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The Influence of Spacecraft Charging on Low‐Energy Ion Measurements Made by RPC‐ICA on Rosetta
Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics, Kiruna, Sweden.ORCID iD: 0000-0003-0673-2264
Swedish Institute of Space Physics, Kiruna, Sweden.
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2020 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 125, no 1, article id e2019JA027478Article in journal (Refereed) Published
Abstract [en]

Spacecraft charging is problematic for low‐energy plasma measurements. The charged particles are attracted to or repelled from the charged spacecraft, affecting both the energy and direction of travel of the particles. The Ion Composition Analyzer (RPC‐ICA) on board the Rosetta spacecraft is suffering from this effect. RPC‐ICA was measuring positive ions in the vicinity of comet 67P/Churyumov‐Gerasimenko, covering an energy range of a few eV/q to 40 keV/q. The low‐energy part of the data is, however, heavily distorted by the negatively charged spacecraft. In this study we use the Spacecraft Plasma Interaction Software to model the influence of the spacecraft potential on the ion trajectories and the corresponding distortion of the field of view (FOV) of the instrument. The results show that the measurements are not significantly distorted when the ion energy corresponds to at least twice the spacecraft potential. Below this energy the FOV is often heavily distorted, but the distortion differs between different viewing directions. Generally, ions entering the instrument close to the aperture plane are less affected than those entering with extreme elevation angles.

Place, publisher, year, edition, pages
John Wiley & Sons, 2020. Vol. 125, no 1, article id e2019JA027478
Keywords [en]
Spacecraft charging, low-energy ions, comet, SPIS, Rosetta
National Category
Fusion, Plasma and Space Physics
Research subject
Space and Plasma Physics
Identifiers
URN: urn:nbn:se:umu:diva-168029DOI: 10.1029/2019JA027478OAI: oai:DiVA.org:umu-168029DiVA, id: diva2:1392845
Available from: 2020-02-13 Created: 2020-02-13 Last updated: 2020-02-14Bibliographically approved
In thesis
1. The effect of spacecraft charging on low-energy ion measurements around comet 67P/Churyumov-Gerasimenko
Open this publication in new window or tab >>The effect of spacecraft charging on low-energy ion measurements around comet 67P/Churyumov-Gerasimenko
2020 (English)Licentiate thesis, comprehensive summary (Other academic)
Alternative title[sv]
Farkostpotentialens effekt på mätningar av lågenergi-joner runt komet 67P/Tjurjumov-Gerasimenko
Abstract [en]

A spacecraft in space interacts with the surrounding environment and aqcuires an electrostatic potential. Charged particles are constantly bombarding the surface of the spacecraft, and at the same time solar EUV radiation induces photoemission, causing electrons to be emitted from the surface. The result is a transfer of charge between the environment and the spacecraft surface, and the surface charges to a positive or negative potential. The charged surface can cause interferences with scientific instruments on board. In this thesis, we investigate how spacecraft charging affects low-energy ion measurements. The Rosetta spacecraft visited comet 67P/Churyumov-Gerasimenko between the years 2014-2016. On board the spacecraft, the Ion Composition Analyzer (ICA) was measuring positive ions in the environment around the comet with the aim of investigating the interaction between cometary particles and the solar wind. Important for this interaction is ions with a low energy. Measuring these ions is, however, difficult due to the charged spacecraft surface. Rosetta was commonly charged to a negative potential, and consequently the measured positive ions were accelerated toward the surface before detection, affecting both their energy and travel direction. In this thesis, we study how the changed travel directions affected the effective field of view (FOV) of the instrument. We use the Spacecraft Plasma Interaction Software (SPIS) to simulate the spacecraft plasma interactions and the ion trajectories around the spacecraft. The results show that the FOV of ICA is severely distorted at low ion energies, but the distortion varies between different viewing directions of the instrument and is dependent on the properties of the surrounding plasma.

Abstract [sv]

En rymdfarkost i rymden växelverkar med omgivningen och laddas upp till en elektrostatisk potential. Laddade partiklar från omgivningen kolliderar ständigt med farkostens yta, och samtidigt inducerar EUV-strålning från solen fotoemission, vilket gör att fotoelektroner emitteras från ytan. Laddning överförs då mellan omgivningen och ytan på farkosten, och ytan laddas upp till en positiv eller negativ potential. Den laddade ytan påverkar mätningar som görs av vetenskapliga instrument ombord på farkosten. I denna avhandling undersöker vi hur farkostpotentialen har påverkat mätningar av lågenergi-joner.Rymdfarkosten Rosetta studerade komet 67P/Tjurjumov-Gera-simenko mellan åren 2014-2016. Jonmasspektrometern ICA mätte positiva joner i omgivningen runt kometen, med syfte att studera hur kometjoner växelverkar med solvinden. Joner med låg energi är viktiga i denna interaktion. På grund av den uppladdade farkosten är det dock svårt att mäta dessa joner. Rosetta var oftast uppladdad till en negativ potential under missionen, och de positiva jonerna som ICA observerade accelererades därför mot farkosten innan de detekterades, vilket ledde till att både deras energi och färdriktning förändrades. I denna avhandling studerar vi hur ICAs effektiva synfält har förändrats på grund av de förändrade partikelbanorna. Vi använder programvaran SPIS (Spacecraft Plasma Interaction Software) för att simulera växelverkan mellan farkosten och omgivningen och upp-laddningen av ytan. Vi studerar sen hur jonerna rör sig genom den resulterande potentialfördelningen i omgivningen. Resultaten visar att ICAs synfält är förvrängt vid låga jonenergier, men effekten varierar mellan olika tittriktningar och påverkas av egenskaperna hos det omgivande plasmat.

Place, publisher, year, edition, pages
Umeå: Department of physics, Umeå University, 2020. p. 48
Series
IRF Scientific Report, ISSN 0284-1703 ; 310
Keywords
Spacecraft charging, low-energy ions, space physics, plasma physics, comet, Rosetta, SPIS
National Category
Fusion, Plasma and Space Physics
Research subject
Space and Plasma Physics
Identifiers
urn:nbn:se:umu:diva-168034 (URN)9789178551910 (ISBN)9789178551927 (ISBN)
Presentation
2020-02-25, Aulan, Institutet för rymdfysik, Rymdcampus 1, Kiruna, 13:00 (English)
Supervisors
Available from: 2020-02-14 Created: 2020-02-14 Last updated: 2020-02-18Bibliographically approved

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