There's also just forces that will be hard to characterize in a model, eg thermal recoil where the heat radiating off an object produces a tiny acceleration in

There's also just forces that will be hard to characterize in a model, eg thermal recoil where the heat radiating off an object produces a tiny acceleration in the opposite direction. The roadster has black panels that will heat up more than the rest of the body work. Then there's other tiny forces like the solar wind. All tiny but over huge time spans their influence keeps widening the error bounds on the simulation.