09/22/19 at 06:01:49 News: Registration for new users has been disabled to discourage spam. If you would like to join the forum please send me an email with your desired screen name to tony at gravitysimulator dot com.

 Pages: 1 2
 Gravitational capture by Europa? (Read 17712 times)
 RGClark Uploader I Love YaBB 2! Posts: 10 Gravitational capture by Europa? 08/05/15 at 12:44:06   Suppose we put a spacecraft in elliptical orbit around Jupiter at the same periapsis distance as Europa. We arrange it so it makes a very close flyby, say less than 10 km, to Europa. How long would it take to be captured by Europa?  Note this is known as ballistic capture or low energy transfer to save on the fuel requirements.     Bob Clark Back to top « Last Edit: 08/06/15 at 05:51:08 by RGClark »     IP Logged
 frankuitaalst Ultimate Member Great site Posts: 1510 Gender: Re: Gravitational capture by Europa? Reply #1 - 08/05/15 at 13:14:39   Interesting question .   Didn't even know it was even possible to have a capture in this configuration ( ie. a system of only one planet , one moon and one not propelled spacecraft ) .   Always thought one would need another body to which energy is exchanged ( dissipated ) , in such a way the second body is not captured but "escapes" the capture.     Edit : Oh , I forgot the sun , which is the fourth body . So capture might be possible .   Will take some simulations to calculate the odds of such a succesful capture . Back to top IP Logged
 Tony YaBB Administrator Posts: 1060 Gender: Re: Gravitational capture by Europa? Reply #2 - 08/05/15 at 14:12:39   Hi Bob, Welcome to the forum! It's not necessary to pass within 10 km.  Objects captured through ballistic capture will enter orbit through Europa's L1 or L2 points.  The captures are only temporary.  The object will also escape through L1 or L2. Here's a simulation.     http://orbitsimulator.com/gravitySimulatorCloud/simulations/1438807842185_Europa _capture.html   This simulation is in a rotating frame that matches Europa's period.  This makes it easy to visualize Europa's L1 and L2 points.  They are both along the Europa/Jupiter line, with L1 being in between Europa and Jupiter, and L2 being external to Europa's orbit. If you can't see Jupiter, zoom out.  Once you're familiar with Jupiter's location, and the location of L1 and L2, zoom in for a more detailed view of the captures and escapes.  Refresh the page if you want to start over.   I made this simulation by realizing that a capture is simply an escape in reverse.  I created 20 objects in orbit around Europa at about 1/2 of a Hill Sphere distance, and ran it in reverse until some escaped.  I then deleted the ones that didn't escape.  I then ran time forwards and saved the Sim. The ones that rapidly escape without going through L1 or L2 simply passed too close to Europa, where 16 s is too high of a time step for that close of a passage.  So those results should not be considered.  Refresh the sim and slow to timestep 8 s for better results. Back to top IP Logged
 Tony YaBB Administrator Posts: 1060 Gender: Re: Gravitational capture by Europa? Reply #3 - 08/05/15 at 14:21:15   In 2007, Earth captured asteroid 2007 RH120 using ballistic capture.  It escaped about 1 year later. http://orbitsimulator.com/gravitySimulatorCloud/simulations/1433806156068_2006%2 0RH120.html Back to top IP Logged
 RGClark Uploader I Love YaBB 2! Posts: 10 Re: Gravitational capture by Europa? Reply #4 - 08/06/15 at 08:33:32   Thanks for those. On the Kerbal forum it was said Kerbal couldn't do "ballistic capture" because it only uses patched conics. Does GravitySimulator use an n-body approximation.     Bob Clark Back to top IP Logged
 RGClark Uploader I Love YaBB 2! Posts: 10 Re: Gravitational capture by Europa? Reply #5 - 08/06/15 at 10:00:32   I assume the pink colored ones are the moons, with Europa the one in the center and the blues are the spacecraft trajectories? About the spacecraft trajectories some are odd looking in that sometimes as they approach Europa, they suddenly move off in right angles to the original path away from Europa. I can see why they might make a sharp turn towards Europa but not away.     Bob Clark Back to top « Last Edit: 08/06/15 at 18:55:01 by RGClark »     IP Logged
 frankuitaalst Ultimate Member Great site Posts: 1510 Gender: Re: Gravitational capture by Europa? Reply #6 - 08/06/15 at 11:30:19   Thanks Tony for the nice simulation . Smart way and strategy to get to the set-up !   I tried to work on this sim and tried to create a bunch of bodies around Europa .   Seemed to work , but the bodies don't show up in the sim , athough they are generated in the list of bodies .    Tried some colors , up to white , but no succes ... Is this feature ( new...) already operational ? Back to top IP Logged
 Tony YaBB Administrator Posts: 1060 Gender: Re: Gravitational capture by Europa? Reply #7 - 08/06/15 at 20:14:04   Quote from RGClark on 08/06/15 at 10:00:32: I assume the pink colored ones are the moons, with Europa the one in the center and the blues are the spacecraft trajectories? About the spacecraft trajectories some are odd looking in that sometimes as they approach Europa, they suddenly move off in right angles to the original path away from Europa. I can see why they might make a sharp turn towards Europa but not away.  Bob Clark This is why orbital dynamics is often counter-intuitive, especially in a rotational frame where "fictitious" forces are introduced.  In the dropdown list, change "Eurpoa" to "Stationary", and watch what this looks like in an inertial frame. Back to top IP Logged
 Tony YaBB Administrator Posts: 1060 Gender: Re: Gravitational capture by Europa? Reply #8 - 08/06/15 at 20:17:03   Quote from frankuitaalst on 08/06/15 at 11:30:19:Thanks Tony for the nice simulation . Smart way and strategy to get to the set-up ! I tried to work on this sim and tried to create a bunch of bodies around Europa . Seemed to work , but the bodies don't show up in the sim , athough they are generated in the list of bodies . Tried some colors , up to white , but no succes ... Is this feature ( new...) already operational ? No new features in the last few days.  Make sure you choose Europa for the reference object, and that you use the correct units for SMA.  Otherwise, they are created inside Jupiter, and get unrealistically ejected at high speeds.  If you like, tomorrow I'll post some detailed instructions. Back to top IP Logged
 Tony YaBB Administrator Posts: 1060 Gender: Re: Gravitational capture by Europa? Reply #9 - 08/06/15 at 20:18:38   Quote from RGClark on 08/06/15 at 08:33:32: Thanks for those. On the Kerbal forum it was said Kerbal couldn't do "ballistic capture" because it only uses patched conics. Does GravitySimulator use an n-body approximation.  Bob Clark Yes, Kerbal can't do this because it is not an n-body simulator.  Gravity Simulator does n-body with Runge Kutta 4th order method. Back to top IP Logged
 RGClark Uploader I Love YaBB 2! Posts: 10 Re: Gravitational capture by Europa? Reply #10 - 08/07/15 at 11:14:48   Quote from Tony on 08/06/15 at 20:18:38: Yes, Kerbal can't do this because it is not an n-body simulator.  Gravity Simulator does n-body with Runge Kutta 4th order method.    Thanks. Pretty cool. I noticed that though some bodies did orbit Europa for a few orbits, after awhile they were all ejected. Is it possible to focus in on those bodies that go into orbit to see their distances from Europa, periods etc.?    In case you're interested I want to find low delta-v trajectories to Europa to allow a landing there. That the spacecraft in orbit would at some point be ejected is alright if the landing already took place. And even for the orbital spacecraft case, it might be possible to just do a small delta-v burn to put it in permanent orbit.   Low cost Europa lander missions. http://exoscientist.blogspot.com/2015/02/low-cost-europa-lander-missions.html      Bob Clark Back to top IP Logged