Technical Article

The high-energy proton instrument (HEPI), a compact Cherenkov radiation space weather monitor

¹ School of Maths and Physics, University of Surrey, Guildford, GU2 7XH, UK
² European Space Operations Centre, European Space Agency, 64293 Darmstadt, Germany
³ European Space Research and Technology Centre, European Space Agency, 2201 AZ Noordwijk, The Netherlands

^* Corresponding author: joseph.o’neill@surrey.ac.uk

Received: 24 January 2025
Accepted: 19 May 2025

Abstract

The monitoring of near-Earth space radiation has been a key component of space agencies’ strategies since their inception. The changes in these radiation fluxes, part of the broader space weather environment, originate from various sources, including high-energy protons emitted in solar particle events. These protons, with energies higher than 300 MeV, are a source of damage to satellites, space station infrastructure and personnel, and also have effects that are observed in aircraft and at ground level. Increasing the number of instruments monitoring the flux of these high-energy protons is vital for the next generation of space-based infrastructure. We present the development and characterisation of a compact Cherenkov radiation detector system for use on CubeSat missions: the high-energy proton instrument, HEPI. This detector displays particle species discrimination and has an inherent energy threshold via the Cherenkov radiation emission mechanism, enabling the system to monitor baseline levels of these high-energy protons and detect surges in the flux. The design of the detector as an instrument to be implemented in a multitude of small-volume satellite missions is presented, alongside the response of HEPI to electrons, galactic cosmic ray muons and protons produced at a beam facility.