would have a constant optical reflection, and constant coefficient of drag, based on size alone, while a cone would vary with orientation. James Van Allen proposed a cylinder, which eventually flew (Explorer 1). The Project Vanguard finally accepted and 50.8 cm satellites. Post mission After the scientific mission ended, Vanguard 3 and two pieces of the upper stage of the rocket used to launch the satellite became derelict objects. Vanguard 3 remains in orbit. The pieces of the upper stage re-entered the atmosphere on 3 April 2014 and 4 February 2015. As Vanguard 1, Vanguard 2, and Vanguard 3 are still orbiting with their drag properties essentially unchanged, they form a baseline data set on the atmosphere of Earth that is over 60 years old and continuing. Vanguard 3 has an expected lifetime of 300 years. References Spacecraft launched in 1959 Derelict satellites orbiting Earth Project Vanguard