What is PADRE?

The solar PolArization and Directivity X-Ray Experiment (PADRE) is NASA cubesat mission to study and dicepher the secrets of the Sun. The mission is a collaboration between the Space Sciences Laboratory – University of California Berkeley (SSL/UCB), Goddard Space Flight Center (GSFC), SouthWest Research Institute (SWRI), University of Applied Sciences and Arts Northwestern Switzerland (FHNW), the Saclay Nuclear Research Centre of the Commissariat à l’énergie atomique (CEA-Saclay).


The Solar HARd X-ray Polarimeter (SHARP) shall determine the degree of polarization (MDP(99%) of 5%) of solar flare non-thermal X-rays produced during the impulsive phase by quantifying the azimuthal distribution of scattered HXRs.

SHARP consists of a cylindrical beryllium scatterer, surrounded by ~1 mm-thick CdTe photon counting detectors instrumented by Timepix3 ASICs.

Bremsstrahlung HXRs from flares are expected to be strongly polarized along magnetic field lines. Measuring the polarization yields a new diagnostics on flare-accelerated electrons: are they strongly beamed (classical thick-target model) or isotropic? The answer to this question would put new constraints on flare acceleration models that were unavailable before.


The Measuring Directivity to Determine Electron Anisotropy (MeDDEA) is a straightforward instrument concept and makes use of existing SO/STIX flight-spare detectors provided by CEA-Saclay. Unlike STIX, MeDDEA does not have grids and does not image HXRs as it is not necessary for the proposed science.

Unambiguous measurements of solar flare electron anisotropy can be obtained through X-ray directivity measurements made by cross-calibrated detectors looking at the same source from two separate points of view. The importance of such ““stereoscopic observations” of solar flares for understanding the nature of the energy spectrum, spatial distribution, and propagation characteristics of energetic electrons in solar flares has been emphasized earlier.