It is about the end-result of this program that was considered "impossible" - a celestial map consisting billions of stars with detailed information about each

It is about the end-result of this program that was considered "impossible" - a celestial map consisting billions of stars with detailed information about each of them, including position and movement. It seems that such a task was considered so difficult in the nineteens, that when they requested it they didn't expected to end up with a solution that would completely cover all the requirements.