The Biomass Production System (BPS) was developed by Orbital Technologies Corporation in partnership with NASA engineers and scientists. It was initially designed for the Shuttle and SpaceHab, but was later modified to fit in the International Space Station (ISS), and it contained two experiments on the ISS in 2002 during expedition 4. The first experiment was a Technology Validation Test (TVT), where the BPS validated several subsystems and technologies that were later used to design the Plant Research Unit (PRU). The second experiment was called Photosynthesis Experiment and System Testing and Operation (PESTO). The PESTO demonstrated that plant productivity (photosynthetic rate, transpiration rate, and biomass) does not differ from ground controls. From this experiment, scientists learned that gas exchange is not directly affected by microgravity, but is affected indirectly by the lack of gravity-driven convection in microgravity.