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Author Topic: Apollo RTCC MFD  (Read 40508 times)
indy91
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« Reply #225 on: July 13, 2017, 04:13:01 PM »

I'm getting flying Apollo 10 and am at loi, however I think the rtcc is giving me a bad ls refsmmat. After uplinking and doing p52 opt 1 Agc can't point the optics at the right stars and I get terrible Loi results, i.e. 436x-137. Will attach scn

edit: this scn is just before refsmmat uplink

I had the same issue at LOI on Apollo 12. Completely forgot about it, or would have included it in my error report. A newly calculated and uploaded REFSMMAT and P52 Opt 1 did the job for me, but that still doesn't explain the error the first time around. Out of curiosity, did you have the NO ATT light remain illuminated long (like ~1 min) after the FDAI slewed to the new orientation? That was always the clue to to me something was amiss.

Both cases sound like an actual bad REFSMMAT then. Even if the LS REFSMMAT was calculated in a wrong way somehow, it would still be a valid REFSMMAT and you would be able to find stars etc. But if the REFSMMAT is actually bad, then alignment problems etc. can happen.

lotisully86, in your scenario I have successfully calculated a LS REFSMMAT and did the alignment. No issues and the LOI ignition attitude from the Apollo 10 flight plan is almost identical with the one from the Maneuver PAD in the RTCC MFD.

Now, in your scenario you still need to perform MCC-4. And your pericynthion is fairly high (76NM), so MCC-4 is indeed necessary. The way to calculate the LS REFSMMAT before MCC-4 is a bit tricky and I haven't really named the REFSMMAT option for this properly. If you have to do two maneuvers between "now" and lunar orbit (MCC-4 and LOI-1), then you need to use the "LS during TLC" option on the REFSMMAT page. If MCC-4 would have been scrubbed or if you want to update the LS REFSMMAT after MCC-4, then the "Landing Site" page has to be used.

In your case you need to go to the Translunar page first and calculate MCC-4. All you need to change is the TIG it seems, everything else is already in the MFD. After that you go to the Lunar Insertion page and calculate LOI-1 with the option to take MCC-4 into account. That is the "LOI-1 w/ MCC" option. After that you go to the REFSMMAT page ("LS during TLC") and there the two burns (MCC-4 and LOI-1) should be displayed with TIG and DV vector. Only then you can calculate the REFSMMAT. It's pretty complicated, but really the only way to take two maneuvers into account.

That still doesn't really explain why you both got a bad REFSMMAT from the RTCC MFD though...
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rcflyinghokie
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« Reply #226 on: July 13, 2017, 08:51:38 PM »

Desired ref...and the flight plan calls for refsmmat. Sorry that could be it I guess, I just figured it might be a typo based on my (very little) understanding of the difference, other than its usage in the lm activation.

Just to be clear, the flight plan changes the REFSMMAT to the lunar landing site prior to MCC4 using the preferred P52 option 1.  After MCC4 (even if it is scrubbed) you should only have to align it to REFSMMAT before LOI.
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lotisully86
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« Reply #227 on: July 14, 2017, 02:24:47 AM »

I'm getting flying Apollo 10 and am at loi, however I think the rtcc is giving me a bad ls refsmmat. After uplinking and doing p52 opt 1 Agc can't point the optics at the right stars and I get terrible Loi results, i.e. 436x-137. Will attach scn

edit: this scn is just before refsmmat uplink

I had the same issue at LOI on Apollo 12. Completely forgot about it, or would have included it in my error report. A newly calculated and uploaded REFSMMAT and P52 Opt 1 did the job for me, but that still doesn't explain the error the first time around. Out of curiosity, did you have the NO ATT light remain illuminated long (like ~1 min) after the FDAI slewed to the new orientation? That was always the clue to to me something was amiss.


No I haven't gotten that behavior or atleast noticed it. I did get a 1301 alarm in one case tho.

lotisully86, in your scenario I have successfully calculated a LS REFSMMAT and did the alignment. No issues and the LOI ignition attitude from the Apollo 10 flight plan is almost identical with the one from the Maneuver PAD in the RTCC MFD.

Now, in your scenario you still need to perform MCC-4. And your pericynthion is fairly high (76NM), so MCC-4 is indeed necessary. The way to calculate the LS REFSMMAT before MCC-4 is a bit tricky and I haven't really named the REFSMMAT option for this properly. If you have to do two maneuvers between "now" and lunar orbit (MCC-4 and LOI-1), then you need to use the "LS during TLC" option on the REFSMMAT page. If MCC-4 would have been scrubbed or if you want to update the LS REFSMMAT after MCC-4, then the "Landing Site" page has to be used.

In your case you need to go to the Translunar page first and calculate MCC-4. All you need to change is the TIG it seems, everything else is already in the MFD. After that you go to the Lunar Insertion page and calculate LOI-1 with the option to take MCC-4 into account. That is the "LOI-1 w/ MCC" option. After that you go to the REFSMMAT page ("LS during TLC") and there the two burns (MCC-4 and LOI-1) should be displayed with TIG and DV vector. Only then you can calculate the REFSMMAT. It's pretty complicated, but really the only way to take two maneuvers into account.

That still doesn't really explain why you both got a bad REFSMMAT from the RTCC MFD though...

Yes the "LS  during TLC" was the option I was originally using, the scn I posted was after making a few attempts then trying just the landing site option. Will give it another shot with following the your steps above. Thanks!

Edit: partial success, had to uplink the REFSMMAT/p52 opt 1 twice tho before I got a good alignment tho.

Does uplinking a REFSMMAT or desired REFSMMAT overwrite the REF flag set by a previous P30? For example, I'm fairly certain that after performing MCC-3, per the checklist there was no p52 opt 3. I know after conducting running P30 and conducting maneuvers, the first p52 subsequently run will have opt 1 preselected. Anyways option 1 is preselected when trying to align to the ls REFSMMAT, so just wondering if the agc is still trying to align to the previous P30 computed REFSMMAT
« Last Edit: July 14, 2017, 04:34:06 AM by lotisully86 » Logged
indy91
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« Reply #228 on: July 14, 2017, 05:43:39 AM »

No I haven't gotten that behavior or atleast noticed it. I did get a 1301 alarm in one case tho.

Yeah, with a bad REFSMMAT that is a common alarm.

Quote
Yes the "LS  during TLC" was the option I was originally using, the scn I posted was after making a few attempts then trying just the landing site option. Will give it another shot with following the your steps above. Thanks!

Edit: partial success, had to uplink the REFSMMAT/p52 opt 1 twice tho before I got a good alignment tho.

Does uplinking a REFSMMAT or desired REFSMMAT overwrite the REF flag set by a previous P30? For example, I'm fairly certain that after performing MCC-3, per the checklist there was no p52 opt 3. I know after conducting running P30 and conducting maneuvers, the first p52 subsequently run will have opt 1 preselected. Anyways option 1 is preselected when trying to align to the ls REFSMMAT, so just wondering if the agc is still trying to align to the previous P30 computed REFSMMAT

Good question. But the answer is probably no. There is only one place where the AGC stores the "Desired REFSMMAT". And an uplink overwrites that. Also, the REFSMMAT calculated internally in the AGC is calculated in P40 and not P30. That's why the procedure to get an alignment for a burn (0, 0, 0 at ignition) is P30, then shortly into P40 and then P52 option 1.

There is one more important part of the procedure I forgot to mention. It is important that the Desired REFSMMAT uplink is the last upink. Usually at the time of the uplink there would also be a state vector uplink and of course the External Delta V update to get the burn solution for MCC-4 into the AGC. Any of those uplinks will overwrite the Desired REFSMMAT at least partially. So there can't be any other uplink between the Desired REFSMMAT uplink and the P52 option 1. I learned this the hard way until I figured out what is going on.
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lotisully86
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« Reply #229 on: July 14, 2017, 06:47:29 AM »

I wondered if there was a preferred order with the uplinks, I was just going by the order in the flightplans. Good to know
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indy91
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« Reply #230 on: July 14, 2017, 07:22:23 AM »

I wondered if there was a preferred order with the uplinks, I was just going by the order in the flightplans. Good to know

Yeah, in that case uplinking the MCC-4 target load after the desired REFSMMAT might have caused your issues. It's always the desired REFSMMAT last in a string of uplink, the order of the other uplinks (state vector, P30 target load etc.) doesn't matter. I guess knowing this isn't so important for the astronauts, MCC-H takes care of it all. But in NASSP we are both astronaut and mission control.  Very Happy

EDIT: I had trouble finding the document where I read about the REFSMMAT uplink issue, but now I found it again. So here, for future reference, the passage from the Colossus 3 and Luminary 1E Program Notes (https://www.ibiblio.org/apollo/Documents/msc05225.pdf):

Quote
1.1.27 Any P27 update will destroy the preferred orientation matrix (e.g. that calculated by P40, P41), except an update of the matrix itself. Therefore, if a preferred alignment is to be part of an update, it should be the last quanitity in the sequence.

The Desired REFSMMAT (a term from the GSOP section 2 and used in the AGC source code) is in this case called preferred orientation matrix. It's the same thing. And this uplink issue is the same for every Colossus and Luminary version.
« Last Edit: July 14, 2017, 07:36:12 AM by indy91 » Logged
lotisully86
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« Reply #231 on: July 14, 2017, 08:45:05 AM »

Thanks for posting that link!
 
Page 19 paragraph 2 provides an answer to why the preburn ha hp prediction in P30 before loi is +3xx/-1xx. I suppose in real world that was a rather reassuring bit of knowledge  Very Happy
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indy91
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« Reply #232 on: July 14, 2017, 08:58:34 AM »

Thanks for posting that link!
 
Page 19 paragraph 2 provides an answer to why the preburn ha hp prediction in P30 before loi is +3xx/-1xx. I suppose in real world that was a rather reassuring bit of knowledge  Very Happy

Yes, P30 simply adds the DV vector to the ignition state vector. It doesn't take into account that the velocity change for LOI-1 isn't instantly. That's how you get those apoapsis and periapsis altitudes. I chose to use the actual orbital parameters after a burn for the Maneuver PAD, because that is what the crews mostly got with the PAD. During the actual Apollo 11 mission they got the P30 values as an additional comment for their LOI-1 Maneuver PAD. "Noun 42 prior to LOI burn are HA, plus 431.3; HP, minus 128.2" I guess it's both useful to know what P30 is going to say, but also in what orbit you will actually end up.
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rcflyinghokie
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« Reply #233 on: July 21, 2017, 10:15:44 AM »

I know it won't matter too much with the MCC helping the missions, but I noticed that the RTCC MFD when calculating LM mass while docked but in the SIVB calculates what appears to be the total mass of the stage.  I assume this is because the LM isn't "created" yet?  I found this by calculating the SPS evasive maneuver and the PAD page gives a LM weight of 78864 which I know is way off. 
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lotisully86
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« Reply #234 on: July 22, 2017, 06:11:24 PM »

I know it won't matter too much with the MCC helping the missions, but I noticed that the RTCC MFD when calculating LM mass while docked but in the SIVB calculates what appears to be the total mass of the stage.  I assume this is because the LM isn't "created" yet?  I found this by calculating the SPS evasive maneuver and the PAD page gives a LM weight of 78864 which I know is way off. 

I also get this, usually just recalculate the pad after sep and reload the dap.

Somewhat related, do you get accurate sep angles on the rtcc tli pad? I usually get good roll and pitch angles but yaw is off by about 45 degrees
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rcflyinghokie
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« Reply #235 on: July 22, 2017, 07:42:12 PM »

Yeah I just reload after the sep as well.  As for the angles I believe Indy told me that they aren't the same in rtcc as the lvdc right now so they won't line up yet.
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indy91
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« Reply #236 on: July 24, 2017, 03:59:43 AM »

I assume this is because the LM isn't "created" yet?

Correct. There is no way of getting the LM mass alone at that point. I could let the RTCC MFD detect the type of vessel it is docked to though. And then it would use a default LM mass if the docked vessel isn't a LM, but a S-IVB with the LM still inside it. I'll look into doing it this way.

Somewhat related, do you get accurate sep angles on the rtcc tli pad? I usually get good roll and pitch angles but yaw is off by about 45 degrees

Even roll and pitch can be a problem in a scenario with fully configured LVDC presettings (Apollo 8, 11 and 14 right now). The yaw issue can probably be fairly easily fixed. The MFD just needs to read the padloaded separation attitude from the LVDC. The general issue with the sep attitude on the TLI PAD is a bit more complicated. It has to do with an inconsistent coordinate transformation, that just by luck works correctly for Apollo 8, but not for Apollo 11. Fixing this might take a while.
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indy91
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« Reply #237 on: August 17, 2017, 10:49:23 AM »

A few updates:

-Iterations can now be stopped by pressing CLC again. The RTCC MFD is fairly prone to getting stuck in calculations, due to user errors or off-nominal cases. Previously there was no way to stop these calculations except restarting Orbiter. Now pressing CLC again will kill the calculation thread. I think this is a very useful feature.
-Added a LOI-1 at pericynthion option (see explanation below).
-Added the missing options of the Translunar Midcourse Correction Processor. Here a complete list of options (based on the actual RTCC) that were available by the time Apollo 8 flew:

-Option 1: X, y, z and t target update.
-Option 2: Free-return, fixed LPO orientation, landing site.
-Option 3: Free-return, free LPO orientation, landing site. (NEW)
-Option 4: Nonfree-return, fixed LPO orientation, landing site (NEW)
-Option 5: Nonfree-return, free LPO orientation, landing site (NEW)
-Option 6: Circumlunar free-return flyby to nominal H_PC (pericynthion height) and phi_PC (pericynthion latitude)
-Option 7: Circumlunar free-return flyby, specified H_PC and nominal phi_PC

The free LPO orientation options probably were never used during an actual flight. They would have been used to save a lunar landing mission that had an off-nominal TLI, just off-nominal enough so that the desirable lunar parking orbit orientation cannot be used. These options save some DV during the LOI maneuver, but don't lead to the planned approach azimuth to the landing site. Missions that depended on a terrain model being loaded into the LGC (Apollo 14 to 17) probably couldn't have used these options. The optimum DV for these free LPO options is with LOI-1 happening exactly at pericynthion. So I added this calculation mode for the LOI-1 maneuver. The optmized trajectory usually has a LOI-1 DV vector with almost exclusively a DVX component. DVY and DVZ are close to 0.

The new non-free return modes use the input pericynthion GET as a fixed parameter. The free-return modes iterate on that time to achieve free return. Other than that the non-free modes are fairly similar. It's still not a full mission optimization like the real RTCC did. Only the TLMCC and LOI-1 as a pair are optimized.
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indy91
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« Reply #238 on: September 16, 2017, 05:28:37 AM »

Forgot to write an update post for the last update. Mostly another option was added for the TLMCC Processor:

-Option 8: SPS Lunar Flyby to specified free return inclination and a desired longitude of Earth landing

I was also asked to write a tutorial for calculating Translunar Midcourse Correction maneuvers with the RTCC MFD. All the available options are based on historical documents about the RTCC, so the real RTCC back in the day had the same options. During a given lunar mission, only a few of the options would actually be used. The options used differ for free-return trajectories (Apollo 8, 10-11) and hybrid trajectories (Apollo 12-17).

Let's say you are flying Apollo 8/10/11 and have completed TLI and all the post-TLI procedures, i.e. LM extraction, evasion maneuvers etc. How the MCCs are getting calculated and executed is (indirectly) specified in the Mission Rules for each mission. Usually there were four planned course corrections on the way to the Moon, at different times spread out over the translunar coasting period. Different calculation options are used for each MCC, see the list of options in the post above. For the free-return missions you would use option 2 of the TLMCC Processor for MCC-1 and MCC-2 and option 1 for MCC-3 and MCC-4. Option 2 optimizes the MCC and LOI-1 maneuvers as a pair and also results in: free return with a lunar flyby at the specified altitude, insertion into a lunar orbit with a fixed approach azimuth to the landing site, and an overflight of the landing site at the desired time of landing.

Because all the necessary parameters for this calculation didn't fit on the "Translunar" page of the RTCC MFD, the parameters for the Lunar Orbit Insertion maneuver, which is part of the calculation, are on the "Lunar Orbit" page. Only the options that include the landing site in the calculation need the parameters on the "Lunar Orbit" page. So that would be options 2-5. For options 1, 6-8 all the necessary numbers are on the "Translunar" page, where you calculate the MCC. Here a list of the necessary input parameters for option 2:

-Time of Ignition (TIG)
-Initial guess for the GET at pericynthion (GET)
-Selenocentric latitude in Earth-Moon plane coordinates (LAT)
-Pericynthion altitude (ALT)

-Desired time of lunar landing (GET)
-Apocynthion altitude for LOI-1 (APA)
-Pericynthion altitude for LOI-1 (PEA)
-Approach azimuth (AZI)
-Landing site latitude (LAT)
-Landing site longitude (LNG)
-Landing site altitude (ALT)

That's a whole bunch of numbers and some of them are difficult to derive from the historical documents. But we have already done most of that work and for almost every Apollo mission these parameters are preloaded in the RTCC MFD. But it's always good to check if  the numbers are there and also correct.

The time of ignition is always user specified. The time is usually relative to TLI or LOI, but the GET from the flight plans for MCC-1 and MCC-2 will do. When all the input parameters are right, press CLC and wait a few seconds. The calculation can take a few moments. Pressing UPL the maneuver solution can then be uplinked to the AGC, if that is desired. This whole procedure should be done for MCC-1 and MCC-2.

The result of the option 2 calculation is not only a Delta V vector to be burned, but it also calculates a new nodal target. The nodal target is a set of coodinates (time, latitude, longitude, altitude) of the intersection between the incoming approach hyperbola before LOI and the resulting lunar parking orbit after LOI. This set of numbers will be stored in the RTCC MFD and can be used for an option 1 calculation. For various reasons MCC-3 and MCC-4 didn't reoptimize the whole mission, as is done with option 2, but they only targeted these previously calculated coordinates. And that's what option 1 is for "X, y, z and t target update". The nodal target was fixed after MCC-2, so the only user input for the option 1 calculation is the TIG. Here all the parameters for option 1:

-Time of Ignition (TIG)
-GET of node (GET)
-Seleographic latitude of node (LAT)
-Selenographic longitude of node (LNG)
-Selenographic altitude of node (ALT)

Calculate and uplink as before. I hope this description helps with using the RTCC MFD for Translunar MCCs. Feel free to ask any question in this thread. I am bad at writing manuals, so I don't really plan to update the RTCC MFD manual (under Doc\Project Apollo - NASSP\Programmers Notes) much until the NASSP 8.0 release.
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