France 1, also known as FR-1, was a French satellite orbited by NASA in a cooperative US-French program to investigate the properties of the ionized layers of Earth's atmosphere by observing how very low frequency (VLF) waves propagate through the ionosphere. The name developed in 1964, when NASA and France's Centre National d'Etudes Spatiales (CNES) agreed, after preliminary sounding rocket experiments, to proceed with the satellite project. CNES provided the satellite and designated it "FR-1" for "France" or "French" satellite number one. The first flight unit was designated FR-1A and the backup unit, FR-1B. The second US-France cooperative satellite, FR-2, was later renamed Eole.