Problem Apollo9 Phasing Burn attitude

[riclourenco]

Hello everyone

I'm having one more problem with LEM's phasing burn after the undoking (GET 93h43). I ran file 16 (name -Before phasing burn) from the scenarios folder of Apollo9, where it starts about 3 minutes before engine ignition, to compare the final attitude of the LEM (after passing T-2 min and hit the RPY of attitude control to "Mode cont") and comparing to my mission at the same GET. In my apollo9 mission I end up with the correct attitude when I hit “Mode cont” at T-2 min. Everything seems to be OK, AGS zero time, LEM stars alignment, RRadar, and the same attitude as in file 16. The only difference is that the CSM is behind the LEM, not in front as in file 16. Consequently when I hit "Mode cont" in RPY atittude control, although the LEM is maneuvered to the right attitude, the LEM loses the RRadar signal because of this. My Ordeal it seems to be correct. In both cases the ordeal is R = 0, P = 0 and Y = 0 and the LEM is facing forward to the direction of movement.

For File 16 of scenerio folder:

https://puu.sh/BGHJr/5fa6ac574d.png

https://puu.sh/BGHK0/94f0c72230.png

and for my mission:

https://puu.sh/BGILr/a72df7e71c.png

https://puu.sh/BGIMa/093fc59d16.png

What can I do wrong for the CSM to stay behind the LEM at the time of burn? I've done the undocking several times before and I always end up like this!

Can I continue with burn anyway, if I get a way for the LEM to have an attitude of R = 0 P = 180 and Y = 0, so that it faces the CSM? in this case the LEM would be facing opposite to the direction of the orbital movement.

I also noticed that the flags of the Quads in my mission are red:

https://puu.sh/BGJuN/144b178216.png

while in file 16 they are gray!

However the LEM RCS in my mission are working fine since they were activated. Is there a problem here to?

Thanks

 

[indy91]

What can I do wrong for the CSM to stay behind the LEM at the time of burn? I've done the undocking several times before and I always end up like this!

Maybe the SM RCS separation burn? That burn has to be done with the CSM facing upwards, but you are burning downwards (-X thrusters and not +X thrusters). If you would use the +X thrusters in that attitude then the CSM ends up behind the LM half an orbit later.

Can I continue with burn anyway, if I get a way for the LEM to have an attitude of R = 0 P = 180 and Y = 0, so that it faces the CSM? in this case the LEM would be facing opposite to the direction of the orbital movement.

Not advisable. After the phasing burn you will come back to the CSM fairly closely (at about 95:20 GET) and if the CSM is behind at phasing then the relative trajectory profile is all messed up and there probably even is a higher chance of colliding with the CSM. So if it was the separation burn that caused your issue, then I would revert to a scenario before the sep burn.

I also noticed that the flags of the Quads in my mission are red:

while in file 16 they are gray!

However the LEM RCS in my mission are working fine since they were activated. Is there a problem here to?

A quad flag becomes red if there is a RCS firing command for a thruster, but it doesn't actually fire. It it quite likely that this will happen during LM activation before the RCS is fully activated, that's normal. Cycling the CWEA circuit breaker open and closed again should clear the flags. Alternatively cycle each of the thruster pair switches to disable and back to enable. If you still get red flags after that then there might be an actual RCS issue, but that seems unlikely.

The logic for determining a thruster failure is also a bit sensitive right now, so you might be getting red flags with frame rate hiccups, or when you are saving a scenario or so. Just use one of the procedures I explained above to clear it again.

 

[riclourenco]

I was making a big mistake and had not noticed. I was thrusting to 1.0 on R1 instead of 10.0 on the separation burn, because I was using + X instead of -X as you said.
It was lack of attention, thanks for the help. Regarding the RCS I did cycle on each of the thruster pair switches to disable and back to enable. Their are now gray and the RCS are working.
 Since I'm asking questions, just to confirm, these are the DV of the maneuver that I have to put in AGS:

https://puu.sh/BGILr/a72df7e71c.png

+00024 DVX AGS N86
-00000 DVY AGS
-00834 DVZ AGS

These are the same values ​​that I have to put in AGC too right?

As you told me in an earlier post:

"The AGS has no auto throttle capability, so you have to throttle the throttle manually to 40%. And about the engine cutoff, it might be that you gave the AGS the wrong DV. DV is 1.0 ft / s not 0.1 ft / s. So if you would like to enter +00837 for 83.7 ft / s burn in lunar orbit you have to use +00084 in Earth orbit. very common mistake. "

I should do load in AGS and AGC like this:
+00003
-00000
-00084

This is correct?

Thanks

 

[indy91]

I should do load in AGS and AGC like this:
+00003
-00000
-00084

This is correct?

Thanks

No, that is the way you have to load it for the AGS in Earth orbit only. The AGC uses the same input format for Earth and lunar orbit, so:

+0002.4 DVX
-0000.0 DVY
-0083.4 DVZ

Least significant digit is always in 0.1 ft/s in the AGC. These are the numbers you have to load in P30. Or whatever the Maneuver PAD said.

 

[riclourenco]

Thank you very much!!

Best regards