Instruments 

IMPAX Atmospheric X-ray Imaging Spectrometer (I-AXIS)

The I-AXIS (Atmospheric X-ray Imaging Spectrometer) instrument is one of two science instruments onboard the IMPAX CubeSat. I-AXIS, designed by the University of Colorado Boulder, will observe and characterize the atmospheric energy deposition produced by relativistic electron microburst precipitation. The instrument generates two-dimensional images of X-ray photons emitted from Earth’s atmosphere by employing a coded aperture imaging technique. These incident photons are spatially modulated before detection and later reconstructed into an image. I-AXIS consists of an array of 12 cadmium-zinc telluride (CZT) detectors, each with a 16 × 16-pixel configuration. This enables simultaneous measurement of photon position and energy within the 50–300 keV range. Eleven detectors use coded apertures to enhance imaging capabilities, while one serves as a reference detector for background comparison. Oriented in the nadir (downward) direction, the instrument achieves a wide field of view and resolution of 44–100 km. This allows for large-scale mapping of microburst events. By combining high temporal resolution measurements with energy-resolved imaging, I-AXIS provides critical data for understanding the role of microbursts in radiation belt dynamics and broader impacts on satellite operations and space weather processes.

IMPAX FIREBIRD Instrument for Relativistic Electrons (I-FIRE) 

The I-Fire (FIREBIRD Instrument for Relativistic Electrons) Instrument is a particle detection instrument designed to directly measure the flux, energy, and temporal behavior of relativistic electrons associated with microburst precipitation. I-FIRE, designed by the University of New Hampshire, is derived from FIREBIRD and AEPEX missions. I-FIRE employs two silicon solid-state detectors with two viewing points: an omnidirectional detector with a 180° field of view to capture the overall electron environment, and a collimated detector with a 45° field of view. This view is aligned with the atmospheric loss cone to isolate electrons that are actively precipitating into the atmosphere. Each detector is enclosed within an aluminum housing and equipped with a thin entrance window that blocks low-energy particles while allowing higher-energy electrons to pass through for measurement. The instrument measures electrons across an energy range of approximately 125 keV to 1 MeV. The electrons are divided into 63 energy channels, which allows for detailed resolution of the electron energy spectrum. This energy resolution is important for identifying energy dispersion, which provides insight into where and how the electrons were scattered within Earth’s magnetosphere. To prevent saturation during high-intensity microburst events, the geometric factor of the collimated detector is intentionally reduced while maintaining sensitivity for lower flux conditions. With a resolution of 20 ms, I-FIRE captures rapid variations in electron precipitation. This allows for precise characterization of microburst timing and intensity. These measurements complement the X-ray imaging provided by I-AXIS. Together, both instruments create a more complete understanding of the physical processes controlling radiation belt dynamics and space weather interactions