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One cannot simply blast into space - be it for commercial or scientific purposes - without taking the space radiation environment into consideration. Because once one leaves the protective inner bubble of Earth’s magnetic field, one is exposed to energetic particles that have been trapped inside the magnetosphere, a large region encapsulating the Earth within which all electrically charged particles must obey the rules of our planet’s magnetic field. The beautiful aurora for instance, are visual evidence of these trapped particles.

The physical properties of the magnetosphere, with its many complex substructures and interactions, are still an important topic of study today. The more spacecraft (and the more technologically complex) we mean to send off into space, the more precise our knowledge needs to be of the radiation environment in space. This is the main objective of a new instrument, called the 3 Dimensions Energetic Electron Spectrometer or 3DEES, that we are preparing in a consortium with the Université Catholique de Louvain (Center for Space Radiations) and QinetiQ Space. It builds on the success of the Energetic Particle Telescope (EPT) on board the PROBA-V satellite. Within this consortium, BIRA-IASB is responsible for the design and mechanical manufacturing of the instrument and for the development of a Mechanical Ground Support Equipment (MGSE) that will be used for on-ground functional and calibration tests. The contract with the European Space Agency (ESA) has just been signed, meaning we can move forward on the development of 3DEES for a launch onboard ESA’s PROBA-3 satellite in 2023.

Studying the particle environment and space weather

Earth's radiation belts and trajectories of trapped particles
(bright blue and yellow arrows). Credit: NASA

Interplanetary space is far from empty, in many ways, but what the new 3DEES instrument is interested in are the highly variable high-energy articles that are populating the magnetosphere. These can disrupt satellites’ measurements, in extreme cases causing them to break down and be lost as happened to JAXA’s Hitomi X-ray Astronomy Satellite in 2016.

3DEES data will serve not only to enlarge our scientific knowledge of the charged particles in the magnetosphere, but also to inform the scientists and engineers that are preparing future space missions and technologies that will encounter this radiation environment.

Indeed, space weather can have a negative impact on technology and people, in space, in the sky and on the ground. To improve the modelling and forecasting of space weather and its effects, and take the necessary measures, the characterization of these high-energy particles in the Earth’s space environment is crucial, i.e. identifying:

  • their source (do they result from solar events or from galactic cosmic rays?)
  • their angle distribution (from which direction do the particles arrive and how many particles come from each angle?),
  • their energy distribution (what is the energy of the particles and how many particles do we find at each energy level?),
  • their acceleration (how do they get accelerated along the magnetic field lines?)

These characteristics fully determine the dynamics of the high-energetic population in the magnetosphere. 3DEES will be able to deliver exactly the information that is needed, in near-real time. The advantage of 3DEES is that it will measure the energy and fluxes of electrons and protons, for the first time, simultaneously in different directions (up to 6 angles spanning about 180° in a plane). Since the particles are trapped within the Earth’s magnetic field, this allows to infer their distribution at other locations as well, further away from the location where 3DEES is measuring.

3DEES design and technical information

3DEES is a considerable leap in technology when compared to its predecessor, the Energetic Particle Telescope (EPT). The instrument has a modular design that consists of a Panoramic Sensor Module (PSM), composed of 3 Orthogonal Sensor Modules (OSM) looking in two perpendicular directions, each with a field-of-view of 14,25°. As such, 3DEES can deliver high-fidelity directional measurements of the energy deposited by charged particles into the PSM at up to six angles spanning about 180° in a plane. In a sense, you could say that with 3DEES, it’s as if six miniaturised EPT’s had been packed together in an instrument of comparable weight and size, making simultaneous observations in different directions, allowing for a more profound scientific study of the Earth’s radiation environment.

The instrument covers the electron and proton energy ranges (100 keV-10 MeV and 4 MeV-50 MeV respectively) required as input to space weather models and products relevant for future European missions and technologies encountering the environment of the radiation belts.

Hitchhiking straight through the heart of the radiation belts with PROBA-3

This first technology demonstration model of 3DEES is foreseen to be launched in April 2023 onboard the European Space Agency’s PROBA-3 satellite (Project for On-Board Autonomy-3). The PROBA-3 mission is actually composed of two separate spacecraft, for which the mission’s main objective is to demonstrate a new technological step in space engineering: formation flying in a fixed position.

One spacecraft (called the coronograph) will carry the three scientific experiments: ASPIICS to study the Sun’s corona (led by the Royal Observatory of Belgium), DARA for measuring the total solar irradiance and 3DEES. The other spacecraft (called the occulter) will act as an occulting disk blocking out the Sun’s brightness to allow ASPIICS to see clearly the much fainter corona. To fulfill this aim, the two spacecraft will need to fly together in a fixed position about 150 meters apart (in a stack configuration), so that the occulting disk remains in exactly the right position to allow ASPIICS to make its measurement. Remarkably, their highly elliptical orbit (600 x 60530 km at around 59° inclination, with an orbital period of 19.7 hours) will bring them straight through the heart of the radiation belts, a fantastic opportunity for researchers to study them.


  • Dr. Karolien Lefever, Head of the Communication and documentation department.
    E-mail: Karolien(dot)Lefever(at)aeronomie(dot)be

Further reading

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One of the clean rooms at BIRA-IASB, where the Engineering department performs all series of tests on new instruments in development.
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The Energetic Particle Telescope (EPT, left), the predecessor of 3DEES, and the 3DEES instrument (middle and right components): the Panoramic Sensor Module (PSM, in the middle in yellow) is detached from the electronics and mounted on the outside of the PROBA-3 coronograph satellite, the Docking Module (the DM, on the right side in black) is mounted on the inside of the satellite.
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Artistic illustration of the two components of the PROBA-3 mission: the coronograph (left), and the occulter (right). Credit: ESA