The project estimates are completely off. Building a 1gigawatt power plant costs 10billion. Let alone building 100 of them. Also making the laser array. Also you can't have reflection without absorption. Also we don't have solar sails that fit the bill.

This project is barely physically and economically plausible. Its not a question of scaling, or engineering. The physics just don't work.

We have a way to get a space craft to 20% of C. Its called Project Orion. https://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propu...