|Function||Expendable launch system|
|Country of origin||United States|
|Diameter||2.44m (8 ft)|
|Launch sites||Vandenberg Air Force Base|
Thor-Agena was a series of orbital launch vehicles. The rockets used the Douglas-built Thor first stage and the Lockheed-built Agena second stages. They are thus cousins of the more-famous Thor-Deltas, which founded the Delta rocket family. The first attempted launch of a Thor-Agena was in January 1959. The first successful launch was on 28 February 1959, launching Discoverer 1. It was the first two-stage rocket to place a satellite into orbit.
Among other uses, the clandestine CORONA program used Thor-Agenas from June 1959 until January 1968 to launch United States military reconnaissance satellites operated by the CIA. During this program, Thor-Agena launch vehicles were used in 145 launch attempts  now known to have been part of satellite surveillance programs.
Also, Alouette 1, Canada's first satellite, was launched on a Thor-Agena-B.
On February 28, 1963, a Thor-Agena rocket carrying a spy satellite into orbit was launched from Vandenberg Air Force Base. The rocket went off course and mission control detonated the rocket at an altitude of 44 km before it could reach orbit. The rocket detonation produced a large circular cloud that appeared over the southwestern United States. Due to its mysterious nature, appearing at a very high altitude and being visible for hundreds of miles, the cloud attracted widespread attention and was published by the news media. The cloud was featured on the cover of Science Magazine in April 1963, Weatherwise Magazine in May 1963, and had a full page image published in the May issue of Life Magazine. Prof. James MacDonald at the University of Arizona Institute for Atmospheric Physics investigated the phenomena and linked the it to the Thor Rocket launch after contacting military personnel at Vandenburg Air Force Base. When the launch records were later declassified, the United States Air Force released a memo explaining that the cloud was the result of a military operation.