Helios-A and Helios-B (also known as Helios 1 and Helios 2), are a pair of probes launched into heliocentric orbit for the purpose of studying solar processes. A joint venture of West Germany's space agency DFVLR (70% share) and NASA (30%), the probes were launched from Cape Canaveral, Florida, on Dec. 10, 1974, and Jan. 15, 1976, respectively. Built by Messerschmitt-Bölkow-Blohm as the main contractor they were the first spaceprobes built outside the US or USSR.

The probes are notable for having set a maximum speed record among spacecraft at 252,792 km/h[1] (157,078 mi/h or 43.63 mi/s or 70.22 km/s or 0.000234c). Helios 2 flew three million kilometers closer to the Sun than Helios 1, achieving perihelion on 17 April 1976 at a record distance of 0.29 AU (or 43.432 million kilometers),[2] slightly inside the orbit of Mercury. Helios 2 was sent into orbit 13 months after the launch of Helios 1. The Helios space probes completed their primary missions by the early 1980s, but they continued to send data up to 1985. The probes are no longer functional but still remain in their elliptical orbit around the Sun.[not verified in body]

Mission background
Scientific instruments
Instrument Name Description
Plasma Experiment Investigation
Measures the velocity and distribution of the solar wind plasma.
Flux-gate Magnetometer
Measures the field strength and direction of low frequency magnetic fields in the Sun’s environment.
Search Coil Magnetometer
Complements the Flux-Gate Magnetometer by measuring the magnetic fields between 0 and 3 kHz.
Plasma Wave Investigation
Measures and analyzes waves of free ions and electrons in the solar wind plasma, 10 Hz to 3 MHz region.
Cosmic Radiation Investigation
Measures protons, electrons and x-rays to determine the distribution of cosmic rays.
Low-Energy Electron and Ion Spectrometer
Investigates the higher energy portion of the crossover region between the solar wind particles and the cosmic rays.
Zodiacal Light Photometer
Measures the scattering of sunlight by interplanetary dust particles.
Micrometeoroid Analyser
Investigates the composition, charge, mass, velocity and direction of interplanetary dust particles.
Mission profile
Helios I sitting atop the Titan IIIE / Centaur launch vehicle
Helios-A sitting atop the Titan IIIE / Centaur launch vehicle.
Launch and trajectory
Trajectory of the Helios space probes.
Timeline of travel
Date Event
Launch of Helios-A
Launch of Helios-B
Closest flyby of the Sun of any spacecraft, performed by Helios II.
Launch configuration diagram
Launch configuration diagram.
A technician stands next to one of the twin Helios spacecraft
A technician stands next to one of the twin Helios spacecraft.
Inspection of Helios 2
Inspection of Helios-B.
Helios probe being encapsulated for launch
A Helios probe being encapsulated for launch.
See also
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1974 in spaceflight
1976 in spaceflight
List of vehicle speed records
Timeline of artificial satellites and space probes


Wilkinson, John (2012), New Eyes on the Sun: A Guide to Satellite Images and Amateur Observation, Astronomers' Universe Series, Springer, p. 37, ISBN 3-642-22838-0

Solar System Exploration: Missions: By Target: Our Solar System: Past: Helios 2

External links

Helios 1 - NSSDC Master Catalog
Helios 2 - NSSDC Master Catalog
Helios 1 Mission Profile by NASA's Solar System Exploration
Helios 2 Mission Profile by NASA's Solar System Exploration
Titan/Centaur D-1T TC-2, Helios A, Flight Data Report
Titan/Centaur D-1T TC-5 Helios B, Flight Data Report
Honeysuckle Creek Tracking Station
Astronautix Helios page
Helios-Project - Max-Planck-Institut für Sonnensystemforschung

Space Encyclopedia

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