For 15 years, the Plant Growth Unit (PGU) was a highly successful platform for shuttle-era astrobotany experiments (1982-97). The PGU was the first American platform to run regular flight experiments on biological life support systems, and its experiments examined seedling growth, lignification, and reproduction. The PGU was designed and built by Lockheed Missiles and Space Company for the Ames Research Center, and was eventually upgraded into its successor, the Plant Growth Facility (PGF).

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