I'm making an orbit simulator, and to make it simpler, i'm only simulating one celestial object(planet, moon, sun) acting on each object(sattelite).

So that the sattelites and rockets can swicth between what planet/moon they are orbiting, i need to figure out the sphere of influence of each planet.

I've found some formulas online, but they all unclude the mass of the smaller object, or the Semi-major axis, which would indicate that a rocket of a mass of, say 100kg, would have a different SOI of the earth than a rocket of 1kg orbiting at the same height.

this confused me since i thought the SOI was always the same no matter what was orbiting (or how fast, or how far away)

I would be happy if someone explained why this is, or if there is some other equation i'm missing, thx!

I'm making an orbit simulator, and to make it simpler, I'm only simulating one celestial object(planet, moon, sun) acting on each object(sattelite).

So that the sattelites and rockets can switch between what planet/moon they are orbiting, I need to figure out the sphere of influence of each planet.

I've found some formulas online, but they all unclude the mass of the smaller object, or the Semi-major axis, which would indicate that a rocket of a mass of, say $100kg$, would have a different SOI(Sphere-Of-Influence) of the earth than a rocket of $1kg$ orbiting at the same height.

This confused me since I thought the SOI was always the same no matter what was orbiting (or how fast, or how far away).

I would be happy if someone explained why this is, or if there is some other information I'm missing, thx!