> ''The practicable and certain way of finding Longitudes'' - satellite navigation.
We figured that out (for varying definitions of "practicable and certain") as early as the invention of the watch.
Actually earlier - the Lunar method was reliably used by Cook and Shackleton. It was only on Cook's 2nd and 3rd voyages that he had K1, the first replica of H4 - Harrison's watch - that Cook referred to "My trusty friend, the watch."