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 1000 kilometers above Earth’s surface and extends up to 9600 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,” says 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 says.
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 says.
Another strategy would station satellites that emit VLF waves in the radiation belts. “The problem is that you’d need quite a lot of energy,” Bortnik says, and large antennas that would be challenging to fit onto spacecraft.
Still, Bortnik points out, the U.S. Air Force’s Demonstration and Science Experiments (DSX) satellite, set for launch in 2016, will carry an instrument to monitor the effects that VLF waves broadcast in space might have on these dangerous electrons. “Those experiments can show how well VLF waves actually do, and maybe change what we think we know about what is needed to clear away electrons,” Bortnik says.
Initial efforts to clear the Van Allen belts targeted electrons because they tend to get trapped there as the result of high-altitude nuclear explosions. In 1962, a U.S. high-altitude nuclear weapons test named Starfish Prime generated a highly energetic artificial electron belt that disabled the first commercial communications satellite, TelStar 1, so researchers sought ways to protect spacecraft from nuclear weapons used in space.
However, it’s the protons in the inner belt that scientists have recently explored. Getting rid of them would potentially open up valuable new orbits for satellites and make travel safer for astronauts, says Maria de Soria-Santacruz Pich, whose Ph.D. work at MIT was on manipulating the Van Allen belts. It might also be impossible.
“Protons are heavy, about 2000 times heavier than electrons, so if you imagine a proton bashing into a piece of silicon, it can do a whole lot more damage than an electron,” Bortnik says. “Clearing them out would be good.”
Pich and her colleagues discovered that a type of VLF electromagnetic wave known as an electromagnetic ion cyclotron (EMIC) wave could potentially disperse protons in the inner belt. Pich says this strategy poses no hazard to Earth—the swarm of protons would be virtually unnoticed in the atmosphere.
Pich and her colleagues recently refined the computational strategy needed to figure out what frequencies space-based antennas should use and how much power is needed. However, Pich also found that to disperse all the protons from the region, you’d need a million 15-meter antennas operating for a few years, “which is indeed not feasible in the near future,” she says.
Nonetheless, Pich noted, her calculations assume that the waves these antennas generate do not bounce back and forth inside the inner belt. If they do, that could greatly improve their effectiveness, potentially making the strategy possible. A satellite mission would decide the matter one way or another, but there’s a lot of engineering work needed to even propose such a mission, she says.
It remains uncertain as to whether removing these radiation belts might 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. “That’s the most any of us can really say at the moment.”
This article originally appeared in print as “Can We Hack the Van Allen Belts?.”
About the Author
Brooklyn-based writer Charles Q. Choi has reported on both the space around our planet and on geoengineering—schemes that would purposefully alter our climate. But the notion of seizing control of the energy enveloping the planet, was a new one to Choi. “The idea that one could engineer space on such a vast scale amazed me,” he says.