Goals: Like its twin, Helios 1, which was launched about 14 months earlier, this spacecraft was to make pioneering measurements of the interplanetary medium from the vicinity of Earth's orbit to about 0.3 AU from the Sun.

Accomplishments: Helios 2 looped around the Sun in an orbit that took it from Earth's orbit (1 AU from the Sun) to about 0.29 AU from the Sun and back again, flying some 3 million km closer to the Sun than did its predecessor. The spacecraft provided information on solar plasma, the solar wind, cosmic rays, and cosmic dust, and also performed magnetic-field and electrical-field experiments.