Evaluating the Radiation Threat
Near-Earth space can be a very dangerous place for both astronauts and satellites. One of the most hazardous environments is the van Allen belts, a doughnut-shaped region, filled with trapped energetic particles, which surrounds the Earth. These particles can damage spacecraft electronics and are one of the main factors that limit the lifetime of commercial spacecraft on orbit.
Scientists have known about the existence of these radiation belts for more than four decades, but their inner workings still remain something of a mystery. Now new research by Dr Richard Horne of the British Antarctic Survey and collaborators at UCLA and University College London - Mullard Space Science Laboratory is revealing what happens during space storms, 12,000 miles (19,200 km) above the Earth, and opening the door to discovering how damage to satellites may be reduced.
On Tuesday 8 April, Dr. Horne will present to the UK/Ireland National Astronomy Meeting in Dublin the first results from a new model that describes how atomic particles are accelerated along the Earth's magnetic field lines by extraordinary electromagnetic waves in the radiation belts. The waves are created in space by low energy electrons and then accelerate a fraction of the particles to very high energies.
"The van Allen belts are highly variable," explained Dr. Horne. "The number of high energy electrons can vary by 1000 times or more over timescales of a few hours to a few days."
"The key scientific problem is to understand how the particles are accelerated to very high energies - millions of electron volts - and how they are lost to the atmosphere.
"Our studies indicate that the waves that cause the acceleration in space are guided along the Earth's magnetic field to the polar regions and down to the ground. We detect these waves at our Halley research station in Antarctica," he said.
The calculations show that the electrons can be accelerated up to relativistic energies on a timescale of about a day during a geomagnetic storm. This is comparable to the observed timescale for electron acceleration in the Earth's radiation belts as measured by satellites.
"This wave theory for electron acceleration works most efficiently in the heart of the outer van Allen belt," said Horne.
"Very energetic radiation belt electrons are known as 'killer' electrons due to the damage they cause to satellites. Our research on when and where acceleration takes place, and on the variability of the radiation belts, has been used to evaluate risk for insurance companies," he added.
NOTES FOR EDITORS
American physicist Dr. James van Allen first discovered the Earth's radiation belts in 1958. His experiment flew on the first U.S. artificial satellite, Explorer 1, which was launched on 31 January 1958.
There are two main belts of high energy charged particles. These particles spiral around magnetic field lines between the Earth's magnetic poles.
The outer belt, which mainly contains electrons from the solar wind, lies between 13,000 and 19,000 km above the Earth. The inner belt (generally about 4,000 km above the Earth) mainly contains protons from the radioactive decay of neutrons and cosmic rays. The behaviour of the particles in the van Allen belts is influenced by the level of solar activity.
Accumulated exposure to energetic particles degrades satellite electronic components and is one of the main factors limiting the lifetime of commercial spacecraft, particularly those that fly through the van Allen belts. This is particularly important for telecommunications satellites and navigation spacecraft, such as the American Global Positioning System (GPS) and the European Galileo constellation that will be launched from 2005 onwards.
The 2003 UK/Ireland National Astronomy Meeting is hosted by the Astronomical Science Group of Ireland (ASGI) with support from (inter alia) the UK Particle Physics and Astronomy Research Council, the Royal Astronomical Society (RAS), the Armagh Observatory, the Dublin Institute for Advanced Studies, Trinity College Dublin, the Royal Irish Academy and the British Council.
From Tuesday 8 April to Wednesday 9 April, Dr. Horne can be contacted via the NAM press office (see above).
Normal contact details:
Dr. Richard B. Horne
MRS Programme British Antarctic Survey
Madingley Roa dCambridgeCB3 0ET
UKTel: +44 (0)1223-221542Fax: +44 (0) 1223-221226
FURTHER INFORMATION AND IMAGES CAN BE FOUND ON THE WEB AT:
An article about James Van Allen in the 17 March 2003 issue of TIME Magazine can be found at:
Date: 1 April 2003
Issued by Jacqueline Mitton and Peter Bond, RAS Press Officers.
NAM PRESS ROOM, Dublin, Ireland (8 -11 April only):