CM/SM separation at reentry Apollo 8 MCC

[Sloppyphan]

I am having an issue at separation, When I get to -15min to EI and hit the CM/SM sep switches, my RCS thrusters all seem to start firing and I spin out of control eventually to gimble lock usually. I am unable to take control of them or if it does register my attempt to fix it just then goes back to full spin once I stop trying to counteract.

I a similar issue before when I would hit RCS CM Press but I was able to get past that just can't remember how right now . .

I've gone through everything and all controls and switches seem to be in the proper place. (Let me know if I need to copy and paste any files) I may not be at a perfect HOR CK pitch and I'm not sure how to do the 45deg ATT SW check on the RSI as not sure how I hold GDN Align and move the yah knob, but I was under the impression that is a check more than anything.

I was feeling real good about understanding the CSM until this one . . .

 

[indy91]

I am having an issue at separation, When I get to -15min to EI and hit the CM/SM sep switches, my RCS thrusters all seem to start firing and I spin out of control eventually to gimble lock usually. I am unable to take control of them or if it does register my attempt to fix it just then goes back to full spin once I stop trying to counteract.

Hmm, but you are actually separating the CM/SM with this, right? It can happen that if you only have the CM/SM sep switch in the up position for a tiny amount of time that the CM/SM separation is not triggered. What is however triggered is the Service Module Jettison Controller (SMJC), which will fire the SM RCS thrusters to pull away the SM from the CM. The thrusters would fire even if the CM and SM are still together. That is why the actual checklists often tell the astronauts to keep the CM/SM sep switch(es) in the up position for at least a second. But that is the SM RCS thrusters, in your case the CM RCS thrusters keep on firing, is that correct?

I'm not sure how to do the 45deg ATT SW check on the RSI as not sure how I hold GDN Align and move the yah knob, but I was under the impression that is a check more than anything.

That one you do by Shift + clicking on GDC Align, that keeps the button pressed. Then you rotate the yaw attitude switch to 45° and back, the normal procedure. Afterwards just click on GDC Align again and it will be unpressed.

 

[Sloppyphan]

Thanks Indy!

I had a feeling it was something "silly" that I had not come across yet . . Thanks . . I had assumed it was the CM rcs but you are right it was the SM firing and I was not separated, held down till Sep 1 till complete and all worked as expect and then completed my first ever ballistic orbiter reentry.

Seriously this is a really amazing sim, to work through this gives such insight to the innovation at that time..

Much appreciation to all the developers and testers

Now time to learn the LEM . .

 

[indy91]

Ah, great that it was something easy to find! And just for completeness, the passage of the AOH talking about this (https://history.nasa.gov/afj/aoh/aoh-v1-2-09-seqsys.pdf), PDF page 35-36

When either or both of these switches are utilized for CM/SM separation, they should be held closed for approximately 0.1 of a second to allow the time-delay relay logic to function properly.

So a case of "oops, we made it too realistic!"