The radiation belts around Earth are loaded with dangerous protons and electrons that can damage spacecraft. Now researchers are launching experiments to see if they can clear away the high-energy particles that pose the hazard by blasting them with radio waves.
When humans began exploring space, the first major find was the Van Allen radiation belts, doughnut-shaped zones of magnetically trapped, highly energetic charged particles. The Van Allen belts consist mainly of two rings: The inner belt starts roughly 1,000 kilometers above Earth’s surface and extends up to 9,600 km, while the outer belt stretches from about 13,500 to 58,000 km above Earth. The location and shapes of the belts can vary, and they can even merge completely.
High-energy protons are found within the area of the inner belt, whose size remains generally stable over the course of years to decades. The outer belt, on the other hand, is home to high-energy electrons and can vary dramatically in size and shape over the course of hours or days.
The huge amounts of radiation in the Van Allen belts can pose major risks for the host of satellites that pass through or orbit within these swaths of space. There are ways to make spacecraft more resistant against this radiation. For instance, spikes on their surfaces known as electron emitters can radiate away excess lower-energy electrons that might otherwise accumulate and cause a spark. In addition, shielding can help keep high-energy protons and electrons from penetrating nonconducting materials and building up inside them, which could lead to a damaging discharge.
However, decades of models and observations suggest a more dramatic solution: using carefully tuned electromagnetic waves to drive these particles out of space and into Earth’s atmosphere. Scientists first explored the idea of dispersing electrons in the outer belt, and they are now targeting protons in the inner belt.
“It’s really mind-boggling to think there could be human control over such huge volumes of space,” said Jacob Bortnik, a space physicist at the University of California, Los Angeles. “On Earth we control nature all the time, like building dams, but the prospect of doing it in space is fascinating -- it seems a bit like science fiction.”
One radiation-clearing strategy involves using very large radio transmitters on the ground to beam very low frequency (VLF) waves upward. These can in principle interact with and scatter charges in the radiation belt and drive them into the upper atmosphere.
“The result would be a little bit like auroras, although you wouldn’t see them,” Bortnik said.
The problem with that approach is getting VLF waves through the ionosphere, the layer of the atmosphere that sits about 80 to 640 km above Earth. “That layer is very conductive, so it’s hard to get signals through it efficiently,” Bortnik said.