Sir Harrie Stewart Wilson Massey FRS (16 May 1908 – 27 November 1983) was an Australian mathematical physicist who worked primarily in the fields of atomic and atmospheric physics.A graduate of the University of Melbourne and Cambridge University, where he earned his doctorate at the Cavendish Laboratory, Massey became an independent lecturer in Mathematical Physics at the Queen's University of Belfast in 1933. He was appointed Goldsmid Professor of Applied Mathematics at University College London, in 1938. During the Second World War, Massey worked at the Admiralty Research Laboratory , where he helped devise countermeasures for German magnetic naval mines, and at the Admiralty Mining Establishment in Havant, where he helped develop British naval mines. In 1943, Mark Oliphant persuaded the Admiralty to release Massey to work on the Manhattan Project. He joined Oliphant's British Mission at the Radiation Laboratory at the University of California, where they worked on the electromagnetic isotope separation process. When Oliphant returned to Britain in 1945, Massey took over the Berkeley Mission. Massey returned to University College, London, in October 1945 to find it badly damaged by bombing, and the Mathematics Department in dingy temporary accommodation. In 1950 he was appointed Quain Professor of Physics and head of the University College, London, Physics Department. The department was merged with Astronomy in 1973, but he remained its head until he retired in 1975. Under his direction, the Physics Department was reoriented towards particle physics and upper atmosphere physics. He worked with the Woomera Rocket Range to develop British Skylark rocket, and was on the governing board of the Anglo-Australian Telescope. He was the chairman of the Committee on Space Research (COSPAR) from 1959 to 1978, and of its British national chapter. He was also the first Chairman of the European Space Sciences Committee, and helped found the European Space Research Organization and the Mullard Space Science Laboratory at University College, London.