The impactor discovery efficiency increases nearly linearly with time for objects of 200 m diameter to 40% efficiency in just four years. While this behavior cannot increase indefinitely we estimate that after 12 years the efficiency may be 80%. This is an interesting value because the Pan-STARRS PS4 system will have 4 the collecting area8 of the PS1 system modelled here and thus the efficiency curve for 200 m diameter objects for PS1 corresponds to the 140 m diameter efficiency curve for PS4. Thus, during its anticipated 10 year survey mission PS4 alone may reach nearly 80% completion for objectsP140 m diameter or larger that will impact in the next 100 years.