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11/19/17 at 08:19:01
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Gravitational capture by Europa? (Read 8092 times)
frankuitaalst
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Re: Gravitational capture by Europa?
Reply #15 - 08/09/15 at 03:21:16
 
excellent explanation Tony in the video !
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frankuitaalst
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Re: Gravitational capture by Europa?
Reply #16 - 08/09/15 at 11:16:25
 
Question to Tony .  
I seem to have problems creating a new body .  
In the Original sim ( Europa capture ) I proceed as following :  
 
(with sim pauzed)  
press m in order to get the menu  
select the menu objects
select the submenu create
change the reference object to "Europa " as I want to create a body around Europa
input data for the new body  : objectnew, mass 1 , ...Sma [b]40000 km
[/b]press apply  
unpauze the sim .  
 
Result : I don't see the new body , which should be around Europa , but zooming much much  further out the body is there, far beyound all planets .  
Looking at the elements of the orbit I observe Sma -3000 Au , sometimes +1000 Au .  
( I repeated the setup several times ...) .  
The orbit of this body also is weird . In case of an elliptical orbit the body seems to go around the sun at perihelium very slow , at aphelion very quick.  
I guess I'm doing someting wrong at setup , but don't know what .  
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Tony
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Re: Gravitational capture by Europa?
Reply #17 - 08/09/15 at 12:19:40
 
When I save a simulation, it retains most of the settings of the parent simulation.  In the case of the Europa Capture simulation, the distribution button is set to "Start, End" because that's how I used it to create multiple objects.  So in the field where you are typing 40000, it is expecting 2 values.  Just press "Start, End" until it turns back into "+/- %" and it should work fine.
 
As an example of how to create 3 objects with sma of 30000, 40000, and 50000 km do the following.
Leave this at Start, End.  Change the number of Objects to 3.  Type 30000, 50000.  Press Create.
 
You don't need to give the particle a mass of 1 kg.  1 kg will not be significant to the simulation, but it will make the RK4 routine do extra math and slow down the sim.  It handles 0 mass particles differently, not doing hundreds of calculations that will ultimately result in 0.  For just one object you won't see the difference, but if you add many objects it will slow you down.
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frankuitaalst
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Re: Gravitational capture by Europa?
Reply #18 - 08/09/15 at 13:07:41
 
Thx Tony , I'm aware of the start/end feature.  
Repaeted the new body , called it frank and gave it 40000 , 50000 km from Europa .  
Simultion was pauzed , then saved it and shared it , so that you can load it .  
The asteroid frank seems to be far out of the solar system .  
No idea what happens . Can you run it ?  
(and delete it after you've checked it ?)
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Tony
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Re: Gravitational capture by Europa?
Reply #19 - 08/09/15 at 13:42:45
 
If you give it 40000, 50000, you must create more than one object.  I just tried it and I get the same result you do if I try to create 1 object and give it a range rather than a +/-%
Either change number of objects > 1, or press Start, End until it reads +/-%.
 
I deleted it at your request, but you don't need to check "share on orbitsimulator".  With "create temporary link" you can copy the link and paste it here.  Then it never appears on the simulations page.
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frankuitaalst
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Re: Gravitational capture by Europa?
Reply #20 - 08/09/15 at 13:56:40
 
Thx Tony .  
Applying +/- for Sma succeeds for 1 body . Fine !
However if I try >1 bodies and apply Start / end with ValStart<ValEnd then the bdoies are created far far away .  
Looking at the Objects Elements I read "NAN" when I look a second time.
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Tony
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Re: Gravitational capture by Europa?
Reply #21 - 08/09/15 at 23:32:46
 
You'll have to send me a screen shot of the Create Objects interface.  I get good results with the method you describe.
 
When I was first getting used to the interface, I would sometimes get the results you describe.  When creating objects around the Sun, I often forgot to change km to AU, and created the objects inside the Sun.  With "collisions" turned off, the object was ejected at faster than light speed until its distance was greater than Javascript can count.  At that point you get NaN (not a number) errors.
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RGClark
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Re: Gravitational capture by Europa?
Reply #22 - 08/12/15 at 01:00:12
 
Thanks for that simulation, Tony. How long after the spacecraft enters elliptical orbit around Jupiter does it enter circular orbit around Europa? What was the delta-v for the circularization burn?
 
  Bob Clark
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Tony
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Re: Gravitational capture by Europa?
Reply #23 - 08/12/15 at 14:14:02
 
Quote from RGClark on 08/12/15 at 01:00:12:
Thanks for that simulation, Tony. How long after the spacecraft enters elliptical orbit around Jupiter does it enter circular orbit around Europa? What was the delta-v for the circularization burn?

 Bob Clark

It will happen the first time the spacecraft ventures into Europa's Hill Sphere through L1 or L2.  It could take as few as 1 orbit, or as many as thousands of orbits.
 
I posted a YouTube a few posts back showing how to make the capture sim.  The vid shows that the circularization burn had a delta v of 336 m/s.  If you weren't interested in a close circular orbit, you could make your orbit permanent with a lower delta-v.
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