EPD instrument suite CAD view on Solar Orbiter

The EPD instrument suite

EPD is an instrument suite, which comprises different sensors that have been designed to measure the spectra, composition, time variations and directional distributions of energetic particles. These measurements will be performed over a partly overlapping energy range encompassing a few keV to 450 MeV/n, with sufficient time, energy, angular and mass resolution to achieve the mission science goals. EPD consists of the following units:

The EPT and HET sensors are colocated on two nearly identical sensor units: EPT-HET1 and EPT-HET2. The ICU serves as a single power and data interface between the spacecraft and all the EPD units. STEP, EPT and HET were developed by the Christian Albrechts University (CAU) of Kiel. SIS was developed by the Johns Hopkins University Applied Physics Laboratory (JHU/APL) and CAU. The ICU was developed by the ESA PI institution at the University of Alcalá, Spain. The location of the different EPD sensor units on the spacecraft is shown in the figure.


EPD energy range and composition (left). EPD FoV in s/c reference frame (right)

The EPD energy range starts with suprathermal electrons ( E > 2 keV) and extents up to low-energy galactic cosmic-ray (~ a few hundred of MeV/n), as shown in the left figure. This is achieved by a combination of the four EPD sensors which measure electrons, protons and ions using different techniques. The right figure shows the fields of view of the different EPD sensors in the spacecraft reference frame. The color-coded background corresponds to the hourly-averaged magnetic field vector distribution as observed by HELIOS-1 during 1975-1981. HELIOS-1 had an in-ecliptic elliptical orbit with a perihelion at 0.31 au and an aphelion at 0.99 au. Note the clustering of the sunward and anti-sunward apertures around the mean Parker spiral direction.

EPD main properties are summarized in the following table:

Geo. Factor (cm2 sr) 8e-3 0.01 0.27 0.2
#FOV 1 2x2 2x2 2
FOV size/aperture 28ºx54º 30º 43º 22
Energy Range e-: 2-160 keV e-: 25-400 keV e-: 0.3-30 MeV 14 keV/n - 20 MeV/n
Ions: 4-160 keV H: 25 keV - 6 MeV H, He4: 7-100 MeV/n
He4: 1.5-6 MeV/n CNO: 13-240 MeV/n
Max Time Resolution(s) 1 1 1 3