Geologist serving on the U.S.S. Enterprise in 2268. The M-5 multitronic computer, while being tested aboard the Enterprise, selected Ensign Carstairs to join the landing party to Alpha Carinae II on Stardate 4729. He was picked over Captain Kirk's choice, Senior Geologist Rawlens, because the ensign had experience surveying geologically similar planets for a mining company while serving in the merchant marine.