Helios (spacecraft)

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Helios A and Helios B were twin solar-observation spacecraft built by Messerschmitt-Bölkow-Blohm for a joint mission between West Germany’s space agency (DLR) and NASA. They were launched from Cape Canaveral in 1974 and 1976, becoming the first space probes built outside the United States and the Soviet Union to leave Earth orbit and travel toward the Sun.

The two probes were designed to study solar processes, including the solar wind, the Sun’s magnetic field, cosmic rays, interplanetary dust, and the zodiacal light. They carried ten scientific instruments and operated in heliocentric orbits with slow, precise spins to keep instruments oriented.

Key facts
- Partners and builders: DLR (West Germany) and NASA; main contractor Messerschmitt-Bölkow-Blohm (MBB).
- Mass and power: about 370–376 kg each; solar panels provided roughly 270 watts.
- Shape and design: central body shaped like a hexagonal/prismatic core with two large cone-shaped solar panels; spacecraft spun at 60 revolutions per minute.
- Orbits: Helios A perihelion ~0.31 AU; Helios B perihelion ~0.29 AU; aphelion around ~0.98–0.99 AU; orbital periods about 190 days (A) and 186 days (B).
- Highlights: Helios-B made the closest solar approach then (0.29 AU) at speeds around 70 km/s (157,000 mph) in 1976, a record that stood until the Parker Solar Probe in 2018.
- Instruments: sensors for solar wind velocity and density, magnetic fields, radio and plasma waves, cosmic rays, zodiacal light, micrometeoroids, and more.
- Mission duration: Helios-A operated through the late 1970s and into 1985; Helios-B remained active into the early 1980s, with last data in 1980–1985. Both probes remain in solar orbits but are no longer functional.

What they accomplished
- They provided detailed data on the solar wind, interplanetary medium, and cosmic rays, extending observations from solar minimum in the late 1970s to solar maximum in the early 1980s.
- They helped map how heat and extreme solar proximity affect spacecraft, contributing to later solar missions and our understanding of the Sun–Earth environment.

Legacy
- The Helios missions significantly advanced solar science and influenced the design of future near-Sun missions, including the later Parker Solar Probe.