Ewen was a British-born astronomer specializing in lunar studies since 1951. During WWII he was part of the secret PLUTO project (Pipe Line Under The Ocean) to supply Allied vehicles in France with gasoline after the Normandy invasion. After meeting Gerard Kuiper at an IAU meeting in Dubline in 1955, he was invited to join the Lunar Project at Yerkes to produce a high-quality photographic atlas of the moon, and subsequently moved with Kuiper to Tucson, Arizona, where this project ultimately resulted in the establishment of the Lunar and Planetary Laboratory. He provided valuable input into the planning and operations of Apollo operations on the Moon. Ewen was much beloved by his colleagues and is remembered for his knowledge, friendliness and charm.