# Orbital simulator and non fixed orbit

#### FLOUR

Hello,
Let's consider a small 3 planet system. One of the planet's is fixed and is a lot heavier than the others. The acelleration is
mP2 * aP2 = - FP3 - FP1
From with the velocity is derived with allows to calculate the positions of the planet's in a simulator program. After running the simulation, The orbit of one of the "moving" planets isn't fixed - some variation occur after each loop.

What can cause this? The other planet (that's not fixed) has an elliptic fixed orbit.
FP = Gravitational Force of Planet
Thanks.

Last edited:
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#### FLOUR

Hello,
some more data about the situation:

Planet 1 - fixed on the center of the referential
Planet 2 - initial distance = 3 AU (start_x= 3 AU, start_y = 0)
Planet 3 - initial distance = 6 AU (start_x= 6 AU, start_y=0)

So Planet 2 is on the "middle" of the system.

Planet 1 is about 1000 times "heavier" than Planet 2.
Planet 3 is about 30 times "heavier" than Planet 2.

Planet 3's orbit is fixed elliptic. Planet 2's orbit has some variation to the initial elliptic orbit.

1) I was under the impression that orbits were suposed to be fixed...
2) I'm guessing the planet in the "middle" is getting heavy interaction from the other planet's...

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