Helios 2 was launched into a solar orbit on 15 January 1976. It had a perihelion of 0.29 AU and an aphelion of 1 AU. Its orbit made it an ideal platform for making long baseline time-of-arrival measurements to obtain source direction. The satellite rotated with a ~ 1-s spin period. The mission ended in 1981.
Information provided by http://heasarc.gsfc.nasa.gov/docs/heasarc/missions/helios2.html