re: Griffin tries to pitch "lifeboat Mars"
The "astronomers" you mention are generally cosmologists, used to doing very narrow field imaging, and taking only a few images at a time. In this case, lunar dust is a factor. They also have little need to manuever
But you're focusing on the passive system, and any active one to pick up the smaller impactors will need a large power source. This can be had by using either solar electric or solar dynamic generating systems. That said, the CAPS deflection system itself requires the use of a space nuclear electric generator, both for propulsion to the target, and to power the lasers to ablate its surface.