TransX Trajectories jumping wildly

[wingnut]

I've been noticing that sometimes the displayed trajectory in TransX plans jumps around violently even several seconds after I made the last change in any stage of the plan with no sign of the trajectory settling down (a little like in flytandem's avatar here in the forum, but much more extreme).

Now, I have a scenario with a Delta Glider in Earth orbit and a TransX plan to depart Earth, encounter it again (orbits to intercept 1.0) and escape again to somewhere else and the trajectory in stages 2 and 3 just won't settle down into a stable prediction.

Before trying the in-orbit scenario I started with a scenario landed at a base on Earth with similar results.

My MFD refresh rate is set to 0.1 seconds.

If someone is motivated to load the scenario: does the "jumping" of the TransX plan trajectory also occur for you and do you have an idea what causes it and how to prevent it?

The scenario is:

BEGIN_DESC
Contains the latest simulation state.
END_DESC

BEGIN_ENVIRONMENT
  System Sol
  Date MJD 51982.5300958703
END_ENVIRONMENT

BEGIN_FOCUS
  Ship GL-01
END_FOCUS

BEGIN_CAMERA
  TARGET GL-01
  MODE Cockpit
  FOV 50.00
END_CAMERA

BEGIN_HUD
  TYPE Surface
END_HUD

BEGIN_MFD Left
  TYPE User
  MODE TransX
  Ship  GL-01
  FNumber 5
  Int 1
  Orbit True
  Vector  4072884.63519 4055192.45836 -3129409.86067
  Vector  6242.46343256 -3845.98701205 2976.0036089
  Double  3.98600439969e+014
  Double  51982.5300959
  Handle Earth
  Handle NULL
  Handle NULL
Select Target
 0 Escape
Autoplan
0 0
Plan type
0 0
Plan
0 1
Plan
0 0
Plan
0 0
Select Minor
 0 None
Manoeuvre mode
0 0
Auto-Center™
0 0
Base Orbit
0 0
Prograde vel.
 1  0
Man. date
 1  51982.5296488
Outward vel.
 1  0
Ch. plane vel.
 1  0
Intercept with
0 0
Orbits to Icept
0 0
Graph projection
0 0
Scale to view
0 0
Advanced
0 0
Pe Distance
 1  7645212
Ej Orientation
 1  0
Equatorial view
0 0
Finvars
  Finish BaseFunction
  Int 2
  Orbit False
  Handle Sun
  Handle Earth
  Handle Earth
Select Target
 0 Earth
Autoplan
0 0
Plan type
0 2
Plan
0 0
Plan
0 0
Plan
0 1
Select Minor
 0 None
Manoeuvre mode
0 0
Auto-Center™
0 0
Base Orbit
0 1
Prograde vel.
 1  0
Man. date
 1  51982.5300957
Outward vel.
 1  0
Ch. plane vel.
 1  0
Intercept with
0 0
Orbits to Icept
0 2
Graph projection
0 0
Scale to view
0 0
Advanced
0 0
Prograde vel.
 4  3328.71481128
Eject date
 1  51985
Outward vel.
 1  0
Ch. plane vel.
 1  0
Finvars
  Finish BaseFunction
  Int 4
  Orbit True
  Vector  1360810376.45 1656769.19879 9093740634.26
  Vector  -537.691652472 -0.697628960598 -3279.02049097
  Double  3.98600439969e+014
  Double  53054.3542109
  Handle Earth
  Handle NULL
  Handle NULL
Select Target
 0 Escape
Autoplan
0 0
Plan type
0 1
Plan
0 0
Plan
0 1
Plan
0 0
Select Minor
 0 None
Manoeuvre mode
0 0
Auto-Center™
0 0
Base Orbit
0 0
Prograde vel.
 1  0
Man. date
 1  51982.530095
Outward vel.
 1  0
Ch. plane vel.
 1  0
Intercept with
0 0
Orbits to Icept
0 0
Graph projection
0 0
Scale to view
0 0
Advanced
0 0
View Orbit
0 0
Finvars
  Finish BaseFunction
  Int 3
  Orbit False
  Handle Sun
  Handle Earth
  Handle Mars
Select Target
 0 Mars
Autoplan
0 0
Plan type
0 2
Plan
0 0
Plan
0 0
Plan
0 2
Select Minor
 0 None
Manoeuvre mode
0 0
Auto-Center™
0 0
Base Orbit
0 1
Prograde vel.
 1  0
Man. date
 1  51982.5295809
Outward vel.
 1  0
Ch. plane vel.
 1  0
Intercept with
0 0
Orbits to Icept
0 0
Graph projection
0 0
Scale to view
0 0
Advanced
0 0
Velocity.
 1  0
Outward angle
 1  0
Inc. angle
 1  0
Inherit Vel.
0 0
Eject date
 1  51982.5295754
Finvars
  Finish BaseFunction
  Int 5
  Orbit False
  Handle Mars
  Handle NULL
  Handle NULL
Select Target
 0 None
Autoplan
0 0
Plan type
0 1
Plan
0 0
Plan
0 2
Plan
0 0
Select Minor
 0 None
Manoeuvre mode
0 0
Auto-Center™
0 0
Base Orbit
0 1
Prograde vel.
 1  0
Man. date
 1  51982.5295797
Outward vel.
 1  0
Ch. plane vel.
 1  0
Intercept with
0 0
Orbits to Icept
0 0
Graph projection
0 0
Scale to view
0 0
Advanced
0 0
Draw Base
0 0
Finvars
  Finish BaseFunction
END_MFD

BEGIN_MFD Right
  TYPE User
  MODE TransX
END_MFD

BEGIN_SHIPS
ISS:ProjectAlpha_ISS
  STATUS Orbiting Earth
  RPOS -3003630.55 5928632.75 -1091273.97
  RVEL 6742.699 3011.192 -2156.374
  AROT 29.99 -0.03 50.05
  AFCMODE 7
  IDS 0:588 10 1:586 10 2:584 10 3:582 10 4:580 10
  NAVFREQ 0 0
  XPDR 466
END
Mir:Mir
  STATUS Orbiting Earth
  RPOS -4802794.38 282905.38 4625527.85
  RVEL -5367.121 -339.309 -5547.637
  AROT 0.00 -44.99 90.00
  AFCMODE 7
  IDS 0:540 10 1:542 10 2:544 10
  XPDR 482
END
Luna-OB1:Wheel
  STATUS Orbiting Moon
  RPOS 978198.18 2012795.15 215.00
  RVEL -1331.066 646.874 0.298
  AROT -0.00 0.00 -152.60
  AFCMODE 7
  IDS 0:560 10 1:564 10
  XPDR 494
END
GL-01:DeltaGlider
  STATUS Orbiting Earth
  RPOS 4072884.64 4055192.46 -3129409.86
  RVEL 6242.463 -3845.987 2976.004
  AROT -52.67 -56.91 90.32
  AFCMODE 7
  PRPLEVEL 0:0.553000 1:0.900000
  NAVFREQ 0 0 0 0
  XPDR 0
  AAP 0:0 0:0 0:0
END
SH-03:ShuttleA
  STATUS Landed Earth
  BASE Habana:4
  POS -82.3976475 23.0005306
  HEADING 70.00
  AFCMODE 7
  PRPLEVEL 0:1.000000 1:1.000000
  NAVFREQ 0 0
  XPDR 0
  PODANGLE 0.0000 0.0000
  DOCKSTATE 0 0.0000
  AIRLOCK 0 0.0000
  GEAR 0 0.0000
  PAYLOAD MASS 0.0 0
END
PB-01:ShuttlePB
  STATUS Landed Earth
  BASE Habana:1
  POS -82.4008617 22.9987859
  HEADING 22.00
  AFCMODE 7
  PRPLEVEL 0:1.000000
  NAVFREQ 0 0
END
GL-02:DeltaGlider
  STATUS Landed Mars
  BASE Olympus:3
  POS -135.4300000 12.7366196
  HEADING 0.00
  AFCMODE 7
  PRPLEVEL 0:1.000000 1:1.000000
  NAVFREQ 0 0 0 0
  XPDR 0
  GEAR 1 1.0000
  AAP 0:0 0:0 0:0
END
SH-01:ShuttleA
  STATUS Landed Moon
  BASE Brighton Beach:1
  POS -33.4375000 41.1184067
  HEADING 0.00
  AFCMODE 7
  PRPLEVEL 0:1.000000 1:1.000000
  NAVFREQ 0 0
  XPDR 0
  PODANGLE 0.0000 0.0000
  DOCKSTATE 0 0.0000
  AIRLOCK 0 0.0000
  GEAR 0 0.0000
  PAYLOAD MASS 0.0 0
END
END_SHIPS

BEGIN_ExtMFD
END

 

[dgatsoulis]

Short answer: you don't have enough prograde velocity to arrive back to Earth after you've completed one orbit around the Sun. But you do have enough to get back to Earth after 2 ship orbits around the Sun.

Long answer:

Now, I have a scenario with a Delta Glider in Earth orbit and a TransX plan to depart Earth, encounter it again (orbits to intercept 1.0) and escape again to somewhere else and the trajectory in stages 2 and 3 just won't settle down into a stable prediction.

Prograde vel.
 4  3328.71481128
Eject date
 1  51985
Outward vel.
 1  0
Ch. plane vel.
 1  0

So you are leaving on 51985 with 3328 m/s hyperbolic excess velocity (all of it in the prograde direction), and you want to get back to Earth after you complete one round around the Sun. Well... Earth isn't going to be there when you arrive.
For pure prograde departures from Earth you need to achieve a trajectory with a period that's a multiple of Earth's orbital period.
[ame="http://en.wikipedia.org/wiki/Orbital_resonance"](See orbital resonance).[/ame]

The first resonance is 1/2 where 1 = how many times the ship will go around the sun and 2 = how many times the Earth will go around the Sun.
So the period of the ship's trajectory is twice the period of the Earth's trajectory.
In order to double the period, you need to multiply the semimajor axis with [math]2^{2/3}=1AU \cdot 2^{2/3}=1.5874AU[/math]With the perihelion at 1AU the aphelion needs to be:
[math]2 \cdot 1.587 \; - \; 1 = 2.1748 \; AU [/math]which gives a hyperbolic excess velocity of ~5.05 km/s

The next resonance is 2/3 (two ship orbits/3 planet orbits)
which needs to increase the period by 3/2 that of the Earth's, giving an SMa of [math]\left(\frac{3}{2}\right)^{2/3} = 1.31037 \; AU[/math], Perihelion = 1AU, Aphelion = 1.62074 AU and V∞ ~3.33 km/s.

You can see that the V∞ of this resonance is very close to the V∞ you have in your plan, so by raising the number of orbits to (2.0) you should get an encounter with Earth. Once you've done that, you'll notice that the cl. approach value stopped jumping around, but the dashed line of nodes doesn't. That's because your trajectory is exactly coplanar to the Earth's so all the points are intersections between the planes.
If you want it to stop doing that, just give a tiny amount of plane change in your transfer (0.001 m/s).

Hope this helps

 

[wingnut]

Very good explanation as always, thank you.

I changed the orbits to intercept to 2.0 and adjusted the prograde and plane change velocities a bit as well as you suggested and the displayed trajectories remain stable now.