This is a Gemini retro rocket. It provided a means of slowing down the two-person Gemini Earth orbiting U.S. spacecraft to permit its reentry into Earth's atmosphere. Four of the rockets fired in ripple fashion upon a signal from the crew or by an automatic signal within the spacecraft. The rockets could also be used to separate the spacecraft from the launch vehicle in case of a high altitude launch abort but were never used in any Gemini missions for this purpose. The motor produced a thrust of 2,580 pounds for 5.4-5.7 seconds. The retro system worked in all ten manned Gemini missions from 1965-1966. The motor shown here was used for testing purposes and was not flown. It was donated to the Smithsonian in 1972 by the prime contractor for the Gemini capsules, the McDonnell Douglas Corp.