On December 10, 1974, NASA launched Helios 1, the first spacecraft designed for close observations of the Sun. This mission marked a significant international collaboration, with West Germany providing the spacecraft and NASA's Goddard Space Flight Center overseeing U.S. involvement. Helios 1 made its closest approach to the Sun on March 15, 1975, traveling faster than any previous spacecraft at a speed of 148,000 miles per hour.
The Helios probes, built by West German company Messerchmitt-Bölkow-Blohm, were the first non-Soviet and non-American spacecraft to enter heliocentric orbit. Each probe weighed 815 pounds and carried 10 instruments to study solar phenomena, including high-energy particle detectors and magnetometers.
Launched from Cape Canaveral on a Titan IIIE-Centaur rocket, Helios 1's success bolstered confidence in the rocket's capabilities for future missions, including the Viking missions to Mars. Helios 1 entered a solar orbit with a period of 190 days, achieving a perihelion of 28.9 million miles, well within Mercury's orbit.
Helios 2 followed on January 15, 1976, and approached even closer to the Sun, reaching 27 million miles at a speed of 150,000 miles per hour. Although its downlink transmitter failed in 1980, the data returned by both Helios probes significantly advanced our understanding of solar dynamics.
Subsequent missions, such as ESA/NASA's Ulysses and NASA's Parker Solar Probe, have built upon the foundation laid by the Helios missions, further exploring the Sun's behavior from unique vantage points. The Parker Solar Probe, launched in 2018, aims to reach within 3.86 million miles of the Sun's surface by 2024, continuing the legacy of solar exploration initiated by Helios.