November 14, 2011

1975: the ARAKS mission on the electron spreading conditions

Logo 50 ans de résultats scientifiques
Logo 50 ans de résultats scientifiques
Long before the starting of the space era, scientists knew the influence of the Sun on the Earth's environment without having an overview of the global situation. In 1975, the space mission ARAKS, aboard two rocket probes, started studying the conditions of electron spreading on the magnetic field's force line.

Anders Celsius (1701-1744) observed the magnetic field disruptions related to the polar aurora Borealis.

Richard Carrington (1826-1875) noted a 24 hour period between the huge solar flare in September 1st, 1859 and the aurora Borealis visible even from the tropical regions.
Kristian Birkeland (1867-1917) performed experiments with a lodestone and cathode rays, reproducing the effects of the aurora Borealis.

Since 1957, with the first satellites, James Van Allen (1914-2006) and other American scientists suggested a scientific satellite was launched within the frame of the research program for the International Geophysical Year from 1957 to 1958.

Following the Soviet Union success of Spoutnik 1 and the embarrassing failure of the first American attempt, the Van Allen's device (Explorer 1) launch was green-lighted. Explorer 1 carried out its mission in February 1st, 1958 and brought back a large quantity of important scientific data which allowed showing that the planet is surrounded by a radiation belt. This was the first major discovery of the space era.

A double radiation belt

In reality, we can consider the radiation belt is composed of two different areas called "inner radiation belt" and "outer radiation belt".

The first one is located between 700 and 10,000 km over the Earth and it is principally composed of very energetic protons (hundreds of MeV with fluence rates of several tens of thousands protons per cm2 per second in the most intense areas) coming from solar wind and cosmic rays, trapped by the Earth's magnetic field.

The outer radiation belt is broader and unfolds between 13,000 and 65,000 km over the Earth. It is also composed of energetic electrons (< 5 MeV) with fluence rate of around a thousand particles per cm2 per second. Particles of both belts are constantly moving at high speed between the Northern and Southern parts of the magnetosphere.

The discovery of a first radiation belt confirmed the works of Carl Störmer (1874-1957) who demonstrated that under certain conditions, energetic particles could be trapped by the Earth's magnetic field.

Establishing a pattern of the trapped particle movement in the belts requires to know the electron spreading conditions along a force line of the magnetic field.

Several important questions for the magnetospheric physics quickly appeared such as the exact geometry of the force lines of the Earth's magnetic field and the problem of the conjugate point accurate localizations (where particles return) of northern and southern ends of a force line and its variations according to the magnetic activity coming from the sun.

After a period of passive studies of the Earth's environment, it appeared that the observed natural phenomena are often difficult to interpret because of the source parameters which control its mechanisms are generally unknown. One of the possible ways to make up for this disadvantage is to perform "active" experiments in which the studied phenomenon is artificially created by a source we can quantitatively know and even command by varying different characteristics.

ARAKS: the active observation

The objective of the ARAKS program (ARtificial Aurora between Kerguelen and Sogra), decided within the frame of the then Franco-Soviet cooperation, was to study the electron spreading conditions in the magnetic field's force line by emitting at shorter intervals electron rays along the path of a rocket-probe launched from the Southern hemisphere (Kerguelen islands) and observing the effects from the conjugate region: Sogra, near Arkhangelsk at a thousand kilometres North of Moscow.

The ARAKS campaign included the two ERIDAN rocket probe launches from the Kerguelen islands in January 26th and February 15th, 1975 respectively. Those rockets carried an impulse operating electron beam gun.

The main scientific objectives were:

  • localization of the conjugate magnetic points thanks to optical (artificial aurora) and radio-frequency effects;
  • study of the injected particle dynamics (backscatter, magnetic reflection);
  • detection and analysis of the interactions between an energetic particle beam and the ionospheric plasma as well as the study of the waves generated by this interaction.

The unloading of the 200 tons of equipments required for the campaign started in October, 1974. The equipment is transshipped on a barge 500 meters away from the port.

In January 26th and February 15th, 1975, two Eridan two stage rockets were launched.

The ARAKS mission in launchtime images

The film (in french), made in 1975, summarizes the main mission stages: from the rocket probe arrival in the Kerguelen islands to the observation of aurora Borealis in Norway for example.

Lengh: 8'22

The ARAKS mission was the last mission performed by CNES within the frame of the rocket probe program.


Special edition on the ARAKS experiment's resultats, Annales de Géophysique, Part 36, number 3, July-September 1980, published by Henri Rème.


  • Scientific contact: Henri REME IRAP (Institut de Recherche en Astrophysique et Planétologie), Toulouse
  • CNES Sun, Heliosphere, Magnetosphere program scientist: Jean-Yves Prado

See also