A type of booster rocket used for unmanned tests of the Mercury project capsule and tractor rocket escape tower.

Little Joe I's were unsophisticated even for their time. Their sub orbital flight trajectories were determined by mixing and matching a cluster of eight solid fuel rockets of various types.

Eight Little Joe I tests were made from Wallops Island, Virginia, starting on August 21, 1959 until April 21 1961. They were intended to demonstrate that a Mercury capsule could stand up the stresses of flight, including emergency aborts, without killing the pilot.

Many flights used boilerplate models of the Mercury capsule, while other flew complete flight models of which some carried a rhesus monkey as a test subject. Not all flights were succesful, but as the purpose of the tests was to find out how the capsule and escape tower would perform under stress anyway, nearly all yielded useful information.

The Little Joe I was 80 inches wide and 48 feet long, including the Mercury capsule and its escape tower.