Ellison Shoji Onizuka (June 24, 1946 - January 28, 1986) was an American astronaut from Hawaii who died during the explosion of the Space Shuttle Challenger, where he was serving as mission specialist on mission STS-51-L.

Onizuka received a Bachelor's degree in aerospace engineering in June 1969, and a Master's in that field in December of the same year, from the University of Colorado. He then entered active duty with the United States Air Force, where he served as a flight test engineer and as a test pilot.

He had been selected for the astronaut program in January 1978, and had previously flown on mission STS-51-C on Space Shuttle Discovery in January 1985, also serving as a mission specialist. He held the rank of Lieutenant Colonel at the time of his death.

Onizuka Air Force Station in Sunnyvale, California, Onizuka Center for International Astronomy at the Mauna Kea Observatory and the Astronaut Ellison S. Onizuka Space Center at Kona International Airport in Hawaii are named after him. Also named in his honor in fiction is a shuttle in Star Trek: The Next Generation, carried aboard USS Enterprise NCC-1701-D.

Two astronomical features were also named after him: an asteroid discovered by Edward L. G. Bowell on February 8, 1984, 3355 Onizuka and a 29 km diameter crater on the moon, Onizuka Crater .