El Onizuka was selected as an astronaut candidate in January 1978, along with fellow Challenger crew members Ron McNair, Dick Scobee and Judy Resnik. After completing a one-year training and evaluation period he was qualified for future shuttle flights as a mission specialist.

His first mission, 51-C, was the January 1985 flight of Discovery, the first shuttle mission flown exclusively for the Department of Defense. A 38-year old Air Force lieutenant colonel, his duties included tracking instruments during launch and re-entry, and deploying a Department of Defense satellite using the shuttle's 50-foot remote arm.

Onizuka was commissioned as a second lieutenant in January 1970 after he received his bachelor and master of science degrees in aerospace engineering from the University of Colorado as a member of the ROTC program. He was then assigned as an aerospace flight test engineer with the Sacramento Air Logistics Center at McClellan Air Force Base in California.

After attending the USAF Test Pilot school, Onizuka was transferred to the Air Force Flight Test Center at Edwards Air Force Base in California. He was awarded the Air Force Commendation Medal, Air Force Meritorious Service Medal and the National Defense Service Medal.

El Onizuka was born June 24, 1946, in Kealakekua, Kona, Hawaii. During his career he logged more than 1,700 hours flight time, including 74 hours in space.

He is survived by his wife, the former Lorna Leiko Yoshida, and their two children, Janelle Mitsue and Darian Lei Shizue.