Subjects -> MATHEMATICS (Total: 1100 journals)     - APPLIED MATHEMATICS (88 journals)    - GEOMETRY AND TOPOLOGY (23 journals)    - MATHEMATICS (812 journals)    - MATHEMATICS (GENERAL) (43 journals)    - NUMERICAL ANALYSIS (24 journals)    - PROBABILITIES AND MATH STATISTICS (110 journals) MATHEMATICS (812 journals)                  1 2 3 4 5 | Last
 Showing 1 - 200 of 538 Journals sorted alphabetically Abakós       (Followers: 5) Abhandlungen aus dem Mathematischen Seminar der Universitat Hamburg       (Followers: 4) Academic Voices : A Multidisciplinary Journal       (Followers: 2) Accounting Perspectives       (Followers: 7) ACM Transactions on Algorithms (TALG)       (Followers: 16) ACM Transactions on Computational Logic (TOCL)       (Followers: 3) ACM Transactions on Mathematical Software (TOMS)       (Followers: 6) ACS Applied Materials & Interfaces       (Followers: 39) Acta Applicandae Mathematicae       (Followers: 1) Acta Mathematica       (Followers: 13) Acta Mathematica Hungarica       (Followers: 2) Acta Mathematica Scientia       (Followers: 5) Acta Mathematica Sinica, English Series       (Followers: 6) Acta Mathematica Vietnamica Acta Mathematicae Applicatae Sinica, English Series Advanced Science Letters       (Followers: 12) Advances in Applied Clifford Algebras       (Followers: 4) Advances in Calculus of Variations       (Followers: 6) Advances in Catalysis       (Followers: 5) Advances in Complex Systems       (Followers: 10) Advances in Computational Mathematics       (Followers: 23) Advances in Decision Sciences       (Followers: 4) Advances in Difference Equations       (Followers: 3) Advances in Fixed Point Theory       (Followers: 8) Advances in Geosciences (ADGEO)       (Followers: 19) Advances in Linear Algebra & Matrix Theory       (Followers: 11) Advances in Materials Science       (Followers: 19) Advances in Mathematical Physics       (Followers: 8) Advances in Mathematics       (Followers: 17) Advances in Nonlinear Analysis       (Followers: 1) Advances in Numerical Analysis       (Followers: 9) Advances in Operations Research       (Followers: 13) Advances in Operator Theory       (Followers: 4) Advances in Porous Media       (Followers: 5) Advances in Pure and Applied Mathematics       (Followers: 10) Advances in Pure Mathematics       (Followers: 11) Advances in Science and Research (ASR)       (Followers: 9) Aequationes Mathematicae       (Followers: 2) African Journal of Educational Studies in Mathematics and Sciences       (Followers: 9) African Journal of Mathematics and Computer Science Research       (Followers: 7) Afrika Matematika       (Followers: 3) Air, Soil & Water Research       (Followers: 13) AKSIOMA Journal of Mathematics Education       (Followers: 3) AKSIOMATIK : Jurnal Penelitian Pendidikan dan Pembelajaran Matematika       (Followers: 1) Al-Jabar : Jurnal Pendidikan Matematika       (Followers: 1) Al-Qadisiyah Journal for Computer Science and Mathematics       (Followers: 1) AL-Rafidain Journal of Computer Sciences and Mathematics       (Followers: 6) Algebra and Logic       (Followers: 7) Algebra Colloquium       (Followers: 4) Algebra Universalis       (Followers: 2) Algorithmic Operations Research       (Followers: 5) Algorithms       (Followers: 12) Algorithms Research       (Followers: 1) American Journal of Computational and Applied Mathematics       (Followers: 10) American Journal of Mathematical Analysis       (Followers: 2) American Journal of Mathematical and Management Sciences       (Followers: 1) American Journal of Mathematics       (Followers: 7) American Journal of Operations Research       (Followers: 8) American Mathematical Monthly       (Followers: 6) An International Journal of Optimization and Control: Theories & Applications       (Followers: 11) Anadol University Journal of Science and Technology B : Theoritical Sciences Analele Universitatii Ovidius Constanta - Seria Matematica Analysis and Applications       (Followers: 1) Analysis and Mathematical Physics       (Followers: 6) Analysis Mathematica Analysis. 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A Mathematical Journal Current Research in Biostatistics       (Followers: 8) Czechoslovak Mathematical Journal       (Followers: 1) Daya Matematis : Jurnal Inovasi Pendidikan Matematika       (Followers: 2) Demographic Research       (Followers: 15) Demonstratio Mathematica

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Similar Journals
 CEAS Space JournalJournal Prestige (SJR): 0.278 Citation Impact (citeScore): 1Number of Followers: 3      Hybrid journal (It can contain Open Access articles) ISSN (Print) 1868-2510 - ISSN (Online) 1868-2502 Published by Springer-Verlag  [2626 journals]
• Autonomous GNC strategy for an asteroid impactor mission
• Abstract: Abstract The Solar System features thousands of Near-Earth Asteroids that could be at collision risk with our planet in the future. Scientists are investigating the possibility of deflecting asteroids from their trajectory by means of a hyper-velocity impactor spacecraft. The aim of this research is to develop and simulate a GNC strategy to control the spacecraft towards its impact with the asteroid. The navigation is based on the use of a camera to estimate the relative position through image analysis and a filtering process. A zero-effort error strategy is adopted for the control. A simulator has been developed to render the simulated images online and test the GNC algorithms. The simulator is used to assess the performance of the strategy on different scenarios and to perform a sensitivity analysis with respect to the environmental and design parameters.
PubDate: 2020-07-02

• Autonomous reconfiguration of a distributed synthetic aperture radar
driven by mission requirements
• Abstract: Abstract This paper introduces a strategy for an autonomous reconfiguration of a fractionated synthetic aperture radar (SAR) spacecraft system. The radar antenna is distributed on a small-satellite formation that can be reconfigured on orbit depending on the mission requirements. Once the acquisition geometry is specified in terms of formation type and the desired requirements are defined, the information is transmitted to the cluster. Hence, each satellite determines its own final state and elaborates the necessary trajectory for maneuvering. The reconfiguration algorithm is decentralized and exists in a distributed computational architecture. Therefore, the spacecraft platforms are assumed to be equal and able to communicate among each other. To demonstrate the viability of the proposed approach, a specific scenario is considered, with a distributed SAR operating at X-band that has to be reconfigured for interferometric applications. Simulation results show that once remote sensing requirements are specified, the developed algorithm can manage autonomously the spacecraft reconfiguration toward the corresponding operative pattern.
PubDate: 2020-06-30

• Stability analysis and flight control design of the winged reusable launch
vehicle ReFEx
• Abstract: Abstract The German Aerospace Center (DLR) is currently studying different technologies for reusable launch vehicles (RLVs) to evaluate and compare their benefits. The project CALLISTO (Cooperative Action Leading to Launcher Innovation in Stage Toss-back Operations) investigates a VTVL (vertical takeoff, vertical landing) concept. In the DLR project ReFEx (reusability flight experiment), in the context of which this paper is presented, a winged VTHL (vertical takeoff, horizontal landing) concept is investigated to develop the key technologies for future winged RLV applications, culminating in a flight experiment to demonstrate the capability of controlled autonomous return flight from supersonic to subsonic speeds. In this paper, analysis of stability and controllability is used on a three-dimensional envelope of points to derive a suitable flight corridor for the re-entry. Second, a controller concept based on inversion of the rotational equations of motion is derived. The validity of the presented controller concept is shown on a preliminary level via comparison of open-loop and closed-loop dynamics at two representative flight points and a time simulation which includes a segment of the planned mission.
PubDate: 2020-06-30

• Laser metrology concept consolidation for NGGM
• Abstract: Abstract The measurement of the static and temporal variation of Earth’s gravity field yields important information on water storage, seasonal and sub-seasonal water cycles, their impact on water levels and delivers key data to Earth’s climate models. The satellite missions GOCE (ESA), GRACE (US-GER) and just recently GRACE Follow-On (US-GER) resulted in a significant improvement on our understanding of the system Earth. To further improve the measurement accuracy of the time-variable gravity field, ESA is investigating the concept of a ‘Next Generation Gravity Mission’ (NGGM), consisting of two pairs of satellites and a heterodyne laser interferometer for inter-satellite ranging. Based on the heritage of the development of the laser ranging interferometer for GRACE Follow-On and the former and ongoing studies for NGGM, two schemes for the Laser Metrology Instrument (LMI) for NGGM, namely the transponder and the retroreflector scheme have been investigated and are presented in this paper. The results include the instrument ranging performance analyses, the laser link acquisition, an instrument reliability assessment and redundancy approach as well as the Technology Readiness Level assessment of the individual instrument units.
PubDate: 2020-06-27

• A cutting edge 6U CubeSat ADCS design for Earth observation with sub-meter
spatial resolution at 230–380 km altitude
• Abstract: Abstract A 6U CubeSat for Earth observation in 230–350 km orbits with sub-meter resolution is presented. The proposed Stable and Highly Accurate Pointing Earth-Imager (SHAPE) system’s attitude determination and control system (ADCS) is composed of a single momentum bias wheel with magnetic bearings at rotational speeds of 6000–7000 rpm and refined magnetorquers. Reaction wheels as instability source are absent. The ADCS stabilizes the spacecraft attitude by counteracting the torques from external disturbances in the thermosphere down to < 1° pointing accuracy and < 0.1° instability. The momentum wheel was sized to an angular momentum of 1 Nms based on the worst-case atmospheric density of the next solar cycle. The 0.5 Am2 magnetorquer dipole moment provides with low power consumption, mass and cost, high reliability and sufficient torque. The ADCS initialisation study revealed three stable start-up modes, while the all-spun state is achieved using a set of thrusters. De-tumbling analysis show that the magnetorquers reduce the tumbling rates with magnitudes of up to 35°/s to mean motion values in less than an orbit using a static gain B-dot controller. A 3U camera design capable of sub-meter spatial resolution at 230 km altitude is presented which complies with the SHAPE spacecraft system design. The instrument has a single deployable primary mirror enabled by a deployment hinge design with hysteresis < 0.5 μ. This payload combined with air-breathing electric propulsion technology at 230 km nominal altitude boosts the SHAPE system Earth observation potential down to sub-meter spatial resolution and enables tuning of the mission lifetime by orbit keeping.
PubDate: 2020-06-18

• Enabling radiation tolerant heterogeneous GPU-based onboard data
processing in space
• Abstract: Abstract The last decade has seen a dramatic increase in small satellite missions for commercial, public, and government intelligence applications. Given the rapid commercialization of constellation-driven services in Earth Observation, situational domain awareness, communications including machine-to-machine interface, exploration etc., small satellites represent an enabling technology for a large growth market generating truly Big Data. Examples of modern sensors that can generate very large amounts of data are optical sensing, hyperspectral, Synthetic Aperture Radar (SAR), and Infrared imaging. Traditional handling and downloading of Big Data from space requires a large onboard mass storage and high bandwidth downlink with a trend towards optical links. Many missions and applications can benefit significantly from onboard cloud computing similarly to Earth-based cloud services. Hence, enabling space systems to provide near real-time data and enable low latency distribution of critical and time sensitive information to users. In addition, the downlink capability can be more effectively utilized by applying more onboard processing to reduce the data and create high value information products. This paper discusses current implementations and roadmap for leveraging high performance computing tools and methods on small satellites with radiation tolerant hardware. This includes runtime analysis with benchmarks of convolutional neural networks and matrix multiplications using industry standard tools (e.g., TensorFlow and PlaidML). In addition, a ½ CubeSat volume unit (0.5U) (10 × 10 × 5 cm3) cloud computing solution, called SpaceCloud™ iX5100 based on AMD 28 nm APU technology is presented as an example of heterogeneous computer solution. An evaluation of the AMD 14 nm Ryzen APU is presented as a candidate for future advanced onboard processing for space vehicles.
PubDate: 2020-06-15

• Latest modification of the deployable space reflector structure with
V-folding bars
• Abstract: Abstract In this paper, a new modification of the mechanical load-bearing ring structure is considered. It is shown that due to the appropriate changes made to the ring, its structure possesses obvious advantages as compared with the previously proposed variant. The projecting tips of the struts to which the central flexible shaping system is attached are replaced by paired levers with torsion springs of new design, which guarantee the smooth deployment of the ring and keep the cables in permanently tensioned condition. In the new modification, the central flexible shaping system is directly attached to the upper and lower hoops of the ring, thereby preventing the bending of struts when the reflector is completely deployed. The new multi-stage deployment scheme of the structure considered in the paper operates without synchronization mechanisms—the upper and lower kinematic chains get deployed not simultaneously as in the previous ring variant but in alternating order. The validity of design computations is confirmed by the FEM mathematical models for which deformations of structural elements, displacement of nodes, and eigenfrequency values are determined. The optimization of structural elements makes it possible to design the mechanical characteristics and strength margin of the ring with a minimal number of elements and minimal cross-sectional values, which simplifies the ring structure on the whole, and reduces its weight.
PubDate: 2020-06-01

• Life cycle cost estimation for high-speed transportation systems
• Abstract: Abstract This paper presents an innovative methodology and tool developed by Politecnico di Torino and the European Space Agency (ESA) to support life cycle cost (LCC) estimation for high-speed transportation systems. This ad hoc built-in tool aims at supporting engineers in cost estimations during conceptual and preliminary design phases. This includes the evaluation of research, development, test and evaluation costs (RDTE costs), production costs as well as direct and indirect operating costs (DOC and IOC). Eventually, the results of the LCC evaluation for two different high-speed transport vehicles is provided and discussed.
PubDate: 2020-06-01

• Numerical simulation of transpiration cooling experiments in supersonic
flow using OpenFOAM
• Abstract: Abstract Transpiration cooling applied to modern ceramic matrix composite materials is an interesting concept for thermal protection of future aerospace applications. Therefore, reliable and accurate numerical tools for the simulation of transpiration cooling processes in complex flow situations and for complex porous geometries are needed. In this study, we present a fully coupled OpenFOAM solver and discuss the choice of suitable interface conditions as well as the coupling of numerical domains at the transpired surface. Additionally, a modified turbulence boundary condition for transpiration through low-porosity materials is proposed. The numerical solver is then applied to validation test cases with a flat and a double-wedge porous sample under blowing ratios up to $$F_{\text{Air}} = 0.75\%$$. The corresponding experiments with Carbon/Carbon samples were performed at the ITLR Hot Gas Facility at supersonic steady-state conditions, i.e. $${\text{Ma}} = 2.5$$ and $$T_{t} = 500\;{\text{K}}$$. The simulation results are in good overall agreement with the experimental data for both test cases while capturing the influences of blowing ratio, as well as variations of the external flow field and in the heat flux distribution. Temperature predictions for the sample surface, within the porous wall, and in the downstream wake region show a good conformity to measurements, whereas deviations are observed in the direct wake. Based on the complementary insights provided by the numerical results, aspects such as the coolant through-flow behaviour as well as the sample’s internal temperature distribution and heat conduction are analysed.
PubDate: 2020-06-01

• Hypersonic transatmospheric and exoatmospheric vehicle design using the
SUAVE tool
• Abstract: Abstract This work reports the introduction of a set of low-fidelity aerodynamic and propulsion models to the preliminary vehicle design suite SUAVE. This enables the capability to predict transatmospheric and exoatmospheric hypersonic flight performance. Verification and validation for the different subsystem modules have been carried out against existing data, namely regarding the propulsion (ramjet, scramjet, LOX/LH2 rocket, combined-cycle engines) and aerothermodynamic (reentry) subcomponents. Two sample test-cases, based on the vehicular properties of the SR-72 vehicle (size and wing area) have been analyzed. A flight range of about 10,000 km for a flight time between 1 h (exoatmospheric flight) and 2h30 (transatmospheric flight) has been determined for a set of theoretical reasonable efficiencies for the subcomponents (chiefly propulsion). The obtained results provide a contribution to hypersonic vehicle development roadmaps, proposing two credible mission profiles (trans- and exoatmospheric) and highlighting the key role of propulsion technology development for the advancement of the state-of-the-art.
PubDate: 2020-06-01

• Detonation–deflagration one-dimensional mode transition analysis for
parallel-plate plasma accelerators
• Abstract: Abstract Parallel-plate pulsed plasma thrusters (PPTs) and quasi-steady MPD thrusters are largely distinguished by the discrete current sheet propagation (also referred as detonation acceleration mode) and stationary steady-phase current patterns (deflagration acceleration mode), respectively. Experimental and numerical research attempts in the past have focused on showing that the two modes of operations could be explained using the same continuum process. Present work proposes a simple unified analytical energy balance model to capture this mode transition in pulsed electromagnetic thrusters. The model is tested for a high-energy PPT developed at NASA-Glenn Research Center, which operates predominantly in the quasi-steady mode. The influence of thruster geometry and circuit parameters on the mode of operation and electrical energy efficiency is analyzed. Based on the analysis of the energy transfer efficiency, it is found that operating the thruster in the quasi-steady mode improves the transfer efficiency by approximately $$10\%$$. It is concluded that the effective electrode length, pulse timing, circuit parameters, and electrode geometry could be optimized to operate the thruster in the quasi-steady/deflagration mode, hence improving the electrical energy transfer efficiency.
PubDate: 2020-06-01

• Design of converging-diverging nozzles with constant-radius centerbody
• Abstract: Abstract Several flow phenomena, such as recirculating wake flows or noise generation, occur in aerodynamic configurations with backward facing steps. In this context, subsonic nozzles with constant-radius centerbodies exist, which enable fundamental research of these phenomena for $$M < 1$$. For the supersonic regime, however, the existing database and knowledge are limited. Therefore, this work presents a design approach for a converging-diverging nozzle with constant-radius centerbody. For the nozzle throat, Sauer’s method is modified to include a centerbody. The method of characteristics is used for the subsequent supersonic portion. Comparing the analytical calculations to numerical simulations results in very good agreement and therefore underlines the feasibility of the chosen approach. Viscosity reduced the Mach number on the exit plane by 1.0–1.2% and therefore had little influence.
PubDate: 2020-06-01

• Influence of T-128 wind tunnel perforated walls on aerodynamic
characteristics of reentry vehicles at transonic speed
• Abstract: Abstract The paper is devoted to the study of the influence of wind tunnel perforated walls on the aerodynamic characteristics of the reentry vehicle model at transonic speed. An experimental investigations were conducted with a model at zero angle of attack in the T-128 TsAGI transonic wind tunnel within the range of Mach numbers M = 0.9–1.1 at three perforation ratios of test section walls F = 2; 6; 10%. Aerodynamic forces and moments acting on the model were measured with a six-component internal strain-gauge balance. A distribution of static pressure on the model surface and on the test section perforated walls was measured along with static pressure fluctuations. Integral parameters of the boundary layer on the perforated wall were measured by means of the rake with total pressure probes. Numerical investigations of the flow around the model in the test section were performed by solving Reynolds Averaged Navier–Stocks (RANS) equations using the Electronic Wind Tunnel software (EWT-TsAGI). Satisfactory agreement was obtained between the computational and experimental data on the effect of the test section perforated walls on the aerodynamic characteristics of the model and the flow parameters on the wall. The influence of the perforation coefficient on the model drag coefficient in the calculations and in the experiment had the same trend. The maximum error of the drag coefficient at a simplified computational model is estimated to be 0.05. The highest effect of perforation on the drag coefficient of reentry vehicle is comprised if 1.05 < M < 1.1 and makes ΔCD ≈ 0.03–0.04.
PubDate: 2020-06-01

• ESTNeT: a discrete event simulator for space-terrestrial networks
• Abstract: Abstract The capabilities of small satellites have improved significantly in recent years. Specifically multi-satellite systems become increasingly popular, since they allow the support of new applications. The development and testing of these multi-satellite systems is a new challenge for engineers and requires the implementation of appropriate development and testing environments. In this paper, a modular network simulation framework for space–terrestrial systems is presented. It enables discrete event simulations for the development and testing of communication protocols, as well as mission-based analysis of other satellite system aspects, such as power supply and attitude control. ESTNeT is based on the discrete event simulator OMNeT++ and will be released under an open source license.
PubDate: 2020-05-26

• From ice to space: a greenhouse design for Moon or Mars based on a
prototype deployed in Antarctica
• Abstract: Abstract The future of human space exploration is aimed at long-term missions to Moon and Mars. Currently, plans are elaborated by NASA, ESA, CNSA and others for a return to the lunar environment within the next decade as an intermediate step towards the goal of reaching the surface of Mars. For sustenance and crew comfort the crew of such long-duration missions should be provided with fresh food on the lunar or Martian surface. Due to the associated power demand, the required resources and technological complexity, this is a major challenge for this kind of missions. To continuously provide fresh food without the need for cargo transfer from Earth towards Moon or Mars an on-site greenhouse system is required, producing the fresh food in situ. The associated effort and cost for all resources to be transported to the base of operation prohibit any waste of resources, requiring a system operating in a (nearly) closed loop. Developing and validating a prototype for an effective and efficient greenhouse, labeled future exploration greenhouse (FEG) for space exploration has been the goal of the EDEN ISS project, funded by the EU, in the past 4 years. This paper shows the results of a design elaboration of the FEG into a greenhouse for planetary deployment on Moon or Mars. Guided by lessons learned from operating the FEG in Antarctica for one year and based on assumptions concerning the mission scenario, e.g. assuming an existing base infrastructure on-site, the presented design incorporates a plant growth area which is more than a factor of two larger than the prototype. The total mass of the cylindrical system, including equipment required during launch, transfer and landing, is about 19 mT, fitting into a Falcon 9 launcher. The versatile design is compatible with a wide variety of mission scenarios, e.g. ESA’s Moon Village, and currently public mission plans.
PubDate: 2020-05-16

• Influence of crop cultivation conditions on space greenhouse equivalent
system mass
• Abstract: Abstract Future crewed space missions will make use of hybrid life support systems to sustain human presence in space and on other planetary bodies. Plants fulfill essential roles in those systems such as carbon dioxide removal, oxygen production, and food production. The systems required to grow plants in space, so-called space greenhouses, are complex and need to be built as efficient as possible. Thereby, the resources mass, volume, energy, and crewtime required to grow a certain amount of food are essential because these parameters define the effectiveness of the space greenhouse. However, the required resources depend on the size of the greenhouse which in turn depends on the productivity of the crops which in turn depend on the cultivation conditions. The output of such a system can be calculated using the Modified Energy Cascade plant production model, which can simulate the food output depending on the cultivation conditions. Traditionally, life support systems are evaluated using the Equivalent System Mass method, which can determine the cost effective life support architecture for a given mission scenario. By combining both, the influence of the cultivation conditions inside the space greenhouse on the effectiveness of the complete system can be investigated. It seems counterintuitive first, but it is more effective to increase the energy per area provided to the plants in the form of light. Although that increases the electrical energy demand per area, the reduction in required cultivation area and, therefore, system size leads to a more efficient system.
PubDate: 2020-05-06

• Design of a direct-detection wind and aerosol lidar for mars orbit
• Abstract: Abstract The present knowledge of the Mars atmosphere is greatly limited by a lack of global measurements of winds and aerosols. Hence, measurements of height-resolved wind and aerosol profiles are a priority for new Mars orbiting missions. We have designed a direct-detection lidar (MARLI) to provide global measurements of dust, winds and water ice profiles from Mars orbit. From a 400-km polar orbit, the instrument is designed to provide wind and backscatter measurements with a vertical resolution of 2 km and with resolution of 2° in latitude along track. The instrument uses a single-frequency, seeded Nd:YAG laser that emits 4 mJ pulses at 1064 nm at a 250 Hz pulse rate. The receiver utilizes a 50-cm diameter telescope and a double-edge Fabry-Pérot etalon as a frequency discriminator to measure the Doppler shift of the aerosol-backscatter profiles. The receiver also includes a polarization-sensitive channel to detect the cross-polarized backscatter profiles from water ice. The receiver uses a sensitive 4 × 4 pixel HgCdTe avalanche photodiode array as a detector for all signals. Here we describe the measurement concept, instrument design, and calculate its performance for several cases of Mars atmospheric conditions. The calculations show that under a range of atmospheric conditions MARLI is capable of measuring wind speed profiles with random error of 2–4 m/s within the first three scale heights, enabling vertically resolved mapping of transport processes in this important region of the atmosphere.
PubDate: 2020-02-17

• Aerodynamic database of the HEXAFLY-INT hypersonic glider
• Abstract: Abstract The present paper is devoted to the aerodynamic characterization and analysis of the HEXAFLY-INT hypersonic glider, developed in the frame of an international project co-funded by the European Community and the European Space Agency. This project aims to design, manufacture and flight test an innovative gliding hypersonic vehicle, which is based on the configuration developed in the previous projects LAPCAT I, II (Steelant et al. in 1st International conference on high-speed vehicle science and technology (HiSST), HiSST-2018-3101064, 26–29/11/2018, Moscow, Russia; Steelant in 15th AIAA international space planes and hypersonic systems and technologies conference, AIAA-2008-2578, 28 April–01 May 2008, Dayton, Ohio, USA) and HEXAFLY (Steelant et al. in 21st AIAA international space planes and hypersonic systems and technology conference, AIAA-2017-2393, 6–9 March 2017, Xiamen, China) and other technologies elaborated in ATLLAS I and II (Steelant et al. in 20th AIAA international space planes and hypersonic systems and technologies conference, AIAA-2015-3677, 5–8 July 2015, Glasgow, Scotland, UK; Steelant in 15th AIAA international space planes and hypersonic systems and technologies conference, AIAA-2008-2582, 28 April–01 May 2008, Dayton, Ohio, USA). The flight experiment consists of a self-controlled glider configuration featuring a high aerodynamic efficiency. This flight demonstrator is equipped with an on-board breakthrough sensing and data acquisition system that will provide valuable aero-thermodynamic and thermo-mechanical data. The measured data will serve to validate the design methodologies and demonstrate the technologies that enable hypersonic transportation. The aerodynamic database comprises an extensive set of CFD simulations of increasing level of accuracy, and an experimental test campaign carried out in the TsAGI T-116 wind tunnel.
PubDate: 2020-02-05

• Polygon stacks and time reference conversions
• Abstract: Abstract This paper describes how a time-based planning system, which supports resource constraints, may be extended such that a resource constraint interval does not have to refer to the start- or end-time of the underlying activity but to any linear combination thereof, such as the middle. This way, an activity with multiple resource constraints referring to different time intervals no longer has to be split into sub-activities, which may simplify the planning model and the algorithm. To be able to describe the necessary transformations, we introduce the concept of PolygonStacks and describe the operations which a typical planning engine requires to intersect the sets of consistent timeline entries of all constraints defined on an activity. We then introduce Sliders and Offsets, which allow specifying the constraint intervals in a more generic way as supported in current planning models. Based on this preparation, we can derive two lemmas, which provide the conversions required by Sliders and Offsets. We continue with several conversion examples and point out how to solve the issues which will occur during implementation. A short sketch of the complexity of our current implementation demonstrates that further work on performance should be considered, even though in practice we observe that the bottleneck of calculation remains within profile calculation rather than PolygonStack operations.
PubDate: 2020-01-27

• Injector-coupled thermoacoustic instabilities in an experimental
LOX-methane rocket combustor during start-up
• Abstract: Abstract This paper reports the investigation of acoustic combustion instability experienced during repetitive ignition testing of a sub-scale LOX-methane rocket thrust chamber. The occurrence of resonant coupling between the LOX injectors and the combustion chamber acoustic modes was assessed from the experimental data recorded during the highly transient phase of operation from ignition up to around 2 s. A method was developed to model the evolution of acoustic properties in both the combustion chamber and the injectors during the transient period. For the LOX injectors, the Woods equation was used to estimate the speed of sound in the two-phase flow. The models were used to identify the corresponding mode frequencies in the unsteady pressure measurements, and show that the high-amplitude instability occurred when they intersected. Very close coupling of less than 3% frequency difference is required for high amplitudes to be observed. However, the condition was necessary but not sufficient for high amplitudes to be reached.
PubDate: 2020-01-08

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