Hap McSween joined the faculty of the Geology Department (now the Department of Earth and Planetary Sciences) in 1977. He earned the BS in chemistry from the Citadel (1967), attending as a Daniel Scholar; the MS in geology from the University of Georgia (1969), where he was a NASA graduate fellow; and the PhD in geology from Harvard (1977). From 1969 to 1974, he was a pilot and officer in the US Air Force in Vietnam.
He served as acting associate dean of the College of Liberal Arts (now Arts and Sciences) from 1985 to 1987 and as department head from 1987 to 1997. He twice served as interim dean of the college.
Named a distinguished professor of science in 1998 and, subsequently, chancellor’s professor, McSween began participating in NASA spacecraft missions in 1997 as a member of the science team for the Mars Global Surveyor Orbiter. In 1999 he led a team of researchers who discovered geologic evidence on a meteorite that water existed deep in Mars’s crust. He then became coinvestigator for the Mars Odyssey spacecraft mission and the Dawn spacecraft mission. McSween is the author of more than one hundred articles in international journals and professional volumes. He is also the author of books that are designed to spread enthusiasm for science to the general public.
He received the Nininger Award for Meteorite Studies (1977), a National Science Foundation Antarctic Service Medal (1982), the Bradley Prize from the Geological Society of Washington (1985), two NASA Group Achievement Awards (1983 and 1998), the Leconte Medallion of the South Carolina Science Council (1999), the Order of the Silver Crescent Award from the Governor of South Carolina (2001), and the Frederick C. Leonard Medal from the Meteoritical Society in 2001. In 1999 he was inducted as the 21st member of the South Carolina Hall of Science and Technology. In 2012 he was awarded the J. Lawrence Smith Medal by the National Academy of Science.
McSween served on 14 NASA teams and panels of critical importance, on several of which he was chief. He also served on several committees for the National Research Council. For the Meteoritical Society, he served as president (1995–96), vice president (1993–94), secretary, and councilor. For the Geological Society of America, he was chair and vice chair of the Planetary Geology Division and chair and vice chair of the southeastern section, among many other committees. He was an associate editor for international journals Icarus, Meteoritics, Geochimica et Cosmochimica Acta, and the Proceedings of the 10th Lunar and Planetary Science Conference.