[rokobobo]

To divert an asteroid, you’d attempt to ablate a part of it, rather than just rely on its reflectivity:

https://en.m.wikipedia.org/wiki/Asteroid_laser_ablation

I imagine that tracking an asteroid and continuously pointing the laser array at a specific portion of it, will be harder than tracking a shiny light sail that’s continuously illuminated by the laser array—but as a whole, I think shooting a laser at an asteroid is one of our best bets, so having that array would be a good tool of planetary defense