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Old 03-22-2019, 01:50 PM   #1
Nikogori
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Default Understanding TransX Escape plan

I've been writing orbiter tutorial for Japanese players for a few years. Now I'm thinking about giving more detailed explanation for TransX Escape plan.
The problem is, there are not so many orbiter players in Japan... no one would correct me even if I made a mistake.

Here is my explanation for TransX Escape plan. Please tell me if there's anything wrong.



In Eject plan you can create interplanetary transfer orbit. How do we get to this transfer orbit from Earth?



In this image below, red line shows the direction towards the transfer orbit from Earth.



Blue curved line is a hyperbolic orbit which is parallel with transfer orbit. (Green circle is parking orbit)
Red line and blue curved line are not the same but the difference is negligible compared with huge distance towards the target planet.

We live in 3-dimensional space. Therefore we can rotate this hyperbolic orbit around red line.



Actually there are infinitely many possible hyperbolic orbits. You can go in the desired direction from above, below and both sides of the planet.



This means there's always one hyperbolic orbit passing over your launch site.
If you use TransX, you can find it using Ej Orientation (Eject Orientation) function in Escape plan.

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Old 03-22-2019, 05:21 PM   #2
Ripley
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Some years ago, THE TransX Gurus (flytandem, dgatsoulis and blixel) shared some preciously interesting infos...

https://www.orbiter-forum.com/showth...96&postcount=1

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Old 03-22-2019, 05:32 PM   #3
Ajaja
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It's good. I wish I had such explanation when I tried to use TransX first time

Quote:
Originally Posted by Nikogori View Post
 In this image below, red line shows the direction towards the transfer orbit from Earth.
They call it "outgoing asymptote direction" in NASA

Quote:
Originally Posted by Nikogori View Post
 This means there's always one hyperbolic orbit passing over your launch site.
I think, there are two hyperbolic orbit passing over the launch site, but taking into account the planet rotation one is always more preferable than other.
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Old 03-22-2019, 09:11 PM   #4
Ajaja
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BTW, it's very easy to create illustrations for those hyperbolas with GMAT:



Code:
Create Spacecraft DefaultSC;
GMAT DefaultSC.DateFormat = TAIModJulian;
GMAT DefaultSC.Epoch = '21545';
GMAT DefaultSC.CoordinateSystem = EarthMJ2000Ec;
GMAT DefaultSC.DisplayStateType = OutgoingAsymptote;
GMAT DefaultSC.OutgoingRadPer = 7100;
GMAT DefaultSC.OutgoingC3Energy = 100;
GMAT DefaultSC.OutgoingRHA = 90;
GMAT DefaultSC.OutgoingDHA = 0;
GMAT DefaultSC.OutgoingBVAZI = 360;
GMAT DefaultSC.TA = 360;

Create ForceModel DefaultProp_ForceModel;
GMAT DefaultProp_ForceModel.CentralBody = Earth;
GMAT DefaultProp_ForceModel.PointMasses = {Earth, Jupiter, Luna, Sun};

Create Propagator DefaultProp;
GMAT DefaultProp.FM = DefaultProp_ForceModel;
GMAT DefaultProp.Type = RungeKutta89;

Create OrbitView DefaultOrbitView;
GMAT DefaultOrbitView.Add = {DefaultSC, Earth};
GMAT DefaultOrbitView.CoordinateSystem = EarthMJ2000Eq;
GMAT DefaultOrbitView.DrawObject = [ true true ];
GMAT DefaultOrbitView.ViewPointReference = Earth;
GMAT DefaultOrbitView.ViewPointVector = [ 100000 10000 0 ];
GMAT DefaultOrbitView.ViewDirection = Earth;
GMAT DefaultOrbitView.ViewUpCoordinateSystem = EarthMJ2000Eq;
GMAT DefaultOrbitView.ViewUpAxis = Z;
GMAT DefaultOrbitView.EnableStars = Off;

Create Variable I;

BeginMissionSequence;
For I = 0:30:330;
   GMAT DefaultSC.EarthMJ2000Ec.OutgoingBVAZI = I;
   Propagate BackProp DefaultProp(DefaultSC) {DefaultSC.ElapsedDays = -3};
	Propagate DefaultProp(DefaultSC) {DefaultSC.ElapsedDays = 6};
   Propagate BackProp DefaultProp(DefaultSC) {DefaultSC.ElapsedDays = -3};
EndFor;
Attached Thumbnails
c3_100.png  
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Old 03-23-2019, 02:08 AM   #5
Nikogori
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Quote:
Originally Posted by Ripley View Post
 Some years ago, THE TransX Gurus (flytandem, dgatsoulis and blixel) shared some preciously interesting infos...

https://www.orbiter-forum.com/showth...96&postcount=1

Test1.avi - YouTube
Thank you! Actually I remember I read this thread a few years ago. I learned a lot from those videos and articles by flytandem, dgatsoulis and blixel. Maybe I should include link to these materials in my tutorial.

Quote:
Originally Posted by Ajaja View Post
 They call it "outgoing asymptote direction" in NASA
I didn't know the "red line" has such a fancy name. Thank you!
Now I need to find Japanese translation of "outgoing asymptote direction"...

Quote:
Originally Posted by Ajaja View Post
 I think, there are two hyperbolic orbit passing over the launch site, but taking into account the planet rotation one is always more preferable than other.
Ah yes! There are always two hyperbolic orbits (one is prograde and the other is retrograde). How didn't I notice this? It's obvious in the 3rd image... Thank you so much.

Quote:
Originally Posted by Ajaja View Post
 BTW, it's very easy to create illustrations for those hyperbolas with GMAT:


Thank you. I'm using Geogebra to draw these diagrams but that GMAT illustration looks cool! I guess I need to learn how to use it.
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