Something I would point out is that this is more of a conceptual proposal than something real NASA is planning on doing. This mission as described here will never happen. With that said it’s still a useful exercise because we will do space probes to Alpha Centauri at some point and doing a pretend proposal for one and solving all the problems that come up when you try to do so will help make it feasible to actually do that type of mission in the future eg. The Europa Clipper or a lot of the other space probes we’ve done.