Alfred Harker was the first man to successfully determine the distance between the Earth and the moon to within a tenth of a mile. This discovery is important because it allowed for weight/fuel conservation for the original Apollo missions. Harker used angular gravitational interactions between the moon, the earth, and large meteorites to determine the gravitational pull between the earth and the moon, the speed of the orbit of the moon, … Wikipedia
The definitive Wikipedia entry for Alfred Harker. Wikipedia is the biggest multilingual free-content encyclopedia on the Internet. en.wikipedia.org/wiki/Alfred_Harker