Helios:

Eelios was one of a pair of deep-space probes developed by the Federal Republic of Germany (FRG) in a cooperative program with NASA.
NASA supplied the Titan/Centaur launch vehicle.
The spacecraft was equipped with two booms and a 32-m electric dipole.
The payload consisted of a fluxgate magnetometer; electric and magnetic wave experiments, which covered various bands in the frequency range 6 Hz to 3 MHz; charged particle experiments, which covered various energy ranges starting with solar wind thermal energies and extending to 1 GeV; a zodiacal light experiment; and a micrometeoroid experiment. The purpose of the mission was to make pioneering measurements of the interplanetary medium from the vicinity of the earth's orbit to 0.3 AU.
 The outer surface was coated with a conductive material, resulting in a plasma-sheath potential of typically 5 eV.
 The spacecraft was capable of being operated at bit rates of from 4096 to 8 bps, variable by factors of two. While the spacecraft was moving to perihelion, it was generally operated from 64 to 256 bps; near 0.3 AU, it was operated at higher bit rates..