1,721,241 research outputs found
Short-term forecasting of solar energetic ions on board LISA
No full textSolar energetic particles (SEPs) pose a hazard to manned and unmanned space missions. Moreover, in LISA (Laser Interferometer Space Antenna) and its precursor mission LISA Pathfinder (LISA-PF) the free-fall test-masses are charged by galactic and solar energetic particles. This process generates spurious forces on the test masses which appears as significant levels of noise in the experiments. It was shown that relativistic solar electron detection can be used for up-to-one-hour forecasting of incoming energetic ions at 1 AU. Contemporary observations of solar electrons, protons and helium nuclei on board LISA will allow us to forecast and investigate the characteristics of SEPs over small steps in longitude
Bridging machine learning and diagnostics of the ESA LISA space mission with equation discovery via explainable artificial intelligence
No full textThe Laser Interferometer Space Antenna (LISA) of the European Space Agency will be the first interferometer for low-frequency (10-4–10-1 Hz) gravitational wave detection in space. LISA will detect spurious accelerations of the test masses, the end mirrors of the interferometer, of the order of femto-g. Amongst spurious signals, Coulomb forces due to stray electric fields coupling with charge deposited on the test masses by galactic and solar particles and the noise associated to the charging process must be monitored during the mission lifetime. Precious clues on spurious forces acting on the test masses have been studied with the LISA Pathfinder mission, meant for the testing of the instrumentation that will be placed on board LISA, in 2016–2017. In this work we present the design and implementation of a workflow leading to equation discovery for the relationship between solar wind speed, galactic cosmic-ray variations and interplanetary magnetic field intensity observations for the diagnostics of LISA. The workflow exploits explainable artificial intelligence tools to build a bridge between the opaque predictions obtained with machine learning (ML) models and data analysis performed by humans with space mission observations. The core step of the workflow is the implementation, tuning and optimisation of an opaque ML regressor explicitly designed for the future LISA mission, based on input observations of the galactic cosmic-ray flux and of the interplanetary magnetic field intensity. The regressor is aimed at reconstructing the solar wind speed, a parameter of fundamental importance, but not available, for the mission environment monitoring. The workflow ends with the application of explainable clustering techniques to the opaque model in order to (i) obtain human-interpretable outputs instead of opaque ones without any noticeable loss in the predictive performance and (ii) discover an equation describing the quantitative relationship between the involved variables, currently missing in the literature. The correlation amongst the transit of interplanetary structures, galactic cosmic-ray variations and LISA test-mass charging is illustrated here
Grad-Shafranov reconstruction of a magnetic cloud: Effects of the magnetic-field topology on the galactic cosmic-ray intensity
Full text linkThe passage of the interplanetary counterpart of a coronal mass ejection was observed at L1 between 2016 August 2 at 14:00 UT and August 3 at 03:00 UT. The transit of shock, sheath and magnetic cloud (MC) regions are identified and the MC configuration is studied through the Grad-Shafranov reconstruction technique. A classical Forbush decrease (FD) in the galactic cosmic ray (GCR) intensity was observed by the particle detector (PD) aboard the European Space Agency LISA Pathfinder (LPF) mission on 2016 August 2. The PD allowed to monitor the GCR intensity at energies above 70 MeV n−1 with a statistical uncertainty of 1% on one-hour binned data. The observed fractional decrease of the GCR intensity around the dip of the event is investigated through a full-orbit particle propagation in the MC and related to the reconstructed magnetic field topology
The role of interplanetary electrons at the time of the LISA missions
No full textLISA (Laser Interferometer Space Antenna) is the first space interferometer devoted to the detection of gravitational waves in the frequency range 10^(-4) to 10^(-1) Hz. Free-fall gold-platinum test masses constitute the mirrors of the interferometer. Solar and galactic particles charging the test masses induce spurious forces that might mimic genuine gravitational wave signals. Proton and helium nuclei are more than 98% in composition of both galactic and energetic solar particles. The charging due to these ions was carefully studied. However, highly penetrating interplanetary electrons play a role similar to helium nuclei at solar minimum and balance more than half of the net charge induced by galactic protons at solar maximum. In this paper, we report the study of LISA test-mass charging and radiation monitor countrate due to interplanetary electrons under different conditions of solar modulation and global solar magnetic field (GSMF) polarity. The radiation monitors designed for the LISA precursor mission, LISA Pathfinder (LISA-PF), were considered. Solar electrons do not produce any detectable signal in the radiation monitors. No relevant increase in the test-mass charging is generated by solar electrons with respect to protons as well. However, we point out that the detection of electrons of solar origin on-board LISA will allow us to short-forecast incoming, intense solar ion fluxes. An optimized environmental survey would lead us to further improve the test-mass discharging process, reduce the overall noise and, possibly, extend the mission lifetime. Important contributions to solar physics and space-weather investigations will be provided as well
Parameterization of galactic cosmic-ray fluxes during opposite polarity solar cycles for future space missions
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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