ALBERT

Description: The Solar Orbiter mission seeks to make connections between the physical processes occurring at the Sun or in the solar corona and the nature of the solar wind created by those processes which is subsequently observed at the spacecraft. The mission also targets physical processes occurring in the solar wind itself during its journey from its source to the spacecraft. To meet the specific mission science goals, Solar Orbiter will be equipped with both remote-sensing and in-situ instruments which will make unprecedented measurements of the solar atmosphere and the inner heliosphere. A crucial set of measurements will be provided by the Solar Wind Analyser (SWA) suite of instruments. This suite consists of an Electron Analyser System (SWA-EAS), a Proton and Alpha particle Sensor (SWA-PAS), and a Heavy Ion Sensor (SWA-HIS) which are jointly served by a central control and data processing unit (SWA-DPU). Together these sensors will measure and categorise the vast majority of thermal and suprathermal ions and electrons in the solar wind and determine the abundances and charge states of the heavy ion populations. The three sensors in the SWA suite are each based on the top hat electrostatic analyser concept, which has been deployed on numerous space plasma missions. The SWA-EAS uses two such heads, each of which have 360° azimuth acceptance angles and ±45° aperture deflection plates. Together these two sensors, which are mounted on the end of the boom, will cover a full sky field-of-view (FoV) (except for blockages by the spacecraft and its appendages) and measure the full 3D velocity distribution function (VDF) of solar wind electrons in the energy range of a few eV to ∼5 keV. The SWA-PAS instrument also uses an electrostatic analyser with a more confined FoV (−24° to +42° × ±22.5° around the expected solar wind arrival direction), which nevertheless is capable of measuring the full 3D VDF of the protons and alpha particles arriving at the instrument in the energy range from 200 eV/q to 20 keV/e. Finally, SWA-HIS measures the composition and 3D VDFs of heavy ions in the bulk solar wind as well as those of the major constituents in the suprathermal energy range and those of pick-up ions. The sensor resolves the full 3D VDFs of the prominent heavy ions at a resolution of 5 min in normal mode and 30 s in burst mode. Additionally, SWA-HIS measures 3D VDFs of alpha particles at a 4 s resolution in burst mode. Measurements are over a FoV of −33° to +66° × ±20° around the expected solar wind arrival direction and at energies up to 80 keV/e. The mass resolution (m/Δm) is 〉 5. This paper describes how the three SWA scientific sensors, as delivered to the spacecraft, meet or exceed the performance requirements originally set out to achieve the mission’s science goals. We describe the motivation and specific requirements for each of the three sensors within the SWA suite, their expected science results, their main characteristics, and their operation through the central SWA-DPU. We describe the combined data products that we expect to return from the suite and provide to the Solar Orbiter Archive for use in scientific analyses by members of the wider solar and heliospheric communities. These unique data products will help reveal the nature of the solar wind as a function of both heliocentric distance and solar latitude. Indeed, SWA-HIS measurements of solar wind composition will be the first such measurements made in the inner heliosphere. The SWA data are crucial to efforts to link the in situ measurements of the solar wind made at the spacecraft with remote observations of candidate source regions. This is a novel aspect of the mission which will lead to significant advances in our understanding of the mechanisms accelerating and heating the solar wind, driving eruptions and other transient phenomena on the Sun, and controlling the injection, acceleration, and transport of the energetic particles in the heliosphere.

Description: Langmuir DOI: 10.1021/la205105m

Description: Materials science experiments under microgravity increasingly rely on advanced optical systems to determine the physical properties of the samples under investigation. This includes video systems with high spatial and temporal resolution. The acquisition, handling, storage and transmission to ground of the resulting video data are very challenging. Since the available downlink data rate is limited, the capability to compress the video data significantly without compromising the data quality is essential. We report on the development of a Digital Video System (DVS) for EML (Electro Magnetic Levitator) which provides real-time video acquisition, high compression using advanced Wavelet algorithms, storage and transmission of a continuous flow of video with different characteristics in terms of image dimensions and frame rates. The DVS is able to operate with the latest generation of high-performance cameras acquiring high resolution video images up to 4Mpixels@60 fps or high frame rate video images up to about 1000 fps@512x512pixels.

Description: Context. The determination of solar wind H I outflow velocity is fundamental to shedding light on the mechanisms of wind acceleration occurring in the corona. Moreover, it has implications in various astrophysical contexts, such as in the heliosphere and in cometary and planetary atmospheres. Aims. We aim to study the effects of the chromospheric Lyα line profile shape on the determination of the outflow speed of coronal H I atoms via the Doppler dimming technique. This is of particular interest in view of the upcoming measurements of the Metis coronagraph aboard the Solar Orbiter mission. Methods. The Doppler dimming technique exploits the decrease of coronal Lyα radiation in regions where H I atoms flow out in the solar wind. Starting from UV observations of the coronal Lyα line from the Solar and Heliospheric Observatory (SOHO), aboard the UltraViolet Coronagraph Spectrometer, and simultaneous measurements of coronal electron densities from pB coronagraphic observations, we explored the effect of the profile of the pumping chromospheric Lyα line. We used measurements from the Solar UV Measurement of Emitted Radiation, aboard SOHO, the Ultraviolet Spectrometer and Polarimeter, aboard the Solar Maximum Mission, and the Laboratoire de Physique Stellaire et Planetaire, aboard the Eight Orbiting Solar Observatory, both from representative on-disc regions, such as coronal holes and quiet Sun and active regions, and as a function of time during the solar activity cycle. In particular, we considered the effect of four chromospheric line parameters: line width, reversal depth, asymmetry, and distance of the peaks. Results. We find that the range of variability of the four line parameters is of about 50% for the width, 69% for the reversal depth, and 35% and 50% for the asymmetry and distance of the peaks, respectively. We then find that the variability of the pumping Lyα profile affects the estimates of the coronal H I velocity by about 9−12%. This uncertainty is smaller than the uncertainties due to variations of other physical quantities, such as electron density, electron temperature, H I temperature, and integrated chromospheric Lyα radiance. Conclusions. Our work suggests that the observed variations in the chromospheric Lyα line profile parameters along a cycle and in specific regions negligibly affect the determination of the solar wind speed of H I atoms. Due to this weak dependence, a unique shape of the Lyα profile over the solar disc that is constant in time can be adopted to obtain the values of the solar wind H I outflow velocity. Moreover, the use of an empirical analytical chromospheric profile of the Lyα, assumed uniform over the solar disc and constant in time, is justifiable in order to obtain a good estimate of the coronal wind H I outflow velocity using coronagraphic UV images.