“Hot” or “killer” electrons, as such harmful particles are sometimes called, are swept up by the Earth's magnetic field into one of two doughnut-shaped radiation belts that encircle the planet. For decades, scientists have wondered whether these belts can be stripped of their electrons on command, a process they call “radiation-belt remediation” (RBR). In recent years, work on RBR has accelerated, with encouraging progress. Much of the research and development is being conducted, in some cases discreetly, by the U.S. Departments of Defense and Energy.
Such work has taken on a new urgency. In early 2024, allegations surfaced of Russian plans to illegally park a nuclear weapon in a crowded strip of space. A detonation there could destroy a larger fraction of satellites than Starfish Prime did, since most space kits today are commercial and lack military “hardening” against the particle storm of a nuclear detonation. Dennis Papadopoulos, a professor emeritus at the University of Maryland, sees this as a catalyst for a new (and secretive) RBR initiative at the Naval Research Laboratory (NRL), for which he will serve as an advisor.
Such efforts aren’t as fanciful as they sound, says Allison Jaynes, a space physicist at the University of Iowa. Lightning bolts, for example, perform a form of RBR all the time. This happens because the radio waves they generate push on hot electrons, causing them to plummet into the atmosphere, where they collide with air molecules and rapidly lose energy in a process known as precipitation. Dr. Jaynes describes this effect as “a complete obliteration” of nearby radiation belts.
The wavelengths needed to knock down energetic particles range from about 10 kilometers to 100 kilometers. Generating such long wavelengths, and therefore low frequencies, is difficult, but not impossible. A few navies broadcast such “very low frequency” (VLF) radio waves to communicate with submerged submarines, using antennas hundreds of meters high. But as things stand now, says Craig Rodger, a physicist at the University of Otago in New Zealand, if the U.S. Navy were to switch its handful of transmitters from “talk-to-the-subs” mode to the best frequencies for RBR, they wouldn't be able to knock down hot electrons fast enough to save satellites.
The problem is the ionosphere, which begins about 50 miles above the Earth’s surface. Here, incoming solar radiation strips electrons from atoms and molecules, creating a layer of electrons that interfere with radio waves. At night, the ionosphere attenuates them by a factor of about 100, Dr. Rodger says. During the day, the attenuation is an order of magnitude greater.
Aim higher
Some are looking to experimental antennas for solutions. With $750,000 in funding from the U.S. Air Force, Morris Cohen and his team at Georgia Tech in Atlanta built a specialized 900-foot-long antenna designed to hop between different frequencies and deployed it horizontally in an Oklahoma field in the summer of 2023. The flexibility afforded by such frequency hopping means that particles with a range of energy levels can be targeted. .over, Dr. Cohen notes, since particles in different parts of space are sensitive to different frequencies, such a tool should make it easier to clear priority orbits. While no breakthroughs have been achieved so far, Dr. Cohen hopes that a similar—but more expensive—upright antenna could offer improvements.
Others hope to bypass the ionosphere altogether. In 2019, the U.S. Air Force Research Laboratory (AFRL) launched a unique satellite called DSX to between 3,700 and 7,500 miles above Earth. In a feat of engineering, it deployed an 80-meter-long, 10,000-volt transmitting antenna (the longest wingspan of any unmanned spacecraft). For nearly two years, the spacecraft generated VLF radio waves that slammed energetic particles into Earth’s atmosphere. Michael Starks, AFRL’s RBR chief, says the mission demonstrated that an orbiting spacecraft could protect space assets from nuclear attack.
There are wilder ideas floating around. The Department of Energy’s Los Alamos National Laboratory wants to use a beam of electrons in space to essentially produce lightning. The NRL, in turn, wants to launch a rocket that would release 3.3 pounds of barium, a metal, into the ionosphere, where sunlight knocks off electrons. The Earth’s magnetic field would cause the resulting barium ions to spiral, creating an electric current that could in turn produce electron-precipitating radio waves.
Such approaches come with risks. Byproducts of the precipitation of the highest-energy particles nibble away at stratospheric ozone, which protects Earth from ultraviolet radiation from the sun. How damaging a large RBR operation would be is still unknown, says Dr. Jaynes of the University of Iowa. The hope, says Dr. Starks of the AFRL, is that if America can demonstrate an effective countermeasure to a nuclear attack on satellites, no adversary will stand a chance. Solar storms, however, will not be so easy to deter.
