“Hot” or “killer” electrons, as such harmful particles are also known, are drawn by the Earth’s magnetic field into one of two doughnut-shaped belts of radiation surrounding the planet. For decades scientists have wondered if these belts could be emptied of their electrons on command, a process they call radiation-belt treatment (RBR). In recent years, work on RBR has accelerated, and encouraging progress has been made. Most of the R&D is carried out, in some cases in secret, by the US departments of Defense and Energy.
Such work has acquired a new urgency. Allegations surfaced of Russian plans to illegally park nuclear weapons in a crowded region of space as early as 2024. An explosion there could destroy a far greater number of satellites than Starfish Prime, since most space equipment today is commercial and lacks military “hardening” against the particle storm of a nuclear explosion. Dennis Papadopoulos, a professor emeritus at the University of Maryland, sees this as the catalyst for a new (and secretive) RBR initiative at the Naval Research Laboratory (NRL), for which he is to serve as an advisor.
Alison Janes, a space physicist at the University of Iowa, says such attempts are not as fanciful as they sound. Lightning bolts, for example, create a form of RBR all the time. This happens because the radio waves they generate put pressure on hot electrons, causing them to descend into the atmosphere, where they collide with air molecules and rapidly lose energy, a phenomenon known as precipitate. Dr. Janes describes this effect as a “complete stripping out” of the surrounding radiation belts.
The wavelengths needed to precipitate energetic particles range from about 10 km to 100 km. Generating such great wavelengths and hence low frequencies is difficult, though not impossible. Some navies emit such “very low frequency” (VLF) radio waves for communication with submerged submarines with the help of antennas hundreds of meters high. However, Craig Rodger, a physicist at the University of Otago in New Zealand, says that if the US Navy switched its handful of transmitters from “talk-to-the-sub mode” to the best frequencies for RBR, they would not be able to precipitate hot electrons fast enough to save satellites.
The problem is the ionosphere, which begins about 80 km above the Earth’s surface. Here, incoming solar radiation strips electrons from atoms and molecules, creating a layer of electrons that interferes with radio waves. At night, the ionosphere weakens them by about 100 times, says Dr. Rodger. In the daytime, the attenuation is more than an order of magnitude greater.
aiming high
Some are exploring alternative solutions with experimental antennas. Using $750,000 of US Air Force money, Morris Cohen and his team at Georgia Tech in Atlanta built a special 275-meter-long antenna, designed to jump between different frequencies, and laid it horizontally across a field in Oklahoma in the summer of 2023. The flexibility that such frequency-hopping offers means that particles with different levels of energy can be targeted. Moreover, Dr. Cohen notes, because particles in different regions of space are sensitive to different frequencies, such a device should make it easier to clear priority orbits. Although no breakthroughs have been made so far, Dr. Cohen hopes that a similar – but more expensive – direct antenna could provide improvements.
Others hope to bypass the ionosphere altogether. In 2019 the US Air Force Research Laboratory (AFRL) launched a unique satellite called DSX to an altitude of 6,000 to 12,000 km above Earth. In a feat of engineering, it deployed an 80-meter, 10,000-volt transmitting antenna (with the longest span of any unmanned spacecraft). For nearly two years, the spacecraft generated VLF radio waves that scattered energetic particles that fell into the Earth’s atmosphere. Michael Starks, AFRL’s chief for RBR, says the mission demonstrated that an orbiting spacecraft could protect space assets from a nuclear attack.
There are even more bizarre ideas afoot. The Energy Department’s Los Alamos National Laboratory aims to create electricity, in essence, by using a space-based electron beam. The NRL, for its part, wants to launch a rocket that would drop 1.5 kilograms of barium, a metal, into the ionosphere, where sunlight detaches electrons. The Earth’s magnetic field makes the resulting barium ions spiral, generating an electric current that could, in turn, produce electron-depleting radio waves.
Such approaches are risky. Byproducts from the precipitation of the highest energy particles destroy stratospheric ozone, which protects the Earth from ultraviolet solar radiation. How damaging a large RBR operation would be is still unknown, says Dr. Janes of the University of Iowa. The hope is that if the United States can demonstrate an effective countermeasure to a nuclear attack on satellites, no adversary will try it, says Dr. Starks of AFRL. Solar storms, however, won’t be so easily stopped.
