03 July 2007

N-body problem

Next time you need some entertainment, check out this Planet simulation game. Although "solving" the three-body problem is not possible, simulations are trivial. For a couple goals, try to get a "Mercury" type planet - closer to the Sun than the Earth, highly elliptical orbit. When you get it, it will precess naturally due to Earth's gravitation (rather than due to general relativity as Einstein proved). And a harder goal is getting a Moon to orbit the Earth (I haven't managed yet).

1 comment:

Anonymous said...

Gee, thanks for wasting an hour of my life.

Some highly unscientific thoughts on getting the Earth-Moon thing based on lots of trial and error:
(1) The satellite has to be smaller than the primary. (Ok, this is probably obvious to most people but took me a minute to figure out.)
(2) Take the initial star, get rid of it, and then recreate it somewhere else. Now the "circle" option will create planets that make elliptical orbits. (Bug or feature?)
(3) I've decided that it's easier to get an orbiter when the primary has an elliptical orbit. If the primary is going faster than average then you have little margin for error. If the primary is going slower than average then you have larger margin for error. I think.
(4) Do you want a prograde or a retrograde satellite? (i.e. if your primary orbits clockwise, do you want your satellite orbiting clockwise or counterclockwise?)

In our Solar System most moons are prograde. So I assumed that that would be easier. But it's not, at least for me. This is how it seems to work. Retrograde seems to be easier to achieve but less stable. Prograde seems to be harder to achieve, but if you get it at all then it seems to be better able to handle perturbations.

I never got it to be totally stable, but on a couple of occasions I was able to get a moon do more than one orbit around a planet. My record is 25 orbits.

Enjoy. :)