Question Gimbal angles and AGS zero time (Apollo9)

[riclourenco]

Hello everyone

I have two questions about the LEM. During the activation of the LEM, at some point we have to load the Gimbal angles of the LEM into the AGC. I'm supposed to read the LEM gimbal angles that I'm going to load in the apollo MFD right?

The GET in which the AGS zero time starts, will it be different for different users. It will depend on the GET that they choose to start the AGS Zero time, right?

Thanks

 

[indy91]

Hello everyone

I have two questions about the LEM. During the activation of the LEM, at some point we have to load the Gimbal angles of the LEM into the AGC. I'm supposed to read the LEM gimbal angles that I'm going to load in the apollo MFD right?

Yes, the PAMFD is displaying the CM IMU angles and the LM IMU angles. The LM IMU angles is what you want for the V41 N20. In reality the LM crew got the CM IMU angles from the CMP and they had to convert it to LM IMU angles as per LM Activation Checklist.

The GET in which the AGS zero time starts, will it be different for different users. It will depend on the GET that they choose to start the AGS Zero time, right?

Thanks

Normally the AGS zero time is a nice and round number like 90h GET or 100h GET. For the initialization you have to do a bit of math then. The AGS wants an input in 0.1 minutes. Example: your current GET is 92:10:30. Then it's the best to use the next full minute (or the full minute after that one). AGS zero time would be 90h GET. So the AGS initialization time is 2:11:00 then (next minute, 90h GET subtracted). In minutes that is 131 min. So you enter 377+01310 on the DEDA, wait until the GET actually becomes 92:11:00 and then press enter on the DEDA.

Of course you won't be able to get the timing 100% right. So in reality the crew got an updated K-Factor (the AGS zero time) that is usually within a second of the nominal number (90h GET). Unfortunately we haven't really figured out yet how mission control was able to determine this updated K-Factor. Maybe they looked at the AGS telemetry and compared it to the LGC telemetry or so. But if you pressing enter with good timing, then this procedure without the K-Factor update is usually good enough.

 

[riclourenco]

Thanks for the answers

What I did was this: I started activating the LEM for the undock. For me AGS initialization arrived at checklist in GET + - 91: 48: 00. What I did was wait for the GET 91h50:00 to have a rounder number, and at that moment I hit enter in the DEDA for 377 + 00000.

But according to what you said, to start AGS zero time with a rounder GET number using GET 90h:00:00, I can go back to GET 91:48:00 (where is my save file is) and hit enter on DEDA 377 + 01100 on GET 91h50:00.

Are these the two ways correct to initialize AGS zero time?

After initialization of the AGS zero time, and later in the checklist, to update the AGS time, all that I have to do is subtract the current GET for the next whole minute or another, by the AGS zero time GET chosen previous, calculate the value in minutes and press enter on the DEDA in the chosen minute. Is this correct?

Thanks!

 

[indy91]

Thanks for the answers

What I did was this: I started activating the LEM for the undock. For me AGS initialization arrived at checklist in GET + - 91: 48: 00. What I did was wait for the GET 91h50:00 to have a rounder number, and at that moment I hit enter in the DEDA for 377 + 00000.

But according to what you said, to start AGS zero time with a rounder GET number using GET 90h:00:00, I can go back to GET 91:48:00 (where is my save file is) and hit enter on DEDA 377 + 01100 on GET 91h50:00.

Are these the two ways correct to initialize AGS zero time?

Yes, the way you did it also works. Of course you then have to input the K-Factor you used in Verb 47, when you want to transfer state vectors from the AGC to the AEA.

After initialization of the AGS zero time, and later in the checklist, to update the AGS time, all that I have to do is subtract the current GET for the next whole minute or another, by the AGS zero time GET chosen previous, calculate the value in minutes and press enter on the DEDA in the chosen minute. Is this correct?

Thanks!

Yes, this is the way they probably did it on all actual flights. An advantage of using the rounded GET (e.g. 90h GET) is also that you can more easily convert a GET to an AGS time. You for example input times for the CSI and TPI maneuvers during a rendezvous.

Check the AOH for the suggested procedures: https://www.hq.nasa.gov/alsj/LM11HandbookVol2.pdf on PDF pages 291 to 294 . You will see it has both methods and V47 even can assist with the method you used orginally. For that method you would press ENTR on both DEDA and DSKY at the same time. To do that there is a "V47" button on the LGC page of the Project Apollo MFD.

 

[riclourenco]

Thank you very much for your answers!