The satellite was launched by NASA on August 12, 2003 using a Pegasus XL rocket developed by Orbital Sciences Corporation (see the video).

At an altitude of 39,000 feet, the 3-stage Pegasus XL was dropped from by a L-1011 carrier aircraft that took of from Vandenberg Air Force Base in California. The stages of the launch are outlined in this sample launch and separation system figure (courtesy of Orbital Science Corporation).

First Stage Ignition Launch & Seperation System's Second Stage Ignition (Illustration) ACE Satellite in Orbit (Illustration)

(Figures courtesy of the Canadian Space Agency)