Apollo 8 in Orbiter2016 with NASSP v8 r1749 status - questions after MCC-5 to splashdown

thermocalc

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Hi to all.

After 1 month I completed Apollo 8 from Lift-off to Splashdown “almost” without a glitch using Orbiter2016 with MOON high resolution textures and NASSP v8 version 1749 (I know I know, I should use Orbiter Beta, but reading others in the forum I “think” to have understood that Apollo 7 and 8 which don’t have “docked vessels” can still be flown “successfully” even in Orbiter 2016, at least I can take advantages of the MOON and EARTH Apollo landmarks for making P22/P23…), with max x20 time acceleration during the long coast phases…and contrary to last year, when I used Apollo 8 in NASSP v7 on Orbiter 2010P1 this time the simulation was relatively smoothly, I never had AGC issues while running time accelerations and all MCC’s messages (almost) came up more or less around the checklist times, so I guess in this year of further development the sim got more robust and stable. A HUGE THANKS to all developers to achieve this target.

I said “almost” as I run into some “inconsistencies” which I would like to share with you, to understand what I did wrong (if it was my fault) or maybe can be traced back to computer issues due to low frame rates when using Orbiter2016.


Q1.

At GET 090:01:20 I got the ENTRY REFSMMAT uplink (090:00:15 according checklist time) and at time 090:05:00 I changed the REFSMMAT from LOI-2 to ENTRY doing P52-option 1. The next P52-option 3 went smoothly (see file “P52 series” for a bunch of them and values I got in N93).

At GET 102:46:50 I got the MCC-5 uplink with LM SV update, target load and ENTRY REFSMMAT (I guess “ENTRY REFSMMAT” in yellow text was just a “note” in the checklist to tell that for MCC-5 the burn attitude is referred to the ENTRY REFSMMAT…changed time back ago…don’t know/think that an ENTRY REFSMMAT (the rotational matrix elements so to speak, was indeed sent up again during the uplink, and if so why there was another P52-preferred to do?). Anyway, I completed the uplink, but after that when doing P52-option 3 at 102:52:00 the optics were far off from the target stars (see “optics not aligned” photo). Anyway I press on, I centered manually the stars and complete P52 (and as you can see from “P52 series” at that time on R2 N93 I got a huge angle difference), but after finishing this P52 a made another P52-optino 3 at time 103:00:00 and everything was correct again…(see again “P52 series” photo).

When the time came for making MCC-5 everything went well, the SXT STAR was there in the SXT at the correct time and Shaft/Trunnion angles as in the burn PAD…so I guess everything went well (indeed I splashdown “somehow”).

So the question is why after the MCC-5 uplink I got the optics out of alignment?

Was it supposed to work like that? Including the weird stars alignment to be manually corrected?

Or was I just “lucky” to be able to complete the mission?

If you are interested I will attach the scenario just few minutes before to get the MCC-5 PAD and after uplink, when doing P52 the stars should not be centered.



Q2

After receiving the final entry pad at 146:03:25 GET time (145:55:00 according checklist) I was supposed to see the Earth horizon pitching up to 268 degree at time 146:31:25, with +/- 5 degree tolerance, but even if I was at that attitude the Earth was not there in the COAS CDR window (again, if you want ti can upload the scenario at this time). Why? Was I in incorrect attitude? Or just the Earth Horizont was not visible as “night time” for A8 mission?

Anyway upon CM/SM separation by putting the CM at the PAD entry attitude at Pitch 152 (R=0, Y=0) I managed to survive and land…so I guess I was not in a too bad wrong attitude; OR is this event to be traced back to the weird issues I experienced at time 102:52:00 when I got that strange optical issue? Did I have indeed a wrong Entry REFSMMAT at all times ???



Q3

When making P61 at some time in the entry checklist it is written to read from the GNC the calculated values form some items to be compared with the ENTRY PAD values, and based on them decide for “PGNCS go / no-go”.

How should I know how to decide if go / no-go for an automatic CMC reentry? How much are the allowable tolerances between the ENTRY PAD and P61 displayed values?

For example I got:

N61 (lat +7.44, long -164.96, hds -1) -> entry PAD was (lat +7.44, long -164.96, lift vector up->which I guess it is “heads down -1).

N60 (Gmax +6.97, V pred 36214, gamma -6.55) -> entry PAD (Gmax 6.5, Vpred 36226, gamma -6.49)

N63 (RTGO 12858, VIO 36293, TEE -20 32) -> entry PAD (RTGO 1260.6 set in EMS, VIO 36315 set in EMS)

After N63 should I manually modify the EMS PAD values entered before to these new values displayed on N63?

Also the predicted time of EI 146:48:53 was slightly off from the PAD value of 146:48:25.

Should I be worried for these “deviations”?



Q4

In the ENTRY PAD the target, splashdown coordinates were +7.44 LAT / -164.96 LONG.

Upon splashdown I got in F16 67: R1 -00024 (I hit the target 2.4 NM short, if my interpretation is correct), R2 +00741 (+7.41 LAT) and R3 -16495 (164.95 LONG) … I guess not so bad.

BUT in the Apollo by Numbers I saw that the actual splashdown coordinates were +8.10 LAT and -165.00 LONG … so if the MCC “knows” where I am heading at all times, why he scrubbed MCC-6 and MCC-7 if he “predicted” a target splashdown in the ENTRY PAD which was not the historical correct one? Or in the MCC calculations the final target splashdown coordinates don’t enter into the actual calculations to be done for up linking a burn vector and TIG?

But anyway, if I got these numbers should I consider my mission a success or a failure?


Thanks for reading me.

Best regards.
 

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rcflyinghokie

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Q1.

At GET 090:01:20 I got the ENTRY REFSMMAT uplink (090:00:15 according checklist time) and at time 090:05:00 I changed the REFSMMAT from LOI-2 to ENTRY doing P52-option 1. The next P52-option 3 went smoothly (see file “P52 series” for a bunch of them and values I got in N93).

At GET 102:46:50 I got the MCC-5 uplink with LM SV update, target load and ENTRY REFSMMAT (I guess “ENTRY REFSMMAT” in yellow text was just a “note” in the checklist to tell that for MCC-5 the burn attitude is referred to the ENTRY REFSMMAT…changed time back ago…don’t know/think that an ENTRY REFSMMAT (the rotational matrix elements so to speak, was indeed sent up again during the uplink, and if so why there was another P52-preferred to do?)
You are receiving an "actual" REFSMMAT rather than a "desired" REFSMMAT. The difference is that an actual replaces what is currently stored in the computer where desired requires an option 1 realignment. In this case, you are getting an updated REFSMMAT which is slightly different from the previous and not a whole new orientation, so an option 3 is all that is needed to torque the platform instead of a coarse align adjustment you would find in an option 1. This also explains the stars not being perfectly aligned, as you will just need a small adjustment to torque to the new REFSMMAT.

Q2

After receiving the final entry pad at 146:03:25 GET time (145:55:00 according checklist) I was supposed to see the Earth horizon pitching up to 268 degree at time 146:31:25, with +/- 5 degree tolerance, but even if I was at that attitude the Earth was not there in the COAS CDR window (again, if you want ti can upload the scenario at this time). Why? Was I in incorrect attitude? Or just the Earth Horizont was not visible as “night time” for A8 mission?

Anyway upon CM/SM separation by putting the CM at the PAD entry attitude at Pitch 152 (R=0, Y=0) I managed to survive and land…so I guess I was not in a too bad wrong attitude; OR is this event to be traced back to the weird issues I experienced at time 102:52:00 when I got that strange optical issue? Did I have indeed a wrong Entry REFSMMAT at all times ???

The horizon track was a check on the PGNS and orientation. You should be able to see the horizon (it is really dark, but there is a line where starts stop) on the 31.7 degree line on the rendezvous window. As the spacecraft gets closer to earth, you will need to pitch slowly to keep the horizon around that line and this will bring your pitch attitude to the proper attitude at EI time by following it. Your entry REFSMMAT should have been ok if you did an option 3 after the uplink at MCC5 and subsequent option 3's with good results.
I do see it says track with COAS, I think that is a relic from when our line wasn't positioned properly, I have fixed that in the checklist.


I am going to defer to @indy91 to answer Q3 and Q4 as they are more up his alley.
 

indy91

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Q3

When making P61 at some time in the entry checklist it is written to read from the GNC the calculated values form some items to be compared with the ENTRY PAD values, and based on them decide for “PGNCS go / no-go”.

How should I know how to decide if go / no-go for an automatic CMC reentry? How much are the allowable tolerances between the ENTRY PAD and P61 displayed values?

For example I got:

N61 (lat +7.44, long -164.96, hds -1) -> entry PAD was (lat +7.44, long -164.96, lift vector up->which I guess it is “heads down -1).

N60 (Gmax +6.97, V pred 36214, gamma -6.55) -> entry PAD (Gmax 6.5, Vpred 36226, gamma -6.49)

N63 (RTGO 12858, VIO 36293, TEE -20 32) -> entry PAD (RTGO 1260.6 set in EMS, VIO 36315 set in EMS)

After N63 should I manually modify the EMS PAD values entered before to these new values displayed on N63?

You can trust the PAD values more than the CMC when it comes to those values for reentry. The reason is, the CMC assumes the shape of the Earth is an oblate spheroid and it calculates altitude relative to that. In Orbiter, even with the introduction of terrain, the Earth is a sphere. The calculations for the PAD also assume a sphere, so they will be closer to actual. Not sure what the exact limits are (the Apollo 8 entry summary document says the limits are TBD, thanks for that...). In any case, the CMC will always be somewhat off in Orbiter.

Also the predicted time of EI 146:48:53 was slightly off from the PAD value of 146:48:25.

Should I be worried for these “deviations”?

Entry interface is the time when you hit 400,000 feet. The time when you hit 0.05g is later, usually 28 seconds later for a lunar entry. That seems to be the difference between those two numbers.

Q4

In the ENTRY PAD the target, splashdown coordinates were +7.44 LAT / -164.96 LONG.

Upon splashdown I got in F16 67: R1 -00024 (I hit the target 2.4 NM short, if my interpretation is correct), R2 +00741 (+7.41 LAT) and R3 -16495 (164.95 LONG) … I guess not so bad.

BUT in the Apollo by Numbers I saw that the actual splashdown coordinates were +8.10 LAT and -165.00 LONG … so if the MCC “knows” where I am heading at all times, why he scrubbed MCC-6 and MCC-7 if he “predicted” a target splashdown in the ENTRY PAD which was not the historical correct one? Or in the MCC calculations the final target splashdown coordinates don’t enter into the actual calculations to be done for up linking a burn vector and TIG?

But anyway, if I got these numbers should I consider my mission a success or a failure?

The way TEI is targeted is not to hit a specific latitude and longitude, but longitude only, using the optimal return in terms of DV. So that optimization might have taken you away a bit from the historical splashdown coordinates already, at least in latitude.

Then after TEI the MCCs are usually targeted to get you back into the entry corridor (flight plath angle), but not the longitude of your splashdown. So there are a lot of variables in determining the maneuvers and the final splashdown site. Your lunar orbit before TEI, the residuals of TEI and then the MCCs won't try to get you back to exact desired splashdown site. And there also might be a difference because of geodetic vs. geographic latitude.
 

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@thermocalc Also, you should precisely cite the Orbiter version in NASSP 8.0, since it is for Orbiter 2016 Beta only, not for the 160828 release.
 

thermocalc

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Hi and thank you ALL for your valuable hints/explanations... :hailprobe:

I can confirm the HRZ CHK was spot on, at DET 43:00 the Earth HRZ was on the 31.7 degree line with P=267, PAD said 268…I had to activate everything in Orbiter to can spot the dark Earth…grids, celestial coordinates, surface markers, but finally it was there as predicted. Happy to see it. Meaning I did all correctly (without realizing).

Nice explanation also for TEI and MCC targeting, I am reading now some mission report files to compare my own mission with the real one...

If I may, I would like to report some others small issues with the checklist (I am referring to “A8 checklists” files stored into NASSO v8 rev.1749 checklist folders, which I was using, don’t know if in the newest revision these issues were already solved/corrected) ... if so please forget what I am going to say.

a) During the execution of P21 at some point the DISKY display the LAT/LOG/ALT in F 06 43, but the checklist says F 06 33 (see “issue 1” photo file), so the checklist should say F 06 43 not f 06 33.

b) From GET +124:40:00 to +129:30:00 you are in PTC roll mode, when you are asked for P52 (see “issue 2” photo file) but the TERMINATE PTC procedure is missing in the checklist, it was always there (mentioned) between any “BEGIN PTC” and “P52”…(see for example “issue 3” versus “issue 2” files).

c) Looking at “issue 3” photo file between the actions to perform from T +139:20:00 to T +142:45:00 are missing the subsequent 3 sets of P23 at T +141:00:00 as well as the ones at T +142:30:00 (mentioned in the original Apollo 8 flight plan) … but HERE I “guess” that these last 5 P23 instances were supposed to be done by the crew only in case on lost of communication…so maybe that’s the reason why they are no mentioned in the checklist…as related to contingency procedures. Am I right?

d) After Splashdown, at some point it is mentioned to turn the “MN BUS TIE BAT A/C and B/C sw to OFF” … doing so all electrical power is lost, DET stop running, CW goes all off, DISKY goes off, GET goes off, internal sounds of the fans goes off, all noise get silenced … I guess this is normal as I saw it was like that also in the original Entry checklist and indeed we are cutting off the electrical power to the CM … but as there are still many things to do before opening the hatch, after flipping the sw off, for which actions must be performed after some particular “times after splashdown” are elapsed…I was just wondering if all internal timers goes off how the crew kept track of time to act proeprly? just using their own swatches? As simple as that?

Thanks again for your patient to read me.

I will surely download the newest revision 1755 for starting Apollo 11 in Orbiter Beta this time for sure...no need surface helpers to land at Tranquility Base ehehehe...

thanks again.
 

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thermocalc

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sorry I attached by mistake all photos twice...don't know how to remove from my old post....really sorry :(
 

rcflyinghokie

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a) During the execution of P21 at some point the DISKY display the LAT/LOG/ALT in F 06 43, but the checklist says F 06 33 (see “issue 1” photo file), so the checklist should say F 06 43 not f 06 33.
You are correct, another checklist "relic" I imagine. I have corrected this.

b) From GET +124:40:00 to +129:30:00 you are in PTC roll mode, when you are asked for P52 (see “issue 2” photo file) but the TERMINATE PTC procedure is missing in the checklist, it was always there (mentioned) between any “BEGIN PTC” and “P52”…(see for example “issue 3” versus “issue 2” files).
Ah good catch here, while "Terminate PTC" is not explicitly mentioned here in the flight plan, it is implicit enough to include for clarity.

c) Looking at “issue 3” photo file between the actions to perform from T +139:20:00 to T +142:45:00 are missing the subsequent 3 sets of P23 at T +141:00:00 as well as the ones at T +142:30:00 (mentioned in the original Apollo 8 flight plan) … but HERE I “guess” that these last 5 P23 instances were supposed to be done by the crew only in case on lost of communication…so maybe that’s the reason why they are no mentioned in the checklist…as related to contingency procedures. Am I right?
This was the interpretation that these were loss of comm contingency sightings, so we didn't include them in the checklist MFD.

d) After Splashdown, at some point it is mentioned to turn the “MN BUS TIE BAT A/C and B/C sw to OFF” … doing so all electrical power is lost, DET stop running, CW goes all off, DISKY goes off, GET goes off, internal sounds of the fans goes off, all noise get silenced … I guess this is normal as I saw it was like that also in the original Entry checklist and indeed we are cutting off the electrical power to the CM … but as there are still many things to do before opening the hatch, after flipping the sw off, for which actions must be performed after some particular “times after splashdown” are elapsed…I was just wondering if all internal timers goes off how the crew kept track of time to act proeprly? just using their own swatches? As simple as that?
You did not lose all electrical power, there are still many systems powered on the post landing bus (vents, compressors, VHF etc) but yes seeing your displays and such cut off is completely normal. The timelines were kept simply by the watches worn by the crew.
 
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thermocalc

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dear Max-Q
thanks a lot for you tips...I tried and it worked like a charm...now I can move on with orbiter beta r90 more confidently as at least I must not to worry to find out the corrects spots/landmarks when requested...at least if i don't get good numbers i will know it is me doing something wrong with the DISKY programs and not due to just pointing the optics in another place...thanks.
:hailprobe: :cheers:(y)
 

thermocalc

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thanks, I will do, I am just downloading the latest revision and do some preparation staff (printing docs, checklists, flight plans, readings all posts) before starting A11....surely I will be back soon in the forum with questions about the LM I guess...new craft and new computers to master...eheheeh...take care out there.
 
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