EPD data overview

EPD measures the composition, spectra and anisotropies of energetic particles at high temporal, spectral, angular and mass resolution. The geometric factors are scaled to avoid saturation by high particle fluxes close to the perihelia. Since Solar Orbiter is a three-axis stabilized s/c, EPD uses multiple apertures and sectoring to cover different pointing directions, providing information about the directional distribution of energetic particles reaching the s/c.
The nominal telemetry budget of EPD is 3600 bps. Nevertheless, the elliptical orbit of Solar Orbiter will place the spacecraftat varying distances from the Earth, which will put restrictionson the instantaneous telemetry allocation available for the in-struments. Although Solar Orbiter has a memory buffer to partlymitigate this effect, the EPD data production has to be planned inadvance in order to maximise its scientific value. For this reason, EPD sensors have the ability to reduce their telemetry rates bychanging the sampling cadences. Higher cadences will be used when the spacecraft is closer to the Sun. Another factor that will affect the instantaneous telemetry rate is solar activity, due tothe adaptive compression scheme used by the units. This will require continuous adjustments of the observing plan in order to stay within the telemetry allocation.
Data produced on the spacecraft will be received on ground in the form of CCSDS packets and distributed to the hosting institutions, where they will be processed and calibrated. All the data will be published to the scientific community 3 months after reception. Four different processing levels are considered:

• Level 0. Raw telemetry.
• Level 1. Uncalibrated data (i.e.~counts).
• Level 2. Calibrated and validated data, ready for scientific use.
• Level 3. Higher processed products (e.g.~pitch angle distributions, browse plots, events lists, etc.).

Level 1 and level 2 products will be released in the form of daily files in Common Data Format (CDF), although other formats might be considered during the mission. A comprehensive description of all the available data products can be read here .
All the data will be stored at the Solar Orbiter Archive along with the data produced by all other Solar Orbiter instruments where it will be publicly accessible. Mirror repositories will also be located at the hosting institutions.

EPD data can be classified in four categories:

• Housekeeping data
• Nominal science data
• Burst mode data
• Low latency data

Housekeeping data

All EPD sensors and the ICU will produce housekeeping data that will be received on ground with the highest priority for monitoring instrument status and health.

Nominal science data

The main data product generated by the instrument will be count rates of energetic particles for selected energy intervals and species identified onboard by the different sensors:

• STEP: Particle intensities in the suprathermal energy range in two channels: an integral channel counting all the particles and an ion channel excluding electrons.
• EPT: Ion and electron intensities in 4 fields of view.
• SIS: Ion intensities for 12 different species in the lower part of the energetic particle spectrum (from ~14 keV/n to ~20 MeV/n) in 2 fields of view.
• HET: Electron and ion intensities for different species in the higher part of the energetic particle spectrum in 4 fields of view

Burst mode data

EPD sensors will be able, for short periods of time, to collect data with the highest cadence (up to 1 second for STEP, EPT and HET and 3 seconds for SIS) and in some cases with higher energy resolution. This is the so-called burst mode.

Low latency data

A subset of the nominal data, with lower cadences and energy resolution will be sent to ground as low latency data. Besides housekeeping, these data will be received on ground with the highest priority, typically the day after they are generated. Their main purpose is to give an overview of the recently acquired data, necessary for checking instrument performance, planning future operations and to select periods of burst mode data to be downlinked to ground.