Energetic events and environments often emit X-rays, from the colliding winds of massive stars, to supernova explosions and their neutron star and black hole remnants, to supermassive black holes in the centers of galaxies, to galaxy clusters--the most massive bound objects in the universe. They all produce both thermal and non-thermal X-rays through their interaction with intervening gas, offering clues about the processes affecting the formation and evolution of galaxies and clusters of galaxies. I will discuss various investigations with NuSTAR--the first focussing E>10 keV observatory--that explore these topics through efforts to extend its capabilities, namely by better understanding and modeling its PSF and background.