The Van Allen Radiation Belt

This blog discusses a very interesting phenomenon in space what we call 'The Van Allen Radiation Belt'.Its existence was theorized prior to space age and it was confirmed by Explorer I and Explorer III missions under Dr. James Van Allen.

The picture shows the radiation belt around the earth. It is a torus of charged energetic particles(i.e. plasma).It can be viewed as two belts(as was mapped by Explorer IV and Pioneer III):-

• The inner Van Allen Radiation Belt
• The outer van Allen Radiation Belt

The outer belt consists mostly of electrons and inner belt consists mostly of protons. The particles in the belt are as high above as 200-1000km over the earth surface while its extent is not more than 7 Earth Radii(RE). They contain particles that can penetrate through 1g/cm2 of shielding.
The Outer Van Allen Belt

Enlarged View of this image The big outer radiation belt extends from an altitude of about 10,000­65,000 km and has its greatest intensity between 14,500­19,000 km. The outer belt is thought to consist of plasma trapped by the Earth's magnetosphere. The USSR's Luna 1 reported that there were very few particles of high energy within the outer belt. The gyroradii for energetic protons would be large enough to bring them into contact with the Earth's atmosphere. The electrons here have a high flux and along the outer edge and electrons with kinetic energy E > 40 keV can drop to normal interplanetary levels within about 100 km (a decrease by a factor of 1000). This drop-off is a result of the solar wind.
The particle population of the outer belt is varied, containing electrons and various ions. Most of the ions are in the form of energetic protons, but a certain percentage are alpha particles and O+ oxygen ions, similar to those in the ionosphere but much more energetic. This mixture of ions suggests that ring current particles probably come from more than one source.
The outer belt is larger and more diffused than the inner, surrounded by a low-intensity region known as the ring current. Unlike the inner belt, the outer belt's particle population fluctuates widely and is generally weaker in intensity (less than 1 MeV), rising when magnetic storms inject fresh particles from the tail of the magnetosphere, and then falling off again.
There is debate as to whether the outer belt was discovered by the US Explorer IV or the USSR Sputnik II/III.

The Inner Van Allen Belt The inner Van Allen Belt extends from roughly 1.1 to 3.3 Earth radii, and contains high concentrations of energetic protons with energies exceeding 100 MeV, trapped by the strong (relative to the outer belts) magnetic fields in the region.
It is believed that protons of energies exceeding 50 MeV in the lower belts at lower altitudes are the result of the beta decay of cosmic ray neutrons. The source of lower energy protons is believed to be proton diffusion due to changes in the magnetic field during geomagnetic storms.

The Van Allen Belt's Impact on Space Travel Solar cells, integrated circuits, and sensors can be damaged by radiation. In 1962, the Van Allen belts were temporarily amplified by a high-altitude nuclear explosion (the Starfish Prime test) and several satellites ceased operation.
Magnetic storms occasionally damage electronic components on spacecraft. Miniaturization and digitization of electronics and logic circuits have made satellites more vulnerable to radiation, as incoming ions may be as large as the circuit's charge. Electronics on satellites must be hardened against radiation to operate reliably.
The Hubble Space Telescope, among other satellites, often has its sensors turned off when passing through regions of intense radiation. An object satellite shielded by 3 mm of aluminum will receive about 2500 rem (25 Sv) per year.
Proponents of the Apollo Moon Landing Hoax have argued that space travel to the moon is impossible because the Van Allen radiation would kill or incapacitate an astronaut who made the trip. Van Allen himself, still alive and living in Iowa City, has dismissed these ideas.
In practice, Apollo astronauts who traveled to the moon spent very little time in the belts and received a harmless dose. Nevertheless NASA deliberately timed Apollo launches, and used lunar transfer orbits that only skirted the edge of the belt over the equator to minimize the radiation. Astronauts who visited the moon probably have a slightly higher risk of cancer during their lifetimes, but still remain unlikely to become ill because of it.

The Van Allen Belt's And Why They Exist It is generally understood that the Van Allen belts are a result of the collision of Earth's magnetic field with the solar wind. Radiation from the solar wind then becomes trapped within the magnetosphere. The trapped particles are repelled from regions of stronger magnetic field, where field lines converge. This causes the particle to bounce back and forth between the earth's poles, where the magnetic field increases.
The gap between the inner and outer Van Allen belts is caused by low-frequency radio waves that eject any particles that would otherwise accumulate there. Solar outbursts can pump particles into the gap but they drain again in a matter of days.
The radio waves were originally thought to be generated by turbulence in the radiation belts, but recent work by James Green of the NASA Goddard Space Flight Center comparing maps of lightning activity collected by the Micro Lab 1 spacecraft with data on radio waves in the radiation-belt gap from the IMAGE spacecraft suggests that they're actually generated by lightning within Earth's atmosphere. The radio waves they generate strike the ionosphere at the right angle to pass through it only at high latitudes, where the lower ends of the gap approach the upper atmosphere.
The Soviets once accused the U.S. of creating the inner belt as a result of nuclear testing in Nevada. The U.S. has, likewise, accused the USSR of creating the outer belt through nuclear testing. It is uncertain how particles from such testing could escape the atmosphere and reach the altitudes of the radiation belts. Likewise, it is unclear why, if this is the case, the belts have not weakened since atmospheric testing was banned by treaty. Thomas Gold has argued that the outer belt is left over from the aurora while Dr Alex Dessler has argued that the belt is a result of volcanic activity.
In another view, the belts could be considered a flow of electric current that is fed by the solar wind. With the protons being positive and the electrons being negative, the area between the belts is sometimes subjected to a current flow, which "drains" away. The belts are also thought to drive aurora, lightning and many other electrical effects.

Removing The Belts The belts are a hazard for artificial satellites and moderately dangerous for human beings and difficult and expensive to shield against.
There is a proposal by the late Robert L. Forward called HiVolt which may be a way to drain at least the inner belt to 1% of its natural level within a year. The proposal involves deploying highly electrically charged tethers in orbit. The idea is that the electrons would be deflected by the large electrostatic fields and intersect the atmosphere and harmlessly dissipate.
Some scientists, however, theorize that the Van Allen belts carry some additional protection against solar wind, which means that a weakening of the belts could harm electronics and organisms, and that they may influence the Earth's telluric current, dissipating the belts could influence the behavior of Earth's magnetic poles.