Taking Control of the Van Allen Belts to Improve Safety in Space
One of the first major finds once space exploration began was the Van Allen radiation belts. These belts are doughnut-shaped zones of magnetically trapped high-energy particles. The Van Allen belts consist of primarily two rings: an inner belt beginning approximately 1000 kilometers above the Earth’s surface and continuing up to 9600km. The second belt begins around 13,500km and extends to 58,000km above the Earth. The locations of the two belts can vary, and they can even merge completely together, forming one extremely wide belt. High-energy protons are found within the inner belt, while high-energy electrons are found within the outer belt.
The extensive amounts of radiation in the Van Allen belts are extremely dangerous to space vehicles and satellites passing through or orbiting near the belts. Traditionally, spacecraft are made resistant to the radiation by applying spikes on their surfaces, called electron emitters. These emitters radiate away excess lower-energy electrons that would build up and cause a spark. Shielding can also help keep high-energy protons and electrons from penetrating nonconducting materials and building up inside them. Scientists are now using tuned electromagnetic waves to drive these dangerous particles out of space and into the Earth’s atmosphere. This method was first tried with electrons in the outer belt, and is now being focused on protons in the inner belt. Removing the protons in the inner belt could potentially open up new orbits for satellites and improve space travel safety for astronauts. Protons are about 2000 times heavier then electrons and therefore potentially much more damaging. Being able to remove these from space could be very beneficial.
One method to clear the radiation involves using large radio transmitters on the ground to direct very low frequency (VLF) waves upward. These should interact and scatter the charges in the belts and drive them into the upper atmosphere. “The result would be a little bit like auroras, although you wouldn’t see them,” says Jacob Bortnik, a space physicist at the University of California, Los Angeles.
[i] The challenge with this method is getting the VLF waves through the ionosphere, the layer of atmosphere that sits 80-640km above the Earth. “That layer is very conductive, so it’s hard to get signals through it efficiently,” Bortnik says. Another strategy is to station VLF emitting satellites in the radiation belts. This however would require a lot of energy, and the necessary large antennas would be difficult to get into a spacecraft.
It is uncertain if removing these radiation belts could potentially have unintended consequences. “At present we don’t think there is any downside to not having them, but as with all things geophysical, it is hard to know all the complex interconnections between the various systems and estimate the full effect of removing the radiation belts completely,” Bortnik says.