Scenario Strange "Multistage" Behavior

[jimd]

I am working on a Multistage version of a Titan 4 and have most everything working but have noticed a strange behavior just prior to launch and during the roll phase of the autopilot.

There is a strange yawing motion while as the autopilot counts down prior to igniting the solids and then during the pitch phase of the autopilot there is again a strange jerky motion as the autopilot appears to be fighting against some other control.

I have created a clean install of Orbiter 2006P1 and 2010P1 and added just the necessary modules to run the simulation but get the same strange result. However, I don't see this same behavior in other peoples add-ons so I know I must be doing something wrong.

Has anyone ever seen this kind of behavior.

BEGIN_DESC
Thia is a variant of the Titan IV rocket with a modified upper stage to be used to launch HL20. 
END_DESC

BEGIN_ENVIRONMENT
  System Sol
  Date MJD 56522.8282205092
END_ENVIRONMENT

BEGIN_FOCUS
  Ship TitanIV
END_FOCUS

BEGIN_CAMERA
  TARGET TitanIV
  MODE Extern
  POS 2.74 -0.42 -98.15
  TRACKMODE TargetRelative
  FOV 70.00
END_CAMERA

BEGIN_HUD
  TYPE Surface
END_HUD

BEGIN_MFD Left
  TYPE Map
  REF Earth
  BTARGET Cape Canaveral
  OTARGET ISS
  ZOOM
  TRACK ON
END_MFD

BEGIN_MFD Right
  TYPE Orbit
  PROJ Ship
  FRAME Equator
  ALT
  REF Earth
  TARGET ISS
END_MFD


BEGIN_SHIPS
TitanIV:multistage/multistage2
  STATUS Landed Earth
  BASE Cape Canaveral:6
  HEADING 180.00
  PRPLEVEL 0:1.000 1:1.000 2:1.000 3:1.000
  NAVFREQ 0 0
  CONFIG_FILE Config\multistage\TitanIV_Long.ini
  GUIDANCE_FILE Config\multistage\TitanIV_Guidance.txt
  CONFIGURATION 0
  STAGE_STATE 2
  STAGE_IGNITION_TIME 0.000
  CURRENT_BOOSTER 1
  CURRENT_STAGE 1
  CURRENT_INTERSTAGE 1
  CURRENT_PAYLOAD 1
  FAIRING 1
END
ISS:ProjectAlpha_ISS
  STATUS Orbiting Earth
  RPOS 3721961.98 -5578141.91 668360.94
  RVEL -6120.009 -3773.387 2752.544
  AROT -55.39 -39.66 174.22
  VROT -0.09 -0.05 -0.00
  PRPLEVEL 0:1.000
  IDS 0:1 100 1:2 100 2:3 100 3:4 100 4:5 100
  NAVFREQ 0 0
  XPDR 466
END
END_SHIPS

 

[PhantomCruiser]

Post your guidance file. It may be something in the roll program portion, if those numbers aren't "good" then the launch can be kind of wild.

 

[astrosammy]

Maybe the guidance file has some error. Could you post it here?
EDIT: Well, same thing as Phantom wrote :lol:

 

[jimd]

Here is the file
This is actually pretty bizarre because the yawing motion starts almost as soon as you start the autopilot and the rocket makes a large Yaw just after it leaves the ground.

More strange yawing seems to take place when the roll program is started at approximately 12 seconds and it stops once the roll is complete.

I have used the guidance file before without any issues so I know it works on its own.

-5=engine(0,100,5)
13=roll(2,87,42,74,-1)
15=pitch(78,75,10)
20=engine(100,57,5)
25=engine(57,57,35)
25=pitch(75,70,20)
45=pitch(70,60,15)
60=engine(57,100,5)
60=pitch(60,50,10)
60=engine(100,100,2)
70=pitch(50,44,10)
80=pitch(44,37,10)
90=pitch(37,29,10)
100=pitch(29,16,12)
112=pitch(16,16,213)
124=jettison()
230=fairing()
335=pitch(16,0,15)
350=pitch(0,0,50)
400=pitch(0,20,55)
455=pitch(20,10,40)
495=pitch(10,0,20)
512=pitch(0,10,25)
537=pitch(10,10,13)
550=pitch(10,10,5)
555=pitch(10,8,245)
780=engine(100,0,2

 

[PhantomCruiser]

OK, I don't have my notes handy, but it looks like at time T+13 you want the rocket to pitch down to 87 degrees, to finish at 74 degrees and roll to heading 042.
Granted I'm using solid rockets on my project, and I'm using an init_pitch_time of 5, it appears that you are trying to do what you want in too short a time.
As a test (and only a test), try giving it more time [13=roll(8,87,42,74,-1)]

Also, the final pich angle of 74 really should match the next pitch command. meaning at T+15 you have it starting at 78, meaning the rocket has to pitch back up from 74, to end up at 75.

edit... notes in hand...
If I were to try it I'd dump T+15 and change it to read...
13=roll(7,87,42,80,-1)
20=pitch(80,75,5)

You could also change your heading in the scenario file, from 180 to 042 is a long way in the time you have allotted (the 2 seconds...). It's no wonder that it's shaking it's tail.

When I get home I'll see if I can give it a go.

 

[jimd]

I understand your comments but this gets even stranger.

At liftoff the ship is indeed oriented at 180 degrees but shortly after that the orientation changes to put the ship at 0 degrees. You can watch this happen on the heading tape but the vehicle actually does not move.

For this reason I modified the heading from 0 degrees to 180 for a relatively short distance to the desired heading.

I have no idea what is going on - its like something is mirror imaged.

Thanks very much for your help.

 

[PhantomCruiser]

No worries mate! Let me know if it works out for you:thumbup:

 

[jimd]

After implementing your suggestion and making a small alteration to the configuration file all the extraneous motion was removed.


Now it really flies!

Thanks -

Next Steps are to get all the eye-candy to make it look more realistic!

 

[PhantomCruiser]

Great! Post some pictures once you get her looking pretty!