From Spaceflight Insider: “Van Allen Probes detect barrier around Earth”

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Spaceflight Insider

5.18.17
Paul Knightly

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The identical Van Allen Probes follow similar orbits that take them through both the inner and outer radiation belts. The highly elliptical orbits range from a minimum altitude of approximately 373 miles (600 kilometers) to a maximum altitude of approximately 23,000 miles (37,000 kilometers). Image & Caption Credit: NASA/JHU-APL

New results from NASA’s Van Allen Probes have revealed the impact humans have on the environment is not limited to physical and chemical impacts on the Earth’s surface, but it also includes radio frequencies extending out into space. The probes have found that very low frequency, or VLF, radio communications interact with particles in space that can form an artificial barrier against high-energy particle radiation from space.

The Van Allen radiation belts have been a fixture of the near-Earth space environment since their discovery at the start of the Space Age, but VLF communications have been a much more recent phenomenon that has seen increased use since the 1960s. VLF communications are primarily utilized to communicate with submarines across vast distances in the ocean from powerful ground stations.

VLF communications were used on a limited basis in the 1960s, but they did not see widespread use until the latter portion of the Cold War. Despite these communications being directed in a downward direction, they can also extend above the surface creating a VLF bubble that is detectable by spacecraft.

“A number of experiments and observations have figured out that, under the right conditions, radio communications signals in the VLF frequency range can, in fact, affect the properties of the high-energy radiation environment around the Earth,” said Phil Erickson, assistant director at the MIT Haystack Observatory located in Westford, Massachusetts.

What the Van Allen Probes have found is that the bubble produced by VLF frequencies corresponds with the inner extent of the Van Allen radiation belts. A comparison of modern data from the Van Allen belts with historical data from the 1960s shows that the Van Allen belt locations today are further from the Earth than they were 50 years ago.

The ability of VLF radio transmissions to impact the near-Earth environment is being studied in further detail. Scientists are studying the possibility of using VLF transmissions in the upper atmosphere to help mitigate the effects of charged particles on spacecraft that are sensitive to major space weather events, such as coronal mass ejections from the Sun.

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