Difficulty with parent bodies

[samuelboland]

Here's what I'm trying to do: I'm trying to make a star, then have a planet orbit that, then a moon orbit that, then an asteroid orbit that, then something smaller orbiting that, etc etc to 10 levels.

Here's my problem: I really like the new idea in this beta whereby you just drag and drop a new planet and it auto-orbits it's parent body, but I can't figure out how to change the "parent" body. If I try to make a moon orbit the earth, it just then orbits the sun. if I can get the moon to orbit the earth, and try to make an asteroid orbit that, I can't get it to, et cetera et cetera.

Any suggestions/possible fixes?

[Dan Dixon]

Thanks for sharing this...

I'll think about how to make what you're trying to do easier to do.

In the short-term, turn on the parent-child lines to see which body is considered the 'parent'. Press the ';' semi-colon key to toggle these lines (or toggle the Relation Lines button). This should help.

The projected paths don't look like they'll be in orbit around the parent, but they are.

Let us know if this helps and how many 'levels' you're able to set up. I've only ever setup a four level system Sun-Planet-Moon-Satellite.

Also... Save the system before you start it so you can reload it if there's a problem and you can share the system you create when you're done.

[monmarfori]

We should have this fixed at the release of sandbox 2.

[samuelboland]

After messing around with it for a few hours, I could only get 5 levels of orbit. (Sun - Earth - Moon - Satellite - Smaller Satellite)

It wasn't at all stable, however. It only lasted for about a quarter of the Earth's rotation around the sun at 1 AU. I MAY be able to get it better later, but until then, I won't share the system. There's so much motion in the system, I don't know how many levels I can get to before it's just too much.

Also, I was using the R4K movement system when doing this. I got much better results with that than the Euler system. 

[Dan Dixon]

After messing around with it for a few hours, I could only get 5 levels of orbit. (Sun - Earth - Moon - Satellite - Smaller Satellite)

And that might be the maximum level at this scale. If more levels were at all stable we'd see examples of them in our own solar system. I just tried orbiting the Sun around a galaxy and a galaxy around a point 10000 times as massive. That's a good test case to reveal a number of bugs with projected paths and other issues. I hope to make this work well before we release v2.

...I was using the R4K movement system when doing this. I got much better results with that than the Euler system.  

RK4 is a little slower but a much more accurate simulator (undetectably slower with only a few bodies). You can directly compare the difference between the original mode (Euler) and the new mode (RK4):
1 - Load 'Earth & Moon'
2 - Hover your mouse over the Moon so you can see the projected path (of the Moon).
3 - Press Shift+S to toggle to RK4 mode.
4 - Notice how the projected path makes a complete oval.
5 - Toggle back (Shift+S) and notice how the path is not complete when in Euler mode.


What is RK4? - A technical answer:
http://en.wikipedia.org/wiki/Runge%E2%80%93Kutta_methods