LM RCS TCA

[Pulp Friction]

Hi folk,

Having a bit of trouble during LM powerup. I keep getting an 'RCS TCA' alarm and some of the RCS thruster quad talkbacks are turning red, typically it seems to be 'System A' quads 2 & 3 and 'System B' quads 1 & 2 although the rest go red during RCS Pressurisation. Can anyone help?

 

[indy91]

Ah, this is a bit of a never ending story for me. The logic for that is still not quite right I think, but in general getting red TCA flags is actually normal during LM activation. That happens when a RCS firing command goes to the thruster, but no actual thrust (or thruster chamber pressure) is sensed. Definitely during the cold fire checks, before the QUAD TCA circuit breakers are closed you will always get the red talkbacks. Usually you can reset them by cycle the CWEA ciruit breaker, or closing/opening each TCA switch individually.

There are still some cases where it doesn't properly reset the red flags, that wouldn't happen in the real LM. But feel free to ignore the talkbacks until the RCS hotfire checks and then reset the flags. After that it shouldn't happen anymore.

 

[Pulp Friction]

Thanks so much, that should get me moving again. Much appreciated.

---------- Post added 06-19-20 at 08:31 AM ---------- Previous post was 06-18-20 at 06:26 PM ----------

Ok, did all you said indy91, and all went well. However, after undocking I attempt to null the undocking dV's and get an RCS TCA alarm and the red flags on the quads again. The RCS isn't firing by the way. I'm stuck again, I'm pretty sure I followed the checklist ok.

 

[indy91]

Well in that case the RCS hasn't been pressurized or something like that. On panel 8, switch Master Arm to On and then He Press - RCS to Fire. Circuit breakers to check are the eight RCS SYS A/B QUAD TCA circuit breakers. On the main panel make sure the two RCS Main SOV talkbacks are gray.

 

[Pulp Friction]

My C/W panel looks like this.

 

[indy91]

Yeah, looks like the RCS hasn't been pressurized. Try that procedure I wrote above.

 

[Pulp Friction]

Worked. You're a genius, thank you.