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Author Topic: Program 20  (Read 1838 times)
abr35
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« on: June 07, 2011, 11:51:45 AM »

I'm having trouble with Program 20 on Apollo 7. I doubt it's a bug because the results are so consistent, so it's probably a step I'm missing. Before separation I transfer the S-IVB state vector to the LM slot (V66). The DAP is configured and activated with SC CONT - CMC and CMC MODE - AUTO. Later after separation, I start P20 and get the flashing 50 18 hit PRO and get the 06 18 display, but this is where things start to get peculiar.

The CSM maneuvers to an incorrect position, sometimes the S-IVB is squarely in the optics, but sometimes it is over the hatch, rendezvous window, or side windows. I've keyed in V76 for the preferred attitude. Now I've tried this in several different scenarios, and the AGC places the CSM in a consistent attitude for each scenario, its just usually the wrong attitude. After pressing ENTR the sextant swings into position and tracks an empty area of space. Now it tracks this empty area like a champ, so I believe that it THINKS its tracking the S-IVB but the S-IVB is somewhere else. Is there a different procedure for updating the state vector when using the booster as the target as opposed to the LM?

Then, I come across problems with taking marks on the S-IVB. After the sextant is in position, the F 50 18 display returns, and I can't do anything about it. Pressing enter just clears the DSKY and brings back the same display, and pressing PRO briefly displays the 06 18 before switching back to F 50 18. So I never get the flashing 51 asking for me to take marks. If I make a mark, I get a program alarm telling me I can't do that (00122). If I enter V57 to start taking marks, I get an OPR ERR. Is this second problem related to the first or is it an entirely different problem?
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meik84
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« Reply #1 on: June 07, 2011, 03:42:56 PM »

You guys never sleep, huh?  Wink Now I'm almost done with one thing, the next is in the line... Rolling Eyes

Quote
Is there a different procedure for updating the state vector when using the booster as the target as opposed to the LM?
Just tried it: PAMFD should update the LM SV, too. Just select AS-205-S4BSTG.
Quote
The CSM maneuvers to an incorrect position, sometimes the S-IVB is squarely in the optics, but sometimes it is over the hatch, rendezvous window, or side windows.
Are you able to get the SIVB in the optics manual? If yes, P20 is working correctly. Optimum tracking attitude doesn't mean that the target has to be in the middle of the area the optics can cover.
Quote
If I enter V57 to start taking marks, I get an OPR ERR. Is this second problem related to the first or is it an entirely different problem?
Good question. From my guts I'd say no. Could be some garbage in the flagwords. I'll take a look at it tomorrow. this night. Wink
Found it: Let the CMC do its automaneuver in P20. When its done (needles centered, flashing V50N18), key PRO. DSKY blanks, FLV50N18 comes back, key ENTR. DSKY blanks again and stays blank. KEY V57E. Have fun.  Happy
Background is that P20 calls routine 60, which can only be terminated with ENTR when you are near the desired attitude and you have trimmed that attitude by keying PRO on FL V50N18 before the ENTR. This caused the OPR ERR light, as routine 60 counts as extended verb and routine 21 (which is called by V57) checks if no such is running when started.
A tip: when you aren't far away from the SIVB, put CMC MODE to FREE or SC CONT to SCS. Otherwise P20 tries to track the booster and will change the attitude rapidly, so that you can't center it in the optics properly. In extreme, you can't call V57, as P20 changes the desired attitude so fast that R60 can't keep up and you don't stand the chance to end it properly. This happens because we're operating P20 out of its limits when we're so close -it is designed for tracking the SIVB (or the LM, resp.) from far away and not from within 10 miles or so!
If your attitude yields to loose the SIVB out of the optics, UPLINK ACTV will come on as a reminder to either hand back the control to the CMC or change the attitude by yourself (fly to the needles on the FDAI).
« Last Edit: June 07, 2011, 06:05:01 PM by meik84 » Logged
Tschachim
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« Reply #2 on: June 10, 2011, 01:12:11 PM »

Hey, I never ever tried P20 and just learned it's working really great!  Happy

I took the scenario from the "Automatic SV Update" thread nearby (http://www.ibiblio.org/mscorbit/mscforum/index.php?topic=2698.0), did a normal SV Update and a SV Update for the S-IVB as "other vessel" (click SRC, type "AS-205-S4BSTG") and switched to SC CONT - CMC, CMC MODE - AUTO. The resulting scenario is attached.

Loading that, key in

V37E 20E
                   F 50 18
PRO
                      06 18
            then F 50 18 when maneuver is complete
ENTR

... and the optics move to the S-IVB, see screenshots, that is really fun.  Very Happy

By the way, irnenginer did a great post about P20, you can do a LOT of things there: http://www.ibiblio.org/mscorbit/mscforum/index.php?topic=822.0

Cheers
Tschachim

* Apollo 7 - P20 Test.scn (153.71 KB - downloaded 70 times.)

* ScreenShot00165.jpg (108.89 KB, 1018x763 - viewed 181 times.)

* ScreenShot00166.jpg (103.38 KB, 1020x762 - viewed 200 times.)
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abr35
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« Reply #3 on: June 11, 2011, 04:50:41 PM »

This all helped very much. Thank you!
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