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  • 401.
    Strizic, Luka
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Crowdsourcing GNSS Jamming Detection and Localization2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Global Navigation Satellite Systems (GNSS) have found wide adoption in various applications, be they military, civilian or commercial. The susceptibility of GNSS to radio-frequency interference can, thus, be very disruptive, even for emergency services, therefore threatening people's lives. An early prototype of a system providing relatively cheap widescale GNSS jamming detection, called J911, is explored in this thesis.

    J911 is smartphone-based crowdsourcing of GNSS observations, most interesting of which are carrier-to-noise-density ratio () and Automatic Gain Control (AGC) voltage. To implement the prototype, an Android application to provide the measurements, a backend to parse and store the measurements, and a frontend to visualize the measurements were developed. In real-world use, the thesis argues, the J911 system would best be implemented over existing Enhanced 9-1-1 (E911) infrastructure, becoming a standardized part of the Public Switched Telephone Network (PSTN).

    The Android application, running on a smartphone, would periodically construct messages to be sent to the backend over an Internet connection. The messages would include: current location from all location providers available in Android OS, observed satellites from all supported constellations, the satellites' , and a timestamp. Once a message is received on the backend, the data would be extracted and stored in a database. The frontend would query the database and produce a map with the collected datapoints overlaid on top of it, whose color indicates received signal strength at that point. When a jammer gets close enough to a few smartphones, they will all be jammed, which is easily observed on the map. On top of that, if enough samples are gathered, a Power Difference of Arrival localization algorithm can be used to localize the jammer.

    The smartphones that the system was planned to be tested with did not support AGC level readings, therefore in order to obtain AGC levels over time, a few SiGe GN3S Samplers, which are radio-frequency frontends, were used. In eastern Idaho, United States, over three nights in July 2017, an exercise, named 2017 DHS JamX, was performed with the help of the US Department of Homeland Security. Sadly, the approval for the publication of the test results did not come in time to be included in this thesis.

  • 402.
    Struckmeier, Oliver
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Aalto University.
    Generating Explanations of Robot Policies in Continuous State Spaces2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Transparency in HRI describes the method of making the current state of a robotor intelligent agent understandable to a human user. Applying transparencymechanisms to robots improves the quality of interaction as well as the userexperience. Explanations are an effective way to make a robot’s decision making transparent. We introduce a framework that uses natural language labels attached to a region inthe continuous state space of the robot to automatically generate local explanationsof a robot’s policy. We conducted a pilot study and investigated how the generated explanations helpedusers to understand and reproduce a robot policy in a debugging scenario.

  • 403.
    Svensson, Martin
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Electron heating in collisionless shocks observed by the MMS spacecraft2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Shock waves are ubiquitous in space and astrophysics. Shocks transform directed particle flow energy into thermal energy. As the major part of space is a collisionless medium, shocks in space physics arises through wave-particle interactions with the magnetic field as the main contributor.The heating processes are scale dependent. The large scale processes governs the ion heating and is well described by magnetohydrodynamics. The small scale processes governs the electron heating lies within the field of kinetic plasma theory and is still today remained disputed. A step towards the answer for the small scale heating would be to measure the scale, in order to relate it to a known instability or other small scale processes.The multi-spacecraft NASA MMS spacecraft carries several high resolute particle and field instruments enabling almost instantaneous 3D particle measurements and accurate measurements of the magnetic field. Also the separation between the four MMS spacecraft is as small as < 8km for a certain mission phase. This allows for new approaches when determining the scale which for shocks has not been possible before when using data from previous multi-spacecraft missions with spacecraft separation much larger. The velocity of the shock is large compared to the spacecraft,thus the shock width cannot be directly measured by each spacecraft. Either a constant velocity has to be estimated or we could use gradients of a certain parameter between the spacecraft as the shock flows over them. The usage of gradients is only possible with MMS as all the spacecraft could for MMS be within the shock simultaneously. The change for a parameter within the shockis assumed to be linear between the spacecraft and measurements. It is also assumed that the gradient of the parameter maximizes in the shock normal direction. Using these assumptions two methods have been developed. They have the same working principles but are using two or four spacecraft for linear estimation at each measurement point. From the gradient and parametric data the shock ramp width could then be found. The parameter used in this thesis is the electron temperature. The methods using one, two and four spacecraft were tested using electron temperature data from different shock crossings. Two problems with the gradient methods were found from the results, giving false data for certain time spans. To avoid these problems, the scale of the electron temperature gradient was determined for roughly half the shock ramp. It was found using the two and four spacecraft methods that an assumption of constant velocity for the shock speed is an uncertain assumption. The shock speed varies over short time scales and in the shock crossings analysed the constant velocity estimations were generally overestimated. From the two and four spacecraft methods roughly half of the temperature rise in the shock ramp occurred over 10.8km or 12.4 lpe. This is almost a factor of two greater than previous scale estimates using Cluster data and a multi-spacecraft timing method for shock speed estimation.From the results it is concluded that the methods when using gradients between spacecraft has some restrictions. They can only be used for MMS data, requires quasi-perpendicular high Mach number and will give false results if the temperature is disturbed by interacting hot plasma clouds. However, even though we have these limitations for the tested gradient methods, they were found better and more reliable compared to previous methods for shock scaling.

  • 404.
    Sánchez-García, Laura
    et al.
    Centro de Astrobiología (CSIC-INTA), Madrid.
    Aeppli, Christoph
    Bigelow Laboratory for Ocean Sciences, Maine.
    Parro, Victor
    Centro de Astrobiología (CSIC-INTA), Madrid.
    Fernández-Remolar, David
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    García-Villadangos, Miriam
    Centro de Astrobiología (CSIC-INTA), Madrid.
    Chong-Diaz, Guillermo
    Department of Geological Sciences, Universidad Católica del Norte, Antofagasta.
    Blanco, Yolanda
    Centro de Astrobiología (CSIC-INTA), Madrid.
    Carrizo, Daniel
    Centro de Astrobiología (CSIC-INTA), Madrid.
    Molecular biomarkers in the subsurface of the Salar Grande (Atacama, Chile) evaporitic deposits2018Inngår i: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 140, nr 1, s. 31-52Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Late Miocene–Pliocene aged hyperarid evaporitic system of Salar Grande is a unique, halite-rich sedimentary basin in the Cordillera de la Costa of the Central Andes (Chile) whose bio-sedimentary record is poorly understood. The persistence of hyperacidity over millions of years, the hypersalinity, and the intense UV radiation make it a terrestrial analogue to assess the potential presence of organic matter in the halite deposits found on Mars. We investigated the occurrence and distribution of biomolecules along a 100-m depth drill down to the ~ 9 Ma old detrital deposits topped by La Soledad Formation (ESF). We have identified two well-defined mineralogical and geochemical units by X-ray diffractometry (XRD) and ion chromatography: a nearly pure halite down to 40 m, and a detrital one down to 100 m depth. One-dimensional GC–MS and two-dimensional GC × GC-TOF–MS gas chromatography–mass spectrometry techniques allowed us to detect a variety of lipidic compounds (n-alkanes, n-alkanols, isoprenoids, steroids, and hopanoids), and a relative abundance of functionalized hydrocarbons (n-fatty acids or n-aldehydes), mostly in the upper halite. We also detected biopolymers and microbial markers by fluorescence sandwich-microarray immunoassays. A dominant prokaryotic origin was associated with halophile bacteria and archaea, with minor contributions of lichens, macrophytes, or higher plants. The lipidic record was also imprinted by oxic (high pristane over phytane ratios) and saline (squalane, and mono-methyl n-alkanes) signatures. The vertical abundance and distribution of biomarkers in the Salar Grande was explained by a generalized effect of xeropreservation, combined with salt encapsulation in the upper halite deposits, or with protective organics-mineral interactions in the deeper detrital unit. The results contribute to the interpretation of terrestrial bio-sedimentary records of halite deposits and their association to environmental conditions. The high potential for preservation of biosignatures at Salar Grande suggests that similar evaporitic deposits in Mars should be priority targets for searching for signs of life.

  • 405.
    Takada, A.
    et al.
    Department of Physics, Cosmic-Ray Group, Kyoto University.
    Tanimori, T.
    Department of Physics, Cosmic-Ray Group, Kyoto University.
    Kubo, H.
    Department of Physics, Cosmic-Ray Group, Kyoto University.
    Miuchi, K.
    Department of Physics, Cosmic-Ray Group, Kyoto University.
    Parker, J.D.
    Department of Physics, Cosmic-Ray Group, Kyoto University.
    Kishimoto, Y.
    Department of Physics, Cosmic-Ray Group, Kyoto University.
    Mizumoto, T.
    Department of Physics, Cosmic-Ray Group, Kyoto University.
    Ueno, K.
    Department of Physics, Cosmic-Ray Group, Kyoto University.
    Kurosawa, S.
    Department of Physics, Cosmic-Ray Group, Kyoto University.
    Iwaki, S.
    Department of Physics, Cosmic-Ray Group, Kyoto University.
    Sawano, T.
    Department of Physics, Cosmic-Ray Group, Kyoto University.
    Taniue, K.
    Department of Physics, Cosmic-Ray Group, Kyoto University.
    Nakamura, K.
    Department of Physics, Cosmic-Ray Group, Kyoto University.
    Higashi, N.
    Department of Physics, Cosmic-Ray Group, Kyoto University.
    Matsuoka, Y.
    Department of Physics, Cosmic-Ray Group, Kyoto University.
    Komura, S.
    Department of Physics, Cosmic-Ray Group, Kyoto University.
    Sato, Y.
    Department of Physics, Cosmic-Ray Group, Kyoto University.
    Arvelius, Sachiko
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Turunen, E.
    EISCAT Scientific Association, Kiruna.
    SMILE-II: Observation of celestial and atmosphereic MeV gamma rays using a balloon-borne wide fields of view Electron-Tracking Compton Camera2011Inngår i: Proceedings of the 20th ESA Symposium on European Rocket and Balloon Programmes and Related Research: 22-26 May 2011, Hyère, France, Noordwijk: European Space Agency, ESA , 2011, s. 567-571Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We have developed an Electron Tracking Compton Camera (ETCC) as an MeV gamma-ray telescope in the next generation. The ETCC consists of a gaseous time projection chamber and a position sensitive scintillation camera. We had launched a small size ETCC loaded on a balloon in 2006, and it was successful to obtain the fluxes of diffuse cosmic and atmospheric gamma rays in the energy range between 125 keV and 1.25 MeV. As the next flight (SMILE-II), we planned a long duration flight using a circumpolar balloon launched from Kiruna, and it will observe the celestial bright sources and the atmospheric gamma-ray burst due to the relativistic electron from the radiation belt. In this paper, we report the concepts of our detector and the performance of the SMILE-Il prototype.

  • 406.
    Takagi, M.
    et al.
    University of Tokyo, Deptartment of Earth & Planetary Science.
    Suzuki, K.
    Tokyo Gakugei University, Department of Astronomy & Earth Science.
    Sagawa, H.
    Max-Planck-Institut für Solar System Research.
    Baron, P.
    National Institute for Information & Communication Technology, Applied Electromagnet Research.
    Mendrok, Jana
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Kasai, Y.
    National Institute for Information & Communication Technology, Applied Electromagnet Research.
    Matsuda, Y.
    Tokyo Gakugei University, Department of Astronomy & Earth Science.
    Influence of CO2 line profiles on radiative and radiative-convective equilibrium states of the Venus lower atmosphere2010Inngår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 115, nr E06Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Influence of CO2 line profiles on vertical temperature distributions in the radiative and radiative-convective equilibria is examined in the Venus atmosphere. The CO2 opacity obtained by the Voigt (Lorentz) profile without the line cutoff is shown to be excessive since this opacity gives surface temperatures of about 860-1020 K in the radiative-convective equilibrium. On the other hand, the opacity obtained by the extremely sub-Lorentzian profiles of Pollack et al. (1993) and Tonkov et al. (1996) are underestimated; the surface temperature obtained with this opacity remains 600 K even in the radiative equilibrium. In this case, convection does not take place below the cloud layer because of the cloud opacity. It is also shown that Fukabori et al.' s (1986) and Meadows and Crisp's (1996) profiles, both of which have intermediate absorption coefficients, give temperature distributions close to the observed one in the radiative-convective equilibrium. In these cases, the convection layer extends from the surface to 30-50 km altitudes. Then, the temperature distribution below the cloud layer is determined by a dry adiabatic lapse rate and the temperature near the cloud bottom. The surface temperature in the radiative-convective equilibrium is strongly affected by the temperature near the cloud bottom in this situation. The detailed structure of the H2SO4 cloud must be taken into account to construct a realistic radiative transfer model.

  • 407.
    Tariq, Usama
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Robotic Grasping of Large Objects for Collaborative Manipulation2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    In near future, robots are envisioned to work alongside humans in professional anddomestic environments without significant restructuring of workspace. Roboticsystems in such setups must be adept at observation, analysis and rational de-cision making. To coexist in an environment, humans and robots will need tointeract and cooperate for multiple tasks. A fundamental such task is the manip-ulation of large objects in work environments which requires cooperation betweenmultiple manipulating agents for load sharing. Collaborative manipulation hasbeen studied in the literature with the focus on multi-agent planning and controlstrategies. However, for a collaborative manipulation task, grasp planning alsoplays a pivotal role in cooperation and task completion.In this work, a novel approach is proposed for collaborative grasping and manipu-lation of large unknown objects. The manipulation task was defined as a sequenceof poses and expected external wrench acting on the target object. In a two-agentmanipulation task, the proposed approach selects a grasp for the second agentafter observing the grasp location of the first agent. The solution is computed ina way that it minimizes the grasp wrenches by load sharing between both agents.To verify the proposed methodology, an online system for human-robot manipu-lation of unknown objects was developed. The system utilized depth informationfrom a fixed Kinect sensor for perception and decision making for a human-robotcollaborative lift-up. Experiments with multiple objects substantiated that theproposed method results in an optimal load sharing despite limited informationand partial observability.

  • 408.
    Tate, C.G.
    et al.
    Department of Physics & Astronomy, University of Tennessee, Knoxville.
    Moersch, J.
    Department of Physics & Astronomy, University of Tennessee, Knoxville, Department of Earth & Planetary Sciences, University of Tennessee, Knoxville.
    Jun, L.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
    Hardgrove, C.
    Department of Earth & Planetary Sciences, University of Tennessee, Knoxville.
    Mischna, M.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
    Litvak, M.
    Space Research Institute, RAS, Moscow.
    Varenikov, A.
    Space Research Institute, RAS, Moscow.
    Mitrofanov, I.
    Space Research Institute, RAS, Moscow.
    Boynton, W.V.
    University of Arizona.
    Deflores, L.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
    Drake, D.
    TechSource, Inc, Los Alamos.
    Fedosov, F.
    Space Research Institute, RAS, Moscow.
    Golovin, D.
    Space Research Institute, RAS, Moscow.
    Harschman, K.
    University of Arizona.
    Kozyrev, A.
    Space Research Institute, RAS, Moscow.
    Lisov, D.
    Space Research Institute, RAS, Moscow.
    Malakhov, A.
    Space Research Institute, RAS, Moscow.
    Milliken, R.E.
    Brown university.
    Mokrousov, M.
    Space Research Institute, RAS, Moscow.
    Nikiforov, S.
    Space Research Institute, RAS, Moscow.
    Sanin, A.B.
    Space Research Institute, RAS, Moscow.
    Starr, R.
    NASA Goddard Space Flight Center.
    Vostrukhin, A.
    Space Research Institute, RAS, Moscow.
    Martin-Torres, Javier
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Instituto Andaluz de Cienccias de la Tierra (CSIC-UGR), Grenada.
    Zorzano, María-Paz
    Centro de Astrobiologia, INTA-CSIC, Madrid.
    Thermal conductivity of the near-surface Martian regolith derived from variations in MSL passive neutron counts and ground temperature measurements2015Konferansepaper (Fagfellevurdert)
  • 409.
    Terkovic, Richard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Dynamic modelling of a landing gear2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Companies in the aerospace industry would benefit from a faster, more flexible wayto investigate physical system issues in the vehicles/aircraft during their lifetime.Current software and hardware provides us with the option of making a systemmodel to simulate investigated problems, saving money and time.This work focuses on a nose landing gear of the Airbus’ fighter jet - EurofighterTyphoon. The landing gear itself is a very complex system designed for highperformance rather than robust usage; it requires a lot of maintenance and testingduring its lifetime. A practical investigation tool is much needed.The primary objective of this work is developing of a simulation model for thenose landing gear in Matlab, Simulink using Simscape library. The model spreadsmainly across two domains: the hydraulic and the multibody domain.The resulting model can simulate extension and retraction behaviour of the realEurofighter nose landing gear under different in-flight conditions. Friction in thehydraulic actuator was derived from the model.Connecting the known parameters of the landing gear subsystems and adjustingthe model to mimic real system behaviour, it can be used to extract the derived parameters,which were previously unknown. The model solves the time-consuminginvestigations and is much more flexible than physical test benches. Finally, it canbe used for future development and planning by simple parameter adjustment.

  • 410.
    Thapliyal, Pradeep K.
    et al.
    Atmospheric and Oceanic Sciences Group, Space Applications Centre, Indian Space Research Organisation, Ahmedabad.
    Shukla, Munn V.
    Atmospheric and Oceanic Sciences Group, Space Applications Centre, Indian Space Research Organisation, Ahmedabad.
    Shah, Shivani
    Atmospheric and Oceanic Sciences Group, Space Applications Centre, Indian Space Research Organisation, Ahmedabad.
    Joshi, P.C.
    Atmospheric and Oceanic Sciences Group, Space Applications Centre, Indian Space Research Organisation, Ahmedabad.
    Pal, P.K.
    Atmospheric and Oceanic Sciences Group, Space Applications Centre, Indian Space Research Organisation, Ahmedabad.
    Kottayil, Ajil
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    An algorithm for the estimation of upper tropospheric humidity from Kalpana observations: Methodology and validation2011Inngår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, nr 1Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study presents a methodology for estimating the upper tropospheric humidity (UTH) for a layer between 500 and 200 hPa from observations in the water vapor channel (5.6–7.2 μm) of the Indian geostationary satellite, Kalpana. Radiative transfer simulations for different UTH conditions have been used to develop the relationship between water vapor channel radiances and UTH. A new technique has been described to include the normalized reference pressure in the algorithm, to account for latitudinal variation of temperature that is derived from a diverse radiosonde profiles data set and is a polynomial function of the latitude for different months. This has an advantage that the forecast or analysis profiles from the operational numerical weather prediction model are not required to compute the normalized reference pressure. The operationally retrieved UTH products have been extensively compared and validated for the period of 1 March to 1 May 2009, using Meteosat-7 UTH products over the Indian Ocean and the UTH computed from the radiosonde profiles. The results suggest that UTH estimates from Kalpana match very well with the Meteosat-7 UTH products having RMS difference of ∼6%. Validation with the UTH computed from the radiosonde observed relative humidity shows that the RMS error of Kalpana UTH is 9.6% and the mean bias is −3.0%. Similar validation of Meteosat-7 UTH with the same set of radiosonde derived UTH shows an RMS error of 13.3% and the bias of −6.5%, which is higher in comparison to the Kalpana UTH.

  • 411.
    Tiainen, Arttu
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Inter-Satellite Link Antennas: Review and The Near Future2017Independent thesis Advanced level (degree of Master (Two Years)), 80 poäng / 120 hpOppgave
    Abstract [en]

    The emerging trend in distributed spacecraft systems of using multiple spacecraft which share functions as opposed to independent spacecraft has given opportunities for missions previously infeasible. Inter-satellite link (ISL) communications provide a direct link within the space segment without need of an intermediate ground segment to relay the data. As the distributed spacecraft systems (DSS) have become less exotic and more complex, the need and demand for inter-satellite antenna systems has increased and the requirements for the antenna systems more diverse and become more demanding. This document is a research of the antennas currently used for ISL, already flown or will be launched in the near future. While the emphasis is strongly in the antennas, the other parts of the ISL communications sub-systems are observed. To limit the scope of the work, optical cross links are not observed in this document. ISL used only for very close proximity, such as several kilometres, are given only limited scope as the main challenges on those do not involve antennas. Furthermore, the major emphasis is given to systems which can be seen as commercially important. This document is divided in five main sections and the conclusions. In the first section the features and the challenges of ISLs are described. In the second section a parametrisation system for antennas is defined and this system is used in following sections to describe the ISL sub-systems and antenna used in them. The third part is a survey of recently flown space missions with ISLs. The fourth section is a survey on the missions which are scheduled to fly in near future and a brief survey of the solutions offered by satellite service providers and manufacturers. Due to the limited technical data available, the fourth section contains far more reverse engineering and assumptions than the survey on legacy missions. The fifth section describes the several families of ISL suitable antennas under development and discusses about several topics which relate to the ISL antenna development. In this part also are defined several example antenna specifications and the applications of those. The study concludes that antennas suitable for inter-satellite links are not inherently different from ground segment communication antennas of the S/C. The major difference is the need for greater coverage, which can be attained by multiple antenna elements, beam steering or antenna pointing. Specific considerations are needed to be taken into account and often the use of ISLs will increase the technical challenges, but it can provide solutions for problems which cannot be solved otherwise.

  • 412.
    Tinetti, Giovanna
    et al.
    Department of Physics & Astronomy, University College London.
    Drossart, Pierre
    Observatoire de Paris.
    Eccleston, Paul
    STFC Rutherford Appleton Laboratory.
    Hartogh, Paul
    Max-Planck-Institut für Sonnensystemforschung.
    Isaak, Kate
    European Space Agency-ESTEC.
    Linder, Martin
    European Space Agency-ESTEC.
    Lovis, Christophe
    Geneva Observatory.
    Micela, Giusi
    INAF: Osservatorio Astronomico di Palermo G.S. Vaiana.
    Ollivier, Marc
    Observatoire de Paris, Institut d’Astrophysique Spatiale.
    Puig, Ludovic
    European Space Agency-ESTEC.
    Ribas, Ignasi
    Institut d’Estudis Espacials de Catalunya (ICE-CSIC).
    Snellen, Ignas
    Leiden University.
    Swinyard, Bruce
    Department of Physics & Astronomy, University College London, STFC Rutherford Appleton Laboratory.
    Allard, France
    Ecole Normale Superieure de Lyon.
    Barstow, Joanna
    Oxford University.
    Cho, James
    Queen Mary University of London.
    Coustenis, Athena
    Observatoire de Paris.
    Cockell, Charles
    Royal Observatory.
    Correia, Alexandre
    Aveiro University.
    Decin, Leen
    University of Leuven.
    Kok, Remco de
    SRON Netherlands Institute for Space Research.
    Deroo, Pieter
    California Institute of Technology, Jet Propulsion Laboratory.
    Encrenaz, Therese
    Observatoire de Paris.
    Forget, Francois
    Campus Jussieu.
    Glasse, Alistair
    Martin-Torres, Javier
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Yurchenko, S. N.
    Department of Physics & Astronomy, University College London.
    The EChO science case2015Inngår i: Experimental astronomy (Print), ISSN 0922-6435, E-ISSN 1572-9508, Vol. 40, nr 2-3, s. 329-391Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The discovery of almost two thousand exoplanets has revealed an unexpectedly diverse planet population. We see gas giants in few-day orbits, whole multi-planet systems within the orbit of Mercury, and new populations of planets with masses between that of the Earth and Neptune—all unknown in the Solar System. Observations to date have shown that our Solar System is certainly not representative of the general population of planets in our Milky Way. The key science questions that urgently need addressing are therefore: What are exoplanets made of? Why are planets as they are? How do planetary systems work and what causes the exceptional diversity observed as compared to the Solar System? The EChO (Exoplanet Characterisation Observatory) space mission was conceived to take up the challenge to explain this diversity in terms of formation, evolution, internal structure and planet and atmospheric composition. This requires in-depth spectroscopic knowledge of the atmospheres of a large and well-defined planet sample for which precise physical, chemical and dynamical information can be obtained. In order to fulfil this ambitious scientific program, EChO was designed as a dedicated survey mission for transit and eclipse spectroscopy capable of observing a large, diverse and well-defined planet sample within its 4-year mission lifetime. The transit and eclipse spectroscopy method, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allows us to measure atmospheric signals from the planet at levels of at least 10−4 relative to the star. This can only be achieved in conjunction with a carefully designed stable payload and satellite platform. It is also necessary to provide broad instantaneous wavelength coverage to detect as many molecular species as possible, to probe the thermal structure of the planetary atmospheres and to correct for the contaminating effects of the stellar photosphere. This requires wavelength coverage of at least 0.55 to 11 μm with a goal of covering from 0.4 to 16 μm. Only modest spectral resolving power is needed, with R ~ 300 for wavelengths less than 5 μm and R ~ 30 for wavelengths greater than this. The transit spectroscopy technique means that no spatial resolution is required. A telescope collecting area of about 1 m2 is sufficiently large to achieve the necessary spectro-photometric precision: for the Phase A study a 1.13 m2 telescope, diffraction limited at 3 μm has been adopted. Placing the satellite at L2 provides a cold and stable thermal environment as well as a large field of regard to allow efficient time-critical observation of targets randomly distributed over the sky. EChO has been conceived to achieve a single goal: exoplanet spectroscopy. The spectral coverage and signal-to-noise to be achieved by EChO, thanks to its high stability and dedicated design, would be a game changer by allowing atmospheric composition to be measured with unparalleled exactness: at least a factor 10 more precise and a factor 10 to 1000 more accurate than current observations. This would enable the detection of molecular abundances three orders of magnitude lower than currently possible and a fourfold increase from the handful of molecules detected to date. Combining these data with estimates of planetary bulk compositions from accurate measurements of their radii and masses would allow degeneracies associated with planetary interior modelling to be broken, giving unique insight into the interior structure and elemental abundances of these alien worlds. EChO would allow scientists to study exoplanets both as a population and as individuals. The mission can target super-Earths, Neptune-like, and Jupiter-like planets, in the very hot to temperate zones (planet temperatures of 300–3000 K) of F to M-type host stars. The EChO core science would be delivered by a three-tier survey. The EChO Chemical Census: This is a broad survey of a few-hundred exoplanets, which allows us to explore the spectroscopic and chemical diversity of the exoplanet population as a whole. The EChO Origin: This is a deep survey of a subsample of tens of exoplanets for which significantly higher signal to noise and spectral resolution spectra can be obtained to explain the origin of the exoplanet diversity (such as formation mechanisms, chemical processes, atmospheric escape). The EChO Rosetta Stones: This is an ultra-high accuracy survey targeting a subsample of select exoplanets. These will be the bright “benchmark” cases for which a large number of measurements would be taken to explore temporal variations, and to obtain two and three dimensional spatial information on the atmospheric conditions through eclipse-mapping techniques. If EChO were launched today, the exoplanets currently observed are sufficient to provide a large and diverse sample. The Chemical Census survey would consist of > 160 exoplanets with a range of planetary sizes, temperatures, orbital parameters and stellar host properties. Additionally, over the next 10 years, several new ground- and space-based transit photometric surveys and missions will come on-line (e.g. NGTS, CHEOPS, TESS, PLATO), which will specifically focus on finding bright, nearby systems. The current rapid rate of discovery would allow the target list to be further optimised in the years prior to EChO’s launch and enable the atmospheric characterisation of hundreds of planets.

  • 413. Tinetti, Giovanna
    et al.
    Martin-Torres, Javier
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Yurchenko, S.N.
    The EChO science case2017Inngår i: EChO - Exoplanet Characterisation Observatory / [ed] Tinetti, Giovanna, Drossart, Pierre, Dordrecht: Springer Netherlands, 2017Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    The discovery of almost two thousand exoplanets has revealed an unexpectedly diverse planet population.We see gas giants in few-day orbits, whole multi-planet systems within the orbit of Mercury, and newpopulations of planets with masses between that of the Earth and Neptune – all unknown in the SolarSystem. Observations to date have shown that our Solar System is certainly not representative of the generalpopulation of planets in our Milky Way. The key science questions that urgently need addressing aretherefore: What are exoplanets made of? Why are planets as they are? How do planetary systems work andwhat causes the exceptional diversity observed as compared to the Solar System? The EChO (ExoplanetCharacterisation Observatory) space mission was conceived to take up the challenge to explain this diversityin terms of formation, evolution, internal structure and planet and atmospheric composition. This requires indepthspectroscopic knowledge of the atmospheres of a large and well-defined planet sample for whichprecise physical, chemical and dynamical information can be obtained.In order to fulfil this ambitious scientific program, EChO was designed as a dedicated survey mission fortransit and eclipse spectroscopy capable of observing a large, diverse and well-defined planet sample withinits four-year mission lifetime. The transit and eclipse spectroscopy method, whereby the signal from the starand planet are differentiated using knowledge of the planetary ephemerides, allows us to measureatmospheric signals from the planet at levels of at least 10-4 relative to the star. This can only be achieved inconjunction with a carefully designed stable payload and satellite platform. It is also necessary to providebroad instantaneous wavelength coverage to detect as many molecular species as possible, to probe thethermal structure of the planetary atmospheres and to correct for the contaminating effects of the stellarphotosphere. This requires wavelength coverage of at least 0.55 to 11 μm with a goal of covering from 0.4to 16 μm. Only modest spectral resolving power is needed, with R~300 for wavelengths less than 5 μm andR~30 for wavelengths greater than this.The transit spectroscopy technique means that no spatial resolution is required. A telescope collecting area ofabout 1 m2 is sufficiently large to achieve the necessary spectro-photometric precision: for the Phase A studya 1.13 m2 telescope, diffraction limited at 3 μm has been adopted. Placing the satellite at L2 provides a coldand stable thermal environment as well as a large field of regard to allow efficient time-critical observationof targets randomly distributed over the sky. EChO has been conceived to achieve a single goal: exoplanetspectroscopy. The spectral coverage and signal-to-noise to be achieved by EChO, thanks to its high stabilityand dedicated design, would be a game changer by allowing atmospheric composition to be measured withunparalleled exactness: at least a factor 10 more precise and a factor 10 to 1000 more accurate than currentobservations. This would enable the detection of molecular abundances three orders of magnitude lower thancurrently possible and a fourfold increase from the handful of molecules detected to date. Combining thesedata with estimates of planetary bulk compositions from accurate measurements of their radii and masseswould allow degeneracies associated with planetary interior modelling to be broken, giving unique insightinto the interior structure and elemental abundances of these alien worlds.EChO would allow scientists to study exoplanets both as a population and as individuals. The mission cantarget super-Earths, Neptune-like, and Jupiter-like planets, in the very hot to temperate zones (planettemperatures of 300 K - 3000 K) of F to M-type host stars. The EChO core science would be delivered by athree-tier survey. The EChO Chemical Census: This is a broad survey of a few-hundred exoplanets, whichallows us to explore the spectroscopic and chemical diversity of the exoplanet population as a whole. TheEChO Origin: This is a deep survey of a subsample of tens of exoplanets for which significantly highersignal to noise and spectral resolution spectra can be obtained to explain the origin of the exoplanet diversity(such as formation mechanisms, chemical processes, atmospheric escape). The EChO Rosetta Stones: Thisis an ultra-high accuracy survey targeting a subsample of select exoplanets. These will be the bright"benchmark" cases for which a large number of measurements would be taken to explore temporalvariations, and to obtain two and three dimensional spatial information on the atmospheric conditionsthrough eclipse-mapping techniques.If EChO were launched today, the exoplanets currently observed are sufficient to provide a large and diversesample. The Chemical Census survey would consist of > 160 exoplanets with a range of planetary sizes,temperatures, orbital parameters and stellar host properties. Additionally, over the next ten years, severalnew ground- and space-based transit photometric surveys and missions will come on-line (e.g. NGTS,CHEOPS, TESS, PLATO), which will specifically focus on finding bright, nearby systems. The current5rapid rate of discovery would allow the target list to be further optimised in the years prior to EChO’s launch and enable the atmospheric characterisation of hundreds of planets.

  • 414.
    Torppa, Johanna
    et al.
    Space Systems Finland.
    Granvik, Mikael
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Department of Physics, University of Helsinki.
    Penttilä, Antti
    Department of Physics, University of Helsinki.
    Reitmaa, Jukka
    Space Systems Finland.
    Tudose, Violeta
    Space Systems Finland.
    Pelttari, Leena
    Space Systems Finland.
    Muinonen, Karri
    Department of Physics, University of Helsinki.
    Bakker, Jorgo
    European Space Astronomy Center.
    Navarro, Vicente
    European Space Astronomy Center.
    O’Mullane, William
    European Space Astronomy Center.
    Added-value interfaces to asteroid photometric and spectroscopic data in the Gaia database2018Inngår i: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 62, nr 2, s. 464-476Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present two added-value interfaces (AVIs) for analyzing photometric and spectroscopic data observed by the Gaia satellite. The Gaia Added-Value Interface for Temporal Analysis (GAVITEA) is used to calculate an estimate for the spin state and shape of an asteroid from its photometric data, and the Gaia Added-Value Interface for Spectral Classification (GAVISC) provides tools to define the taxonomic type and surface absorption coefficient based on spectroscopic asteroid data. Computations are mainly carried out using well-known methods of asteroid data analysis but the AVIs also offer the possibility to test novel methods that are specifically developed for analyzing temporally sparse photometric data, typical for Gaia.

  • 415.
    Ullán, Aurora
    et al.
    Departamento de Teoría de la Señal y Comunicaciones, Escuela Politécnica Superior , Universidad de Alcalá, Madrid.
    Zorzano Mier, Maria-Paz
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Martin-Torres, Javier
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Valentin-Serrano, Patricia
    nstituto Andaluz de Ciencias de la Tierra (CSIC - UGR), Granada.
    Kahanpää, Henrik
    Finnish Meteorological Institute, Helsinki.
    Harri, Ari-Matti
    Finnish Meteorological Institute, Helsinki.
    Gómez-Elvira, Javier
    Centro de Astrobiologí a (CSIC-INTA), Torrejón de Ardoz, Madrid.
    Navarro, Sara
    Centro de Astrobiología (CSIC - INTA), Torrejón de Ardoz, Madrid.
    Analysis of wind-induced dynamic pressure fluctuations during one and a half Martian years at Gale Crater2017Inngår i: Icarus (New York, N.Y. 1962), ISSN 0019-1035, E-ISSN 1090-2643, Vol. 288, s. 78-87Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Rover Environmental Monitoring Station (REMS) instrument on-board the Mars Science Laboratory (MSL) has acquired unprecedented measurements of key environmental variables at the base of Gale Crater. The pressure measured by REMS shows modulations with a very structured pattern of short-time scale (of the order of seconds to several minutes) mild fluctuations (typically up to 0.2 Pa at daytime and 1 Pa at night-time). These dynamic pressure oscillations are consistent with wind, air and ground temperature modulations measured simultaneously by REMS. We detect the signals of a repetitive pattern of upslope/downslope winds, with maximal speeds of about 21 m/s, associated with thermal changes in the air and surface temperatures, that are initiated after sunset and finish with sunrise proving that Gale, a 4.5 km deep impact crater, is an active Aeolian environment. At nighttime topographic slope winds are intense with maximal activity from 17:00 through 23:00 Local Mean Solar Time, and simultaneous changes of surface temperature are detected. During the day, the wind modulations are related to convection of the planetary boundary layer, winds are softer with maximum wind speed of about 14 m/s. The ground temperature is modulated by the forced convection of winds, with amplitudes between 0.2 K and 0.5 K, and the air temperatures fluctuate with amplitudes of about 2 K. The analysis of more than one and a half Martian years indicates the year-to-year repeatability of these environmental phenomena. The wind pattern minimizes at the beginning of the south hemisphere winter (Ls 90) season and maximizes during late spring and early summer (Ls 270). The procedure that we present here is a useful tool to investigate in a semi-quantitative way the winds by: i) filling both seasonal and diurnal gaps where wind measurements do not exist, ii) providing an alternative way for comparisons through different measuring principia and, iii) filling the gap of observation of short time-wind variability, where the REMS wind-sensor is blind

  • 416.
    Vakkada Ramachandran, Abhilash
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Design and Testing of Thermal Chambers for Space Qualification and Planetary Protection2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 417.
    Velikova, Mariya
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Calibration and Validation of Satellite Altimetry Data over the Pertuis Charentais Region in France: An Analysis of Tidal Correction Impact: Master Thesis Report2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 418.
    Vijayan, Ria
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Wheel-terrain contact angle estimation for planetary exploration rovers2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    During space missions, real time tele-operation of a rover is not practical because of significant signal latencies associated with inter planetary distances, making some degree of autonomy in rover control desirable. One of the challenges to achieving autonomy is the determination of terrain traversability. As part of this field, the determination of motion state of a rover on rough terrain via the estimation of wheel-terrain contact angles is proposed.

    This thesis investigates the feasibility of estimating the contact angles from the kinematics of the rover system and measurements from the onboard inertial measurement unit (IMU), joint angle sensors and wheel encoders. This approach does not rely on any knowledge of the terrain geometry or terrain mechanical properties.

    An existing framework of rover velocity and wheel slip estimation for flat terrain has been extended to additionally estimate the wheel-terrain contact angle along with a side slip angle for each individual wheel, for rough terrain drive. A random walk and a damped model are used to describe the evolution of the contact angle and side slip angle over an unknown terrain. A standard strapdown algorithm for the estimation of attitude and velocity from IMU measurements, is modified to incorporate the 3D kinematics of the rover in the implementation of a nonlinear Kalman filter to estimate the motion states. The estimation results from the filter are verified using tests performed on the ExoMars BB2. The obtained contact angle estimates are found to be consistent with the reference values.

  • 419.
    Villlalba Corbacho, Víctor Manuel
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Cranfield University.
    Vibro-acoustic monitoring for in-flight spacecraft2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The concept of using the vibration transmitted through the structure of space systems whilst they are in flight for monitoring purposes is proposed and analysed.The performed patent review seems to indicate that this technique is not currently used despite being, in principle, a good way to obtain valuable knowledge about the spacecraft’s condition. Potential sources of vibration were listed and some of them were down-selected via a trade-off analysis for implementation in a numerical model of a CubeSat structure. Models were proposed for the sources chosen and implemented in the Ansys Workbench software, along with a simplified structure designed to be representative of a generic picosatellite mission.The results confirmed very different amplitude and frequency ranges for the sources of interest, which would make it difficult to monitor them with one type of sensor.Basic system requirements for accelerometer operating under space conditions were derived and commercial sources were identified as already having the technologies needed.The conclusion was a positive evaluation of the overall concept, although revising negatively the initial expectations for its performance due to the diversity encountered in the sources.

  • 420.
    Walden, Aleksi
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    SMOS satellite hardware anomaly prediction methods based on Earth radiation environment data sets2016Independent thesis Advanced level (degree of Master (Two Years)), 80 poäng / 120 hpOppgave
    Abstract [en]

    SMOS (Soil Moisture and Ocean Salinity) is ESA's Earth Explorer series satellite carrying the novel MIRAS (Microwave Imaging Radiometer with Aperture Synthesis) interferometric synthetic aperture radar. Its objective is monitoring and studying the planet's water cycle by following the changes in soil moisture levels and ocean surface salt concentrations on a global scale. The success of the mission calls for nearly uninterrupted operation of the science payload. However, the instrument experiences sporadically problems with its hardware, which cause losses of scientific data and may require intervention from ground to resolve. The geographical areas in which most of these anomalies occur, polar regions and the South-Atlantic anomaly, give cause to assume these problems are caused by charged particles in the planet's ionosphere. In this thesis, methods of predicting occurrence of hardware anomalies from indicators of Earth radiation environment are investigated.

  • 421.
    Walford, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Integration of an Electric Propulsion High Voltage Unit into the FLP2 SmallSat Testbench2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This paper is based around the test bench for the Flexible LEO Platform, a proposed small satellite platform for use in Low Earth Orbit. The main focus of the paper is the integration of a High Voltage Unit into this test bench. The High Voltage Unit is used to power the Electric Propulsion Subsystem that is being developed at Airbus DS and is likely to be used in the platform. This integration focusses primarily on the data link between the on-board computer and the Power Control and Distribution Unit which supplies power to the High Voltage Unit, but no study on an on-board data link is complete without looking at the link from the satellite to ground.

    The paper will mainly build on two pieces of prior work completed in the development of this platform. The first updated data chain between the ground and the on-board computer from packet level to frame level. The second began the electrical integration of the Power Control and Distribution Unit into the satellite test bench.

    The key areas addressed in the paper are firstly, the implementation of code within the on-board software to command the Power Control and Distribution Unit (both simulated and real) through telecommand and identify the corresponding telemetry that is produced. Secondly, confirmation of a working data chain from the Ground Station to the High Voltage Unit of the Electric Propulsion Subsystem, via the Power Control and Distribution Unit, and if the chain is incomplete, linking them together fully. Thirdly, the robust test of this data chain to ensure that both the simulated and real engine can be controlled. Finally, a detailed documentation of the result along with the software developed and the production of a user manual.

  • 422.
    Webster, Christopher R.
    et al.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
    Mahaffy, Paul R.
    NASA Goddard Space Flight Center.
    Atreya, Sushil K.
    University of Michigan, Ann Arbor.
    Flesch, Gregory J.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
    Mischna, Michael A.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
    Meslin, Pierre-Yves
    Institut de Recherche en Astrophysique et Planetologie, Toulouse.
    Farley, Kenneth A.
    California Institute of Technology, Pasadena.
    Conrad, Pamela G.
    NASA Goddard Space Flight Center.
    Christensen, Lance E.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
    Pavlov, Alexander A.
    NASA Goddard Space Flight Center.
    Martin-Torres, Javier
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Zorzano, María-Paz
    Centro de Astrobiologia, INTA-CSIC, Madrid.
    McConnochie, Timothy H.
    Department of Astronomy, University of Maryland, College Park.
    Owen, Tobias
    University of Hawaii, Honolulu.
    Eigenbrode, Jennifer L.
    NASA Goddard Space Flight Center.
    Glavin, Daniel P.
    NASA Goddard Space Flight Center.
    Steele, Andrew
    Carnegie Institution of Washington, Washington, DC..
    Malespin, Charles A.
    NASA Goddard Space Flight Center.
    Jr., P. Douglas Archer
    Jacobs Technology, NASA Johnson Space Center.
    Sutter, Brad
    Jacobs Technology, NASA Johnson Space Center.
    Coll, Patrice
    Laboratoire Inter-Universitaires des Systèmes Atmosphériques, Paris.
    Freissinet, Caroline
    NASA Goddard Space Flight Center.
    McKay, Christopher P.
    NASA Ames Research Center, Division of Space Sciences and Astrobiology, Mail Stop 245-3, Moffett Field, CA , NASA Ames Research Center.
    Moores, John E.
    York University, Toronto.
    Schwenzer, Susanne P.
    Open University, Milton Keynes.
    Lemmon, Mark T.
    Texas A&M University, College Station.
    Mars methane detection and variability at Gale crater2015Inngår i: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 347, nr 6220, s. 415-417Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Reports of plumes or patches of methane in the Martian atmosphere that vary over monthly timescales have defied explanation to date. From in situ measurements made over a 20-month period by the Tunable Laser Spectrometer (TLS) of the Sample Analysis at Mars (SAM) instrument suite on Curiosity at Gale Crater, we report detection of background levels of atmospheric methane of mean value 0.69 ± 0.25 ppbv at the 95% confidence interval (CI). This abundance is lower than model estimates of ultraviolet (UV) degradation of accreted interplanetary dust particles (IDP’s) or carbonaceous chondrite material. Additionally, in four sequential measurements spanning a 60-sol period, we observed elevated levels of methane of 7.2 ± 2.1 (95% CI) ppbv implying that Mars is episodically producing methane from an additional unknown source.

  • 423.
    Webster, Christopher R.
    et al.
    NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA.
    Martin-Torres, Javier
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Instituto Andaluz de Ciencias de la Tierra, Granada.
    Zorzano, María-Paz
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Centro de Astrobiologia, Instituto National de Tecnica Aerospacial, Madrid.
    Vasavada, Ashwin R
    NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA.
    Background levels of methane in Mars' atmosphere show strong seasonal variations2018Inngår i: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 360, nr 6393, s. 1093-1096Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Variable levels of methane in the martian atmosphere have eluded explanation partly because the measurements are not repeatable in time or location. We report in situ measurements at Gale crater made over a 5-year period by the Tunable Laser Spectrometer on the Curiosity rover. The background levels of methane have a mean value 0.41 ± 0.16 parts per billion by volume (ppbv) (95% confidence interval) and exhibit a strong, repeatable seasonal variation (0.24 to 0.65 ppbv). This variation is greater than that predicted from either ultraviolet degradation of impact-delivered organics on the surface or from the annual surface pressure cycle. The large seasonal variation in the background and occurrences of higher temporary spikes (~7 ppbv) are consistent with small localized sources of methane released from martian surface or subsurface reservoirs.

  • 424.
    Wedlund, Cyril Simon
    et al.
    Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering.
    Kallio, Esa
    Finnish Meteorological Institute, Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering.
    Alho, Markku
    Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering.
    Nilsson, Hans
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Wieser, Gabriella Stenberg
    Swedish Institute of Space Physics.
    Gunell, Herbert
    Swedish Institute of Space Physics / Institutet för rymdfysik , Belgian Institute for Space Aeronomy, Brussels.
    Behar, Etienne
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Pusa, J.
    Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering.
    Gronoff, Guillaume
    Science Directorate, Chemistry and Dynamics Branch, NASA Langley Research Center, Hampton, Virginia.
    The atmosphere of comet 67P/Churyumov-Gerasimenko diagnosed by charge-exchanged solar wind alpha particles2016Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 587, artikkel-id A154Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Context. The ESA/Rosetta mission has been orbiting comet 67P/Churyumov-Gerasimenko since August 2014, measuring its dayside plasma environment. The ion spectrometer onboard Rosetta has detected two ion populations, one energetic with a solar wind origin (H+, He2+, He+), the other at lower energies with a cometary origin (water group ions such as H2O+). He+ ions arise mainly from charge-exchange between solar wind alpha particles and cometary neutrals such as H2O. Aims. The He+ and He2+ ion fluxes measured by the Rosetta Plasma Consortium Ion Composition Analyser (RPC-ICA) give insight into the composition of the dayside neutral coma, into the importance of charge-exchange processes between the solar wind and cometary neutrals, and into the way these evolve when the comet draws closer to the Sun. Methods. We combine observations by the ion spectrometer RPC-ICA onboard Rosetta with calculations from an analytical model based on a collisionless neutral Haser atmosphere and nearly undisturbed solar wind conditions. Results. Equivalent neutral outgassing rates Q can be derived using the observed RPC-ICA He+/He2+ particle flux ratios as input into the analytical model in inverse mode. A revised dependence of Q on heliocentric distance Rh in AU is found to be Rh -7.06Rh-7.06 between 1.8 and 3.3 AU, suggesting that the activity in 2015 differed from that of the 2008 perihelion passage. Conversely, using an outgassing rate determined from optical remote sensing measurements from Earth, the forward analytical model results are in relatively good agreement with the measured RPC-ICA flux ratios. Modelled ratios in a 2D spherically-symmetric plane are also presented, showing that charge exchange is most efficient with solar wind protons. Detailed cometocentric profiles of these ratios are also presented. Conclusions. In conclusion, we show that, with the help of a simple analytical model of charge-exchange processes, a mass-capable ion spectrometer such as RPC-ICA can be used as a "remote-sensing" instrument for the neutral cometary atmosphere.

  • 425.
    Weighton, David
    et al.
    Luleå tekniska universitet.
    Pellinen-Wannberg, Asta
    Umeå universitet.
    Barabash, Victoria
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Molin, Sven
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    The development of masters programs in space science and technology in northern Scandinavia2008Inngår i: Proceedings of the 59th International Astronautical Congress: Glascow, Scotland, 29 Sept - 3 Oct 2008, 2008Konferansepaper (Annet vitenskapelig)
  • 426.
    Wenzel, Andreas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Onboard Convex Optimization for Powered Descent Landing of EAGLE2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Future space exploration missions require new solutions in Guidance, Navigation and Control (GNC) for autonomous landing. The German Aerospace Centre, DLR, is developing the environment for autonomous GNC Landing experiments, EAGLE, acting as a demonstrator for vertical take-off and landing. The goal of this thesis is to develop a prototype real-time applicable guidance function based on convex optimal control theory for powered descent landing, which can be implemented and tested on the on-board computer of EAGLE. Applying loss less convexification, the powered descent landing fuel-optimal control problem is converted into a second order cone problem. A discretization and transcription method is designed in order to solve the resulting non-linear program by means of the embedded conic solver ECOS and the developed algorithm is verified by a comparison of simulation results for an example pinpoint landing on Mars.  In addition, a heuristic kinematic estimation for the fuel-optimal flight time is added, which defines a fixed flight time for the convex trajectory optimization problem. This enables to automatically generate trajectories optimized for the estimated flight time and given initial and final conditions. A processor-in-the-loop test proofs the potential to apply the developed guidance function on the onboard computer of EAGLE, while simulations with different sets of initial and final conditions reveal that the trajectories computed by the guidance function require more fuel than the actual fuel-optimal trajectory due to an inaccurate flight time estimation for several simulation sets. Therefore, the guidance function developed in this thesis provides a first step towards an optimal trajectory generation framework on-board of EAGLE.

  • 427.
    Wetzel, G.
    et al.
    Karlsruhe Institute of Technology.
    Oelhaf, H.
    Karlsruhe Institute of Technology.
    Berthet, G.
    CNRS.
    Bracher, A.
    Universität Bremen.
    Cornacchia, C.
    CNR, IMAA.
    Feist, D.G.
    Max-Planck-Institut.
    Fischer, H.
    Karlsruhe Institute of Technology.
    Fix, A.
    Iarlori, M.
    Università Degli Studi dell'Aquila.
    Kleinert, A.
    Karlsruhe Institute of Technology.
    Lengel, A.
    Karlsruhe Institute of Technology.
    Milz, Mathias
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Mona, L.
    CNR, IMAA.
    Muller, S.C.
    University of Bern.
    Ovarlez, J.
    CNRS.
    Pappalardo, G.
    CNR, IMAA.
    Piccolo, C.
    CNR.
    Paspollini, P.
    CNR.
    Renard, J-P
    CNRS.
    Rizi, V.
    Università Degli Studi dell'Aquila.
    Rohs, S.
    Schiller, C.
    Stiller, G.
    Karlsruhe Institute of Technology.
    Weber, M.
    Universität Bremen.
    Zhang, G.
    Karlsruhe Institute of Technology.
    Validation of MIPAS-ENVISAT H2O operational data collected between July 2002 and March 20042013Inngår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 13, nr 11, s. 5791-5811Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Water vapour (H2O) is one of the operationally retrieved key species of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) instrument aboard the Environmental Satellite (ENVISAT) which was launched into its sun-synchronous orbit on 1 March 2002 and operated until April 2012. Within the MIPAS validation activities, independent observations from balloons, aircraft, satellites, and ground-based stations have been compared to European Space Agency (ESA) version 4.61 operational H2O data comprising the time period from July 2002 until March 2004 where MIPAS measured with full spectral resolution. No significant bias in the MIPAS H2O data is seen in the lower stratosphere (above the hygropause) between about 15 and 30 km. Differences of H2O quantities observed by MIPAS and the validation instruments are mostly well within the combined total errors in this altitude region. In the upper stratosphere (above about 30 km), a tendency towards a small positive bias (up to about 10 %) is present in the MIPAS data when compared to its balloon-borne counterpart MIPAS-B, to the satellite instruments HALOE (Halogen Occultation Experiment) and ACE-FTS (Atmospheric Chemistry Experiment, Fourier Transform Spectrometer), and to the millimeter-wave airborne sensor AMSOS (Airborne Microwave Stratospheric Observing System). In the mesosphere the situation is unclear due to the occurrence of different biases when comparing HALOE and ACE-FTS data. Pronounced deviations between MIPAS and the correlative instruments occur in the lowermost stratosphere and upper troposphere, a region where retrievals of H2O are most challenging. Altogether it can be concluded that MIPAS H2O profiles yield valuable information on the vertical distribution of H2O in the stratosphere with an overall accuracy of about 10 to 30% and a precision of typically 5 to 15% - well within the predicted error budget, showing that these global and continuous data are very valuable for scientific studies. However, in the region around the tropopause retrieved MIPAS H2O profiles are less reliable, suffering from a number of obstacles such as retrieval boundary and cloud effects, sharp vertical discontinuities, and frequent horizontal gradients in both temperature and H2O volume mixing ratio (VMR). Some profiles are characterized by retrieval instabilities.

  • 428.
    Wickramanayake, Anura
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Ekman, Jonas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Hobbs, Stephen
    School of Engineering, Cranfield University, Cranfield, Bedford.
    Mine induced deformation measurements using SAR interferometry at high latitudes2012Konferansepaper (Fagfellevurdert)
  • 429.
    Wickramanayake, Anura
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Hanshel, Michael
    MDA.
    Hobbs, Stephen
    Cranfield University.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Ekman, Jonas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Lehrbass, Brad
    MDA Geospatial Services.
    Seasonal Variation of Coherence in SAR Interferograms in Kiruna, Northern Sweden2016Inngår i: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 37, nr 2, s. 370-387Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This article presents the results of a study conducted to quantify the seasonal variation of coherence in synthetic aperture radar (SAR) interferograms in Kiruna, Northern Sweden. In SAR interferometry (InSAR), coherence is an important concept that provides a good indication of the phase stability of the scatterers. Therefore, in this study, the degree of coherence is used as a parameter to identify the seasonal variation interferograms. For this study, 34 Radarsat-2 ultra-fine beam mode (U6D) images of the Kiruna area (67°51ʹN, 20°14ʹE) and the improved digital elevation model (DEM) created by merging the Radarsat-2 DEM and ASTER DEM were used to produce 561 differential interferograms. The interferograms were arranged in three different ways for the analysis, with the first including common master interferograms (with the summer master image), the second including the sequential interferograms that have the shortest temporal baseline, and the third accounting for all possible combinations of the interferograms (full network of interferograms). Following this step, the variation of coherence for forest areas, urban areas, and flat waste rock areas was studied. This study shows that interferograms generated for the Kiruna region exhibit seasonal variations in coherence due to the ground snow layer in winter. Furthermore, when there is water on the ground due to the melting of the snow layer (in the spring) or due to rains in autumn, the coherence is reduced considerably. Another significant feature is that there is a significant change in summer-to-summer coherence for some regions even over the course of a few years. Based on this study, it is clear that the winter Radarsat-2 U6D beam mode images are not suitable for differential interferometric SAR (DInSAR) deformation measurements in flat waste rock regions in Kiruna. It is expected that even with winter images, PSInSAR or CTM techniques will be able to provide better deformation measurements, but, in this study, those techniques were not assessed. The next step will be to study the seasonal variations in coherence in natural or man-made targets/persistent scatterers using persistent scatter InSAR (PSInSAR) or coherence target monitoring (CTM) techniques

  • 430.
    Wiens, R.C.
    et al.
    Los Alamos National Laboratory, Space Remote Sensing, Los Alamos National Laboratory, Los Alamos, International Space and Response Division, Los Alamos National Laboratory.
    Maurice, Sylvestre
    Institut de Recherche en Astrophysique et Planetologie, Toulouse.
    Martin-Torres, Javier
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    ChemCam: Chemostratigraphy by the First Mars Microprobe2015Inngår i: Elements, ISSN 1811-5209, E-ISSN 1811-5217, Vol. 11, nr 1, s. 33-38Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The ChemCam laser-induced breakdown spectrometer on the rover Curiosity has provided more than 200,000 spectra from over 5000 different locations on Mars. This instrument is the first chemical microprobe on Mars and has an analytical footprint 0.3–0.6 mm in diameter. ChemCam has observed a measure of hydration in all the sedimentary materials encountered along the rover traverse in Gale Crater, indicating the ubiquity of phyllosilicates as a constituent of the analyzed sandstones, mudstones, and conglomerates. Diagenetic features, including calcium sulfate veins, millimeter-thick magnesium-rich diagenetic ridges, and manganese-rich rock surfaces, provide clues to water–rock interactions. Float clasts of coarse-grained igneous rocks are rich in alkali feldspars and some are enriched in fluorine, indicating greater magmatic evolution than expected on Mars. The identification of individual soil components has contributed to our understanding of the evolution of Martian soil. These observations have broadened our understanding of Mars as an active and once habitable planet.

  • 431.
    Wikström, Alf
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Sandahl, Ingrid
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Space education in Kiruna, Northern Sweden2005Inngår i: Advances in Geosciences, ISSN 1680-7340, E-ISSN 1680-7359, Vol. 3, s. 35-40Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The town of Kiruna in the north of Sweden has a concentration of space activities and space research with, for example, the Swedish Institute of Space Physics, Esrange, the ESA Salmijärvi satellite station, and EISCAT (European Incoherent Scatter Radar) Scientific Association. The Department of Space Science is a joint department between the two most northern universities in Sweden, Luleå University of Technology and Umeå University in collaboration with the Swedish Institute of Space Physics. It offers a range of education programmes in the space field. There are bachelor and master programmes in space engineering, and a bridging programme for students without a science background from secondary school. The Department also contributes to courses for teachers, Ph.D. courses and secondary school level courses. One master's program and a three week summer course are given entirely in English and welcome international students. Thanks to good cooperation with Esrange students can build and fly experiments on high altitude balloons and sounding rockets and also take a large responsibility for the management of the projects. Close interaction with research and industry is an important part of the education.

  • 432.
    Williams, K.E.
    et al.
    NASA Ames Research Center, Division of Space Sciences and Astrobiology, Mail Stop 245-3, Moffett Field, CA.
    McKay, Christopher P.
    NASA Ames Research Center, Division of Space Sciences and Astrobiology, Mail Stop 245-3, Moffett Field, CA.
    Persson, Fredrik
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    The surface energy balance at the Huygens landing site and the moist surface conditions on Titan2012Inngår i: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 60, nr 1, s. 376-385Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Huygens Probe provided a wealth of data concerning the atmosphere of Titan. It also provided tantalizing evidence of a small amount of surface liquid. We have developed a detailed surface energy balance for the Probe landing site. We find that the daily averaged non-radiative fluxes at the surface are 0.7 W m -2, much larger than the global average value predicted by McKay et al. (1991) of 0.037 W m -2. Considering the moist surface, the methane and ethane detected by the Probe from the surface is consistent with a ternary liquid of ethane, methane, and nitrogen present on the surface with mole fractions of methane, ethane, and nitrogen of 0.44, 0.34, and 0.22, respectively, and a total mass load of ∼0.05 kg m -2. If this liquid is included in the surface energy balance, only a small fraction of the non-radiative energy is due to latent heat release (∼10 -3 W m -2). If the amount of atmospheric ethane is less than 0.6×10 -5, the surface liquid is most likely evaporating over timescales of 5 Titan days, and the moist surface is probably a remnant of a recent precipitation event. If the surface liquid mass loading is increased to 0.5 kg m -2, then the liquid lifetime increases to ∼56 Titan days. Our modeling results indicate a dew cycle is unlikely, given that even when the diurnal variation of liquid is in equilibrium, the diurnal mass variation is only 3% of the total liquid. If we assume a high atmospheric mixing ratio of ethane (>0.6×10 -5), the precipitation of liquid is large (38 cm/Titan year for an ethane mixing ratio of 2×10 -5). Such a flux is many orders of magnitude in excess of the photochemical production rate of ethane

  • 433.
    Woldu, Yared
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Fritz, Anton
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Using CFD to analyze thermal and optical influence on a zero pressure balloon at floating condition2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The ability to control the trajectory and understanding the atmospheric effects on the flight performance of a scientific high altitude balloon has long been an aspiring ambition. This thesis work analyses the thermal and optical environments at float using the simulation software, ANSYS FLUENT. The objectives for this thesis were to evaluate how the solar angle, sunshine factor and the ground emissivity altered the altitude for the balloon during floating condition in Steady-state simulations. A transient simulation was conducted to evaluate the diurnal cycle effects on the altitude of the balloon. The understanding of how the parameters influence the altitude will make it possible to autonomously route the balloon to desired altitudes where you have a favorable wind direction.

    Performing steady-state simulations showcased the significance of certain parameters. Different solar angles greatly influenced the temperature gradient on the balloon and hence a larger lifting force acted on the balloon when the sun was at its highest point. Varying the cloudiness mostly affected the maximum temperature distribution and did not affect the minimum temperature distribution. The steady-state simulations also indicated a limited but noticeable dependence on the ground emissivity. From the transient simulations it was further enhanced how great of influence the solar angle have, which was illustrated by running diurnal cycles. It was also apparent that there are great differences depending on the seasons. For future applications, it would be of interest to investigate the effects caused by wind velocities in the steady-state case. A comparative analytic solution should be performed in order to validate the simulation results.

  • 434.
    Xavier, Prince K.
    et al.
    Met Office Hadley Centre, Exeter.
    John, Viju O.
    Met Office Hadley Centre, Exeter.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Ajayamohan, R.S.
    Canadian Centre for Climate Modelling and Analysis, University of Victoria.
    Sijikumar, S.
    Space Physics Laboratory, Trivandrum.
    Variability of Indian summer monsoon in a new upper tropospheric humidity data set2010Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 37, nr 5, s. L05705-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using a new data set we demonstrate the variability of upper troposphere humidity (UTH) associated with the Indian Summer Monsoon (ISM). The main advantage of the new data set is its all-sky representation which is essential to capture the full variability of humidity even in cloudy areas. We show that UTH undergoes significant variations during the active/break phases of the monsoon and discuss the mechanisms. The interannual variations of monsoon are also well reflected in the UTH. A preliminary investigation into the cause of the 2009 monsoon failure reveals anomalous subsidence and suppressed convection over the monsoon region due to anomalous warm conditions in the equatorial Pacific throughout the summer. The large scale drying of the upper troposphere may also have contributed to a negative feedback in suppressing convection. Citation: Xavier, P. K., V. O. John, S. A. Buehler, R. S. Ajayamohan, and S. Sijikumar (2010), Variability of Indian summer monsoon in a new upper tropospheric humidity data set

  • 435.
    Yamauchi, M
    et al.
    Swedish Institute of Space Physics (IRF), Kiruna, Sweden.
    Sergienko, T
    Swedish Institute of Space Physics (IRF), Kiruna, Sweden .
    Enell, C-F
    EISCAT Scientific Association, Kiruna, Sweden.
    Schillings, Audrey
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Slapak, Rikard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Johnsen, M G
    Tromsø Geophysical Observatory (TGO), UiT the Arctic University of Norway, Tromsø, Norway.
    Tjulin, A
    EISCAT Scientific Association, Kiruna, Sweden.
    Nilsson, Hans
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement. Swedish Institute of Space Physics (IRF), Kiruna, Sweden .
    Ionospheric Response Observed by EISCAT During the 6–8 September 2017 Space Weather Event: Overview2018Inngår i: Space Weather: The international journal of research and applications, ISSN 1542-7390, E-ISSN 1542-7390, Vol. 16, nr 9, s. 1437-1450Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present ionospheric plasma conditions observed by the EISCAT radars in Tromsø and on Svalbard, covering 68°–81° geomagnetic latitude, during 6–8 September 2017. This is a period when X2.2 and X9.3 X‐ray flares occurred, two interplanetary coronal mass ejections (ICMEs) arrived at the Earth accompanied by enhancements of MeV‐range energetic particle flux in both the solar wind (SEP event) and inner magnetosphere, and an AL < −2,000 substorm took place. (1) Both X flares caused enhancement of ionospheric electron density for about 10 min. The X9.3 flare also increased temperatures of both electrons and ions over 69°–75° geomagnetic latitude until the X‐ray flux decreased below the level of X‐class flares. However, the temperature was not enhanced after the previous X2.2 flare in the prenoon sector. (2) At around 75° geomagnetic latitude, the prenoon ion upflow flux slightly increased the day after the X9.3 flare, which is also after the first ICME and a SEP event, while no outstanding enhancement was found at the time of these X flares. (3) The upflow velocity sometimes decreased when the interplanetary magnetic field (IMF) turned southward. (4) Before the first ICME arrival after the SEP event under weak IMF with Bz ~0 nT, a substorm‐like expansion of the auroral arc signature took place without local geomagnetic signature near local midnight, while no notable change was observed after the ICME arrival. (5) AL reached <−2,000 nT only after the arrival of the second ICME with strongly southward IMF. Causality connections between the solar/solar wind event and the ionospheric responses remain unclear.

  • 436.
    Yamauchi, Masatoshi
    et al.
    Swedish Institute of Space Physics, Kiruna.
    Slapak, Rikard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Cusp Current System: An Energy Source View2018Inngår i: Electric Currents in Geospace and Beyond / [ed] Andreas Keiling Octav Marghitu Michael Wheatland, Hoboken, N.J.: John Wiley & Sons, 2018, s. 339-358Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    Electric currents in the cusp region are reviewed from viewpoints of history and energy conversion. During late 1980s and early 1990s, there were debates on the cause of the cusp region current system (cusp Region 0 field‐aligned current [FAC] and cusp Region 1 FAC, and relevant ionospheric current). The major debates were whether the cusp part Region 1 FAC is an extension of the non‐cusp‐part dayside Region 1 FAC or whether they are generated in different regions independently. The independency of the cusp current system, which was demonstrated by many observations, suggests additional extraction of energy from the magnetosheath‐like flow (e.g., deceleration) inside the polar magnetosphere. An extra deceleration is theoretically possible by adding a substantial local obstacle such as the outflowing ionospheric ions through the mass‐loading effect, which conserves momentum but not kinetic energy. Thus, two different dynamo (J · E < 0) mechanisms most likely exist between the dayside Region 1 and 2 FACs and cusp Region 1 and 0 FACs, forming “double openness,” which was introduced by Vasyliunas [1995]. The other debates (e.g., roles of mesoscale FACs, mapping to high latitude, and current carriers problems) are also reviewed in the light of new observational knowledge after Cluster.

  • 437.
    Yamauchi, Masatoshi
    et al.
    Swedish Institute of Space Physics, Kiruna.
    Slapak, Rikard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Energy conversion through mass loading of escaping ionospheric ions for different Kp values2018Inngår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 36, nr 1, s. 1-12Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    By conserving momentum during the mixing of fast solar wind flow and slow planetary ion flow in an inelastic way, mass loading converts kinetic energy to other forms-e.g. first to electrical energy through charge separation and then to thermal energy (randomness) through gyromotion of the newly born cold ions for the comet and Mars cases. Here, we consider the Earth's exterior cusp and plasma mantle, where the ionospheric origin escaping ions with finite temperatures are loaded into the decelerated solar wind flow. Due to direct connectivity to the ionosphere through the geomagnetic field, a large part of this electrical energy is consumed to maintain field-aligned currents (FACs) toward the ionosphere, in a similar manner as the solar wind-driven ionospheric convection in the open geomagnetic field region. We show that the energy extraction rate by the mass loading of escaping ions (δK) is sufficient to explain the cusp FACs, and that 1K depends only on the solar wind velocity accessing the mass-loading region (usw) and the total mass flux of the escaping ions into this region (mloadFload), as δK ∼-mloadFloadu2 sw=4. The expected distribution of the separated charges by this process also predicts the observed flowing directions of the cusp FACs for different interplanetary magnetic field (IMF) orientations if we include the deflection of the solar wind flow directions in the exterior cusp. Using empirical relations of μ 0α KpC1:2 and Fload/exp.0:45Kp/for Kp D 1-7, where u0 is the solar wind velocity upstream of the bow shock, δK becomes a simple function of Kp as log10.δK/log10 0:2 &dw=elta;KpC 2 log10.KpC1:2)+Cconstant. The major contribution of this nearly linear increase is the Fload term, i.e. positive feedback between the increase of ion escaping rate Fload through the increased energy consumption in the ionosphere for high Kp, and subsequent extraction of more kinetic energy 1K from the solar wind to the current system by the increased Fload. Since Fload significantly increases for increased flux of extreme ultraviolet (EUV) radiation, high EUV flux may significantly enhance this positive feedback. Therefore, the ion escape rate and the energy extraction by mass loading during ancient Earth, when the Sun is believed to have emitted much higher EUV flux than at present, could have been even higher than the currently available highest values based on Kp D 9. This raises a possibility that the ion escape has substantially contributed to the evolution of the Earth's atmosphere.

  • 438.
    Zamora Merino, Victor
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Development of Monitoring and Control Capabilities between Remote Robotic Systems and the METERON Infrastructure2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 439.
    Zamouril, Jakub
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Flight Software Development for Demise Observation Capsule2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This work describes the process of the design of a flight software for a space-qualified device, outlines the development and testing of the SW, and provides a description of the final product. The flight software described in this work has been developed for the project Demise Observation Capsule (DOC). DOC is a device planned to be attached to an upper stage of a launch vehicle and observe its demise during atmospheric re-entry at the end of its mission. Due to constraint on communication time during the mission and the need to maximize the amount of transferred data, a custom communication protocol has been developed.

  • 440.
    Zhang, Weidong
    et al.
    Department of Automation, Shanghai Jiaotong University.
    Lin, Chen
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Multivariable smith predictors design for nonsquare plants2006Inngår i: IEEE Transactions on Control Systems Technology, ISSN 1063-6536, E-ISSN 1558-0865, Vol. 14, nr 6, s. 1145-1149Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The goal of this brief is to provide a solution to the optimal design problem of decoupled multivariable Smith Predictor for general linear stable plants with multiple time delays. The design procedure is divided into three steps. In the first step, a nonsquare plant is factored into the "delay free" part and delay part, and the "delay free" part is further factored into minimum phase part and nonminimum phase part. In the second step, the factorization is utilized to analytically derive the optimal multivariable Smith Predictor based on only output feedback. Finally, the controller is shaped by a filter for specified inputs and a simple procedure is developed to quantitatively tune the closed-loop response expressed in time domain or frequency domain

  • 441.
    Zhang, Weidong
    et al.
    Department of Automation, Shanghai Jiaotong University.
    Lin, Chen
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Ou, Linlin
    Department of Automation, Shanghai Jiaotong University.
    Algebraic solution to H2 control problems: II. The multivariable decoupling case2006Inngår i: Industrial & Engineering Chemistry Research, ISSN 0888-5885, E-ISSN 1520-5045, Vol. 45, nr 21, s. 7163-7176Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The control of multivariable systems with time delays is an important problem in linear control systems. The goal of this paper is to develop an algebraic design method for multivariable systems with multiple time delays. In the method, the algebra-based input-output design technique is adopted, because it is easy to understand and use, and it requires no state variables. We focus mainly on decoupled response. First, all stabilizing decoupling controllers are parametrized. Second, the optimal decoupling controller is derived by minimizing the sensitivity function. Finally, the performance and robustness are analyzed and a simple tuning rule is developed for quantitative performance and robustness. The most important feature of the proposed method is that the controller is optimal, analytical, and can provide decoupling response. Typical examples are provided to illustrate the proposed method

  • 442.
    Zhou, X-Z
    et al.
    Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles.
    Angelopoulos, V.
    Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles.
    Poppe, A.R.
    Space Science Laboratory, University of California, Berkeley.
    Halekas, J.S.
    Space Science Laboratory, University of California, Berkeley.
    Khurana, K.K.
    Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles.
    Kivelson, M.G.
    Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles.
    Fatemi, Shahab
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Holmström, Mats
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Lunar dayside current in the terrestrial lobe: ARTEMIS observations2014Inngår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 119, nr 5, s. 3381-3391Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report Acceleration, Reconnection, Turbulence and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) dual-probe observations of two events in the terrestrial magnetotail lobe, both characterized by upward moving heavy ions of lunar origin at one of the probes that is magnetically connected with the dayside lunar surface. By treating magnetic measurements at the other probe as the unperturbed lobe fields, we obtain background-subtracted magnetic perturbations (most significantly in Bz) when the first probe moved in the dawn-dusk direction across flux tubes magnetically connected to the Moon. These magnetic perturbations indicate the presence of field-aligned current above the lunar surface. By examining possible carriers of field-aligned current, we find that lunar heavy ions and accompanying electrons both contribute considerably to the current. Observations of the field-aligned current also suggest that the charging process at the dayside lunar surface and the associated lobe plasma environment, which have traditionally been viewed as a one-dimensional current balance problem, are actually more complicated. These observations give the first insights into how heavy ions affect the lunar dayside environment in terms of multispecies plasma dynamics.

  • 443.
    Čierny, Ondrej
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Precision Closed-Loop Laser Pointing System for the Nanosatellite Optical Downlink Experiment2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The use of advanced small-satellite platforms has become increasingly more popular in the recent years. Several private companies are investing enormous capital into constellations of small satellites that are designed to provide highly data-intensive global services, such as rapid Earth imaging or fast worldwide Internet access. The scientific community is also interested in the development of miniature and high throughput platforms, for instance in the area of microwave radiometry or hyperspectral imaging.

    The current state of the art nanosatellite radio frequency (RF) communications systems struggle to keep up with the increasing downlink demand and satellite data processing capabilities. Laser communications (lasercom) offers various advantages: increased bandwidth, smaller size, weight, power consumption, and a license-free spectrum.

    While the narrow beamwidths allow lasercom to achieve higher data rates than RF, they, however, also result in higher pointing requirements for the spacecraft. Precision laser pointing systems have been successfully demonstrated on bigger satellites, but not on a nanosatellite scale, where the size and weight constraints are so severe. The Nanosatellite Optical Downlink Experiment (NODE) developed at MIT is a lasercom terminal designed to demonstrate the technologies required for a high-speed optical downlink using commercial off-the-shelf components within the constraints of a typical 3U CubeSat. NODE augments the bus attitude control system with a compact fine laser pointing stage to compensate for the spacecraft body pointing error.

    This thesis focuses on the development and laboratory verification of the laser pointing system for NODE. A control scheme utilizing a miniature fast steering mirror (FSM) used to track a beacon uplink signal from the ground station is presented. An on-orbit FSM calibration algorithm is developed to improve the control robustness and precision. A novel sampling approach that enables closed-loop FSM control is proposed and implemented. The method focuses on simultaneous sampling of the beacon and an internal feedback signal on a single detector. Finally, a hardware-in-the-loop testbed is built in the laboratory with components that were selected for NODE, and the system is functionally verified and analyzed with regards to pointing accuracy. Experimental results show that the pointing requirements given by the mission link budget are met, and that the system performs reliably under various laboratory-simulated conditions.

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