Titan surface launch anomaly

[BrianJ]

Hi,
I've come across a strange "anomaly" while trying to launch from the surface of Titan.
If anyone has the time, I'd be grateful to get confirmation or whether its just me!

It seems the surface of Titan is very "sticky" - I have to apply nearly twice the vessel "weight" in upwards thrust to lift off the surface.
Once airborne, normal thrust/weight physics resumes.
Here is a pic of a DG sitting on Titan surface, not going anywhere even though thrust > weight.


Here is a scenario with DG resting on Titan surface - increase Hover thrust gradually and observe how much thrust is required before liftoff occurs.

BEGIN_DESC

END_DESC

BEGIN_ENVIRONMENT
  System Sol
  Date MJD 53651.5404849351
  Help CurrentState_img
END_ENVIRONMENT

BEGIN_FOCUS
  Ship GL-01
END_FOCUS

BEGIN_CAMERA
  TARGET GL-01
  MODE Extern
  POS 2.243855 -86.946346 -1.289155
  TRACKMODE TargetRelative
  FOV 50.00
END_CAMERA

BEGIN_HUD
  TYPE Surface
END_HUD

BEGIN_MFD Left
  TYPE Surface
  SPDMODE 1
END_MFD

BEGIN_MFD Right
  TYPE Map
  REF Titan
  POS 0.00 0.00
END_MFD

BEGIN_SHIPS
GL-01:DeltaGlider
  STATUS Orbiting Titan
  RPOS 1518363.173 515218.410 -2014452.476
  RVEL 9.2785 -3.9411 5.8258
  AROT 119.389 43.551 54.324
  AFCMODE 7
  PRPLEVEL 0:0.527089 1:0.897217
  NAVFREQ 0 0 0 0
  XPDR 0
  HOVERHOLD 0 1 0.0000e+000 0.0000e+000
  GEAR 1.0000 0.0000
  AAP 0:0 0:0 0:0
END
END_SHIPS

BEGIN_ExtMFD
END

BEGIN_DX9ExtMFD
END

Also, the HUD data display (top left of screen in glass cockpit) disagrees with the Orbiter display-mode thrust vector value.

From my own experiments this "excess thrust force required to liftoff" effect depends on the damping parameter value for the vessel touchdown points.

If anyone can confirm if they also see this effect, or not, I'd be grateful.

I've only tested on the Moon and Titan so far - no effect evident on the Moon, only Titan.

Cheers,
BrianJ

 

[misha.physics]

I'll try it a little bit later. What version of Orbiter are you testing? I have Orbiter 2016 and Orbiter x86 build on GitHub (from January 11 of this year).

 

[BrianJ]

Thanks!
using Orbiter2016 (tested both default and D3D9 Graphics Client - both seem pretty much the same).

 

[misha.physics]

I tried your scenario with Orbiter 2016+D3D9Client, and it's the same anomaly. And OpenOrbiter too.

I have to apply nearly twice the vessel "weight" in upwards thrust to lift off the surface.

Yes.

Once airborne, normal thrust/weight physics resumes.

Yes.

Also, the HUD data display (top left of screen in glass cockpit) disagrees with the Orbiter display-mode thrust vector value.

Yes, and this problem remains even after lifting off the surface.
And yes, that isn't occur on the Moon.

From my own experiments this "excess thrust force required to liftoff" effect depends on the damping parameter value for the vessel touchdown points.

I don't know how it works for now, but it seems to be completely possible. You could compare these parameters and points with the Moon case.

 

[BrianJ]

Hi,
thanks so much for testing
It seems that's the way it is in Orbiter2016.
It's not a huge problem - unless you have an underpowered vessel that needs to land and take-off on Titan
I'll just have to increase the max. thrust to cope with the "sticky" surface.

Also, the HUD data display (top left of screen in glass cockpit) disagrees with the Orbiter display-mode thrust vector value.
Yes, and this problem remains even after lifting off the surface.

Could this be a difference between thrust in vacuum v.s atmosphere? Must have a look in the docs.
EDIT: Yep, I guess that's what it is. Doesn't explain the unexpected behaviour at Titan surface though.

Cheers,
BrianJ