Solar probes Helios 1 and 2

The closest distance between Helios 2 and the Sun was 0.29 AU, while the closest approach of Helios 1 to the Sun was 0.31 AU. The solar probes were exposed to a maximum solar radiation of 11.87 and 10.44 solar constants, respectively. The operational life of Helios 2 was almost five years, although the original life expectance had been only 1 1/2 years. The Helios 1 and Helios 2 missions have provided valuable information regarding the space between Earth and Sun. It is now known which structures predominate in this space. Expectations regarding a spiral structure of the solar-interplanetary magnetic field could be confirmed, while a hypothesis regarding a large spatial gradient of the galactic cosmic radiation had to be rejected.