One of two spacecraft launched in the mid-1970s to study the Sun, its magnetic field, the solar wind, and gamma radiation. Helios 1, the first cooperative deep-space venture between the USA and West Germany, was launched in December 1974, and Helios 2 in January 1976. Their orbits took them within 45 million km of the Sun, the closest approach of any spacecraft. The rockets were able to withstand a temperature of about 370° C because of their special heat-dispersal systems. The two spacecraft acted in concert to gather data, and Helios 2 was especially successful in monitoring gamma radiation. Both spacecraft were built in West Germany and launched by NASA. Contact was lost with Helios 1 on 10 February 1986 and with Helios 2 on 3 March 1980.