1965: Air Force Cambridge Research Laboratories at Hanscom AFB, Mass., completed a scientific first by bouncing and photographing a laser beam off Explorer 22, Ionospheric Beacon Satellite. This allowed scientists to determine the exact distance between two or more points on earth. Explorer 22 involved the largest international participation to date in a NASA mission: some 50 scientific groups in 32 countries ran more than 80 ground tracking stations. Satellite laser ranging (SLR) began shortly after the satellite’s magnetic stabilization, during the satellite’s daily flyovers. This allowed highly accurate measurements of Explorer 22’s orbit, making it possible for the irregularities of the Earth’s shape and density to be more accurately mapped.
