Overview

The solar PolArization and Directivity X-Ray Experiment is a NASA solar mission led by the Space Sciences Laboratory at the University of California Berkeley that launched on 23-Jun-2025 to study the acceleration mechanism in solar flares. It consists of two x-ray instruments, the solar HARd x-ray Po- larimeter (SHARP) and the Measuring Directivity to Determine Anisotropy (MeDDEA) instrument. Funded by the Heliophysics Flight Opportunities in Research and Technology Program (H-FORT) program, PADRE is a 12U space- craft in a low-Earth orbit. The science goal of the mission is investigate the dominant electron acceleration mechanisms in large solar flares and its science objective is to determine the degree of beaming of accelerated electrons in large solar flares. The two instruments achieve this objective and associated requirement with two different but complimentary approaches. SHARP will de- termine the degree of polarization of x-ray Bremsstrahlung photons to constrain the electron pitch angle anisotropy. In coordination with Solar Orbiter STIX, MeDDEA will determine the amount of X-ray Bremsstrahlung directiv- ity. MeDDEA includes Solar Orbiter STIX spare Caliste-SO detectors and will compare its spectral x-ray measurements with those taken by STIX while at different heliographic angles.

MeDDEA provides hard X-ray spectroscopy measurements with a full Sun field of view. Unlike STIX is does not include imaging grids and therefore produces only spectra and not images. It measures hard X-ray emission from the Sun in the energy range of 5 to 100 keV, observing emission from both the hot flare plasma in the solar corona as well as energetic electrons accelerated in solar flares.

MeDDEA consists of 4 individual Caliste-SO detectors with 12 pixels each, 8 large pixels and 4 small pixels. It records individual x-ray events, the time of arrival, energy and pixel number. These data are downlinked on demand while an onboard process bins these data into individual spectra to provide summary data at a regular cadence.

Publications and Presentations

For more information about this mission and the MeDDEA instrument, see the following references

• An Overview of the Measuring Directivity to Determine Electron Anisotropy (MeDDEA) CubeSat Observatory

• The solar PolArization and Directivity X-Ray Experiment (PADRE) Mission Concept

• Constraining Electron anisotropy in large solar flares with multi-point solar hard x-ray observations; the solar HARd x-ray polarization and Directivity X-Ray Experiment (PADRE) mission

• The Solar PolArization and Directivity X-Ray Experiment (PADRE)