for Journals by Title or ISSN for Articles by Keywords help
 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
Similar Journals
 CEAS Space JournalJournal Prestige (SJR): 0.278 Citation Impact (citeScore): 1Number of Followers: 2      Hybrid journal (It can contain Open Access articles) ISSN (Print) 1868-2510 - ISSN (Online) 1868-2502 Published by Springer-Verlag  [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

• 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
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
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
• 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

JournalTOCs
School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
Email: journaltocs@hw.ac.uk
Tel: +00 44 (0)131 4513762
Fax: +00 44 (0)131 4513327

Home (Search)
Subjects A-Z
Publishers A-Z
Customise
APIs