I want to design and launch a improbably large space-mirror. If it were properly focused on earth (curvature adapting to distance from the planet), and given li

I want to design and launch a improbably large space-mirror. If it were properly focused on earth (curvature adapting to distance from the planet), and given light-speed delay, we could direct a telescope upon it and see the state of earth 6.52x years ago, where the mirror is x parsecs away from earth. Roadblock: probably not a scientifically viable proposition, given space debris and lack of ability to build something that large/durable. Solution: write a sci-fi short story with this as a plot element, and call it good.