Instrument Type
Particle
Developed by APL for NASA’s REAL CubeSat mission, which Dartmouth College’s Robyn Millan leads and Montana State University operates, the REAL instrument leverages advances in miniaturization to capture a more complete picture of energetic-particle dynamics in Earth’s radiation environment than previous missions could provide. This novel capability opens the door to improved understanding of space weather effects in low Earth orbit (LEO) while also making such unparalleled observations accessible to future small, low-cost spacecraft.
Launched from Vandenberg Space Force Base on July 23, 2025, REAL observes high-energy particles in Earth’s outer Van Allen Belt—a doughnut-shaped region that contains energetic electrons, including so-called “killer electrons” that are so energetic that they can penetrate satellite shielding and trigger damaging electrical discharges or operational anomalies.
Scientists have spent decades seeking to better understand and predict the radiation belts’ behavior, including through the Van Allen Probes mission, which spent nearly seven years studying the mechanisms that produce and erode the belts. Populations of energetic electrons in the outer belt, in particular, can build up and then rapidly drop off, pouring particles into Earth’s atmosphere in events that unfold sometimes in milliseconds and other times in minutes or even hours. Certain loss processes, however, can only be examined well at low altitudes, as radiation belt particles are about to hit the atmosphere.
These energetic electron precipitation (EEP) events play an important role in the dynamics of the belts. But while researchers have identified plasma waves as likely drivers of the cascades, the underlying physics—such as whether electron scattering occurs gradually through diffusive processes or rapidly through nonlinear interactions—is still uncertain.
REAL, however, can distinguish between these potential modes. As the CubeSat flies in LEO, it points the REAL particle detector along Earth’s magnetic field to watch as electrons ranging from 40,000 electron volts to 2 million electron volts enter the atmosphere. From there, it can simultaneously measure the quantity, energy, and angle of the particles as they fall toward the atmosphere—a first-of-its-kind capability—making it possible for scientists to identify the forces that shook those particles free in the first place.
Just as importantly, this novel capability demonstrates that measurements once requiring large, resource-intensive missions can now be achieved with compact, cost-effective instruments on small satellites, paving the way for such missions as CubeSat constellations that could continuously observe Earth’s radiation environment and help us to better protect the space-based systems modern society depends on.
To learn more about the REAL instrument, read NASA’s technology highlight about REAL.
