, and the time tagged state vectors etc.

To use it, you first need to activate and initialize it. PLN->ACT and then INI.

Here you have the choice of using 2 tables, one is called CSM and the other LM, but in reality they just can store vessel information (ie you can put the SIVB data in the LM slot to compute its impact) We are going to initialize both with the CSM and LM. Start with the CSM table (TAB=CSM) and select the CSM with VEH. Then on the right press AUT and that will populate vessel propellants and masses etc. Then send them to the MPT with M55 and M50. Do the same with the LM table, selecting the LM in VEH etc.

After this is complete, press VPS and we will initialize the state vectors of the vehicles. The left buttons are the CSM table and right buttons the LM table. First we will update the vector of the CSM. Press DC, type "Columbia" (just the vessel name here) and press enter and your DC VECTOR cell should populate. Then press TUP and type DC to move it to the anchor vector. Repeat this process on the right hand side for the LM.

Now you should be able to do a few things, first you can get your sunrise/sunset times. Also when you compute a maneuver, you get an option to send it to the MPT and it will populate on the MPT itself. If you have already done the plane change, start by placing the LM ascent on the table. You will also notice when you compute burns you get a new VTI option, this is the vector time, or the state vector time of the vehicle you want it to use. If, for example, you haven't burned a plane change yet and you put the plane change burn on the MPT, you would need to use a vector time after that burn to compute the ascent so it takes into account the new projected position of the CSM. Additionally, now on your SV update in RTCC, your time tags will be based on where the vehicle is projected to be at that time. So you can give for example the CSM a LM SV with an INS+10 minutes SV so it knows where to expect the LM.

NOTE: You wont be able to get a maneuver pad using the MCC the same way, so the best thing is to use the MPT to compute things, then inactivate it and then compute a maneuver pad after the calculation. You can easily switch on and off the MPT with that ACT button in the top left.

Hope this helps a little more, its a beast I know but its a repetition/practice thing for sure!
 

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OK! I now know when the sun will rise (172:42:51 in my case). (Out of curiosity, would the pitch and yaw values point the vessel directly at the sun?)

This RTCC is really an incredible tool, but also (for me) incredibly complex. Every maneuver (TLI, MCC, LOI, etc.) requires learning a whole new RTCC function. The thing is onion-like as I peel away layer after layer, and so far I've only scratched the surface.

I'm going to copy-paste these posts into my upcoming nine-volume collection "A Brief Introduction to the RTCC: A Beginners Guide"

Thanks again for your excellent explanation and your patience.
 

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Possibly another RTCC question (?).... I just completed the Plane Change burn, and noticed I didn't get the ullage automatically. I know you can use the DIR ULLAGE to manually do this (at least until you have to hit PRO on the DSKY) but what am I missing when I set up my burn? I did make an RTCC input for a 4-jet 13 sec ullage when computing the burn, but that info apparently didn't get uplinked to the CMC. So I'm missing a step here.

I guess because it's a simulation the burn went off fine (not sure it would have in the real world), but I did end up having to trim out a fairly large VGX, I'd guess because I didn't have the 13 seconds of RCS burn before SPS ignition.
 

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Possibly another RTCC question (?).... I just completed the Plane Change burn, and noticed I didn't get the ullage automatically. I know you can use the DIR ULLAGE to manually do this (at least until you have to hit PRO on the DSKY) but what am I missing when I set up my burn? I did make an RTCC input for a 4-jet 13 sec ullage when computing the burn, but that info apparently didn't get uplinked to the CMC. So I'm missing a step here.

I guess because it's a simulation the burn went off fine (not sure it would have in the real world), but I did end up having to trim out a fairly large VGX, I'd guess because I didn't have the 13 seconds of RCS burn before SPS ignition.
Ullage is not automatic in the CSM, you always have to use the THC +X (preferred) or DIR ULLAGE button. The reason you put it in the RTCC is so it takes it into account for the maneuver pad.

You control the jets used for ullage (PGNS burn) with the DAP, you can set 2 or 4 jet x translation here.

When you are in P40 and AVG G is enabled (tig-30s) then the CMC will integrate any dV it senses including ullage so your residuals still turn out properly.
 

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Ullage is not automatic in the CSM, you always have to use the THC +X
Aarrgh I should know this :mad:

Moving on, calculating the ascent, I'm running through this process a few times trying to learn and I have a few questions:

First, the flight plan has us update the REFSMMAT to Lift-Off Orient. What do we do here? The best option I could come up with was using the RTCC Landing Site REFSMMAT and updating the time to the estimated lift-off time?

You then can use the LLT, set your target to your CSM, TTH to your estimated liftoff time (you can use what you used for the CSM plane change here), and your DT (time from insertion to TPI) to 45 minutes, and RDO to 32 fps. Then try calculating a solution.
To get a solution I also had to enter a VTI time, and not knowing exactly what to do here I just stuck in a time (171:00:00) that allowed me to get a solution, but what should I really do here?

Anyway, after making some probably wrong assumptions and bouncing back and forth between the LLT and ASC pages I came up with a Lift-Off at 171:35:08.90 and a TPI of 172:27:16 (subsequent run-throughs produced the same times +/- a few seconds). I was starting to think I had a grip on this, but then....
Then we want to determine the insertion time. You use the checkout monitor with your ascent maneuver on the MPT here and you can get your insertion time (should be the GET in the top left) which you need for the tweak burn
I'm stumped here. Not sure what the checkout monitor is. The MPT page shows a GETBI of 171:35:09 (my liftoff time), dV 6047.6 Ha 44.1 Hp 9.0 (in the ballpark?). But I don't know where to go from there. So I can't get an insertion time.

In order to move on with the process, I made up my own approximate insertion time by adding the burn time to the lift off time, just so I could work forward with practicing setting things up for the tweak burn. On the REN page, who is the Chaser, and who is the Target? When I opened the page the Chaser was the CSM and the Target was the LM, seemed to me it should be the other way around? Besides that I entered the parameters as you instructed, and no other issues here (yet).
Before disabling the MPT, you can use the plane change and ascent you have on there to uplink time tagged state vectors per the flight plan. After, make sure the MPT is inactive after this. You should then be able to compute the ascent pad, have the updated tig for the alignment and P12.
Going back to my previous comment, I'm just not clear on how to work the MPT. FWIW I'm starting this process just after the plane change maneuver, so on the Mission Plan Table I only see one line, that looks like the ascent. Active/Inactive is clear enough but I really don't understand what's going on.

Anyway I'm trudging on, but before I do this "for real" I need to figure some stuff out with the MPT, starting with finding the insertion time.

Thanks
 

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First, the flight plan has us update the REFSMMAT to Lift-Off Orient. What do we do here? The best option I could come up with was using the RTCC Landing Site REFSMMAT and updating the time to the estimated lift-off time?
That's exactly what you do! You have to make sure though that you update the landing site in the UTI->LS page. Select your LM and hit CLC. Then you can go to the REFSMMAT page and select landing site and update it.

To get a solution I also had to enter a VTI time, and not knowing exactly what to do here I just stuck in a time (171:00:00) that allowed me to get a solution, but what should I really do here?
Ah yes I didn't really explain MPT use too much, but VTI is the vector time. So basically this is the "state vector" time it uses to compute a burn/maneuver. For ascent, this ideally should be less than an hour before liftoff (if LO was say 142:21:00 you would just round down to 142:00:00 or similar). Basically you just use your best judgement here you want it close to but not too close to the TIG of your intended burn.

I'm stumped here. Not sure what the checkout monitor is. The MPT page shows a GETBI of 171:35:09 (my liftoff time), dV 6047.6 Ha 44.1 Hp 9.0 (in the ballpark?). But I don't know where to go from there. So I can't get an insertion time.
MCC Displays MSK 1619. After your ascent is on the MPT (and assuming it's maneuver 1) you will hit CLC and use U02,LEM,MVE,1,,MCT and that should compute your insertion time in the top left.

In order to move on with the process, I made up my own approximate insertion time by adding the burn time to the lift off time, just so I could work forward with practicing setting things up for the tweak burn. On the REN page, who is the Chaser, and who is the Target? When I opened the page the Chaser was the CSM and the Target was the LM, seemed to me it should be the other way around? Besides that I entered the parameters as you instructed, and no other issues here (yet).
That should be close enough, doing the approximation on the MPT/checkout monitor just lets you put a TIG in there so you don't have to after all the rush of post insertion. The tweak is usually 3 minutes after shut down so the less you have to mess with RTCC the better.

I am pretty sure the chaser should be the LM and target the CSM, but I need to verify since for whatever reason it defaults to the opposite. I will get a confirmation on that.

Going back to my previous comment, I'm just not clear on how to work the MPT. FWIW I'm starting this process just after the plane change maneuver, so on the Mission Plan Table I only see one line, that looks like the ascent. Active/Inactive is clear enough but I really don't understand what's going on.
So in a nut shell, the MPT allows you to "store" maneuvers so that other maneuvers can be computed as if the previous ones were performed. Let's use TEC/ENTRY for example. Say you wanted to figure out if you need to burn certain MCC's based on mission rules. You compute your first MCC and put it on the MPT. Then you can determine how much dV would be needed for later MCCs way ahead of time. You can also use this to compare dVs of MCCs say if you skilled all but MCC7, you could see what dV it would have. This is useful to avoid unnecessary MCCs as well as avoid unnecessarily large ones.

Another example is of course your ascent. You could compute your entire ascent before the CSM even runs a plane change. By computing the PC and putting it on the MCC, you can compute your ascent because now the MPT knows where the CSM "will be" after a plane change. If you didn't use MPT, you would have to burn the PC and THEN compute the ascent.

I hope that helps explain a little?
 

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OK, with your help I think I'm making progress. But still hitting some potholes....

I've run through the process of setting up the RTCC to calculate the lunar ascent a few times now. Setting up the MPT, LLT, ASC etc. I've got times for liftoff, insertion, TPI, sunrise. I've set up the REN page for the tweak burn.

But after a lot of RTCC experimentation, I can't figure out how I can turn this info into a lunar ascent burn and PAD. What are my next steps?

FWIW I'm at about T+166:00:00 in the simulation, about to do a P52 Option 1 L/O Orient in the CSM, Dave and Jim are still frolicking on the lunar surface.

EDIT: also, after I've run through this RTCC set-up process, if I save the scenario will it stay set up? It seems like I need to start from scratch every time I open a saved scenario.
 
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rcflyinghokie

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But after a lot of RTCC experimentation, I can't figure out how I can turn this info into a lunar ascent burn and PAD. What are my next steps?
To get a pad in the maneuver pad section you need to mark MPT as inactive.

EDIT: also, after I've run through this RTCC set-up process, if I save the scenario will it stay set up? It seems like I need to start from scratch every time I open a saved scenario.
So it should keep all of your MPT information saved. Depending on the processor though you might need to reinsert certain information.
 

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I'm wondering if I'm doing something wrong because after I make the MPT inactive, and generate the lunar ascent PAD, my pad doesn't populate any of the AGS (DEDA) entries.
 

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I'm wondering if I'm doing something wrong because after I make the MPT inactive, and generate the lunar ascent PAD, my pad doesn't populate any of the AGS (DEDA) entries.
Did you recalculate the ascent first?
 

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So after I make the MPT inactive, recalculate the ascent, then try to get the PAD?
 

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So after I make the MPT inactive, recalculate the ascent, the try to get the PAD?
Yeah you still need to "send" or "transfer" the burn data. With MPT active you are transferring it to the MPT only. With it inactive you are sending it so things like uplinks and the maneuver pad can use it. You just need to do the process again, normally just recalculating with your current values.
 
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