Ready for Orbit
Date: 11 Mar 1960
Launched on a direct solar orbit trajectory, Pioneer 5 successfully reached heliocentric orbit between Earth and Venus to demonstrate deep space technologies and to provide the first map of the interplanetary magnetic field.
The spacecraft had originally been intended for a Venus flyby, but the mission was sent instead to explore interplanetary space. Pioneer 5 carried Telebit, the first digital telemetry system operationally used on a U.S. spacecraft; it was first tested on Explorer 6. The system used a 5-watt or a 150-watt transmitter, with a 5-watt transmitter acting as driver. Information rates varied from 64 to 8 to 1 bit per second.
Controllers maintained contact with Pioneer 5 until 26 June 1960, to a record distance of 36.2 million km (about 22.5 million miles) from Earth (later surpassed by Mariner 2). The probe, using its 18.1-kg (about 40 .lbs) suite of scientific instruments, confirmed the existence of previously conjectured interplanetary magnetic fields.