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Author Topic: $#%^&$% Gimbal Lock  (Read 3845 times)
almostfm
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« on: August 08, 2006, 01:42:56 AM »

While running the Apollo 7 VAGC launch scenario, I decided to simuate a crew rest period (OK, I took a nap, and let the sim run).  When I came back, I had drifted into gimbal lock  Duh!

Is there any sort of documentation floating around on how to get the platform realigned?  The CMC general doc in my \Doc\Project Apollo - NASSP\Check List\G&C checklist\colossus_1A_249 folder mentions using V41 N20 to coarse align the ICDU's, and I did that, but it now thinks the gimbal angles are 0,0,0 (which is what it says to do when in gimbal lock). 

Beyond that, I don't have a clue what the next step is.  I tried updating the state vector using P27 and the state vector update spreadsheet, but loading the data into the AGC didn't seem to do anything. I also tried running P54, but when I start it (N37E 54E), it says I'm running program 54, but the "Prog" light on the left of the DSKY lights, and I get a flashing "37" in the verb field.  Basically, I can go to P00H, but that's about it.

Is there a procedure written down somewhere on how to realign while in orbit?  If not, (and there are bits and pieces here and there that someone can point me towards), I'd be more than happy to write up a procedure for it (documentation is a good part of what I do IRL).

  thanks,
  Scott
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dseagrav
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« Reply #1 on: August 08, 2006, 04:18:56 AM »

Cage the IMU, wait 5 seconds or so, uncage it. That will put the IMU back in operation at 0,0,0.

The realign procedure is discussed elsewhere but I'll paste it here too:

 P54 IMU COARSE ALIGNMENT VIA POINTING

V37E54E - Flashes V04N06 which asks for what type of alignment you want.
PRO - Flashes V06N34 asks for the mission time for alignment. This is the time for which the
alignment is computed for.
V25E - ( I use MT 0:30:00, you should make it farther out )
+00000E HOURS
+00030E MINUTES
+00000E SECONDS
PRO - Flashes V06N22 which are the new gimbal angles that the IMU will go to
PRO - Flashes V50N25 (PLEASE-PERFORM CHECKLIST 00015)
ENTR - PRO will get you an error. Flashes V01N70

you will do the next few steps twice with 2 stars. Look out your front cockpit window. cntrl-uparrow cntrl-leftarrow then cntrl-F9. Turn on the Planetarium mode with celestial markers turned on to Apollo AGC Nav stars. You will se stars 40 and 44 (Altair and Enif). Go back to the DSKY.

(You may need to pick different stars depending on your situation. CHECK FOR THE STARS prior to selecting them!)

V21E
40E
PRO
V22E
+57476E
PRO - Flashes V53

Go back to the cockpit window. Align the spacecraft so that the crew optical sight or the HUD center aligns with Altair (zoom way in using Z to get as lined up as possible. Once you're lined up enter

ENTR
PRO
PRO

which will send you back up above to do the whole thing over with ENIF but instead you enter 44 in the V01N70 screen and should not have to modify the V0694 screen. After all that you will se FV06N05 this is the error in your measurement. It should be less then 00100. enter V32E to start over or PRO to proceed. Then hit PRO again. Finally you will see FV5025 and you will enter ENTR00ENTR. This will bring you back to POOH. Prograde your orbit with [ , watch out for gimbal lock. If everything went according to plan at the mission time you specified the gimbal angles should be R270 P0.00 Y0.00. (or at least close I get about 4 degrees off max).

Bear in mind that now you can use leftshift-keypadenter to press the ENTER key without leaving the COAS to maximize targetting.
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almostfm
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« Reply #2 on: August 08, 2006, 05:56:41 PM »

OK, let me start "fresh", and give that procedure a try.

  thanks,
  Scott
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irnenginer
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« Reply #3 on: August 08, 2006, 07:04:49 PM »

I think you have to run P53 prior to P54 if you gimbal lock like that. it is discussed elswhere tooo but to be nice: Wink

V37E53E
ENTR  (Ball will go to all zeros)
PRO
you'll see F 06 94
V22E
+57476E
PRO
Sight 2 two stars like below. The only diffence is you enter the star code after making the sight so you enter for say star 40

ENTR
PRO
V21E
40E
PRO

After that then run P54 as dseagrav explains
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almostfm
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« Reply #4 on: August 09, 2006, 03:33:40 AM »

I think you have to run P53 prior to P54 if you gimbal lock like that. it is discussed elswhere tooo but to be nice: Wink

V37E53E
ENTR  (Ball will go to all zeros)
PRO
you'll see F 06 94
V22E
+57476E
PRO
Sight 2 two stars like below. The only diffence is you enter the star code after making the sight so you enter for say star 40

ENTR
PRO
V21E
40E
PRO

After that then run P54 as dseagrav explains

  That did it!  Many thanks to you and dseagrav.  I spent most of the day yesterday looking for how to realign the platform, so I must have missed running P53.  I'm going to try to get some time this week, and document the procedure for exactly how to do this.  When I've got it done, I'd like to forward it to somebody (I think Christophe is the "document guy") for possible inclusion in the docs.

  I can't write code, but I can do documents, so maybe I can contribute.

  thanks,
  Scott
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Christophe
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« Reply #5 on: August 16, 2006, 03:52:28 PM »

Hi!
I' know that I'm a bit late with the G&C checklist because I was very busy in real life last month an I just come back from 10 days of hollydays. 
New parts of the G&C check (including the P40's and P50's) should come very soon.

Cheers
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BigDAS
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« Reply #6 on: August 16, 2006, 04:17:47 PM »

Hi!
I' know that I'm a bit late with the G&C checklist because I was very busy in real life last month an I just come back from 10 days of hollydays. 
New parts of the G&C check (including the P40's and P50's) should come very soon.

Cheers

You have a REAL life?? I'm jealous! Sad
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BigDAS

"We should, in my judgement, put a man on Mars by the end of this century"
Vice President Spiro T. Agnew - July 16, 1969
Christophe
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« Reply #7 on: August 16, 2006, 04:58:45 PM »

Quote
You have a REAL life?? I'm jealous!

I usually say around me that my "REAL JOB" is ... Project Apollo.  Very Happy Evil or Very Mad
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almostfm
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« Reply #8 on: August 17, 2006, 12:10:24 AM »

Hi!
I' know that I'm a bit late with the G&C checklist because I was very busy in real life last month an I just come back from 10 days of hollydays. 
New parts of the G&C check (including the P40's and P50's) should come very soon.

Cheers

  Christophe,

  I hope you don't think I was pushing for more documentation.  The stuff you've produced has been a huge help, and makes it a lot more interesting than just button pushing Thumbs Up

  What I was thinking was that when it comes time to write up the "Initialization Procedures" part of the documentation, I'd like to lend a hand, if you'll have me.  I write documentation (and teach computer classes) for a living, so I might be useful to you.

  take care,
  Scott
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Swatch
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« Reply #9 on: August 17, 2006, 09:00:42 AM »

Hey almostfm, although I'll have to differ to Christoph on helping with the checklists (mainly because he has a format pretty well hammered out), I'd like to suggest another section of documentation that is severly lacking. 

For many out there, the Apollo spacecraft will seem like an extremely complicated piece of engineering, which it is.  However, not everyone will be able to sit down and read the Apollo Operations Handbook before they give up and get discouraged and move on to another add-on.  What I think is needed is a condensed version.  A leyman's handbook, if you will.  If you wanted to start working on that, it'd be a great help.

The Scope:  An overview of the systems and their basic requirements during a mission.  If you want a good template for what I'm talking about check out Rob Conley's Mercury Familiarization Guide.  Something like this for Apollo would be EXTREMELY helpful in learning the ropes.  Most don't need a highly technical explenation of the systems, just a conceptual understanding.  Personally I feel that Conley's Familiarization Guide is just about the best add-on doc I've ever come across in the Orbiter-verse.
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My Project Apollo Work:
CM Visual
 -VC (~75% complete: texture work beginning again; mesh-78%; texture-70%)
Propulsion Particle Improvements (Focused on S1B right now, BETA 1.0 has been commited)
New Docking Method (~50% complete: research complete; coding partially completed, testing not underway)

Future Work:  (if it's here, it's deemed unnecessary to upcoming release)

Older Work:  (if it's here, it's fair game to whoever wants to improve)
EMS Implementation (committed: minor flaws, but groundwork is there, needs extensive testing)
EMS scrolls (committed: not refined, but usable)
SM Visual (committed: mesh-finished, texture-60%; possibly revisited in future)
J2 Texture (commited: room for improvement)
LRV (committed: mesh-finished, texture-90%; in future a ground up rebuild may be in order, but not on my plans)
Christophe
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« Reply #10 on: August 17, 2006, 09:37:26 AM »

I totally agree with you Swatch;
Sometime I wonder if I would be able to write such a doc and I 'm afraid the answer is no; mainly due to my poor English knowledge.
So Almostfm, of course you're largely welcome to help writing the doc  Happy
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dseagrav
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« Reply #11 on: August 17, 2006, 09:54:19 AM »

Speaking of user docs, anyone else think we should have a disclaimer on them?
Something to the effect of "This is a somewhat advanced-level simulation demanding a fair amount of learning on the part of the user, a familiarity with space flight and good working knowledge of English language is required"?
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movieman
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« Reply #12 on: August 17, 2006, 10:02:48 AM »

Well, we could wire up the checklist code I started adding and use the MFD to select checklists to run, then the problem wouldn't be such a problem... just follow the flashing boxes Happy.
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BigDAS
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« Reply #13 on: August 17, 2006, 12:31:43 PM »

Nah, just include a Kneeboard, like MSFS. Press a key, Kneeboard pops up with a menu of checklists.

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BigDAS

"We should, in my judgement, put a man on Mars by the end of this century"
Vice President Spiro T. Agnew - July 16, 1969
Swatch
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« Reply #14 on: August 17, 2006, 01:04:22 PM »

dseagrav:  I agree that a disclaimer might be a good idea.  The other thing we should do though is make sure that Realism 0 mode is a very basic flight system.  (much in the way that we do now where the program does the necessary switching).

movieman:  We definately need to get that implimented, it's just about the most innovative thing I've heard of for the MFD.  Also like you said it eleminates many of the language barriers or at least alleviates them.  The Familiarization Guide however is definately a necessity of sorts for all NASSP-anauts.

BigDAS:  That's fine and all, but its not very well integrated with the Orbiter way of things.  The Checklist part of the MFD would be very accessable.
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My Project Apollo Work:
CM Visual
 -VC (~75% complete: texture work beginning again; mesh-78%; texture-70%)
Propulsion Particle Improvements (Focused on S1B right now, BETA 1.0 has been commited)
New Docking Method (~50% complete: research complete; coding partially completed, testing not underway)

Future Work:  (if it's here, it's deemed unnecessary to upcoming release)

Older Work:  (if it's here, it's fair game to whoever wants to improve)
EMS Implementation (committed: minor flaws, but groundwork is there, needs extensive testing)
EMS scrolls (committed: not refined, but usable)
SM Visual (committed: mesh-finished, texture-60%; possibly revisited in future)
J2 Texture (commited: room for improvement)
LRV (committed: mesh-finished, texture-90%; in future a ground up rebuild may be in order, but not on my plans)
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