SCIENCE sciencemag.org 3 JANUARY 2020 • VOL 367 ISSUE 6473 9PHOTO: SCIENCE HISTORY IMAGES/ALAMY STOCK PHOTO
T
he U.S. military thought it had cleared
the decks when, on 9 July 1962, it
heaved a 1.4-megaton nuclear bomb
some 400 kilometers into space: Or-
biting satellites were safely out of
range of the blast. But in the months
that followed the test, called Starfish Prime,
satellites began to wink out one by one, in-
cluding the world’s first communications
satellite, Telstar. There was an unexpected
aftereffect: High-energy electrons, shed by
radioactive debris and trapped by Earth’s
magnetic field, were fritzing out the satel-
lites’ electronics and solar panels.
Starfish Prime and similar Soviet tests
might be dismissed as Cold War misadven-
tures, never to be repeated. After all, what
nuclear power would want to pollute space
with particles that could take out its own
satellites, critical for communication, naviga-
tion, and surveillance? But military planners
fear North Korea might be an exception: It
has nuclear weapons but not a single func-
tioning satellite among the thousands now in
orbit. They quietly refer to a surprise orbital
blast as a potential “Pearl Harbor of space.”
And so, without fanfare, defense scien-
tists are trying to devise a cure. Three spaceexperiments—one now in orbit and two be-
ing readied for launch in 2021—aim to gather
data on how to drain high-energy electrons
trapped by Earth’s magnetic field in radia-
tion belts encircling the planet. The process,
called radiation belt remediation (RBR), al-
ready happens naturally, when radio waves
from deep space or from Earth—our own
radio chatter, for example, or emissions
from lightning—knock electrons trapped in
Earth’s Van Allen radiation belts into the up-
per atmosphere, where they quickly shed en-
ergy, often triggering aurorae.
“Natural precipitation happens all the
time,” says Craig Rodger, a space physicist
at the University of Otago. But it would
not nearly be fast enough to drain nuclear-
charged radiation belts, where electron
fluxes can be millions of times higher than
in Earth’s Van Allen belts.
Scientists got a glimpse of a potential
solution from NASA’s Van Allen Probes,
which launched in 2012 and ducked in and
out of Earth’s radiation belts until the mis-
sion ended last summer. It offered a deep
dive into natural remediation processes,
showing how radio waves resonate with
high-energy electrons, scattering them
down the magnetic field lines and sweep-
ing them out of the belts. “Compared to10 years ago, we just know so much more
about how these wave-particle interactions
work,” says Geoff Reeves, a space physicist
at Los Alamos National Laboratory.
Now, researchers are ready to try artifi-
cial remediation, by beaming radio waves
into the belts. Physicists have tested using
the U.S. Navy’s very low frequency (VLF) an-
tenna towers, powerful facilities used to com-
municate with submarines, says Dan Baker,
director of the Laboratory for Atmospheric
and Space Physics at the University of Colo-
rado, Boulder, and a lead investigator on the
Van Allen Probes. The antennae of the High-
frequency Active Auroral Research Program
in Alaska and the giant dish of the Arecibo
Observatory in Puerto Rico might also be en-
listed to generate cleansing radio beams.
An orbiting RBR platform, closer to the
target, could be more effective. In June
2019, the U.S. Air Force launched what it
bills as the largest uncrewed structure ever
flown in space: the DSX dipole antenna.
Nearly as long as a U.S. football field, DSX’s
primary mission is to transmit VLF waves
into the Van Allen belts and measure pre-
cipitating particles with onboard detectors.
“It’s a new way to prod the belts and explore
basic questions in space physics,” says DSX’s
principal investigator, James McCollough atIN DEPTH
By Richard StoneSPACE PHYSICSU.S. military tests radiation belt cleanup in space
Aurorae were seen widely
after Starfish Prime, a
1962 nuclear test in space.Radio waves could sweep belts clean of satellite-killing particles after nuclear sneak attack
Published by AAAS