Apollo 8 - NASSP v1858 - optics issues or my mistakes?

[thermocalc]

Hi to all,

I started Apollo 8 again from scratch using NASSP 1858 to enjoy P22s while in lunar orbit to get more acquainted with moon landing marks without stress due to the LM , all went well until MCC-5 when I got the ENTRY REFSMMAT and I was supposed to do P52 REFSMMAT at approx 103h GET .

The 1st and 2nd stars were this time not “centered” but quit off (from an earlier my question I came to know this was normal as the “actual” rather than the desired” REFSMMAT was uplinked), but this time while moving manually the optics to center them I faced the following situation (not there last year when I did the same mission with Orbiter2016, not “beta”).

Photo 1 shows the 1st star with MODE – CMC, when going into MODE – MAN, SPEED – HI with F 51 using the “W-S-A-D” keys I cannot move the optic beyond this position (see photo 2) -> “jam optic effect” (?)

Moreover, if I release the keys the optic doesn’t stay there but it “spring back” to another position, see photo 3 (“spring back effect” (?)).

I also got the the same “spring back effect” , from optic as in photo 2 to position as photo 3, even if I keep continuously pressing the keys but I switch SPEED from HI to MED or MED to LO. About changing speed the optics spring back.

Basically I cannot complete the alignment this time.

Thinking back, I saw these “jammed optic positions effect” -> the optic doesn’t move beyond a given position even if keep pressings the WSDA buttons,

and “spring back effect” -> upon releasing the WSDA keys for marking the optic goes back to another position,….

all times while in P52s, P22s and P23s, when optics have to switch from CMC control to MAN control (ex. P22 Manual Optic no problems, P22 Auto Optic or P22 Landing site tracking, P52 and all P23s) … but I was always in MODE – MAN with F51 on the DSKY.

As the CMC was most of time spot on on the landmarks and stars I thought that these “weird effects” where due to COLOSSUS itself run on A8 (thinking that maybe when I run A8 with Orbiter 2016 there was another CMC sw installed) and indeed I managed good results until now (even with the P23s) as the effects were minimal…but having seen both effects now in more details I guess something was maybe always wrongs?

If I do something wrong please advise, if not I attached two scenarios:

one just before starting P52 option 3 (after the MCC-5 CMC uplink ended),

the other when I am on the last star to mark still in F51 and Man optics and if you try to move the optics with WSAD keys you should experience both effects I was referring to.

Thanks for let me know.

photo 4,5,6 same effects for the 2nd star: photo 4 - the off position, photo 5 - the max optic excursion position keeping pressing keys, photo 6 where the optic spring back upon releasing the WSAD keys.

 

[thermocalc]

Hi, sorry ... I didn't know this issues was well know, I found an old treat looking around ... so ok, I did the P06 CMC standby procedure followed by the setting of the DRIFT and REFSMMAT flags as indicated, and now everything works, I just made the MCC-5 burn and all stars were according the PAD.
Sorry for not having paid attention before to the old treats...kind regards to all.

 

[indy91]

There is multiple things going on here.

Thinking back, I saw these “jammed optic positions effect” -> the optic doesn’t move beyond a given position even if keep pressings the WSDA buttons,

The optics system of course has limits in trunnion and shaft angles, so it's normal that you can't move it beyond a certain point.

The 1st and 2nd stars were this time not “centered” but quit off (from an earlier my question I came to know this was normal as the “actual” rather than the desired” REFSMMAT was uplinked)

I'm starting to think this is a bad idea. I have conflicting information about what they intended to do on the actual mission here. Another reason why the difference is so large is that MCC-5 currently does landing point control (getting the landing point back to 165°W) instead of just corridor control (only fixing the entry angle with MCC-5). They would have done landing point control with MCC-5, but only if the new landing point on the current trajectory would be quite far off from the one planned for TEI. So in the future the MCC will probably not do landing point control with MCC-5, the DV for that burn will be smaller, making the change to the Entry REFSMMAT uplinked for MCC-5 smaller. But uplinking the REFSMMAT directly is not something they actually did on the real mission either. Of course they accidentally entered P01 and so had to get a new REFSMMAT anyway. But that was after MCC-5 and reading the transcript they don't seem to have gotten an REFSMMAT update with MCC-5, neither the actual one nor desired.

For your "spring-back" effect you have probably now read in other threads that this a currently known issue that shouldn't really happen. From a hardware point of view the CMC is allowed to drive the optics even with the switch in manual and that is what is going on in your scenario. From a software point of view this shouldn't be possible to be happening and we have never found a document that indicates this would be a bug specific to Apollo 8 and 9 (the CMC versions where have gotten the issue). It seems right now there is just a random risk that this issue will occur whenever you just did a burn with P40. In P40 the Optics Coupling Data Units are used to drive the TVC instead of the optics and something goes wrong when exiting P40, either a CMC software bug or NASSP bug, we don't know yet. But we really need to try understanding this issue as it's not uncommon.

 

[indy91]

From a hardware point of view the CMC is allowed to drive the optics even with the switch in manual and that is what is going on in your scenario.

As it turns out, this is incorrect. For Apollo 14 they added a new program to the CMC, Program 24, Rate-aided optics. In that program, and in that program only, is the CMC allowed to drive the optics in manual mode. It helps the fact that sometimes you have to command fairly large optics rates just to keep the sextant on the landmark. The automatic drive does this for you and you just have to manually place the reticle on exactly the target you want to track.

And to enable this functionality they made a hardware change to the Apollo 14 (and later) CSM, bypassing the optics mode switch for one signal to allow CMC commands to go through in manual optics mode. So this couldn't have happened on Apollo 8 and the software really had no need to safeguard against it happening. This will be fixed in the next NASSP update.

 

[thermocalc]

thanks for these nice technical updates Indy, anyway I splashdown and I am happy to report back to the team that my A8 mission was "smooth" for what concerns all MCCs uplinks and checklists steps...now I just uploaded the new version 1870 and started again A11, but his is another story