Millan is an associate professor of physics and astronomy at Dartmouth College. Her research includes the use of high-altitude scientific balloon experiments to study Earth's radiation belts, specifically, the loss of relativistic electrons from the outer radiation belts into Earth's atmosphere. Millan is principal investigator for the BARREL (Balloon Array for RBSP Relativistic Electron Losses) project, in which two balloon launches in 2013 and 2014 (of 20 such balloons) floated in the circular wind patterns above the South Pole. Each balloon tracked electrons from space that get swept up in Earth's magnetic field and slide down into Earth's atmosphere. The first test of BARREL—funded by NASA and also supported by NSF's Office of Polar Programs that supports Logistics of all research in Antarctica—began in December 2008.