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 Showing 1 - 200 of 872 Journals sorted alphabetically 3D Printing and Additive Manufacturing       (Followers: 20) Abakós       (Followers: 4) ACM Computing Surveys       (Followers: 27) ACM Journal on Computing and Cultural Heritage       (Followers: 8) ACM Journal on Emerging Technologies in Computing Systems       (Followers: 12) ACM Transactions on Accessible Computing (TACCESS)       (Followers: 3) ACM Transactions on Algorithms (TALG)       (Followers: 15) ACM Transactions on Applied Perception (TAP)       (Followers: 5) ACM Transactions on Architecture and Code Optimization (TACO)       (Followers: 9) ACM Transactions on Autonomous and Adaptive Systems (TAAS)       (Followers: 7) ACM Transactions on Computation Theory (TOCT)       (Followers: 12) ACM Transactions on Computational Logic (TOCL)       (Followers: 3) ACM Transactions on Computer Systems (TOCS)       (Followers: 18) ACM Transactions on Computer-Human Interaction       (Followers: 15) ACM Transactions on Computing Education (TOCE)       (Followers: 5) ACM Transactions on Design Automation of Electronic Systems (TODAES)       (Followers: 4) ACM Transactions on Economics and Computation ACM Transactions on Embedded Computing Systems (TECS)       (Followers: 3) ACM Transactions on Information Systems (TOIS)       (Followers: 19) ACM Transactions on Intelligent Systems and Technology (TIST)       (Followers: 8) ACM Transactions on Interactive Intelligent Systems (TiiS)       (Followers: 3) ACM Transactions on Multimedia Computing, Communications, and Applications (TOMCCAP)       (Followers: 9) ACM Transactions on Reconfigurable Technology and Systems (TRETS)       (Followers: 6) ACM Transactions on Sensor Networks (TOSN)       (Followers: 8) ACM Transactions on Speech and Language Processing (TSLP)       (Followers: 9) ACM Transactions on Storage ACS Applied Materials & Interfaces       (Followers: 29) Acta Automatica Sinica       (Followers: 2) Acta Informatica Malaysia Acta Universitatis Cibiniensis. 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 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  [2351 journals]
• Calibration OGSEs for multichannel radiometers for Mars atmosphere studies
• Authors: J. J. Jiménez; F. J Álvarez; M. Gonzalez-Guerrero; V. Apéstigue; I. Martín; J. M. Fernández; A. A. Fernán; I. Arruego
Pages: 127 - 145
Abstract: This work describes several Optical Ground Support Equipment (OGSEs) developed by INTA (Spanish Institute of Aerospace Technology—Instituto Nacional de Técnica Aeroespacial) for the calibration and characterization of their self-manufactured multichannel radiometers (solar irradiance sensors—SIS) developed for working on the surface of Mars and studying the atmosphere of that planet. Nowadays, INTA is developing two SIS for the ESA ExoMars 2020 and for the JPL/NASA Mars 2020 missions. These calibration OGSEs have been improved since the first model in 2011 developed for Mars MetNet Precursor mission. This work describes the currently used OGSE. Calibration tests provide an objective evidence of the SIS performance, allowing the conversion of the electrical sensor output into accurate physical measurements (irradiance) with uncertainty bounds. Calibration results of the SIS on board of the Dust characterisation, Risk assessment, and Environment Analyzer on the Martian Surface (DREAMS) on board the ExoMars 2016 Schiaparelli module (EDM—entry and descent module) are also presented, as well as their error propagation. Theoretical precision and accuracy of the instrument are determined by these results. Two types of OGSE are used as a function of the pursued aim: calibration OGSEs and Optical Fast Verification (OFV) GSE. Calibration OGSEs consist of three setups which characterize with the highest possible accuracy, the responsivity, the angular response and the thermal behavior; OFV OGSE verify that the performance of the sensor is close to nominal after every environmental and qualification test. Results show that the accuracy of the calibrated sensors is a function of the accuracy of the optical detectors and of the light conditions. For normal direct incidence and diffuse light, the accuracy is in the same order of uncertainty as that of the reference cell used for fixing the irradiance, which is about 1%.
PubDate: 2018-06-01
DOI: 10.1007/s12567-018-0194-8
Issue No: Vol. 10, No. 2 (2018)

• Model-based software engineering for an optical navigation system for
spacecraft
• Authors: T. Franz; D. Lüdtke; O. Maibaum; A. Gerndt
Pages: 147 - 156
Abstract: The project Autonomous Terrain-based Optical Navigation (ATON) at the German Aerospace Center (DLR) is developing an optical navigation system for future landing missions on celestial bodies such as the moon or asteroids. Image data obtained by optical sensors can be used for autonomous determination of the spacecraft’s position and attitude. Camera-in-the-loop experiments in the Testbed for Robotic Optical Navigation (TRON) laboratory and flight campaigns with unmanned aerial vehicle (UAV) are performed to gather flight data for further development and to test the system in a closed-loop scenario. The software modules are executed in the C++ Tasking Framework that provides the means to concurrently run the modules in separated tasks, send messages between tasks, and schedule task execution based on events. Since the project is developed in collaboration with several institutes in different domains at DLR, clearly defined and well-documented interfaces are necessary. Preventing misconceptions caused by differences between various development philosophies and standards turned out to be challenging. After the first development cycles with manual Interface Control Documents (ICD) and manual implementation of the complex interactions between modules, we switched to a model-based approach. The ATON model covers a graphical description of the modules, their parameters and communication patterns. Type and consistency checks on this formal level help to reduce errors in the system. The model enables the generation of interfaces and unified data types as well as their documentation. Furthermore, the C++ code for the exchange of data between the modules and the scheduling of the software tasks is created automatically. With this approach, changing the data flow in the system or adding additional components (e.g., a second camera) have become trivial.
PubDate: 2018-06-01
DOI: 10.1007/s12567-017-0173-5
Issue No: Vol. 10, No. 2 (2018)

• A concept of active mount for space applications
• Authors: A. Souleille; T. Lampert; V. Lafarga; S. Hellegouarch; A. Rondineau; G. Rodrigues; C. Collette
Pages: 157 - 165
Abstract: Sensitive payloads mounted on top of launchers are subjected to many sources of disturbances during the flight. The most severe dynamic loads arise from the ignition of the motors, gusts, pressure fluctuations in the booster and from the separation of the boosters. The transmission of these dynamic forces can be reduced by mounting payloads on passive isolators, which comes at the expense of harmful amplifications of the motion at low frequency due to suspension resonances. To bypass this shortcoming, this paper presents a novel concept of active mount for aerospace payloads, which is easy to install, and meets two objectives. The first one is a high damping authority on both suspension resonances and flexible resonances without compromising the isolation and large stability margins of the closed loop system due to the collocation of the actuator and the sensor. The second one is a broadband reduction of the dynamic force transmitted to the payload, which was achieved in terms of 16 dB. The concept is presented in the first part of the paper and studied numerically and experimentally on a single degree of freedom isolator. A commercial isolator has been chosen for the purpose of the demonstration. The second part of the paper is dedicated to experimental validations on multi-degree of freedom scaled test benches. It is shown that the force feedback allows damping of both suspension and flexible modes (first and second modes, respectively), and significantly reducing the force transmitted in some broad frequency ranges.
PubDate: 2018-06-01
DOI: 10.1007/s12567-017-0180-6
Issue No: Vol. 10, No. 2 (2018)

• The Aurora space launcher concept
• Authors: Alexander Kopp; Sven Stappert; David Mattsson; Kurt Olofsson; Erik Marklund; Guido Kurth; Erwin Mooij; Evelyne Roorda
Pages: 167 - 187
Abstract: This paper gives an overview about the Aurora reusable space launcher concept study that was initiated in late-2015/early-2016. Within the Aurora study, several spaceplane-like vehicle configurations with different geometries, propulsion systems and mission profiles will be designed, investigated and evaluated with respect to their technical and economic feasibility. The first part of this paper will discuss the study logic and the current status of the Aurora studies and introduces the first vehicle configurations and their system design status. As the identification of highly efficient structural designs is of particular interest for Aurora, the structural design and analysis approach will be discussed in higher level of detail. A special design feature of the Aurora vehicle configurations is the utilization of the novel thin-ply composite material technology for structural mass reductions. Therefore, the second part of this paper will briefly discuss this technology and investigate the application and potential mass savings on vehicle level within simplified structural analysis studies. The results indicate that significant mass savings could be possible. Finally, an outlook on the next steps is provided.
PubDate: 2018-06-01
DOI: 10.1007/s12567-017-0184-2
Issue No: Vol. 10, No. 2 (2018)

• Modal analysis of passive flow control for the turbulent wake of a generic
planar space launcher
• Authors: S. Loosen; V. Statnikov; M. Meinke; W. Schröder
Pages: 189 - 202
Abstract: The turbulent wake of a generic planar space launcher equipped with two passive flow control devices is simulated using a zonal RANS–LES method and analyzed by dynamic mode decomposition (DMD). In the first approach, the effect of a classical boat tail on the wake is examined. In the second concept, a flow control device consisting of semi-circular lobes integrated at the base shoulder of the main body is used. The objective of the two concepts is to reduce the reattachment length and thus the lever arm of the forces as well as to stabilize the separated shear layer. Using a boat tail, the reattachment length can be reduced by 50%. Furthermore, it is shown that the semi-circular lobes enhance the turbulent mixing and the shear layer growth rate. Hence, they significantly reduce the reattachment length by about 75%. The semi-circular lobes partially reduce undesired low-frequency pressure fluctuations on the nozzle surface. However, this reduction is achieved at the expense of an increase of high-frequency pressure fluctuations due to intensified small turbulent scales. The DMD analysis of the velocity field reveals that the large-scale coherent structures featuring a wave length of two step heights observed in the reference configuration without flow control can be suppressed by the lobes. The spanwise wave length of the coherent structures seems to depend on the geometry of the lobes, since all detected spatial DMD modes show a spanwise periodicity being equal to the distance between two lobes.
PubDate: 2018-06-01
DOI: 10.1007/s12567-017-0183-3
Issue No: Vol. 10, No. 2 (2018)

• Experimental assessment of the performance of ablative heat shield
materials from plasma wind tunnel testing
• Authors: S. Löhle; T. Hermann; F. Zander
Pages: 203 - 211
Abstract: A method for assessing the performance of typical heat shield materials is presented in this paper. Three different material samples, the DLR material Zuram, the Airbus material Asterm and the carbon preform Calcarb were tested in the IRS plasma wind tunnel PWK1 at the same nominal condition. State of the art diagnostic tools, i.e., surface temperature with pyrometry and thermography and boundary layer optical emission spectroscopy were completed by photogrammetric surface recession measurements. These data allow the assessment of the net heat flux for each material. The analysis shows that the three materials each have a different effect on heat flux mitigation with ASTERM showing the largest reduction in surface heat flux. The effect of pyrolysis and blowing is clearly observed and the heat flux reduction can be determined from an energy balance.
PubDate: 2018-06-01
DOI: 10.1007/s12567-017-0186-0
Issue No: Vol. 10, No. 2 (2018)

• Experimental validation of solid rocket motor damping models
• Authors: Cristina Riso; Sebastiaan Fransen; Franco Mastroddi; Giuliano Coppotelli; Francesco Trequattrini; Alessio De Vivo
Pages: 213 - 230
Abstract: In design and certification of spacecraft, payload/launcher coupled load analyses are performed to simulate the satellite dynamic environment. To obtain accurate predictions, the system damping properties must be properly taken into account in the finite element model used for coupled load analysis. This is typically done using a structural damping characterization in the frequency domain, which is not applicable in the time domain. Therefore, the structural damping matrix of the system must be converted into an equivalent viscous damping matrix when a transient coupled load analysis is performed. This paper focuses on the validation of equivalent viscous damping methods for dynamically condensed finite element models via correlation with experimental data for a realistic structure representative of a slender launch vehicle with solid rocket motors. A second scope of the paper is to investigate how to conveniently choose a single combination of Young’s modulus and structural damping coefficient—complex Young’s modulus—to approximate the viscoelastic behavior of a solid propellant material in the frequency band of interest for coupled load analysis. A scaled-down test article inspired to the Z9-ignition Vega launcher configuration is designed, manufactured, and experimentally tested to obtain data for validation of the equivalent viscous damping methods. The Z9-like component of the test article is filled with a viscoelastic material representative of the Z9 solid propellant that is also preliminarily tested to investigate the dependency of the complex Young’s modulus on the excitation frequency and provide data for the test article finite element model. Experimental results from seismic and shock tests performed on the test configuration are correlated with numerical results from frequency and time domain analyses carried out on its dynamically condensed finite element model to assess the applicability of different equivalent viscous damping methods to describe damping properties of slender launch vehicles in payload/launcher coupled load analysis.
PubDate: 2018-06-01
DOI: 10.1007/s12567-017-0191-3
Issue No: Vol. 10, No. 2 (2018)

• Architectural elements of hybrid navigation systems for future space
transportation
• Authors: Guilherme F. Trigo; Stephan Theil
Pages: 231 - 250
Abstract: The fundamental limitations of inertial navigation, currently employed by most launchers, have raised interest for GNSS-aided solutions. Combination of inertial measurements and GNSS outputs allows inertial calibration online, solving the issue of inertial drift. However, many challenges and design options unfold. In this work we analyse several architectural elements and design aspects of a hybrid GNSS/INS navigation system conceived for space transportation. The most fundamental architectural features such as coupling depth, modularity between filter and inertial propagation, and open-/closed-loop nature of the configuration, are discussed in the light of the envisaged application. Importance of the inertial propagation algorithm and sensor class in the overall system are investigated, being the handling of sensor errors and uncertainties that arise with lower grade sensory also considered. In terms of GNSS outputs we consider receiver solutions (position and velocity) and raw measurements (pseudorange, pseudorange-rate and time-difference carrier phase). Receiver clock error handling options and atmospheric error correction schemes for these measurements are analysed under flight conditions. System performance with different GNSS measurements is estimated through covariance analysis, being the differences between loose and tight coupling emphasized through partial outage simulation. Finally, we discuss options for filter algorithm robustness against non-linearities and system/measurement errors. A possible scheme for fault detection, isolation and recovery is also proposed.
PubDate: 2018-06-01
DOI: 10.1007/s12567-017-0187-z
Issue No: Vol. 10, No. 2 (2018)

• Multiple spacecraft configuration designs for coordinated flight missions
• Authors: Federico Fumenti; Stephan Theil
Pages: 251 - 271
Abstract: Coordinated flight allows the replacement of a single monolithic spacecraft with multiple smaller ones, based on the principle of distributed systems. According to the mission objectives and to ensure a safe relative motion, constraints on the relative distances need to be satisfied. Initially, differential perturbations are limited by proper orbit design. Then, the induced differential drifts can be properly handled through corrective maneuvers. In this work, several designs are surveyed, defining the initial configuration of a group of spacecraft while counteracting the differential perturbations. For each of the investigated designs, focus is placed upon the number of deployable spacecraft and on the possibility to ensure safe relative motion through station keeping of the initial configuration, with particular attention to the required $$\varDelta V$$ budget and the constraints violations.
PubDate: 2018-06-01
DOI: 10.1007/s12567-018-0193-9
Issue No: Vol. 10, No. 2 (2018)

• Laser ignition of a multi-injector LOX/methane combustor
• Authors: Michael Börner; Chiara Manfletti; Justin Hardi; Dmitry Suslov; Gerhard Kroupa; Michael Oschwald
Pages: 273 - 286
Abstract: This paper reports the results of a test campaign of a laser-ignited combustion chamber with 15 shear coaxial injectors for the propellant combination LOX/methane. 259 ignition tests were performed for sea-level conditions. The igniter based on a monolithic ceramic laser system was directly attached to the combustion chamber and delivered 20 pulses with individual pulse energies of $${33.2 \pm 0.8 \,\text{ mJ }}$$ at 1064 nm wavelength and 2.3 ns FWHM pulse length. The applicability, reliability, and reusability of this ignition technology are demonstrated and the associated challenges during the start-up process induced by the oxygen two-phase flow are formulated. The ignition quality and pressure dynamics are evaluated using 14 dynamic pressure sensors distributed both azimuthally and axially along the combustion chamber wall. The influence of test sequencing on the ignition process is briefly discussed and the relevance of the injection timing of the propellants for the ignition process is described. The flame anchoring and stabilization process, as monitored using an optical probe system close to the injector faceplate connected to photomultiplier elements, is presented. For some of the ignition tests, non-uniform anchoring was detected with no influence onto the anchoring at steady-state conditions. The non-uniform anchoring can be explained by the inhomogeneous, transient injection of the two-phase flow of oxygen across the faceplate. This characteristic is verified by liquid nitrogen cold flow tests that were recorded by high-speed imaging. We conclude that by adapting the ignition sequence, laser ignition by optical breakdown of the propellants within the shear layer of a coaxial shear injector is a reliable ignition technology for LOX/methane combustors without significant over-pressure levels.
PubDate: 2018-06-01
DOI: 10.1007/s12567-018-0196-6
Issue No: Vol. 10, No. 2 (2018)

• Performance analysis of an IMU-augmented GNSS tracking system on board the
MAIUS-1 sounding rocket
• Authors: Benjamin Braun; Andreas Grillenberger; Markus Markgraf
Abstract: Satellite navigation receivers are adequate tracking sensors for range safety of both orbital launch vehicles and suborbital sounding rockets. Due to high accuracy and its low system complexity, satellite navigation is seen as well-suited supplement or replacement of conventional tracking systems like radar. Having the well-known shortcomings of satellite navigation like deliberate or unintentional interferences in mind, it is proposed to augment the satellite navigation receiver by an inertial measurement unit (IMU) to enhance continuity and availability of localization. The augmented receiver is thus enabled to output at least an inertial position solution in case of signal outages. In a previous study, it was shown by means of simulation using the example of Ariane 5 that the performance of a low-grade microelectromechanical IMU is sufficient to bridge expected outages of some ten seconds, and still meeting the range safety requirements in effect. In this publication, these theoretical findings shall be substantiated by real flight data that were recorded on MAIUS-1, a sounding rocket launched from Esrange, Sweden, in early 2017. The analysis reveals that the chosen representative of a microelectromechanical IMU is suitable to bridge outages of up to thirty seconds.
PubDate: 2018-05-08
DOI: 10.1007/s12567-018-0206-8

• OMA analysis of a launcher under operational conditions with time-varying
properties
• Authors: M. Eugeni; G. Coppotelli; F. Mastroddi; P. Gaudenzi; S. Muller; B. Troclet
Abstract: The objective of this paper is the investigation of the capability of operational modal analysis approaches to deal with time-varying system in the low-frequency domain. Specifically, the problem of the identification of the dynamic properties of a launch vehicle, working under actual operative conditions, is studied. Two OMA methods are considered: the frequency-domain decomposition and the Hilbert transform method. It is demonstrated that both OMA approaches allow the time-tracking of modal parameters, namely, natural frequencies, damping ratios, and mode shapes, from the response accelerations only recorded during actual flight tests of a launcher characterized by a large mass variation due to fuel burning typical of the first phase of the flight.
PubDate: 2018-05-08
DOI: 10.1007/s12567-018-0209-5

• Generic framework for vessel detection and tracking based on distributed
marine radar image data
• Authors: Gregor Siegert; Julian Hoth; Paweł Banyś; Frank Heymann
Abstract: Situation awareness is understood as a key requirement for safe and secure shipping at sea. The primary sensor for maritime situation assessment is still the radar, with the AIS being introduced as supplemental service only. In this article, we present a framework to assess the current situation picture based on marine radar image processing. Essentially, the framework comprises a centralized IMM–JPDA multi-target tracker in combination with a fully automated scheme for track management, i.e., target acquisition and track depletion. This tracker is conditioned on measurements extracted from radar images. To gain a more robust and complete situation picture, we are exploiting the aspect angle diversity of multiple marine radars, by fusing them a priori to the tracking process. Due to the generic structure of the proposed framework, different techniques for radar image processing can be implemented and compared, namely the BLOB detector and SExtractor. The overall framework performance in terms of multi-target state estimation will be compared for both methods based on a dedicated measurement campaign in the Baltic Sea with multiple static and mobile targets given.
PubDate: 2018-04-28
DOI: 10.1007/s12567-018-0208-6

• MACS-Mar: a real-time remote sensing system for maritime security
applications
• Authors: Jörg Brauchle; Steven Bayer; Daniel Hein; Ralf Berger; Sebastian Pless
Abstract: The modular aerial camera system (MACS) is a development platform for optical remote sensing concepts, algorithms and special environments. For real-time services for maritime security (EMSec joint project), a new multi-sensor configuration MACS-Mar was realized. It consists of four co-aligned sensor heads in the visible RGB, near infrared (NIR, 700–950 nm), hyperspectral (HS, 450–900 nm) and thermal infrared (TIR, 7.5–14 µm) spectral range, a mid-cost navigation system, a processing unit and two data links. On-board image projection, cropping of redundant data and compression enable the instant generation of direct-georeferenced high-resolution image mosaics, automatic object detection, vectorization and annotation of floating objects on the water surface. The results were transmitted over a distance up to 50 km in real-time via narrow and broadband data links and were visualized in a maritime situation awareness system. For the automatic onboard detection of floating objects, a segmentation and classification workflow based on RGB, IR and TIR information was developed and tested. The completeness of the object detection in the experiment resulted in 95%, the correctness in 53%. Mostly, bright backwash of ships lead to an overestimation of the number of objects, further refinement using water homogeneity in the TIR, as implemented in the workflow, couldn’t be carried out due to problems with the TIR sensor, else distinctly better results could have been expected. The absolute positional accuracy of the projected real-time imagery resulted in 2 m without postprocessing of images or navigation data, the relative measurement accuracy of distances is in the range of the image resolution, which is about 12 cm for RGB imagery in the EMSec experiment.
PubDate: 2018-04-25
DOI: 10.1007/s12567-018-0207-7

• MICROSCOPE mission: drag-free and attitude control system expertise
activities toward the scientific team
• Authors: Stéphanie Delavault; Pascal Prieur; Thomas Liénart; Alain Robert; Pierre-Yves Guidotti
Abstract: Microscope is a CNES-ESA-ONERA-CNRS-OCA-DLR-ZARM mission dedicated to the test of the Equivalence Principle with an improved accuracy of 10−15. The 300 kg drag-free microsatellite was launched on April 25th 2016 into a 710 km dawndusk sun-synchronous orbit for a 2-year mission. To comply with stringent requirements, the drag-free and attitude control system (DFACS) involves the scientific accelerometer as main sensor and a set of 8 cold gas proportional thrusters. Once in mission mode, within the CNES drag-free expertise center (CECT) the DFACS team provides several services to the system and to the scientific mission center: cold gas monitoring and management, ‘Attitude’ ancillary data, DFACS expertise ancillary data. For this purpose, expertise tools have been implemented in the CECT, using the flexibility and efficiency of Matlab™ utilities. This paper presents the role of the CECT within the mission and details the expertise activities of the DFACS team illustrated with some typical in flight results.
PubDate: 2018-04-24
DOI: 10.1007/s12567-018-0205-9

• In-orbit performance of the LISA Pathfinder drag-free and attitude control
system
• Authors: A. Schleicher; T. Ziegler; R. Schubert; N. Brandt; P. Bergner; U. Johann; W. Fichter; J. Grzymisch
Abstract: LISA Pathfinder is a technology demonstrator mission that was funded by the European Space Agency and that was launched on December 3, 2015. LISA Pathfinder has been conducting experiments to demonstrate key technologies for the gravitational wave observatory LISA in its operational orbit at the L1 Lagrange point of the Earth–Sun system until final switch off on July 18, 2017. These key technologies include the inertial sensors, the optical metrology system, a set of µ-propulsion cold gas thrusters and in particular the high performance drag-free and attitude control system (DFACS) that controls the spacecraft in 15 degrees of freedom during its science phase. The main goal of the DFACS is to shield the two test masses inside the inertial sensors from all external disturbances to achieve a residual differential acceleration between the two test masses of less than 3 × 10−14 m/s2/√Hz over the frequency bandwidth of 1–30 mHz. This paper focuses on two important aspects of the DFACS that has been in use on LISA Pathfinder: the DFACS Accelerometer mode and the main DFACS Science mode. The Accelerometer mode is used to capture the test masses after release into free flight from the mechanical grabbing mechanism. The main DFACS Science Mode is used for the actual drag-free science operation. The DFACS control system has very strong interfaces with the LISA Technology Package payload which is a key aspect to master the design, development, and analysis of the DFACS. Linear as well as non-linear control methods are applied. The paper provides pre-flight predictions for the performance of both control modes and compares these predictions to the performance that is currently achieved in-orbit. Some results are also discussed for the mode transitions up to science mode, but the focus of the paper is on the Accelerometer mode performance and on the performance of the Science mode in steady state. Based on the achieved results, some lessons learnt are formulated to extend the results to the drag-free control system to be designed for future space-based gravity wave observatories like LISA.
PubDate: 2018-04-24
DOI: 10.1007/s12567-018-0204-x

• Orbital Hub: a concept for human spaceflight beyond ISS operations
• Authors: Stephan S. Jahnke; Volker Maiwald; Claudia Philpot; Dominik Quantius; Oliver Romberg; Wolfgang Seboldt; Vincent Vrakking; Conrad Zeidler
Abstract: The International Space Station (ISS) is the greatest endeavour in low-Earth orbit since the beginning of the space age and the culmination of human outposts like Skylab and Mir. While a clear schedule has yet to be drafted, it is expected that ISS will cease operation in the 2020s. What could be the layout for a human outpost in LEO with lessons learnt from ISS' What are the use cases and applications of such an outpost in the future' The System Analysis Space Segment group of the German Aerospace Center investigated these and other questions and developed the Orbital Hub concept. In this paper an overview is presented of how the overall concept has been derived and its properties and layouts are described. Starting with a workshop involving the science community, the scientific requirements have been derived and Strawman payloads have been defined for use in further design activities. These design activities focused on Concurrent Engineering studies, where besides DLR employees participants from the industry and astronauts were involved. The result is an expandable concept that is composed of two main parts, the Base Platform, home for a permanent crew of up to three astronauts, and the Free Flyer, an uncrewed autonomous research platform. This modular approach provides one major advantage: the decoupling of the habitat and payload leading to increased quality of the micro-gravity environment. The former provides an environment for human physiology experiments, while the latter allows science without the perturbations caused by a crew, e.g. material experiments or Earth observation. The Free Flyer is designed to operate for up to 3 months on its own, but can dock with the space station for maintenance and experiment servicing. It also has a hybrid propulsion system, chemical and electrical, for different applications. The hub’s design allows launch with just three launches, as the total mass of all the hub parts is about 60,000 kg. The main focus of the design is on autonomy and reducing crew maintenance and repair efforts, and reducing the need for extravehicular activities. Following a description of the design approach and technical details, cost estimation and a detailed discussion of the use cases for such a station concept, along with the possible scenarios of international cooperation, are also presented in this paper.
PubDate: 2018-04-11
DOI: 10.1007/s12567-018-0203-y

• Measurement of fracture toughness of metallic materials produced by
additive manufacturing
• Authors: O. Quénard; O. Dorival; Ph. Guy; A. Votié; K. Brethome
Abstract: This study focuses on the microstructure and mechanical properties of metallic materials produced by additive layer manufacturing (ALM), especially the laser beam melting process. The influence of the specimen orientation during the ALM process and that of two post-build thermal treatments were investigated. The identified metal powder is Ti-6Al-4V (titanium base). Metallographic analysis shows their effects on the microstructure of the metals. Mechanical experiments involving tensile tests as well as toughness tests were performed according to ASTM (American Society for Testing and Materials) norms. The results show that the main influence is that of the thermal treatments; however the manufacturing stacking direction may lead to some anisotropy in the mechanical properties.
PubDate: 2018-04-03
DOI: 10.1007/s12567-018-0202-z

• Thank you to our CEAS Space Journal Reviewers
• PubDate: 2018-03-08
DOI: 10.1007/s12567-018-0198-4

• Autonomous vision-based navigation for proximity operations around binary
asteroids
• Authors: Jesus Gil-Fernandez; Guillermo Ortega-Hernando
Abstract: Future missions to small bodies demand higher level of autonomy in the Guidance, Navigation and Control system for higher scientific return and lower operational costs. Different navigation strategies have been assessed for ESA’s asteroid impact mission (AIM). The main objective of AIM is the detailed characterization of binary asteroid Didymos. The trajectories for the proximity operations shall be intrinsically safe, i.e., no collision in presence of failures (e.g., spacecraft entering safe mode), perturbations (e.g., non-spherical gravity field), and errors (e.g., maneuver execution error). Hyperbolic arcs with sufficient hyperbolic excess velocity are designed to fulfil the safety, scientific, and operational requirements. The trajectory relative to the asteroid is determined using visual camera images. The ground-based trajectory prediction error at some points is comparable to the camera Field Of View (FOV). Therefore, some images do not contain the entire asteroid. Autonomous navigation can update the state of the spacecraft relative to the asteroid at higher frequency. The objective of the autonomous navigation is to improve the on-board knowledge compared to the ground prediction. The algorithms shall fit in off-the-shelf, space-qualified avionics. This note presents suitable image processing and relative-state filter algorithms for autonomous navigation in proximity operations around binary asteroids.
PubDate: 2018-02-23
DOI: 10.1007/s12567-018-0197-5

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