Solar Orbiter SWA Sensors & Locations

Solar Orbiter SWA Sensor Locations 

THE SWA sensor accommodations on the satellite are shown above (Credit:ESA). The SWA/HIS and SWA/PAS sensors need relatively narrow fields of view which are centred on the Sun-direction, since the protons, alpha-particles and heavy ions generally arrive at the spacecraft from the Sun direction with very little thermal spread and only modest angular deflection due to the spacecraft motion.  These fields of view are provided by cut-outs in the corners of the spacecraft heat shield. Conversely, electrons have large thermal spread and can arrive from any direction.  Thus the SWA/EAS sensor is mounted in the spacecraft shadow at the end of the instrument boom, such that the amount of field-of-view blockage by the spacecraft and its appendages is minimised.

• SWA/EAS - The Electron Analyser System
• SWA/PAS - The Proton-Alpha particle Sensor
• SWA/HIS - The Heavy Ion Sensor
• SWA/DPU - The Data Processing Unit
• SWA Sensor Characteristics

SWA/EAS - The Electron Analyser System

The SWA/EAS system was built by UCL/MSSL with technical and hardware contributions from Laboratoire de Physique des Plasmas (LPP), Paris.

SWA/EAS makes a high temporal resolution determination of the 3D electron velocity distributions in the solar wind, in order to be able to separate out the key core, halo and strahl populations of electrons, and derive their moments (density, temperature, bulk velocity, heat flux).

SWA/EAS consists of two top-hat electrostatic analyser heads with an aperture deflection system (ADS) and a novel variable geometric factor system (VGFS). Orthogonal mounting of the 2 sensors in the spacecraft shadow at the end of the boom and the ± 45° aperture deflection provides an almost 4π steradian field-of-view required (less only that blocked by the spacecraft and its appendages) to fully measure the electron velocity distribution functions and thereby provide moments (density, temperature, velocity, pressure tensor, heat flux) and/or full electron pitch angle distributions at all times.

The sensor field of view is illustrated below:

Key challenges for EAS: These include dealing with the radiation environment (150 krad over mission lifetime), the thermal environment (nominal temperature in the spacecraft shadow at the end of the boom is -180 °C, whereas a pointing failure of the spacecraft may result in full Sun exposure at distances as close as 0.28 AU!), large dynamic range of electron fluxes over orbital range, and the impact of the spacecraft potential, photo- and secondary electrons on the measurements made at this novel accomodation location at the end of the boom.

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SWA/PAS - The Proton Alpha Particle Sensor

The SWA/PAS system was built by Institut de Recherche en Astrophysique et Planétologie (IRAP), Toulouse, with technical and hardware contributions from UCL/MSSL and Charles University, Prague.

SWA/PAS measures the velocity distribution of the major ionic species at a time resolution equivalent to the ambient proton cyclotron period and determine their moments (density, temperature, velocity, pressure tensor).

SWA/PAS consists of an electrostatic analyser with an ion steering (IS) system at the aperture.  It is designed to measure the full 3D velocity distribution functions of the major solar wind species, protons and α-particles, in the energy range ≤ 0.2–20 keV/q. 

Key challenges for SWA/PAS: These included the development of a sensor heat shield to deal with the Sun-facing thermal environment, engineering the structure of the sensor to adequately protect against the 150 krad radiation environment over mission lifetime, and to design the sensor to handle the large dynamic range of the expected ion fluxes.

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SWA/HIS - The Heavy ion Sensor

The SWA/HIS system was built by Southwest Research Institute(SwRI), San Antonio, Texas, with technical and hardware contributions from IRAP, Toulouse, the University of Michigan, the University of New Hampshire and NASA/Goddard Space Flight Center.

SWA/HIS consists of a Sun-facing entrance aperture system with ion steering (IS) to divert ions from a range of incoming elevation/azimuth angles into the electrostatic analyser (ESA) module, coupled with a time-of-flight (TOF) telescope with solid state detectors (SSD) for total ion energy measurements. HIS measures five key properties for all ions: mass in the range 2-56 amu/q, charge (q), energy and direction of incidence (θ, φ). 

Key challenges for SWA/HIS: These included development of a sensor heat shield to deal with the Sun-facing thermal environment, engineering the structure of the sensor to adequately support the ultra-thin carbon foils for the TOF telescope during launch and to protect against the 150 krad radiation environment over mission lifetime, and to design the sensor to handle the large dynamic range of the expected ion fluxes.

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SWA/DPU - The Data Processing Unit

The SWA/DPU was built under the leadership of the Institute of Physics of Interplanetary Space (IFSI), Rome, by an inductrial consortium led by Techno System Developments s.r.l., Pozzuoli, Italy.

The SWA sensor suite is integrated and serviced by a common DPU, which provides a single power, telemetry, and control interface to the spacecraft as well as power, switching, commanding, data handling and data compression functions for all of the sensors. The DPU is designed to be fault tolerant and has redundancy on critical sub-systems. The main processing capability is provided by a LEON processor core and numerically intensive processing is performed by a specialist digital signal processor.

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SWA Sensor Characteristics

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