Meadville Space Center

Project Apollo - NASSP => Programming => Topic started by: irnenginer on September 15, 2008, 07:40:57 PM



Title: vAGC Action Items for 7.0
Post by: irnenginer on September 15, 2008, 07:40:57 PM
Here is the list of items I am aware of that need attention before a 7.0 release in order to insure a mission capable vAGC for Apollo 7, in order of importance:

1. TVC DAP instability : The TVC DAP is unstable, meaning that the Spacecraft can and will spin off wildly during AGC controlled SPS burns of of durations above a few seconds. This has been tracked to an issue between the interaction of the AGC and how the TVC is currently implemented. Currently agc control commands are translated immediately into thrust vector changes. There needs to be a control loop implemented so that TVC movement is damped. We cannot fly a mission without this

2. Pad load completion and accuracy: Most of the pad loads have been verified but there are still a few "best guess" numbers use that impacts AGC accuracy. These will need to be addressed These include but are not limited to

AYO
AXO
PGNCSALT
TVC DAP parameters in relation to the 1 issue
Whatever is causing small error in the state vectors at launch.

3. VHF Ranging: The inclusion of VHF ranging between the SIVB and the CSM will make the rendezvous go much easier and more "by the numbers" but admittedly it is not necessary for a successful mission.


Title: Re: vAGC Action Items for 7.0
Post by: bluespace88 on September 16, 2008, 05:27:18 PM
Now that I'm done with the state vector stuff, I'd like to help out with some of the vAGC implementation if you don't mind.


Title: Re: vAGC Action Items for 7.0
Post by: irnenginer on September 23, 2008, 11:08:49 PM
I just updated the CSM padload worksheet with the latest I have. It should now work with Excel 2007, I have updated the lunar and solar data to what is now in the scenerio load and added several updates to the parameters that should get everything up to date as of now.  :ThumbsUp432:

I did find something that might effect accuracy of both the worksheet and the manual state vector update. There is about a .01% difference in the the computed AGC number when using negative numbers compared to other more accurate methods (such as the virtual AGC environment and another method using SCILAB). I believe it is because of inherit precision constraints in VBA. To this end I have started using SCILAB more for computational stuff including PADLOAD development. It is like MATLAB but is free. One nice feature is that I can now output the whole padload in CMPAD format for copy/paste into a scenario.


Title: Re: vAGC Action Items for 7.0
Post by: Tschachim on September 24, 2008, 10:27:15 AM
Thanks a lot for the update! I took a look at the Apollo 7 numbers and have some comments and remarks:

I noticed that some values differ a lot from the previous values (= the currently used values), for example AZO from 278.87... to 99.66... Were the values really that off? Do you have an Apollo 7 scenario with the new values and did you test them already?

Also I noticed some smaller bugs, again Apollo 7 only:

- CSMMASS is 14481 kg, not 13491 kg
- RTED1 is 1.69107, not 0.5 for LEO returns. I attached an older version of this excel, which contains a calculation sheet for this value
- EMDOT is 29.9 kg/s, not 26.85 kg/s
- POLYNUM (+X) are wrong, the correct values are in the Apollo 7 scenario calculated by kneecaps here: http://www.ibiblio.org/mscorbit/mscforum/index.php?topic=1697.0
- TAZEL1 (P03 targets) are missing, they are at the end of the attached excel (and in the Apollo 7 scenario)

To this end I have started using SCILAB more for computational stuff including PADLOAD development. It is like MATLAB but is free. One nice feature is that I can now output the whole padload in CMPAD format for copy/paste into a scenario.

That's very interesting, I'll try to take a look at SCILAB. Did you write a script or something like this for the padload calculation and output? Would it be possible to put the SCILAB script/file/whatever to CVS, too?  :)

Cheers
Tschachim


Title: Re: vAGC Action Items for 7.0
Post by: irnenginer on September 24, 2008, 11:34:30 PM
The numbers you see are more scratch numbers of things I was trying but did not get them fixed back for the post. I am working on some improved AZO,AXO,andAYO numbers, the 278deg number is still pretty good

The TAZEL number I just missed, I did not know anyone played around with P03.

Yes I created a script file to do the math. I am still polishing it some before I throw it in CVS, give me a day or two.


Title: Re: vAGC Action Items for 7.0
Post by: Tschachim on September 25, 2008, 09:37:10 AM
The TAZEL number I just missed, I did not know anyone played around with P03.

You did know, but you got distracted by drywalling your basement: http://www.ibiblio.org/mscorbit/mscforum/index.php?topic=1751.0  :)

Yes I created a script file to do the math. I am still polishing it some before I throw it in CVS, give me a day or two.

That's cool, thanks in advance!

Cheers
Tschachim


Title: Re: vAGC Action Items for 7.0
Post by: Christophe on September 25, 2008, 03:23:57 PM
Hi irnenginer!
I noticed the ADRA  (Atlantic Discrete Recovery Area) emem I included in the past were dropped from the new VAGC CSM padload worksheet.   :?
The use is for the launch abort mode III.

The values were:

LAT            2254   1014
            3400   3401
LON            3403   3402
            3402   3403

With the following comments:

Atlantic Discrete Recovery Area. This is the target landing point following a launch abort mode III. It allows for the DESPLR to compute the DR (SPLERROR) displayed in V82 N50 (R1). Values extract from the official Operational Abort plan for Apollo 9, tested and validate in sim.


Would it be possible to add it again?




Title: Re: vAGC Action Items for 7.0
Post by: irnenginer on September 25, 2008, 11:16:59 PM
Thanks for the catch. I will get that back in there. :Duh!39835:


Title: Re: vAGC Action Items for 7.0
Post by: Christophe on September 27, 2008, 06:56:30 AM
Thanks for the catch. I will get that back in there. :Duh!39835:

Thanks!  :)


Title: Re: vAGC Action Items for 7.0
Post by: bluespace88 on October 01, 2008, 03:33:42 PM
1. TVC DAP instability : The TVC DAP is unstable, meaning that the Spacecraft can and will spin off wildly during AGC controlled SPS burns of of durations above a few seconds. This has been tracked to an issue between the interaction of the AGC and how the TVC is currently implemented. Currently agc control commands are translated immediately into thrust vector changes. There needs to be a control loop implemented so that TVC movement is damped. We cannot fly a mission without this
I will see what I can do about the damping action.