PDI not working ?

[Joker]

Hello everybody,
I'm having a trouble with my PDI P63 on Apollo 11.
To explain, I started by a launch scenario, everything looked fine during lunar coasting, the LM is orbiting around the Moon, undocked, initialization completed, DOI done, and when I launch P63 (around 25 minutes before PDI) there is a long "COMP ACTY" falling on "PROG" light with a 01406 alarm.
Maybe I missed something ?
Thanks .

 

[kuddel]

Hi Joker,
the 1406 alarm indicates a "Bad return from ROOTPSRS".
The comments on ROOTPSRS might give a hint.
Without really knowing, I would suspect that the root finder subroutine did not succeed finding a root in N iterations (whatever N might be) and therefore it might be too soon (or to late) to run P63...

Maybe issuing P63 later (or sooner?) might give better results.

 

[indy91]

Very likely that the predicted time of landing in the LGC wasn't sufficiently close enough for the ignition algorithm to find the time of ignition. On the DOI calculation page of the RTCC MFD you can find a button to uplink an updated TLAND to the LGC. Just do that some time before entering P63 and I think it will work.

 

[Joker]

Thanks for your replies ;-)
I've just tried what you told but the same issue...
Could it be an AGS problem this the LGC ? Is it possible to land without the AGS ?
Thanks ;-)

 

[indy91]

No, not an AGS issue. Have you had a DOI calculated before uplinking the TLAND? Otherwise you might have just uplinked the planned landing time again, which is in the LGC anyway. That's the usual procedure, DOI solution going together with a uplinked TLAND.

TLAND not being right for your specific trajectory is still most likely the cause, it is in most cases for that specific program alarm. If you want I can take a look at your post DOI scenario, to see what it could be.

 

[Joker]

Hello !

Thanks a lot for your quick response ;-) and sorry my later I was in holiday

I've (re!)tried with another lauch scenario ... but the same issue !

Here's is the scenario in witch you'll see by yourself ;-)

Thanks a lot for your help ;-)

 

[indy91]

I found two things wrong in the scenario:

The LM state vector in the LGC is still showing an about 60x60NM orbit (in Verb 82). Did you not use P40 for DOI? Or accidentally uplinked a CSM state vector maybe. The fix for this is of course another state vector uplink to the LGC with the vessel Eagle and to the LM slot.

The liftoff reference time (TEPHEM) is wrong in both CMC and LGC. I noticed that you have the CMC circuit breakers pulled. It must have scrambled that part of the erasable memory in the CMC when you pulled the breakers or at some point before. Not sure. In any case, PAMFD (on the LGC init page) is looking directly at the CMC memory and you probably then initialized the LGC to the wrong (the same) TEPHEM. A fix for this is to set the TEPHEM in the LGC to the nominal liftoff time:

V25 N01E
1706E
00000E
20017E
20501E

I did this and the state vector update and then the P63 ignition algorithm works. Everything else seems to be good in your scenario (LM alignment etc). Just the landing time is a bit early.

 

[Joker]

Thanks for your light-speed response Indy ;-)

I'll try this as soon as possible !!!

So my error was to load TEPHEM just by looking at PAMFD without checking in the PAD load worksheet ... Apologize !

For the states vectors, I always reload them when reloading a scenario.

Once again, thanks a lot ;-)

I will tell you

See you :thumbup:

 

[indy91]

So my error was to load TEPHEM just by looking at PAMFD without checking in the PAD load worksheet ... Apologize !

Well, powering down the CMC is not normally done, so it was caused by trying to activate the LGC without having the CMC up and running. And you probably just got unlucky that the CMC did bad things with the TEPHEM when it got unpowered. Usually the CMP in the CSM has to read the TEPHEM values out of his computer and tells them to the other guys in the LM per voice. Obviously not possible with a powered down CMC. So doing things the nonstandard way sometimes can lead to unwanted surprises. :lol:

 

[Joker]

Hello !

Indy : I tried your tips, and works fine :thumbup: thanks !!!

Now, an other issue (yes I'am the 1000-issues-man with PDI )

I've tried an other thing. Starting with an Apollo11 scenario but trying to land at Taurus-Lithrow (I choosed this one because it's almost the same longitude than Tranquillity) and happened ... the same "01406" prog error !
I've checked every thing (state vector, TLAND, TEPHEM ...) and no way to land the LM with that "01406" issue...

I attached the scenario file.

Any idea ?

Thanks a lot ;-)

 

[indy91]

The landing site coordinates in the LGC need an update I think. You already put the right ones in the RTCC MFD, so just go to the state vector page press MOD to go to the landing site vector update page and press uplink to get the coordinates from the RTCC MFD to the LGC. Then I don't get the program alarm in your scenario...

but something else I have never seen. It goes directly to the 06 63 display (instead of 06 61) and I can't proceed from there. Very strange, not sure what is going on.

 

[Joker]

Hi Indy !

The landing site update ... what a beginner mistake lol !
Apologize ;-)

I tried this yesterday and for me it rolls normally (06 61and the pdi starts) ... strange ...
Do you want that I post my corrected scenario ? Maybe it will help you comparing ?

See you

 

[abr35]

I recently had the same alarm in P63 trying out the new Apollo 11 MCC-H. IMU is aligned, had low residuals on DOI, TLAND has been updated, landing site is correct.

I've been trying to figure this alarm out for a few days. Anything I could be missing? I deleted Columbia from the scenario due to file size.

 

[jalexb88]

Unfortunately I cannot run your scenario properly, Orbiter loads but I am sitting somewhere one earth and the LM is not loaded at all. I believe this is because you deleted the CSM from the scenario...this can have some bad effects like this. Please if you can, post a scenario without deleting anything from it and I can see what I can find

 

[indy91]

I managed to repair the scenario, just a few lines deleted too much (from the S-IVB).

It looks like your TEPHEM isn't quite right. It is:

00000, 20017, 40000

Did the CMC have this as well? Or just a typo maybe?

 

[abr35]

The CSM did have that as well. Double checked it before I deleted Columbia. Never monkeyed with the Tephem address on the way out.

 

[indy91]

The CSM did have that as well. Double checked it before I deleted Columbia. Never monkeyed with the Tephem address on the way out.

That third value of it should definitely not have 40000. 40000 is the largest negative number in octal. Not sure what could have changed that in the CMC. Maybe a really bad frame rate dip. Bad news is, even if I set that to the nominal liftoff value (20501) P63 still fails. I'll try a few more things.

EDIT: Found the issue. There is another one of those bad 40000 values in the scenario:

EMEM2474 40000

That is part of the ignition algorithm, so a rather bad one to have the wrong value. If I change it to the original value of 77731 then P63 works. So your scenario has two bad values:

EMEM1710 20501
EMEM2474 77731

If I edit the scenario to have those two values then the ignition algorithm works. But I really have no idea what caused this to happen. Time acceleration too high or a bad frame rate dip are my only guesses, but I've never had this happen myself.

 

[abr35]

Time acceleration never went over 10x. This would had to have happened after the LGC cb was in I assume?

Did have a restart light from going in and out of 10x accel very quickly. I think it reset my REFSMAT flag as well. Flown a number of different landings, honestly never had seen this before lol.