Robert M. Walker, Ph.D., professor of physics in Arts & Sciences and faculty fellow for the McDonnell Center for Space Sciences, died Feb. 11 in Brussels, Belgium after an extended battle with stomach cancer. He was 74.

Walker worked on the frontiers of space research for more than three decades. He was director of the McDonnell Center for the Space Sciences, which was established in 1974 with a gift from the late James S. McDonnell. He was a member of two expeditions (1984-85 and in 1990-91) to collect meteorites in Antarctica. He also studied the first lunar samples from the Apollo missions.