The Sun and its extended atmosphere, the heliosphere, is a very complex system. The inner planets of the Solar System, including the Earth, lie within the heliosphere and its influence can sometimes be clearly detected by researchers and scientists during phases of high solar activity.

The Solar Orbiter mission, part of the European Space Agency’s Cosmic Vision program, is a new mission (launch planned in 2017) intended to explore the Sun and its heliosphere to improve our understanding of Space weather and its effects on Earth. It will observe the Sun and collect measures in an orbit ranging from 0.28 (closer than Mercury) to 1.4 AU (the Earth is at 1 AU). In addition, this mission will provide with a natural laboratory to study processes in fundamental physics, astrophysics and plasma physics that cannot be studied elsewhere in such detail.

The scientific payload of Solar Orbiter is composed of ten experiments. Among the instruments, the Solar Wind Analyser suite (SWA) will provide comprehensive in-situ measurements with very high temporal resolution of solar wind’s particles composition (ions, protons and electrons) and velocity distributions. The final goal is to establish the fundamental physical links between the highly dynamic magnetised atmosphere of the Sun and the solar wind in all its quiet and disturbed states.

SWA is in turn composed of four sensors devoted to the analysis of particles at different energy levels. Two of the instruments measure electrons (Electron Analyser Sensor, or EAS), one measures protons and alpha particles (Proton Analyser Sensor, or PAS) and one measures heavy ions which are a minor constituent of the solar wind (Heavy Ion Sensor, or HIS). The instruments will independently measure 3D velocity distribution functions, evaluate density, speed, temperature and thermal flux of the plasma composing solar wind.

The DPU project will:

• Provide single interfaces to the spacecraft for power, telemetry, tele-commands and power management;
• Provide commands management, data handling and data compression for the four instruments;
• Provide the Electrical Ground Support Equipment (EGSE) for the instrument suite;
• Contribute to the on-board data compression SW definition.
• Contribute to the implementation of the Mechanical Ground Support Equipment (MGSE);
• Contribute to sensor definition;

Italy cooperate at the SWA experiment providing the Data Processing Unit (DPU) through a project having Roberto Bruno of Institute for Space Astrophysics and Planetology (IAPS) as the scientific responsible and SWA Co-Principal Investigator.

The role of Planetek Italia

Project is in charge of a group of companies composed by TSD, Planetek Italia, Sitael and SSI. Planetek activities focus on the EGSE SW layer and on the on-board software for scientific data processing.

We have two main roles: the first is the development of the scientific software on-board (including scientific data processing and compression, as already mentioned) and the second is the design and development of software sub-system in the Electrical Ground Support Equipment (EGSE).

Both these aspects inherit from SpacePDP experience: modules already developed have been customised in order to accommodate for the SWA suite specific needs. The Data Processing Unit on-board is based on a LEON2 processor module (as SpacePDP), and includes as well the Space Wire interfaces (again part of SpacePDP). The EGSE itself on the other hand is aimed to the DPU verification and thus includes a customisation of the FPGA module implementing Space Wire core. It has to simulate in fact DPU’s external interfaces which the interaction with the DPU pass for.

SWA sensors collect the particles composing the wind; one of the main task in the on-board data handling is the evaluation of “moments” in phase space, i.e. mathematical expressions able to characterise wind considered as a plasma flux. However, as evidenced by the scientific team, such a calculation needs of a significant percentage of total computational resources, so we are developing optimal implementation custimised to the specific data involved. The same approch has been adopted in order to define which is the compression techniques best fitting to data.