 This could be updated in the field with new targets and better information about the flight paths with relative ease, gaining accuracy for little cost.One of the unavoidable effects on the warhead's trajectory was the mass of the Earth, which is not even, and contains many mass concentrations that pull on the warhead.Through the 1960s, the Defense Mapping Agency (now part of National Geospatial-Intelligence Agency) mapped these with increasing accuracy, feeding that information back into the Minuteman fleet.