Comment by rvnx

We now have realistic simulators like: http://orbit.medphys.ucl.ac.uk/ -> (it's free and open-source: https://github.com/orbitersim/orbiter )

so now the main problem is building the hardware, there are a lot of solutions for the software part.

Before there were no general-purpose simulators, and barely usable computers (2 MHz computer with 2 KB of memory...), so all you could do was hardcoding the path and use rather constrained algorithms.