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Virtual AGC
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Christophe



Joined: 09 Feb 2005
Posts: 280
Location: France

PostPosted: Wed May 03, 2006 5:38 pm    Post subject: Reply with quote

While working on the G&C check I run into trouble with the navigation inacuracy of the vAGC:

- It seems that the vAGC clock is sometimes reset to zero when restarting a saved scenario and sometime not.

- even if I do a state vector update, using the irnenginer excel spreadsheet, I have some fantaisist values about the apsis as well as the current altitude (V82 N44). Even if I take into account the radius difference between the "NASA earth" and the "Orbiter earth". I should at least find the same semi Major axis.?

The consequence is: during a P21, orbital navigation, the error in longitude builds up linearly. (In latitude too but of course less)
I wonder how we can navigate with that and above all, how to get a reliable P37 for earth orbit reentry.

have someone any ideas?
(I have to write something on the check Wink )
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Christophe



Joined: 09 Feb 2005
Posts: 280
Location: France

PostPosted: Wed May 03, 2006 11:01 pm    Post subject: Reply with quote

Still trying to figure out the problem with vAGC I described above.

Could someone explain to me the difference between EMEM 0024/0025 and EMEM 1204/1205.
I know the two first one (0024/0025) are the octal numbers of CMC time, but I wonder what are the seconds one, 1204/1205. There are almost the same digits with about 2 sec delta in one of my scenario.

Help would be greatly appreciated. I'm working on the P27 check and wanted to explain how to update CMC clock time. In fact, I've understood how to do but I'm still curious.
Thanks.
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irnenginer



Joined: 29 Jan 2006
Posts: 64

PostPosted: Thu May 04, 2006 1:38 am    Post subject: Reply with quote

1204/1205 are formally called PIPTIME.

They are the time the DOWNLINK State Vector was valid 1170-1203. The State Vector will update periodically; every few seconds during POOH. Which is why it is a couple of seconds different from the CMC clock.

I have been working on the inaccuracy in AGC and Orbiter for some time (though not very hard lately). I think it mostly has to do with what the AGC is programmed for Earth Parameters and what Orbiter simulates. Including things like Earth rotation in addition to radius. There are also some fudge factors in some of the PAD LOADS that could probably use some better accuracy.
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Christophe



Joined: 09 Feb 2005
Posts: 280
Location: France

PostPosted: Thu May 04, 2006 8:43 am    Post subject: Reply with quote

Thanks irnenginer for replying.

A couple of question more:

- Now I'm able to do the following CMC updates:
* V71: State vector update (contiguous block)
* V72: non contiguous
* V73: CMC clock update by increment
* For the V70, Liftoff time update, although this is less usefull in orbiter than the others, I would like to implement it in the checklist. the issue is I can't figure out how to compute the two octal numbers that match a given delta time in seconds. Would it be possible for you to update your very usefull excel doc with a new macro:
It would be fine if we could enter a value in sec (or in centisec) and then we get the two required octal numbers. I have to admitt that the "most significant part" and the "least significant part" of the data it's quite confusing for me and my little brain Confused

- In order to avoid disturbing people by always asking "what does this mean and what does that mean", could somebody just tell me where I can find the corresponding EMEM? Are they somewhere on the vAGC code? Any doc somewhere in the web?

Thanks a lot.
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irnenginer



Joined: 29 Jan 2006
Posts: 64

PostPosted: Thu May 04, 2006 2:56 pm    Post subject: Reply with quote

I can do you one better.

I already have a spreadsheet for computing all the pad loads, including launch time. Assuming CVS is working I will commit it when I get home from work.

I best resource for determining what is what and where is the printout of the source code.

http://www.ibiblio.org/apollo/ListingColossus249.zip

You want to look at the Erasable Assignments section, near the top. It lists all the variables. somtimes the comments will tell what what is what but not always, particularlly when it comes to scaling of the variable. The last trick is to convert the Addresses that are in the switchable banks to the octal EMEM address. it is computing in the form.

Code:
Address EX,YYYY
EMEM=X-2(400)+Y IN OCTAL
such that E5,1502 -> EMEM3102


Good Luck
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movieman



Joined: 25 Nov 2004
Posts: 1018

PostPosted: Thu May 04, 2006 3:03 pm    Post subject: Reply with quote

Also, as mentioned elsewhere, it's better to use CMPAD and LMPAD entries in the scenario than EMEM values. It's basically the same, but only the Virtual AGC code processes them.
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Christophe



Joined: 09 Feb 2005
Posts: 280
Location: France

PostPosted: Thu May 04, 2006 4:56 pm    Post subject: Reply with quote

Thanks a lot.
I will study the doc.
The very usefull goal would to be able to put the LM state vector into the AGC (as well as the CSM vector into the LGC too), in order to get the rendezvous programs to work. I think especially to P17 and P20 in colossus 249.
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Christophe



Joined: 09 Feb 2005
Posts: 280
Location: France

PostPosted: Fri May 05, 2006 8:19 pm    Post subject: Reply with quote

Hi irnenginer and movieman.

Did you see the new orbiter 2006: it includes a scenario editor that can display the state vector in flight, wheb simulation is running.
I read the doc and in the developper section it is said that you can add options for a specific addon.
Is somebady able to add a feature in order to convert the orbiter state vector in the octal number we could eventually put into the AGC via P27?
That would be great!

I don't know if this is possible.
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irnenginer



Joined: 29 Jan 2006
Posts: 64

PostPosted: Sat May 06, 2006 4:15 am    Post subject: Reply with quote

Not only is it possible, you can do that now using the VAGC State Vector Update spreadsheet.

I have also added PadLoad Worksheet. It has the current computations for the Apollo 8 Pad Load.

Movieman,
I use "EMEM" generically when talking about the 4 octals for AGC memory addresses since they are the same as used in entering data in the AGC directly. I'll be good from now on and use CMPAD in Scenerios. Laughing
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Christophe



Joined: 09 Feb 2005
Posts: 280
Location: France

PostPosted: Sat May 06, 2006 7:47 am    Post subject: Reply with quote

irnenginer wrote:
Not only is it possible, you can do that now using the VAGC State Vector Update spreadsheet.


I know that. Your spreadsheet is very usefull.
I would just say that to use it you have to get out of the simulation and to take the SV numbers from the saved or current scenario. Another solution is to run the sim in window mode. For my own I don't like this mode too much because , may be it's stupid, while seeing the window toolbar around my panel remembers me I'm in front of my PC and not really into the space Wink
It would be better if we could do that while running the scn, in full screen mode.
Since the scn editor seems to have a possibility of specific addon improvement I was wondering if the spreadsheet, or at least something that did the same computation could be implemented in the scn editor.
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mikaelanderlund



Joined: 07 Dec 2005
Posts: 57

PostPosted: Thu Jun 01, 2006 11:36 am    Post subject: Reply with quote

Hi vAGC fans,

I am very interested and curious about how to use the vAGC in the Apollo 8 vAGC scenarios, but my knowledge in the subject is limited. So, is there someone who can give me some discription or manual how to use the vAGC in the Apollo 8 scenories? Please send it to me.

Mikael
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movieman



Joined: 25 Nov 2004
Posts: 1018

PostPosted: Thu Jun 01, 2006 11:50 am    Post subject: Reply with quote

http://history.nasa.gov/alsj/a15/a15Delco.html

is a good start, though it's for a later version of the AGC software. For example, the TLI program doesn't exist in the Apollo 8 software, it was entirely controlled from the ground.
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mikaelanderlund



Joined: 07 Dec 2005
Posts: 57

PostPosted: Thu Jun 01, 2006 12:25 pm    Post subject: Reply with quote

Thanks. but 181mb manual Shocked Maybe something more simple for a novice Very Happy

Mikael, and I am still interested in vAGC
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Tschachim



Joined: 26 Nov 2004
Posts: 1272

PostPosted: Thu Jun 01, 2006 1:04 pm    Post subject: Reply with quote

Hi Mikael,

I'm working on new "standard mode" checklists, which will cover not only the AGC++ but also the Virtual AGC. The existing documentation is a little bit scattered over the web site and this forum as usual. Wink

You should start with the "Virtual AGC/Apollo 8 - Prelaunch" scenario (starts 3h before launch) or Virtual AGC/Apollo 8 - Launch scenario (starts 20min before launch).

To get into orbit you can use Christophe's Word checklists (Doc/Project Apollo - NASSP/Check List folder in your beta installation) or the existing standard mode checklists ( http://nassp.sf.net/user/checklist-standard.html ), but ignore the DSKY interaction here and use the old "Virtual Apollo" docu ( http://nassp.sf.net/user/virtualapollo/ch03.html ) for that.

For things to try in orbit you'll find some checklists/procedures here: http://www.ibiblio.org/mscorbit/phpBB2/viewtopic.php?t=421

I hope this helps for the first steps.

Cheers
Tschachim
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mikaelanderlund



Joined: 07 Dec 2005
Posts: 57

PostPosted: Thu Jun 01, 2006 1:31 pm    Post subject: Reply with quote

Thank you very much Tschachime, I am going to try it this evening! The standard mode checklist, including vAGC, would be very nice. Do you think or do you know if it is possible to go to the moon and back with the vAGC in Apollo 8 mission?

Mikael
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