NASA's REAL CubeSat instrument enables high-fidelity measurements of energetic particles in Earth's radiation belts.

A new instrument developed for NASA's Relativistic Electron Atmospheric Loss (REAL) CubeSat mission is providing unprecedented measurements of high-energy particles in Earth's radiation belts. The compact instrument, also called REAL, can simultaneously measure the quantity, energy, and angle of electrons as they fall into the atmosphere, a first-of-its-kind capability for a CubeSat. This allows scientists to capture rapid microbursts of electron loss that last only 100 milliseconds, which previous single-direction sensors on CubeSats were too slow to resolve.

The instrument affects our understanding of the Van Allen radiation belts, which pose hazards to satellites in Earth orbit, including GPS and communications satellites. The outer belt contains 'killer electrons' that can penetrate satellite shielding and cause damage. By better understanding how these electrons are lost from the belts, scientists can improve predictions of space weather effects.

Launched on July 23, 2025, the REAL instrument includes three sensor heads—low, medium, and high energy—with multiple look directions integrated into a 3U CubeSat. The low-energy head uses an electrostatic analyzer with 36 apertures and two look directions to measure electrons from 1 keV to 40 keV. The medium-energy head has five apertures and the high-energy head has four, each spanning 20 degrees of pitch angle, using solid-state detectors. Together, they measure electrons from 40 keV to 2 MeV with time resolution as short as 20 milliseconds.

The REAL mission is led by principal investigator Robyn Millan of Dartmouth College, with instrument scientist Thomas Sotirelis at the Johns Hopkins Applied Physics Laboratory, where the instrument was developed. The instrument's pitch-angle-resolved measurements distinguish between precipitating, quasi-trapped, and trapped electron populations, helping to determine whether electron scattering occurs through gradual diffusion or rapid nonlinear interactions driven by plasma waves.

Next steps involve analyzing the data from REAL to investigate the relative importance of different loss mechanisms and identify which waves are responsible for electron fallout. This knowledge will improve models of radiation belt dynamics and enhance protection for satellites and astronauts in low Earth orbit.