Looking at your code, there are a lot of repeated parts like:
self.mercury = loader.loadModel("models/planet_sphere")
self.mercury.reparentTo(self.orbit_root_mercury)
self.mercury.setScale(0.385 * self.sizescale)
self.mercury.setPos(0.38 * self.orbitscale, 0, 2)
self.mer_tex = loader.loadTexture("models/mercury_1k_tex.jpg")
self.mercury.setTexture(self.mer_tex, 1)
self.merCollider = self.mercury.attachNewNode(CollisionNode('mercnode'))
self.merCollider.node().addSolid(CollisionSphere(0, 0, 0, 1))
self.venus = loader.loadModel("models/planet_sphere")
self.venus.reparentTo(self.orbit_root_venus)
self.venus.setScale(0.923 * self.sizescale)
self.venus.setPos(0.72 * self.orbitscale, 0, 0)
self.ven_tex = loader.loadTexture("models/venus_1k_texa.jpg")
self.venus.setTexture(self.ven_tex, 1)
self.venCollider = self.venus.attachNewNode(CollisionNode('vencnode'))
self.venCollider.node().addSolid(CollisionSphere(0, 0, 0, 1))When you’ve some repeated code, that’s a clue about something you can improve from an software engineering point of view. I didn’t study your code deeply, but these parts of code which define the planets suggest me that you may improve your code defining a class Planet and inserting the “right” code inside it.