Goals: Helios 1 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: As it looped around the Sun in an orbit that took it from Earth's orbit (1 AU from the Sun) to about 0.3 AU from the Sun and back again, Helios 1 studied the solar wind, magnetic and electric fields, cosmic rays, and dust in interplanetary space. It flew within 47 million km of the Sun at a speed of 238,000 km per hour, the closest any human-made object had been. Its data indicated the presence of 15 times more micrometeorites close to the Sun than there are near Earth.