Apollo8 TLI, MCCs, P21, P22 and P23

[thermocalc]

dears,
I started Apollo8 mission, I managed to do the TLI and also the 1st MCC, i.e. MCC-1 and I think "hope" to be on the way to the moon .... even if not so sure :-( for what I have to say below.
I follows all steps in the checklists but I had some issues/doubts.

Q1) at time of the MCC-1 when I am supposed to enter into V41N92 the shaft/trunnion angles of the reference star in the PAD to check for proper alignment... the star was not there in the SXT, it was visible in the SCT, but it was much lower that the center crosshair .... so for some reasons I was out of attitude? anyway I did the MCC-1 burn to test P40 and at the end of the burn i got a perigee height of 138.1 nmi instead of the 138.9 in the PAD ... so i think i was not so bad out of alignment---I did the transfer of the uplinked SV from the LM slot to the CSM slot by V47E when requested by the checklist, does it means that I can continue with the mission and any error will be taken into considerations at the next MCC-2 burns by updated real time MCC PADs? what can cause the fact that the star was not centered in the SXT? -> note: when I run P40 burns in Apollo7 the stars mentioned in the PADs were always visible...(at least for the first 2 SPS burns ... I didn't complete all mission burns yet)

Q2) when they ask to do P22 orbital tracking at LOI time of 69:10:00 GET the values of LAT-LONG-ALT I get are not the same; doing P22 at 9h40m I got LAT -00963, LONG -17726, ALT +00398; when I did P22 at 17h 48m I got LAT -01298, LONG +15409, ALT +02356 ... should I be worried? anyway, is it normal for the AGC to get the activity lump ON for 3-4min before to give out the answer? the LAT/LON/ALT are referred to what? MOON or EART? if MOON I can understand the meaning, it tells me were I am suppose to be at LOI time, if EARTH why I should care about the groundtrack of the CSM when I am at the LOI? but if it is the MOON, how the AGC knowns "when to switch" from EARTH reference and MOON reference to calculate LAT/LONG/ALT?

Q3) when they asked to do P23 with a star and a landmark (number 10) ... I got the star in the optics but the landmark number 10 I never see it in the SXT view .... after all the landmarks are moving very fast, so I bet I was not synchronized with the landmark appearing in the SXT field of view at time of the observation... so the question is: can i superimpose the required star with another landmark number that happen to be in the SXT field of view at time of observation? if so, am I suppose to enter the new landmark code that i used in R2 when i get the flashing F05 71, to tell the AGC that I changed the landmark from what I told him when doing F05 70? or I cannot do that?

thank you for any help.
Paolo

 

[indy91]

dears,
I started Apollo8 mission, I managed to do the TLI and also the 1st MCC, i.e. MCC-1 and I think "hope" to be on the way to the moon .... even if not so sure :-( for what I have to say below.
I follows all steps in the checklists but I had some issues/doubts.

Q1) at time of the MCC-1 when I am supposed to enter into V41N92 the shaft/trunnion angles of the reference star in the PAD to check for proper alignment... the star was not there in the SXT, it was visible in the SCT, but it was much lower that the center crosshair .... so for some reasons I was out of attitude? anyway I did the MCC-1 burn to test P40 and at the end of the burn i got a perigee height of 138.1 nmi instead of the 138.9 in the PAD ... so i think i was not so bad out of alignment---I did the transfer of the uplinked SV from the LM slot to the CSM slot by V47E when requested by the checklist, does it means that I can continue with the mission and any error will be taken into considerations at the next MCC-2 burns by updated real time MCC PADs? what can cause the fact that the star was not centered in the SXT? -> note: when I run P40 burns in Apollo7 the stars mentioned in the PADs were always visible...(at least for the first 2 SPS burns ... I didn't complete all mission burns yet)

Potentially the optics not being zeroed when you did this procedure, but I would do a P52 option 3 as a check on your alignment. If the alignment is wrong but close then MCC-1 won't have been too bad and in doubt you will get a MCC-2 that corrects any errors (then hopefully with a good alignment).

Q2) when they ask to do P22 orbital tracking at LOI time of 69:10:00 GET the values of LAT-LONG-ALT I get are not the same; doing P22 at 9h40m I got LAT -00963, LONG -17726, ALT +00398; when I did P22 at 17h 48m I got LAT -01298, LONG +15409, ALT +02356 ... should I be worried?

I assume you mean P21? Each of those P21s were probably done with different state vectors and some pre and some post MCC-1. Also, I think the goal is to find the perilune and that will not be at exactly 69:10h so you might have to iterate manually on that time. Add or remove a minute from the time until the altitude is minimized.

anyway, is it normal for the AGC to get the activity lump ON for 3-4min before to give out the answer?

Yeah that is normal. The AGC has to numerically integrate the CSM state vector from the current time to 69:10h. That takes a while.

the LAT/LON/ALT are referred to what? MOON or EART?

Whatever the sphere of influence at the specified GET for P21 is. So in this case definitely the Moon.

if MOON I can understand the meaning, it tells me were I am suppose to be at LOI time, if EARTH why I should care about the groundtrack of the CSM when I am at the LOI? but if it is the MOON, how the AGC knowns "when to switch" from EARTH reference and MOON reference to calculate LAT/LONG/ALT?

Yeah the goal of this excercise is to find the perilune location, altitude and time using the onboard computer capabilities. Apollo 8 did a few such tests, not sure if it was something Jim Lovell just wanted to do or if if was to test the AGC.

The AGC switches the reference between Earth and Moon when the state vector reaches a specific distance from the Moon, essentially the sphere of influence of the Moon.

Q3) when they asked to do P23 with a star and a landmark (number 10) ... I got the star in the optics but the landmark number 10 I never see it in the SXT view .... after all the landmarks are moving very fast, so I bet I was not synchronized with the landmark appearing in the SXT field of view at time of the observation... so the question is: can i superimpose the required star with another landmark number that happen to be in the SXT field of view at time of observation? if so, am I suppose to enter the new landmark code that i used in R2 when i get the flashing F05 71, to tell the AGC that I changed the landmark from what I told him when doing F05 70? or I cannot do that?

You never enter landmark codes into the AGC, the AGC doesn't know about them. But you can enter new landmark coordinates after you already did the marks, that also works with e.g. P52 by the way, entering a new star code after marking.

Disclaimer for P23: we developers haven't figured it 100% as well. Some potential issues with the sextant and some inherent issues with the Earth in Orbiter (which is spherical, not an ellipsoid like in reality). So don't expect to get great P23 results, we never had good results either. We'll figure it out, one day...

 

[thermocalc]

Thank you again Indy for you replies.
about the missed star at MCC1 - I re-run the scenario I saved few hours earlier to cross check, and at the right time after getting the PAD and setting up the burn I saw the correct star in the right place, same at MCC3 (MCC2 was "scrubbed" so the PAS said) ... so I think i made something wrong the first time, :lol:
about the rest thanks now is clearer; instead I am not sure to have understood you correctly about P22, but first I will search around the forum what have already being done/said about P22, if really cannot figure out by myself I am sorry but I will start a new post.
I am still not arrived in lunar orbit yet, so I still have time and for the time being Apollo 7 P22 can wait....
eheheheh....time ago, I remember to ask around how to do time accelerations in NASSP, now that finally I can run a full mission with real checklists thanks to all good work done by you guys there are so many things to be handled/understood that if in the real Apollo 8 it took 69h to get to LOI it takes me almost one full week to get there due to limited time to run NASSP....last weekend I almost risk a new divorce from my new wife as I spent all Saturday and Sunday in front of my PC and when not, reading NASA docs on my desk and even going bed before sleeping...:facepalm:
thanks again, Paolo

 

[indy91]

I usually use 10 to 50x time acceleration during coasting phase. As long as the frame rate doesn't drop that should be fine. Using 50x during translunar coast makes those long phases a lot more bearable for full mission flying. I tend to use the outside view or a panel with very few switches and displays during time acceleration, as panels with a lot going on (especially the CSM main panel) are the biggest frame rate killers in NASSP.

 

[thermocalc]

thanks for the advice, up to 30x I am ok, higher than that I got weird things going on with the FDAI balls ... once I managed to go up to x60 using MissionTimer.MFD, but now even using that above 30 is difficult ... maybe I was doing it not in the cockpit view...I didn't think about it. I will check again.:thumbup: