Mercury-Atlas 6, the February 20, 1962 flight of John Glenn, proved to be a testing experience both for Mission Control and for Kraft. One book on the history of the Apollo program calls it "the single event that decisively shaped Flight Operations."[22] The mission, the first orbital flight by an American, unfolded normally until Glenn began his second orbit. At that point Kraft's systems controller, Don Arabian, reported that telemetry was showing a "Segment 51" indicator.