Apollo 11 LM cold fire not firing

Zuppermati

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Good evening

I have been kinda busy with life, but after a 1 year long hiatus I have managed to resume my Apollo 11 simulation.

I am currently stuck at T+99:40:00, where I am supposed to perform an "RCS cold fire" with the LM. The checklist tells me to enable the linear translation and then fire the TTCA up. The action should result in some caution and warning lights popping out in the LM. The only issue is that the RCS does not fire at all and I am getting no warnings at all. When I switch to linear translation, I am supposed to hear a female voice saying "translation", which is part of orbiter's standard sound pack, but in this particulat instance I can't hear anything. For the record, if I switch to the CSM and perform the same operations I can hear the voice and the SM's RCS fires perfectly.

I would love to give you more informations but I have zero clue about what went wrong. I tried to redo the whole simulation from T+98:00 to see if I did anything wrong, but nothing. The only thing I can say is that I am getting an ASC pressure light.

Does anyone have any clue? Many thanks in advance.
 

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Hello,

I believe that this behaviour is normal. You should not get the RCS jets to fire during the Cold Fire test, as this test is intented to verify the ACA/TTCA signals, and check that they are correct. You check both rotation (ACA) and translation (TTCA) and verify the DSKY for signals. During the Hot Fire test, then you will get the jets to fire.

Best regards,
 

Zuppermati

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Hello,

I believe that this behaviour is normal. You should not get the RCS jets to fire during the Cold Fire test, as this test is intented to verify the ACA/TTCA signals, and check that they are correct. You check both rotation (ACA) and translation (TTCA) and verify the DSKY for signals. During the Hot Fire test, then you will get the jets to fire.

Best regards,
Hello

Thank you for your time, but I still believe that there's something wrong. Other than the fact that the "Quad Flags & RCS TCA warning lights" are supposed to light up according to the checklist, and they are not, I am supposed to wait for the DSKY to display 00252 on the first row, and 00125 when I release the TTCA. I waited for 5 whole minutes with my finger pressing the translation up button, but still nothing.
 

indy91

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Hmm, then the TTCA commands aren't coming through to the LGC. Could be a wrong joystick configuration or some switch setting. Do you have any joystick enabled as the TTCA in the NASSP setting of the Orbiter launchpad?
 
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Miriam

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Maybe I'm just to plain, but have you ever tried Ctrl + Numpad /? Not that you just deactivated the RCS by accident. I stumble on this from time to time especially when hacking something in the DSKY or DEDA. "Verb...gnah! Shift and Divide, not Ctrl and Divide!" ?
 

Zuppermati

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Hello. Unfortunately, both your suggestions did not work. No joypad is enabled and the RCS is activated (if I press F8 to change the view, I can see that it is set on LIN and it's not OFF). I even checked on a quicksave of the docking phase from the same session and the RCS works just fine over there.
 

indy91

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Then I will need to check in your scenario what could be wrong. Maybe something with the LGC or so...
 

Zuppermati

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Then I will need to check in your scenario what could be wrong. Maybe something with the LGC or so...
I appreciate your time. I had to convert it to .txt since this forum does not allow scn files as far as I know
 

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indy91

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I had to convert it to .txt since this forum does not allow scn files as far as I know

I think there are different size limits for scn files vs. txt files. And NASSP files have been exceeding the limit for scenarios ever since the AEA memory also had to be saved.

I don't know more yet, but something in your LGC seems buggy. Like, not even simple DSKY inputs like Verb 1 Noun 1 are properly working. Not sure what is causing that. But there seems to be a simple fix, just do a V37E 00E. Follow that with the current step you are doing, V11 N10E 5E and then the output channel 5 data will appear in register 1, that is currently blank. And when I then do any translation inputs they appear on the DSKY.

I will have to investigate more how you got into this situation. Never seen the LGC behave like this.
 

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I had something like a 'partially hung' LGC when I flew Apollo 12. Brought it out of Standby, went through the checklist and had a bad surprise at liftoff: the DAP didn't work, despite passing the cold/hot fire test before. Had to go back before P12, did a V36 and everything was fine again. No idea how that happened.
 

Zuppermati

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I think there are different size limits for scn files vs. txt files. And NASSP files have been exceeding the limit for scenarios ever since the AEA memory also had to be saved.

I don't know more yet, but something in your LGC seems buggy. Like, not even simple DSKY inputs like Verb 1 Noun 1 are properly working. Not sure what is causing that. But there seems to be a simple fix, just do a V37E 00E. Follow that with the current step you are doing, V11 N10E 5E and then the output channel 5 data will appear in register 1, that is currently blank. And when I then do any translation inputs they appear on the DSKY.

I will have to investigate more how you got into this situation. Never seen the LGC behave like this.
I have savestates for basically the entire mission up to that point. Do you want me to give you anything in particular?
 

indy91

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I have savestates for basically the entire mission up to that point. Do you want me to give you anything in particular?

Unless it is just seconds before the scenario you already posted it's probably not going to be more useful than the current scenario already is.

But maybe your memory of events could help. I figured out one more thing about your issue. The AGC doesn't continually update the DSKY, instead it keeps a "copy" of the DSKY state in its memory. And only when there is a change to the required DSKY state does it actually output the signals to the DSKY to update it. That DSKY state in the AGC memory is what gets send out on telemetry and look at that, there is a mismatch between AGC and DSKY.

In the scenario you posted the three DSKY registers are entirely blank. Looking at my LM Telemetry Client it actually has what I would consider the normal display if you did V11 N10E 5E. It has 00000 in R1 and 00005 in R3. If I try to call V11 N10E 5E again then R1 stays blank because it already is 00000. But what does actually work is doing some TTCA commands. Then R1 needs to change and the AGC does send updated digits. Does that work for you now?

Now, what exactly happened when you did V11 N10E 5E, if you can remember. What should have happened is that the DSKY has 00000 in R1 and 00005 in R3. Then if you do TTCA commands R1 would change. Where in this sequence of events did it differ for you from the nominal behavior?
 

Zuppermati

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Unless it is just seconds before the scenario you already posted it's probably not going to be more useful than the current scenario already is.

But maybe your memory of events could help. I figured out one more thing about your issue. The AGC doesn't continually update the DSKY, instead it keeps a "copy" of the DSKY state in its memory. And only when there is a change to the required DSKY state does it actually output the signals to the DSKY to update it. That DSKY state in the AGC memory is what gets send out on telemetry and look at that, there is a mismatch between AGC and DSKY.

In the scenario you posted the three DSKY registers are entirely blank. Looking at my LM Telemetry Client it actually has what I would consider the normal display if you did V11 N10E 5E. It has 00000 in R1 and 00005 in R3. If I try to call V11 N10E 5E again then R1 stays blank because it already is 00000. But what does actually work is doing some TTCA commands. Then R1 needs to change and the AGC does send updated digits. Does that work for you now?

Now, what exactly happened when you did V11 N10E 5E, if you can remember. What should have happened is that the DSKY has 00000 in R1 and 00005 in R3. Then if you do TTCA commands R1 would change. Where in this sequence of events did it differ for you from the nominal behavior?
Hi indy, a quick update

Now that you made me notice it, I have absolutely no idea why the 3 rows were blank. What is even weirder is that if I use the quicksave of the same simulation but from a minute earlier, which I have attached on this message, and I reach once more for V11N10, R1 and R3 displays 00000 and 00005 respectively as expected and everything works, which is even weirder since I have redone the entire mission from T+98 just to be sure I was doing everything correctly!
I know I might sound pretentious but I am 99% sure I followed the checklist and didn't do anything else since I always follow it like a bible.

But, still, thanks for the help. If you think this was because of a bug and you still want to take a better look, just ask me for what you need

EDIT: still, I'm not getting any warning lights as expected. But that's secondary stuff. What's more interesting is that on the ROLL cold fire everything that was supposed to print 00051 prints 00052 instead. I don't know if that's negligible or bad
 

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indy91

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still, I'm not getting any warning lights as expected. But that's secondary stuff.

Ok, so even if your first scenario, where the DSKY state is a little bit buggy, I can press the / button on the Numpad, which switches to translation (and I do get the sound for that). And then I press 2 on the Numpad to translate updwards and as a result I get a 0252 in R1 on the DSKY, a new master alarm caused by the RCS TCA light (I pressed the master alarm button when starting the scenario to turn it off) and 4 quad flags for "failed" thrusters. All without doing the V37E 00E to fix the buggy DSKY state. Just start the scenario, master alarm button, switch to translation, translate upwards.

And I do think it's an actual bug. Because the LGC and DSKY should never have a mismatch. But right now this could be a bug in any place, including in the actual LGC software by doing some unusual sequence of DSKY inputs (unlikely, but not impossible). Or somewhere in the actual NASSP code, no idea.


What's more interesting is that on the ROLL cold fire everything that was supposed to print 00051 prints 00052 instead. I don't know if that's negligible or bad

That's negligible. This is the number of ACA counts, converted from analog to digital. 0 at no deflection, 52 at full deflection of the joystick. The ACA does have some tolerances though for what is actually full deflection, so different LM Activation Checklists list different values, because each ACA on each mission was very slightly different there. Apollo 12 LM Activation Checklist says 51, the Apollo 13 one actually says 45 to 57 is acceptable. So 51 or 52 are well within the margin. I guess the ACA in NASSP will always have 52.
 
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