Since 1997, the Airbus A300 Zero-g aircraft - the world's largest for parabolic flights - has been used by ESA, CNES, DLR and industrial customers to provide repeated microgravity periods of up to 20 seconds for research purposes. It is managed by Novespace, a subsidiary of CNES. ESA runs typically two parabolic campaigns annually. Scientists are regularly invited to submit experiment proposals for review and selection by peers.