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  Subjects -> COMPUTER SCIENCE (Total: 2134 journals)
    - ANIMATION AND SIMULATION (31 journals)
    - ARTIFICIAL INTELLIGENCE (105 journals)
    - AUTOMATION AND ROBOTICS (106 journals)
    - CLOUD COMPUTING AND NETWORKS (67 journals)
    - COMPUTER ARCHITECTURE (10 journals)
    - COMPUTER ENGINEERING (11 journals)
    - COMPUTER GAMES (22 journals)
    - COMPUTER PROGRAMMING (26 journals)
    - COMPUTER SCIENCE (1241 journals)
    - COMPUTER SECURITY (50 journals)
    - DATA BASE MANAGEMENT (13 journals)
    - DATA MINING (38 journals)
    - E-BUSINESS (22 journals)
    - E-LEARNING (31 journals)
    - ELECTRONIC DATA PROCESSING (22 journals)
    - IMAGE AND VIDEO PROCESSING (40 journals)
    - INFORMATION SYSTEMS (106 journals)
    - INTERNET (97 journals)
    - SOCIAL WEB (53 journals)
    - SOFTWARE (34 journals)
    - THEORY OF COMPUTING (9 journals)

COMPUTER SCIENCE (1241 journals)                  1 2 3 4 5 6 7 | Last

Showing 1 - 200 of 872 Journals sorted alphabetically
3D Printing and Additive Manufacturing     Full-text available via subscription   (Followers: 25)
Abakós     Open Access   (Followers: 4)
ACM Computing Surveys     Hybrid Journal   (Followers: 31)
ACM Journal on Computing and Cultural Heritage     Hybrid Journal   (Followers: 9)
ACM Journal on Emerging Technologies in Computing Systems     Hybrid Journal   (Followers: 17)
ACM Transactions on Accessible Computing (TACCESS)     Hybrid Journal   (Followers: 3)
ACM Transactions on Algorithms (TALG)     Hybrid Journal   (Followers: 15)
ACM Transactions on Applied Perception (TAP)     Hybrid Journal   (Followers: 5)
ACM Transactions on Architecture and Code Optimization (TACO)     Hybrid Journal   (Followers: 9)
ACM Transactions on Autonomous and Adaptive Systems (TAAS)     Hybrid Journal   (Followers: 9)
ACM Transactions on Computation Theory (TOCT)     Hybrid Journal   (Followers: 12)
ACM Transactions on Computational Logic (TOCL)     Hybrid Journal   (Followers: 3)
ACM Transactions on Computer Systems (TOCS)     Hybrid Journal   (Followers: 18)
ACM Transactions on Computer-Human Interaction     Hybrid Journal   (Followers: 16)
ACM Transactions on Computing Education (TOCE)     Hybrid Journal   (Followers: 8)
ACM Transactions on Design Automation of Electronic Systems (TODAES)     Hybrid Journal   (Followers: 6)
ACM Transactions on Economics and Computation     Hybrid Journal  
ACM Transactions on Embedded Computing Systems (TECS)     Hybrid Journal   (Followers: 3)
ACM Transactions on Information Systems (TOIS)     Hybrid Journal   (Followers: 20)
ACM Transactions on Intelligent Systems and Technology (TIST)     Hybrid Journal   (Followers: 8)
ACM Transactions on Interactive Intelligent Systems (TiiS)     Hybrid Journal   (Followers: 5)
ACM Transactions on Multimedia Computing, Communications, and Applications (TOMCCAP)     Hybrid Journal   (Followers: 9)
ACM Transactions on Reconfigurable Technology and Systems (TRETS)     Hybrid Journal   (Followers: 6)
ACM Transactions on Sensor Networks (TOSN)     Hybrid Journal   (Followers: 8)
ACM Transactions on Speech and Language Processing (TSLP)     Hybrid Journal   (Followers: 9)
ACM Transactions on Storage     Hybrid Journal  
ACS Applied Materials & Interfaces     Hybrid Journal   (Followers: 35)
Acta Automatica Sinica     Full-text available via subscription   (Followers: 2)
Acta Informatica Malaysia     Open Access  
Acta Universitatis Cibiniensis. Technical Series     Open Access  
Ad Hoc Networks     Hybrid Journal   (Followers: 11)
Adaptive Behavior     Hybrid Journal   (Followers: 10)
Advanced Engineering Materials     Hybrid Journal   (Followers: 29)
Advanced Science Letters     Full-text available via subscription   (Followers: 11)
Advances in Adaptive Data Analysis     Hybrid Journal   (Followers: 9)
Advances in Artificial Intelligence     Open Access   (Followers: 15)
Advances in Calculus of Variations     Hybrid Journal   (Followers: 6)
Advances in Catalysis     Full-text available via subscription   (Followers: 5)
Advances in Computational Mathematics     Hybrid Journal   (Followers: 19)
Advances in Computer Engineering     Open Access   (Followers: 4)
Advances in Computer Science : an International Journal     Open Access   (Followers: 16)
Advances in Computing     Open Access   (Followers: 2)
Advances in Data Analysis and Classification     Hybrid Journal   (Followers: 58)
Advances in Engineering Software     Hybrid Journal   (Followers: 29)
Advances in Geosciences (ADGEO)     Open Access   (Followers: 17)
Advances in Human Factors/Ergonomics     Full-text available via subscription   (Followers: 23)
Advances in Human-Computer Interaction     Open Access   (Followers: 21)
Advances in Materials Science     Open Access   (Followers: 15)
Advances in Operations Research     Open Access   (Followers: 12)
Advances in Parallel Computing     Full-text available via subscription   (Followers: 7)
Advances in Porous Media     Full-text available via subscription   (Followers: 5)
Advances in Remote Sensing     Open Access   (Followers: 52)
Advances in Science and Research (ASR)     Open Access   (Followers: 6)
Advances in Technology Innovation     Open Access   (Followers: 6)
AEU - International Journal of Electronics and Communications     Hybrid Journal   (Followers: 8)
African Journal of Information and Communication     Open Access   (Followers: 9)
African Journal of Mathematics and Computer Science Research     Open Access   (Followers: 4)
AI EDAM     Hybrid Journal   (Followers: 2)
Air, Soil & Water Research     Open Access   (Followers: 14)
AIS Transactions on Human-Computer Interaction     Open Access   (Followers: 7)
Algebras and Representation Theory     Hybrid Journal   (Followers: 1)
Algorithms     Open Access   (Followers: 11)
American Journal of Computational and Applied Mathematics     Open Access   (Followers: 5)
American Journal of Computational Mathematics     Open Access   (Followers: 4)
American Journal of Information Systems     Open Access   (Followers: 6)
American Journal of Sensor Technology     Open Access   (Followers: 4)
Anais da Academia Brasileira de Ciências     Open Access   (Followers: 2)
Analog Integrated Circuits and Signal Processing     Hybrid Journal   (Followers: 7)
Analysis in Theory and Applications     Hybrid Journal   (Followers: 1)
Animation Practice, Process & Production     Hybrid Journal   (Followers: 5)
Annals of Combinatorics     Hybrid Journal   (Followers: 4)
Annals of Data Science     Hybrid Journal   (Followers: 12)
Annals of Mathematics and Artificial Intelligence     Hybrid Journal   (Followers: 12)
Annals of Pure and Applied Logic     Open Access   (Followers: 4)
Annals of Software Engineering     Hybrid Journal   (Followers: 13)
Annals of West University of Timisoara - Mathematics and Computer Science     Open Access  
Annual Reviews in Control     Hybrid Journal   (Followers: 8)
Anuario Americanista Europeo     Open Access  
Applicable Algebra in Engineering, Communication and Computing     Hybrid Journal   (Followers: 2)
Applied and Computational Harmonic Analysis     Full-text available via subscription   (Followers: 1)
Applied Artificial Intelligence: An International Journal     Hybrid Journal   (Followers: 12)
Applied Categorical Structures     Hybrid Journal   (Followers: 4)
Applied Clinical Informatics     Hybrid Journal   (Followers: 3)
Applied Computational Intelligence and Soft Computing     Open Access   (Followers: 14)
Applied Computer Systems     Open Access   (Followers: 2)
Applied Informatics     Open Access  
Applied Mathematics and Computation     Hybrid Journal   (Followers: 33)
Applied Medical Informatics     Open Access   (Followers: 12)
Applied Numerical Mathematics     Hybrid Journal   (Followers: 5)
Applied Soft Computing     Hybrid Journal   (Followers: 17)
Applied Spatial Analysis and Policy     Hybrid Journal   (Followers: 7)
Applied System Innovation     Open Access  
Architectural Theory Review     Hybrid Journal   (Followers: 3)
Archive of Applied Mechanics     Hybrid Journal   (Followers: 6)
Archive of Numerical Software     Open Access  
Archives and Museum Informatics     Hybrid Journal   (Followers: 156)
Archives of Computational Methods in Engineering     Hybrid Journal   (Followers: 6)
arq: Architectural Research Quarterly     Hybrid Journal   (Followers: 8)
Artifact     Open Access   (Followers: 2)
Artificial Life     Hybrid Journal   (Followers: 7)
Asia Pacific Journal on Computational Engineering     Open Access  
Asia-Pacific Journal of Information Technology and Multimedia     Open Access   (Followers: 1)
Asian Journal of Control     Hybrid Journal  
Assembly Automation     Hybrid Journal   (Followers: 2)
at - Automatisierungstechnik     Hybrid Journal   (Followers: 1)
Australian Educational Computing     Open Access   (Followers: 1)
Automatic Control and Computer Sciences     Hybrid Journal   (Followers: 6)
Automatic Documentation and Mathematical Linguistics     Hybrid Journal   (Followers: 5)
Automatica     Hybrid Journal   (Followers: 13)
Automation in Construction     Hybrid Journal   (Followers: 8)
Autonomous Mental Development, IEEE Transactions on     Hybrid Journal   (Followers: 8)
Balkan Journal of Electrical and Computer Engineering     Open Access  
Basin Research     Hybrid Journal   (Followers: 5)
Behaviour & Information Technology     Hybrid Journal   (Followers: 51)
Big Data and Cognitive Computing     Open Access   (Followers: 4)
Biodiversity Information Science and Standards     Open Access   (Followers: 1)
Bioinformatics     Hybrid Journal   (Followers: 342)
Biomedical Engineering     Hybrid Journal   (Followers: 16)
Biomedical Engineering and Computational Biology     Open Access   (Followers: 13)
Biomedical Engineering, IEEE Reviews in     Full-text available via subscription   (Followers: 19)
Biomedical Engineering, IEEE Transactions on     Hybrid Journal   (Followers: 36)
Briefings in Bioinformatics     Hybrid Journal   (Followers: 49)
British Journal of Educational Technology     Hybrid Journal   (Followers: 173)
Broadcasting, IEEE Transactions on     Hybrid Journal   (Followers: 12)
Bulletin of Social Informatics Theory and Application     Open Access  
c't Magazin fuer Computertechnik     Full-text available via subscription   (Followers: 1)
CALCOLO     Hybrid Journal  
Calphad     Hybrid Journal   (Followers: 2)
Canadian Journal of Electrical and Computer Engineering     Full-text available via subscription   (Followers: 15)
Capturing Intelligence     Full-text available via subscription  
Catalysis in Industry     Hybrid Journal   (Followers: 1)
CEAS Space Journal     Hybrid Journal   (Followers: 2)
Cell Communication and Signaling     Open Access   (Followers: 2)
Central European Journal of Computer Science     Hybrid Journal   (Followers: 5)
CERN IdeaSquare Journal of Experimental Innovation     Open Access   (Followers: 4)
Chaos, Solitons & Fractals     Hybrid Journal   (Followers: 3)
Chemometrics and Intelligent Laboratory Systems     Hybrid Journal   (Followers: 15)
ChemSusChem     Hybrid Journal   (Followers: 7)
China Communications     Full-text available via subscription   (Followers: 8)
Chinese Journal of Catalysis     Full-text available via subscription   (Followers: 2)
CIN Computers Informatics Nursing     Hybrid Journal   (Followers: 11)
Circuits and Systems     Open Access   (Followers: 15)
Clean Air Journal     Full-text available via subscription   (Followers: 1)
CLEI Electronic Journal     Open Access  
Clin-Alert     Hybrid Journal   (Followers: 1)
Clinical eHealth     Open Access  
Cluster Computing     Hybrid Journal   (Followers: 2)
Cognitive Computation     Hybrid Journal   (Followers: 3)
COMBINATORICA     Hybrid Journal  
Combinatorics, Probability and Computing     Hybrid Journal   (Followers: 4)
Combustion Theory and Modelling     Hybrid Journal   (Followers: 14)
Communication Methods and Measures     Hybrid Journal   (Followers: 14)
Communication Theory     Hybrid Journal   (Followers: 25)
Communications Engineer     Hybrid Journal   (Followers: 1)
Communications in Algebra     Hybrid Journal   (Followers: 3)
Communications in Computational Physics     Full-text available via subscription   (Followers: 2)
Communications in Information Science and Management Engineering     Open Access   (Followers: 4)
Communications in Partial Differential Equations     Hybrid Journal   (Followers: 4)
Communications of the ACM     Full-text available via subscription   (Followers: 52)
Communications of the Association for Information Systems     Open Access   (Followers: 16)
COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering     Hybrid Journal   (Followers: 3)
Complex & Intelligent Systems     Open Access   (Followers: 1)
Complex Adaptive Systems Modeling     Open Access  
Complex Analysis and Operator Theory     Hybrid Journal   (Followers: 2)
Complexity     Hybrid Journal   (Followers: 6)
Composite Materials Series     Full-text available via subscription   (Followers: 8)
Computación y Sistemas     Open Access  
Computation     Open Access   (Followers: 1)
Computational and Applied Mathematics     Hybrid Journal   (Followers: 3)
Computational and Mathematical Biophysics     Open Access   (Followers: 1)
Computational and Mathematical Methods in Medicine     Open Access   (Followers: 2)
Computational and Mathematical Organization Theory     Hybrid Journal   (Followers: 2)
Computational and Structural Biotechnology Journal     Open Access   (Followers: 1)
Computational and Theoretical Chemistry     Hybrid Journal   (Followers: 9)
Computational Astrophysics and Cosmology     Open Access   (Followers: 1)
Computational Biology and Chemistry     Hybrid Journal   (Followers: 13)
Computational Chemistry     Open Access   (Followers: 2)
Computational Cognitive Science     Open Access   (Followers: 2)
Computational Complexity     Hybrid Journal   (Followers: 4)
Computational Condensed Matter     Open Access  
Computational Ecology and Software     Open Access   (Followers: 10)
Computational Economics     Hybrid Journal   (Followers: 10)
Computational Geosciences     Hybrid Journal   (Followers: 18)
Computational Linguistics     Open Access   (Followers: 23)
Computational Management Science     Hybrid Journal  
Computational Mathematics and Modeling     Hybrid Journal   (Followers: 9)
Computational Mechanics     Hybrid Journal   (Followers: 5)
Computational Methods and Function Theory     Hybrid Journal  
Computational Molecular Bioscience     Open Access   (Followers: 2)
Computational Optimization and Applications     Hybrid Journal   (Followers: 8)
Computational Particle Mechanics     Hybrid Journal   (Followers: 1)
Computational Research     Open Access   (Followers: 1)
Computational Science and Discovery     Full-text available via subscription   (Followers: 2)
Computational Science and Techniques     Open Access   (Followers: 1)
Computational Statistics     Hybrid Journal   (Followers: 15)
Computational Statistics & Data Analysis     Hybrid Journal   (Followers: 36)
Computer     Full-text available via subscription   (Followers: 106)
Computer Aided Surgery     Open Access   (Followers: 6)
Computer Applications in Engineering Education     Hybrid Journal   (Followers: 8)
Computer Communications     Hybrid Journal   (Followers: 16)

        1 2 3 4 5 6 7 | Last

Similar Journals
Journal Cover
CEAS Space Journal
Journal Prestige (SJR): 0.278
Citation Impact (citeScore): 1
Number of Followers: 2  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1868-2510 - ISSN (Online) 1868-2502
Published by Springer-Verlag Homepage  [2352 journals]
  • Evaluation and optimization of heat transfer at the interfaces of
           spacecraft assemblies
    • Abstract: This paper presents the experimental and numerical work achieved in the aim of evaluating the heat transfer at the interfaces of threaded spacecraft assemblies, where Thermal Interface Materials (TIMs) are placed between two surfaces to improve the thermal performance. Developing a model to predict thermal resistance for such an assembly is a serious challenge, which has to take various influencing parameters into account. First, mechanical and thermal experiments used to characterise TIMs are summarised. Second, a numerical model capable of representing the behaviour of these materials is built. To verify the mechanical model, the preload of a single fastener assembly is measured and compared with a simulation. The thermo-mechanical model is verified by an assembly heated by a power resistor to evaluate the thermal aspects. The proposed material model is able to predict the loss of preload caused by creep/relaxation of the TIM and the temperature distribution of the assembly. This work is part of a broader study that seeks to develop a multi-physics approach to evaluate the heat transfer at interfaces of space application assemblies.
      PubDate: 2019-06-01
       
  • On the accuracy of the SGP4 to predict stellar occultation events using
           ENVISAT/GOMOS data and recommendations for the ALTIUS mission
    • Abstract: In preparation for the operations of the ALTIUS mission, research is carried out to assess the accuracy of the SGP4 orbital propagator in predicting stellar occultation events. The quantification of the accuracy and its consequent improvement will enable reliable measurement planning and, therefore, maximize the number of measurements. To this end, predictions are made for the timing of occultations for the GOMOS instrument on-board the ENVISAT, which are then compared to actual occultation occurrences. It is found that the error is substantial but follows a trend that can be interpolated. This enables devising a method for highly accurate predictions given a sufficient number of data points. Statistically significant results for the accuracy of the propagator and a calibration method are presented. Recommendations for a measurement planning procedure of ALTIUS are formulated.
      PubDate: 2019-06-01
       
  • ACLAD: a new philosophy for launcher coupled load analyses
    • Abstract: The new ACLAD philosophy for launcher/spacecraft mechanical-coupled load analysis (CLA) is presented. ACLAD stands for “A CLA a Day”. We encourage the development of a work method that would allow spacecraft manufacturers to perform a very high number of CLA, instead of once or twice per each program as done today. Such analyses provide the best possible estimation of the spacecraft loads during flight and often underline that the mechanical requirements are much higher than the actual need. If performed many times during a project, CLA could help prevent overdesign and overtesting by inducing lower specifications. Lower costs and mass of the structures could be attained. Some possible implementations of ACLAD are presented in this paper.
      PubDate: 2019-06-01
       
  • Robustness of Astrix Fiber Optic Gyros in space radiative environment
    • Abstract: When developing the Fiber Optics Gyro Astrix™ family, Airbus and Ixblue faced the problematics of the possible radiation effects on optical and opto-electronics parts. After bibliographic research on the subject, selection of parts was made according to existing knowledge, and batch qualification tests performed to quantify the radiation effects. On-ground test results were introduced in worst case optical budget for the optical loop dimensioning. Several years later, following consequent in-orbit data gathering, we can assess that radiation effect are barely noticeable and that inertial performances remain tremendously stable. The careful design of the Astrix optical loop and the proper selection of opto parts were mastered key factor for such an in-flight success.
      PubDate: 2019-06-01
       
  • Finite element modelling and performance optimization of an ion thruster
           depending on the nature of the propellant
    • Abstract: The electrostatic propulsion is a class of space propulsion which makes use of electrical power and this kind of systems are characterized by high exhaust velocities and specific impulse, enhancing the propulsive performances of thrusters compared to conventional chemical thrusters. Since the ionized particle exhaust velocity is a function of the ratio between the electrical charge and their molecular mass, the obvious solution is to use ions with low electrical charge–molecular mass ratio. Currently, the most used propellant for the space propulsion is the Xenon gas, as it has a series of important advantages, but is quite expensive when compared to other propellants. This paper aims to make an optimization of the ideal ion propulsion systems depending on the nature of the propellant, like common used substances in the space propulsion, but also other substances which are potential candidates for this application. A variety of ion thruster performances will be analyzed, such as force, specific impulse, efficiency for the same power available onboard, the same accelerating voltage, and the same ion current. Also, for the Xenon case a numerical simulation was performed to highlight the behavior and trajectory of the ionized particles and their velocity. The conclusion obtained following the study is that a reasonable ion thruster regarding the dimensions should use an accelerating potential of at least 4000 V and 2 A of ion current.
      PubDate: 2019-06-01
       
  • Accurate numerical simulation on the structural response of the VEGA
           payload fairing using modal coupling approach
    • Abstract: Structural aeroacoustic interactions are of great interest in the design and manufacture of aerospace structures. During the lift off and the early phases of the launch various external loads like steady accelerations, random and broadband frequency vibrations, acoustic loads due to jet noise and fluid–structure interactions act on the lightweight panel structure of the payload fairing. Thereby internal vibrational loads and instability effects may be caused by the interaction of various mechanical loads and acoustic noise acting on the cylindrical shell structure. Within the project “Prediction of Acoustic Loads on Space Structures” funded by the European Space Agency (ESA) an aeroelastic coupling approach has been built up. Therein, the aerodynamic loads on the VEGA payload fairing (PLF) have been determined for different flight conditions by the use of the open-source CFD solver SU2. Due to the different discretization between the computational fluid dynamics (CFD) and computational structural dynamics (CSD) mesh the approach of Radial Basis Function (RBF) has been used to interpolate the resulting pressure distribution onto the structural model. According to that the dynamic response of the PLF has been analyzed by taking the basic aerodynamic forces, structural vibration and acoustic pressure fluctuations into account. An intrinsic part of this work is the numerical simulation and assessment of the interaction between structural vibrations, transonic flow and acoustic pressure fluctuations during the early launch phase.
      PubDate: 2019-06-01
       
  • An academic approach to the multidisciplinary development of liquid-oxygen
           turbopumps for space applications
    • Abstract: Since 2015, the Technical University of Munich and the German Aerospace Center have intensified their research on liquid-oxygen turbopumps for space propulsion applications in a joined project. Together, they concentrate on the special challenges concerning the design, construction and operation of parts of turbopumps, as well as the development and validation of tools to interpret and predict the aforementioned. This is accompanied by experimental works on the level of components of the pump, the bearing unit and seals. Alongside this, numerical tools are used which have been developed both commercially and at the Technical University of Munich. The research combines the expertise of several institutes in the fields of space propulsion, applied mechanics, rotordynamics and numerical mechanics in a multidisciplinary approach. The incorporation of student and doctoral theses allows for the investigation of the components of liquid-oxygen turbopumps in a very wide variety. High emphasis is put on the interaction between the turbopump subsystems. The present paper presents the work on each subsystem and the links between them.
      PubDate: 2019-06-01
       
  • Effects of the rotational vehicle dynamics on the ascent flight trajectory
           of the SpaceLiner concept
    • Abstract: During the preliminary design of space transportation systems, the vehicle dynamics are commonly reduced to a point-mass model for definition of the flight trajectory. While this approach effectively reduces the number of model parameters in the design process, it neglects the rotational dynamics of the vessel completely. Since the rotational degrees of freedom (DOF) have a significant influence on the vehicle’s controllability, a sole analysis of the translational dynamics is insufficient to assess the general feasibility of the concept. This study investigates the ascent flight trajectory of the SpaceLiner vehicle, a concept for a hypersonic suborbital space plane, based on a newly developed 6-DOF flight dynamics simulation to determine the influence of the rotational dynamics on the vehicle’s controllability and performance. The first part of this paper will focus on the developed vehicle model which features a transient inertia model, as well as an algorithmic-designed flight control system. The second part will present several simulations of nominal and off-nominal ascent trajectories. Based on the results it will be shown that SpaceLiner’s thrust vector control system is sufficiently dimensioned for the investigated mission scenarios, while the vehicle performance is only slightly influenced by the rotational dynamics.
      PubDate: 2019-06-01
       
  • Dynamic guidance of orbiter gliders: alignment, final approach, and
           landing
    • Abstract: A new algorithm capable of guiding an orbiter glider to a target point with a prescribed alignment and descent path angle is presented. This algorithm can initiate Terminal Area Energy Management (TAEM) before reaching steady state and perform the Final Approach and Landing (FA&L). During TAEM, runway alignment is done through a moving virtual target derived from steady state, while during FA&L, a transient (or flare) is used to reach the extremely shallow descent path angles. All decisions are made dynamically relying solely on local information (position, speed, attitude, and atmospheric parameters), and all structural limits of the glider are respected at all times. As a proof of concept, a Space Shuttle return flight is simulated. For a large multitude of initial conditions and targets, the algorithm is able to consistently deliver distance errors below 19 m (transverse errors below 4 m), alignment errors below \(1^{\circ }\) , descent path angles at the intended \(-\,2^{\circ }\) , and vertical descent speeds below 8.5 m/s with control time intervals of 0.1 s.
      PubDate: 2019-06-01
       
  • Integration of thermo-elastic characteristics in finite element method
           reduced models
    • Abstract: A simple method for integrating thermo-elastic characteristics in finite element method (FEM) reduced models is presented. Methods like Guyan or Craig-Bampton reductions are widely used in the space industry, as they drastically decrease the size of models and also allow safe model exchanges between companies without disclosing sensitive technologies. On the other hand, reduced models cannot be implemented in thermo-elastic analyses, which are of paramount importance for spacecrafts mainly for on-orbit sizing and pointing analyses. The new presented method is simple to implement and consists of replacing the dropped thermo-elastic characteristics of the reduced models by a set of interface forces and moments. These are computed by clamping the physical FEM model at its interfaces and applying unit thermal loads on the different internal zones. An analytical and a numerical example are presented. The implementation in FEM shows high accuracy.
      PubDate: 2019-06-01
       
  • Influence of transpiration cooling on second-mode instabilities
           investigated on hypersonic, conical flows
    • Abstract: In the present study, the influence of active cooling on hypersonic boundary-layer transition at different Mach numbers, from 7 up to 10, is investigated. The analyses are carried out on a \(7^\circ\) half-angle, blunted cone with different nose radii and various gas injection mass flow rates. In all cases, low mass fluxes, which do not inducing visible shocks in the schlieren images, are applied. As injection gas nitrogen is used. At the considered free stream conditions, second modes are the dominant boundary-layer instabilities, which are consequently the focus of this study. The stability analyses are performed by means of the stability code NOLOT, NOnLOcal Transition analysis, of the German Aerospace Center (DLR). The influence of different mass injections on the frequencies and growth rates of the second modes is analyzed in detail. The effect on the transition onset locations is discussed. The numerical predictions are compared with experimental results. The experimental data referred to in the present study were obtained in the DLR High Enthalpy Shock Tunnel Göttingen.
      PubDate: 2019-05-18
       
  • Sentinel-1 SAR instrument improved flight predictions based on measured
           in-orbit data
    • Abstract: The Sentinel-1A SAR mission was launched in April 2014, followed by the Sentinel-1B Spacecraft in April 2016. Since then, several sets of in-orbit data have been evaluated to correlate the thermal model for being able to provide more detailed in-flight predictions. The need for detailed in-flight predictions is justified by the fact that the imaging performance of a SAR instrument depends mainly on the thermal performance of its high dissipative units. Components reaching their temperature limits during operational time define the end of the imaging phase, and thus the timespan during which and how often imaging operations can take place. An STM (Structural/Thermal Model) test correlation is standard throughout all missions, which usually delivers a very reliable model for further in-flight predictions. Nevertheless, this correlation does not give information about thermo-optical property degradation or environmental influences, because the effects in space on the thermally active surfaces are very hard to predict. For this reason, thermal engineers use relatively conservative values for in-flight predictions and End-of-Life thermal performance assessments. This might lead to mission performance limitations which predict a too short feasible imaging time of the Radar instrument. For this reason, the first approach was to evaluate the early acquired in-orbit data and to correlate the thermal model with the thermal configuration at Begin-of-Life to assess the maximum possible high dissipative imaging time possible for the Begin-of-Life situation. Then the flight data over a longer timespan were evaluated to determine potential temperature trends which could be caused by thermo-optical property degradation as well as seasonal-related influences. These two assessments combined, allow a thermal performance prediction for Mission End-of-Life, and thus a reliable determination of potential SAR imaging performance over the full mission time. The paper will present the correlation results of the initially measured in-flight data, the determined long-term in-orbit data over 3 years, and the combination of both assessments including its impact on SAR imaging performance over the full mission.
      PubDate: 2019-05-18
       
  • Ballistic and mechanical characteristics of paraffin-based solid fuels
    • Abstract: In a hybrid rocket, paraffin-based fuels are characterised by high regression rates and zero chemical explosion potential. However, paraffin wax is a brittle material and exhibits poor mechanical strength. The production of large-scale paraffin motors is a challenging task because of the poor structural performance of such motors. The addition of polymers and metallic additives to paraffin wax can considerably enhance mechanical performance. In this study, three different paraffin-based fuels, namely paraffin–aluminium (P–Al), paraffin–boron (P–B), and paraffin–carbon black (P–CB), were prepared using polyethylene (PE) polymer additive. The effects of these additives on the thermal, mechanical, and ballistic performance of the paraffin-based fuels were examined. The mechanical strength of these fuels was evaluated using compressive tests. Differential scanning calorimetry (DSC) experiments were performed to study the thermal decomposition of these paraffin-based fuels. A lab-scale ballistic evaluation motor was used to study the regression rates in a gaseous oxygen environment. The results revealed that the addition of the polymer and metallic additives improved the mechanical strength of fuels. The DSC results demonstrated that the addition of the additives accelerated oxidation and improved the heat release rate during combustion. The oxidation enthalpies for the P–Al, P–B, and P–CB samples were 291, 274, and 268 J/g, respectively. Finally, the ballistic results indicated that the regression rate decreased when 10 wt% PE was added to the paraffin wax, and such depreciation of regression rate due to polymer addition was compensated by the addition of the Al, B, and CB additives.
      PubDate: 2019-05-10
       
  • Satellite laser ranging at 100 kHz pulse repetition rate
    • Abstract: Current satellite laser ranging (SLR) systems work at laser repetition rates of some 10 Hz up to about 10 kHz. However, using a laser repetition rate of 100 kHz offers several advantages. First, a laser with lower pulse energy can be used, while nevertheless the same amount of returns is received for a given target. Second, a poor single-shot precision (e.g. due to a long laser pulse) can be counteracted, as the statistical error decreases with the number of individual measurements. These two factors increase the number of options concerning the laser source and may also help to make the system inherently eye safe. Lastly, it may also help to gather data more quickly and thus increase the number of targets that can be tracked per system. A high repetition rate SLR system has been installed at the Uhlandshöhe observatory in Stuttgart, Germany. Using an effective repetition rate of 100 kHz and a pulse energy of \(50 \,\upmu \hbox {J}\) , various typical SLR targets could be ranged successfully, including LAGEOS and global navigation system satellites at altitudes of around 20,000 km. A comparative orbit analysis, using data taken by other SLR stations at the same time, shows that a normal point scatter in the order of 1 cm is achieved despite the rather poor single-shot precision of about 60 cm. These results show an interesting potential especially for future low-cost SLR systems that may utilize this technique to achieve competitive performance with small, low-energy lasers.
      PubDate: 2019-04-26
       
  • Development and qualification of the Feed-Select Mechanism for the
           Polarimetric and Helioseismic Imager on-board Solar Orbiter
    • Abstract: The Solar Orbiter Polarimetric and Helioseismic Imager (SO/PHI) will provide maps of the magnetic vector and of the line-of-sight velocities in the solar photosphere. For reaching its science goals, SO/PHI is equipped with two telescopes: the high resolution channel (HRT) and the full disk channel (FDT). Since both optical channels are fed into a common path including the camera, the need arises for a highly precise mechanism, which selects only one telescope at a time: the Feed-Select Mechanism (FSM). The mechanism therefore needs to serve two purposes: (1) directing one channel towards the camera, (2) shutting the second channel to not disturb the measurement of the observing channel. In this paper we will describe the different design features, as well as the design verification and qualification of the mechanism.
      PubDate: 2019-04-24
       
  • Ship tracking results from state-of-the-art space-based AIS receiver
           systems for maritime surveillance
    • Abstract: Norway currently operates four satellites with Automatic Identification System (AIS) receivers. The first-generation satellites, AISSat-1 and AISSat-2, are equipped with a two-channel, single-antenna AIS receiver, while NorSat-1 and NorSat-2 are equipped with an improved AIS receiver capable of decoding on all four AIS channels and using the two antennas installed on the NorSat satellites. This paper aims to investigate the ship tracking performance enhancement realised by the technology improvements of antenna diversification, frequency diversification, and advanced algorithms. The ship tracking capability of the NorSat satellites is presented and shown to yield a significant improvement, up to a 20% point increase, over the first AISSat generation ship tracking capability. A further 20% point increase is achieved in select areas using frequency diversity introduced in the AIS system since the development of the AISSat satellites. In addition, NorSat-1 detected 34% more vessels than AISSat-2 over the same timeframe. The contribution to the performance improvement from the incremental improvements in decoding algorithms, antenna diversity, and frequency diversity is indicated in the results. The results indicate that, in the short term, upgrading to the latest algorithms, low noise electronics, and taking advantage of antenna diversity is the greatest performance enhancer. In the medium and long term, the frequency diversity likely yields the greatest performance enhancement.
      PubDate: 2019-04-11
       
  • Quasi-impulsive maneuvers to correct mean orbital elements in LEO
    • Abstract: An approach is developed to compute quasi-impulsive maneuvers to steer the orbital elements of a spacecraft to a desired value. Using Gauss variational equations it is possible to define the location along the orbit as well as the magnitude of the maneuver(s) so that specific orbital elements can be changed with little influence on the others. The possibility to include the effect of the perturbations allows an accurate evaluation of the time required to reach the maneuvering location. Including a model of the propulsion system makes the simulation more realistic, if compared with an impulsive maneuver implementation, since a burning arc can replace the instantaneous change of the orbital elements, which is instead associated with the impulsive approach. Simulations have been performed to compare perturbed and unperturbed cases and the results from the comparisons are presented.
      PubDate: 2019-03-28
       
  • Fast, robust and near-optimal approximation of GTO trajectories and
           payload capacities of multistage rockets
    • Abstract: A method for automatically generating approximate trajectories for multistage rockets, launching into a geostationary transfer orbit, is presented. It can either be used to generate an initial guess or to determine the payload capacity of a given launcher. Only the apogee is directly optimized. When the maximum payload of the launcher is used, the perigee will gravitate towards its target value. The method is applicable to configurations consisting of three stages or two stages plus boosters. The trajectory is divided into three steps, one for each stage plus one for all boosters. Five control parameters are used: The first is the constant pitch rate, used during the pitch over maneuver. The other four define the angle of attack rate functions. A declining exponential function is used for \(\dot{\alpha }_2(t)\) , whereas \(\dot{\alpha }_3(t)\) is chosen so that \(\alpha _3(t)\) becomes an inverted parabola. The trajectory algorithm consists of an outer and an inner loop. The outer loop varies the pitch rate to attain the correct apogee. It calls the inner loop, which adjusts the two parameters that define \(\dot{\alpha }_2(t)\) so that the flight path angle rate at the end of the second step becomes zero. Tests were performed for a model of Ariane 40. Its payload capacity was determined in less than \({30}\hbox { s}\) and the result matched the one produced by a conventional approach. Moreover, a Monte Carlo simulation, based on the Ariane 40 model, was performed for both applications. The success rate was 94% for the first and 93% for the second case.
      PubDate: 2019-03-15
       
  • Magnetic Mars dust-removal technology
    • Authors: Francisco J. Arias; Salvador De Las Heras
      Abstract: Environmental data recorded by the Mars exploration rovers show that the martian dust is magnetic containing mostly the strong magnetic mineral magnetite ( \({\text {Fe}}_3{\text {O}}_4\) ). On the other hand, it is known that dust settling onto the surface of solar arrays can affect the utility on solar power on any Mars mission, and particulary for long-term operation. Dust obscuration of solar arrays can be a special issue for the case of a future 6-month sample fetching rover (SFR) mission, where the current baseline architecture contemplates the use of solar array and where dust storms can jeopardize the entire mission, not only affecting the supply of energy for locomotion but for the communication with the Mars ascent vehicle (MAV). Today, available dust-removal techniques have been classified into four categories: natural, mechanical, electromechanical, and electrostatic. However, by aforementioned, an additional category may be included in this portfolio based in the magnetic properties of the martian dust. Here a first scoping study for a magnetic Mars dust technology is outlined. Finally, a specific ad hoc magnetic technology is proposed an analyzed.
      PubDate: 2019-02-04
      DOI: 10.1007/s12567-019-0235-y
       
  • Structural development of ultra-lean-burn preburners for small liquid
           engines
    • Authors: Jaehan Yoo; Seong-up Ha; Soo Yong Lee
      Abstract: An ultra-lean-burn preburner has been developed by KARI. This paper describes the general structural design, the results of the finite element analyses (FEA) and the experimental results related to structural issues during the development. Before the fabrication, two burst experiments with the specimens simulating the brazing joints were performed and compared with the FEA results, which increases the reliability of the analyses and the design. Also, 2D FEA of the combustion chamber cooling channel were performed for the first combustion region upstream of the liquid oxygen (LOX) hole and the second region downstream of the hole, where the hottest spot locates downstream of the region between the adjacent LOX holes. Various structural modifications were analyzed by 3D FEA and a screen structure was introduced to reduce the stress over highly stressed regions. During the development, some proof and leakage tests were performed for the head, the chamber with and without flange, and the preburner assembly, of which the burst test was performed. Several firing tests of the assembly were performed to show the operation without any structural failure.
      PubDate: 2019-02-01
      DOI: 10.1007/s12567-019-0238-8
       
 
 
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