On the timescales it would be truly useful, any reasonable power source would degrade and electronics would fail due to solar radiation. That would be made wors

On the timescales it would be truly useful, any reasonable power source would degrade and electronics would fail due to solar radiation. That would be made worse because (I think) a stable orbit would be outside the Van Allen belts and subject to stronger radiation. Physical plates would be best... but honestly, a visible and obviously man made object in orbit would be in and of itself symbolic and perhaps inspiring to a follow up civilization if ours were to collapse and enter a dark age.