Wouldn't you have to deal with radiation that you are normally shielded from in Earth`s atmosphere? That may be more difficult to shield from than producing a normal clean room.
Given the volume and mass payload capabilities of the upcoming Starship/Superheavy, cheaply lifting bulk quantities of lead into space may actually be a reasonable proposal in the next five years rather than ultra-expensive pie-in-the-sky fantasy as it was during the age of disposable rockets.