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 CEAS Space Journal   [SJR: 0.221]   [H-I: 5]   [0 followers]  Follow         Hybrid journal (It can contain Open Access articles)    ISSN (Print) 1868-2510 - ISSN (Online) 1868-2502    Published by Springer-Verlag  [2352 journals]
• A new method for optimization of low-thrust gravity-assist sequences
• Authors: V. Maiwald
Pages: 243 - 256
Abstract: Recently missions like Hayabusa and Dawn have shown the relevance and benefits of low-thrust spacecraft concerning the exploration of our solar system. In general, the efficiency of low-thrust propulsion is one means of improving mission payload mass. At the same time, gravity-assist maneuvers can serve as mission enablers, as they have the capability to provide “free energy.” A combination of both, gravity-assist and low-thrust propulsion, has the potential to generally improve mission performance, i.e. planning and optimization of gravity-assist sequences for low-thrust missions is a desirable asset. Currently no established methods exist to include the gravity-assist partners as optimization variable for low-thrust missions. The present paper explains how gravity-assists are planned and optimized, including the gravity-assist partners, for high-thrust missions and discusses the possibility to transfer the established method, based on the Tisserand Criterion, to low-thrust missions. It is shown how the Tisserand Criterion needs to be adapted using a correction term for the low-thrust situation. It is explained why this necessary correction term excludes an a priori evaluation of sequences and therefore their planning and an alternate approach is proposed. Preliminary results of this method, by application of a Differential Evolution optimization algorithm, are presented and discussed, showing that the method is valid but can be improved. Two constraints on the search space are briefly presented for that aim.
PubDate: 2017-09-01
DOI: 10.1007/s12567-017-0147-7
Issue No: Vol. 9, No. 3 (2017)

• Exploratory numerical experiments with a macroscopic theory of interfacial
interactions
• Authors: D. Giordano; P. Solano-López; J. M. Donoso
Pages: 257 - 277
Abstract: Phenomenological theories of interfacial interactions are founded on the core idea to model macroscopically the thin layer that forms between media in contact as a two-dimensional continuum (surface phase or interface) characterised by physical properties per unit area; the temporal evolution of the latter is governed by surface balance equations whose set acts as bridging channel in between the governing equations of the volume phases. These theories have targeted terrestrial applications since long time and their exploitation has inspired our research programme to build up, on the same core idea, a macroscopic theory of gas–surface interactions targeting the complex phenomenology of hypersonic reentry flows as alternative to standard methods in aerothermodynamics based on accommodation coefficients. The objective of this paper is the description of methods employed and results achieved in the exploratory study that kicked off our research programme, that is, the unsteady heat transfer between two solids in contact in planar and cylindrical configurations with and without interface. It is a simple numerical-demonstrator test case designed to facilitate quick numerical calculations but, at the same time, to bring forth already sufficiently meaningful aspects relevant to thermal protection due to the formation of the interface. The paper begins with a brief introduction on the subject matter and a review of relevant literature within an aerothermodynamics perspective. Then the case is considered in which the interface is absent. The importance of tension (force per unit area) continuity as boundary condition on the same footing of heat-flux continuity is recognised and the role of the former in governing the establishment of the temperature-difference distribution over the separation surface is explicitly shown. Evidence is given that the standard temperature-continuity boundary condition is just a particular case. Subsequently the case in which the interface is formed between the solids is analysed. The coupling among the heat-transfer equations applicable in the solids and the balance equation for the surface thermodynamic energy more conveniently formulated in terms of the surface temperature is discussed. Results are illustrated and commented for planar and cylindrical configuration; they show unequivocally that the thermal-protection action of the interface turns out to be driven exclusively by thermophysical properties of the solids and of the interface; accommodation coefficients are not needed. Future work of more fluid-dynamics nature is mentioned in the concluding section.
PubDate: 2017-09-01
DOI: 10.1007/s12567-017-0148-6
Issue No: Vol. 9, No. 3 (2017)

• Sea-level transitioning dual bell nozzles
• Authors: Ralf Stark; Chloé Génin
Pages: 279 - 287
Abstract: A detailed study was conducted to evaluate the impact of sea-level transitioning dual bell nozzles on the payload mass delivered into geostationary transfer orbit by Ariane 5 ECA. For this purpose, a multitude of Vulcain 2 and Vulcain 2.1 nozzle extension contours were designed. The two variable parameters were the position of the wall inflection and the constant wall pressure of the nozzle extension. Accounting for the two variable parameters, an approved analytical method was applied to predict the impact of the dual bell nozzles on the payload mass.
PubDate: 2017-09-01
DOI: 10.1007/s12567-017-0154-8
Issue No: Vol. 9, No. 3 (2017)

• OWLS as platform technology in OPTOS satellite
• Authors: J. Rivas Abalo; J. Martínez Oter; I. Arruego Rodríguez; A. Martín-Ortega Rico; J. R. de Mingo Martín; J. J. Jiménez Martín; B. Martín Vodopivec; S. Rodríguez Bustabad; H. Guerrero Padrón
Abstract: The aim of this work is to show the Optical Wireless Link to intraSpacecraft Communications (OWLS) technology as a platform technology for space missions, and more specifically its use within the On-Board Communication system of OPTOS satellite. OWLS technology was proposed by Instituto Nacional de Técnica Aeroespacial (INTA) at the end of the 1990s and developed along 10 years through a number of ground demonstrations, technological developments and in-orbit experiments. Its main benefits are: mass reduction, flexibility, and simplification of the Assembly, Integration and Tests phases. The final step was to go from an experimental technology to a platform one. This step was carried out in the OPTOS satellite, which makes use of optical wireless links in a distributed network based on an OLWS implementation of the CAN bus. OPTOS is the first fully wireless satellite. It is based on the triple configuration (3U) of the popular Cubesat standard, and was completely built at INTA. It was conceived to procure a fast development, low cost, and yet reliable platform to the Spanish scientific community, acting as a test bed for space born science and technology. OPTOS presents a distributed OBDH architecture in which all satellite’s subsystems and payloads incorporate a small Distributed On-Board Computer (OBC) Terminal (DOT). All DOTs (7 in total) communicate between them by means of the OWLS-CAN that enables full data sharing capabilities. This collaboration allows them to perform all tasks that would normally be carried out by a centralized On-Board Computer.
PubDate: 2017-11-11
DOI: 10.1007/s12567-017-0178-0

• The design and development of low- and high-voltage ASICs for space-borne
CCD cameras
• Authors: N. Waltham; Q. Morrissey; M. Clapp; S. Bell; L. Jones; M. Torbet
Abstract: The CCD remains the pre-eminent visible and UV wavelength image sensor in space science, Earth and planetary remote sensing. However, the design of space-qualified CCD readout electronics is a significant challenge with requirements for low-volume, low-mass, low-power, high-reliability and tolerance to space radiation. Space-qualified components are frequently unavailable and up-screened commercial components seldom meet project or international space agency requirements. In this paper, we describe an alternative approach of designing and space-qualifying a series of low- and high-voltage mixed-signal application-specific integrated circuits (ASICs), the ongoing development of two low-voltage ASICs with successful flight heritage, and two new high-voltage designs. A challenging sub-system of any CCD camera is the video processing and digitisation electronics. We describe recent developments to improve performance and tolerance to radiation-induced single event latchup of a CCD video processing ASIC originally developed for NASA’s Solar Terrestrial Relations Observatory and Solar Dynamics Observatory. We also describe a programme to develop two high-voltage ASICs to address the challenges presented with generating a CCD’s bias voltages and drive clocks. A 0.35 μm, 50 V tolerant, CMOS process has been used to combine standard low-voltage 3.3 V transistors with high-voltage 50 V diffused MOSFET transistors that enable output buffers to drive CCD bias drains, gates and clock electrodes directly. We describe a CCD bias voltage generator ASIC that provides 24 independent and programmable 0–32 V outputs. Each channel incorporates a 10-bit digital-to-analogue converter, provides current drive of up to 20 mA into loads of 10 μF, and includes current-limiting and short-circuit protection. An on-chip telemetry system with a 12-bit analogue-to-digital converter enables the outputs and multiple off-chip camera voltages to be monitored. The ASIC can drive one or more CCDs and replaces the many discrete components required in current cameras. We also describe a CCD clock driver ASIC that provides six independent and programmable drivers with high-current capacity. The device enables various CCD clock parameters to be programmed independently, for example the clock-low and clock-high voltage levels, and the clock-rise and clock-fall times, allowing configuration for serial clock frequencies in the range 0.1–2 MHz and image clock frequencies in the range 10–100 kHz. Finally, we demonstrate the impact and importance of this technology for the development of compact, high-performance and low-power integrated focal plane electronics.
PubDate: 2017-11-07
DOI: 10.1007/s12567-017-0181-5

• Ka-band to L-band frequency down-conversion based on III–V-on-silicon
photonic integrated circuits
• Authors: K. Van Gasse; Z. Wang; S. Uvin; B. De Deckere; J. Mariën; L. Thomassen; G. Roelkens
Abstract: In this work, we present the design, simulation and characterization of a frequency down-converter based on III–V-on-silicon photonic integrated circuit technology. We first demonstrate the concept using commercial discrete components, after which we demonstrate frequency conversion using an integrated mode-locked laser and integrated modulator. In our experiments, five channels in the Ka-band (27.5–30 GHz) with 500 MHz bandwidth are down-converted to the L-band (1.5 GHz). The breadboard demonstration shows a conversion efficiency of − 20 dB and a flat response over the 500 MHz bandwidth. The simulation of a fully integrated circuit indicates that a positive conversion gain can be obtained on a millimeter-sized photonic integrated circuit.
PubDate: 2017-11-03
DOI: 10.1007/s12567-017-0179-z

• Space gravitational wave antenna DECIGO and B-DECIGO
• Authors: Mitsuru Musha; DECIGO Working Group
Abstract: Since the direct detection of gravitational wave will give us a fruitful insight about the early universe or life of stars, laser interferometric gravitational wave detectors with the strain sensitivity of higher than 10−22 have been developed. In Japan, the space gravitational wave detector project named DECi-hertz Gravitational wave Observatory (DECIGO) has been promoted which consists of three satellites forming equilateral triangle-shaped Fabry–Perot laser interferometer with the arm length of 1000 km. The designed strain sensitivity of DECIGO is 2 × 10−24/√Hz around 0.1 Hz whose targets are gravitational waves originated from the inspiral and the merger of black hole or neutron star binaries and from the inflation at the early universe, and no ground-based gravitational wave detector can access this observation band. Before launching DECIGO in 2030s, a milestone mission named B-DECIGO is planned which is a downsized mission of DECIGO. B-DECIGO also has its own scientific targets in addition to the feasibility test for DECIGO. In the present paper, DECIGO and B-DECIGO projects are reviewed.
PubDate: 2017-11-02
DOI: 10.1007/s12567-017-0177-1

• An afocal telescope configuration for the ESA ARIEL mission
• Authors: Vania Da Deppo; Mauro Focardi; Kevin Middleton; Gianluca Morgante; Enzo Pascale; Samuele Grella; Emanuele Pace; Riccardo Claudi; Jérôme Amiaux; Josep Colomé Ferrer; Thomas Hunt; Miroslaw Rataj; Carles Sierra-Roig; Iacopo Ficai Veltroni; Paul Eccleston; Giuseppina Micela; Giovanna Tinetti
Abstract: Atmospheric Remote-Sensing Infrared Exoplanet Large Survey (ARIEL) is a candidate as an M4 ESA mission to launch in 2026. During its 3.5 years of scientific operations, ARIEL will observe spectroscopically in the infrared (IR) a large population of known transiting planets in the neighbourhood of the solar system. ARIEL aims to give a breakthrough in the observation of exoplanet atmospheres and understanding of the physics and chemistry of these far-away worlds. ARIEL is based on a 1 m class telescope feeding a collimated beam into two separate instrument modules: a spectrometer module covering the waveband between 1.95 and 7.8 μm and a combined fine guidance system/visible photometer/NIR spectrometer. The telescope configuration is a classic Cassegrain layout used with an eccentric pupil and coupled to a tertiary off-axis paraboloidal mirror. To constrain the thermo-mechanically induced optical aberrations, the primary mirror (M1) temperature will be monitored and finely tuned using an active thermal control system based on thermistors and heaters. They will be switched on and off to maintain the M1 temperature within ± 1 K by the telescope control unit (TCU). The TCU is a payload electronics subsystem also responsible for the thermal control of the spectrometer module detectors as well as the secondary mirror mechanism and IR calibration source management. The TCU, being a slave subsystem of the instrument control unit, will collect the housekeeping data from the monitored subsystems and will forward them to the master unit. The latter will run the application software, devoted to the main spectrometer management and to the scientific data on-board processing.
PubDate: 2017-11-01
DOI: 10.1007/s12567-017-0175-3

• A concept of active mount for space applications
• Authors: A. Souleille; T. Lampert; V. Lafarga; S. Hellegouarch; A. Rondineau; G. Rodrigues; C. Collette
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: 2017-10-30
DOI: 10.1007/s12567-017-0180-6

• Fourier transform spectrometers for remote sensing of planetary
atmospheres and surfaces
• Authors: Alexey Shakun; Oleg Korablev; Boris Moshkin; Alexey Grigoriev; Nikolay Ignatiev; Igor Maslov; Oleg Sazonov; Dmitry Patsaev; Andrey Kungurov; Alexander Santos-Skripko; Alexander Zharkov; Igor Stupin; Dmitry Merzlyakov; Vladislav Makarov; Fedor Martinovich; Yuri Nikolskiy; Victor Shashkin
Abstract: In planetary research, Fourier transform infrared spectrometers (FTIR) solve a number of important scientific goals related both to the atmosphere and to the surface sounding. For remote orbital measurements, these goals are the thermal sounding of the atmosphere using, in particular, the 15-µm CO2 band, sensitive detections of minor gaseous species and aerosol characterization. FTIR can address similar atmospheric science goals when observing from a planetary surface allowing for better-resolved boundary layer and achieving greater accuracy (longer integration) for minor species detection. For studies of planetary surfaces, characterization of mineralogical composition in a wide IR range including sensitive measurements of hydration of the soil on airless bodies can be done. We outline a family of FTIR instruments dedicated to studies of Mars and the Moon. TIRVIM is a channel of ACS on ExoMars TGO (in orbit around Mars since October 2016). It is a 2-inch interferometer for nadir and solar occultation measurements of Mars’ atmosphere. It covers a spectral range of 1.7–17 µm with spectral resolution up to 0.13 cm−1. LUMIS is a similar instrument for Luna-Resource Orbiter (Luna-26) Roscosmos mission dedicated to the search for hydration of the lunar regolith in the 6-µm band. The spectral range of LUMIS is broad (1.7–17 µm), but its sensitivity is optimized for the 4–8 µm region. The spectral resolution is 50 cm−1. We also describe recent developments focused on technical solutions for miniaturized FTIR instruments with a very high spectral resolution (0.05 cm−1 and higher). The prototype targets measurements of minor atmospheric species from the surface of Mars using the Sun tracking. One important task is to provide a high precision of interferometer’s mirror movement. Another task is the development of a precise two-coordinate mechanism to seek for and follow the Sun.
PubDate: 2017-10-23
DOI: 10.1007/s12567-017-0176-2

• A comparative study of programming languages for next-generation
astrodynamics systems
• Authors: Helge Eichhorn; Juan Luis Cano; Frazer McLean; Reiner Anderl
Abstract: Due to the computationally intensive nature of astrodynamics tasks, astrodynamicists have relied on compiled programming languages such as Fortran for the development of astrodynamics software. Interpreted languages such as Python, on the other hand, offer higher flexibility and development speed thereby increasing the productivity of the programmer. While interpreted languages are generally slower than compiled languages, recent developments such as just-in-time (JIT) compilers or transpilers have been able to close this speed gap significantly. Another important factor for the usefulness of a programming language is its wider ecosystem which consists of the available open-source packages and development tools such as integrated development environments or debuggers. This study compares three compiled languages and three interpreted languages, which were selected based on their popularity within the scientific programming community and technical merit. The three compiled candidate languages are Fortran, C++, and Java. Python, Matlab, and Julia were selected as the interpreted candidate languages. All six languages are assessed and compared to each other based on their features, performance, and ease-of-use through the implementation of idiomatic solutions to classical astrodynamics problems. We show that compiled languages still provide the best performance for astrodynamics applications, but JIT-compiled dynamic languages have reached a competitive level of speed and offer an attractive compromise between numerical performance and programmer productivity.
PubDate: 2017-09-26
DOI: 10.1007/s12567-017-0170-8

• Dynamical analysis of rendezvous and docking with very large space
infrastructures in non-Keplerian orbits
• Authors: Andrea Colagrossi; Michèle Lavagna
Abstract: A space station in the vicinity of the Moon can be exploited as a gateway for future human and robotic exploration of the solar system. The natural location for a space system of this kind is about one of the Earth–Moon libration points. The study addresses the dynamics during rendezvous and docking operations with a very large space infrastructure in an EML2 Halo orbit. The model takes into account the coupling effects between the orbital and the attitude motion in a circular restricted three-body problem environment. The flexibility of the system is included, and the interaction between the modes of the structure and those related with the orbital motion is investigated. A lumped parameter technique is used to represents the flexible dynamics. The parameters of the space station are maintained as generic as possible, in a way to delineate a global scenario of the mission. However, the developed model can be tuned and updated according to the information that will be available in the future, when the whole system will be defined with a higher level of precision.
PubDate: 2017-09-26
DOI: 10.1007/s12567-017-0174-4

• CAMELOT: Computational-Analytical Multi-fidElity Low-thrust Optimisation
Toolbox
• Authors: Marilena Di Carlo; Juan Manuel Romero Martin; Massimiliano Vasile
Abstract: Computational-Analytical Multi-fidElity Low-thrust Optimisation Toolbox (CAMELOT) is a toolbox for the fast preliminary design and optimisation of low-thrust trajectories. It solves highly complex combinatorial problems to plan multi-target missions characterised by long spirals including different perturbations. To do so, CAMELOT implements a novel multi-fidelity approach combining analytical surrogate modelling and accurate computational estimations of the mission cost. Decisions are then made using two optimisation engines included in the toolbox, a single-objective global optimiser, and a combinatorial optimisation algorithm. CAMELOT has been applied to a variety of case studies: from the design of interplanetary trajectories to the optimal de-orbiting of space debris and from the deployment of constellations to on-orbit servicing. In this paper, the main elements of CAMELOT are described and two examples, solved using the toolbox, are presented.
PubDate: 2017-09-22
DOI: 10.1007/s12567-017-0172-6

• Model-based software engineering for an optical navigation system for
spacecraft
• Authors: T. Franz; D. Lüdtke; O. Maibaum; A. Gerndt
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: 2017-09-18
DOI: 10.1007/s12567-017-0173-5

• NanoVipa: a miniaturized high-resolution echelle spectrometer, for the
monitoring of young stars from a 6U Cubesat
• Authors: G. Bourdarot; E. Le Coarer; X. Bonfils; E. Alecian; P. Rabou; Y. Magnard
Abstract: We introduce to astrophysical instrumentation and space optics the use of virtually imaged phased array (VIPA) to shrink échelle spectrometers and/or increase their resolution. Here, we report on both a concept of an echelle spectrometer with resolution $$R=50{,}000$$ (@653nm), which fits a 6U nanosatellite platform ( $${{1{\rm U}= 10\,{\rm cm} \times 10\,{\rm cm} \times 10\,{\rm cm}}}$$ ), and on our laboratory tests on a $$R=200{,}000$$ demonstrator. The outline of our paper is as follows: Sect. 1 introduces our concept of a 6U payload comprising an échelle spectrometer based on the VIPA. We present also the science cases of monitoring young stars, and the wider science landscape amenable with larger telescopes. Section 2 gives a more detailed description of the VIPA and of its implementation in a cross-dispersed spectrometer. Section 3 shows the first results at $$R=200{,}000$$ we already achieved at the Institut de Planétologie et d’Astrophysique de Grenoble (IPAG). Finally, Sect. 4 is a discussion on the remaining technical points to study.
PubDate: 2017-08-03
DOI: 10.1007/s12567-017-0168-2

• Implementing model-based system engineering for the whole lifecycle of a
spacecraft
• Authors: P. M. Fischer; D. Lüdtke; C. Lange; F.-C. Roshani; F. Dannemann; A. Gerndt
Abstract: Design information of a spacecraft is collected over all phases in the lifecycle of a project. A lot of this information is exchanged between different engineering tasks and business processes. In some lifecycle phases, model-based system engineering (MBSE) has introduced system models and databases that help to organize such information and to keep it consistent for everyone. Nevertheless, none of the existing databases approached the whole lifecycle yet. Virtual Satellite is the MBSE database developed at DLR. It has been used for quite some time in Phase A studies and is currently extended for implementing it in the whole lifecycle of spacecraft projects. Since it is unforeseeable which future use cases such a database needs to support in all these different projects, the underlying data model has to provide tailoring and extension mechanisms to its conceptual data model (CDM). This paper explains the mechanisms as they are implemented in Virtual Satellite, which enables extending the CDM along the project without corrupting already stored information. As an upcoming major use case, Virtual Satellite will be implemented as MBSE tool in the S2TEP project. This project provides a new satellite bus for internal research and several different payload missions in the future. This paper explains how Virtual Satellite will be used to manage configuration control problems associated with such a multi-mission platform. It discusses how the S2TEP project starts using the software for collecting the first design information from concurrent engineering studies, then making use of the extension mechanisms of the CDM to introduce further information artefacts such as functional electrical architecture, thus linking more and more processes into an integrated MBSE approach.
PubDate: 2017-07-12
DOI: 10.1007/s12567-017-0166-4

• 3D thermography for improving temperature measurements in thermal vacuum
testing
• Authors: D. W. Robinson; R. Simpson; J. A. Parian; A. Cozzani; G. Casarosa; S. Sablerolle; H. Ertel
Abstract: The application of thermography to thermal vacuum (TV) testing of spacecrafts is becoming a vital additional tool in the mapping of structures during thermal cycles and thermal balance (TB) testing. Many of the customers at the European Space Agency (ESA) test centre, European Space Research and Technology Centre (ESTEC), The Netherlands, now make use of a thermal camera during TB-TV campaigns. This complements the use of embedded thermocouples on the structure, providing the prospect of monitoring temperatures at high resolution and high frequency. For simple flat structures with a well-defined emissivity, it is possible to determine the surface temperatures with reasonable confidence. However, for most real spacecraft and sub-systems, the complexity of the structure’s shape and its test environment creates inter-reflections from external structures. This and the additional complication of angular and spectral variations of the spacecraft surface emissivity make the interpretation of the radiation detected by a thermal camera more difficult in terms of determining a validated temperature with high confidence and well-defined uncertainty. One solution to this problem is: to map the geometry of the test specimen and thermal test environment; to model the surface temperatures and emissivity variations of the structures and materials; and to use this model to correct the apparent temperatures recorded by the thermal camera. This approach has been used by a team from NPL (National Physical Laboratory), Psi-tran, and PhotoCore, working with ESA, to develop a 3D thermography system to provide a means to validate thermal camera temperatures, based on a combination of thermal imaging photogrammetry and ray-tracing scene modeling. The system has been tested at ESTEC in ambient conditions with a dummy spacecraft structure containing a representative set of surface temperatures, shapes, and spacecraft materials, and with hot external sources and a high power lamp as a sun simulator. The results are presented here with estimated temperature measurement uncertainties and defined confidence levels according to the internationally accepted Guide to Uncertainty of Measurement as used in the IEC/ISO17025 test and measurement standard. This work is understood to represent the first application of well-understood thermal imaging theory, commercial photogrammetry software, and open-source ray-tracing software (adapted to realize the Planck function for thermal wavebands and target emission), and to produce from these elements a complete system for determining true surface temperatures for complex spacecraft-testing applications.
PubDate: 2017-07-11
DOI: 10.1007/s12567-017-0167-3

• On the Radau pseudospectral method: theoretical and implementation
• Authors: Marco Sagliano; Stephan Theil; Michiel Bergsma; Vincenzo D’Onofrio; Lisa Whittle; Giulia Viavattene
Abstract: In the last decades the theoretical development of more and more refined direct methods, together with a new generation of CPUs, led to a significant improvement of numerical approaches for solving optimal-control problems. One of the most promising class of methods is based on pseudospectral optimal control. These methods do not only provide an efficient algorithm to solve optimal-control problems, but also define a theoretical framework for linking the discrete numerical solution to the analytical one in virtue of the covector mapping theorem. However, several aspects in their implementation can be refined. In this framework SPARTAN, the first European tool based on flipped-Radau pseudospectral method, has been developed. This paper illustrates the aspects implemented for SPARTAN, which can potentially be valid for any other transcription. The novelties included in this work consist specifically of a new hybridization of the Jacobian matrix computation made of four distinct parts. These contributions include a new analytical formulation for expressing Lagrange cost function for open final-time problems, and the use of dual-number theory for ensuring exact differentiation. Moreover, a self-scaling strategy for primal and dual variables, which combines the projected-Jacobian rows normalization and the covector mapping, is described. Three concrete examples show the validity of the novelties introduced, and the quality of the results obtained with the proposed methods.
PubDate: 2017-06-23
DOI: 10.1007/s12567-017-0165-5

• Repetitive laser ignition by optical breakdown of a LOX/H 2 rocket
combustion chamber with multi-injector head configuration
• Authors: Michael Börner; Chiara Manfletti; Gerhard Kroupa; Michael Oschwald
Abstract: This paper reports on the repetitive laser ignition by optical breakdown within an experimental rocket combustion chamber. Ignition was performed by focusing a laser pulse generated by a miniaturized diode-pumped Nd:YAG laser system. The system, which delivers 33.2 mJ in 2.3 ns, was mounted directly to the combustion chamber. The ignition process and flame stabilization was investigated using an optical probe system monitoring the flame attachment across the 15 coaxial injector configuration. 1195 successful ignitions were performed proving the reliability of this laser ignition system and its applicability to the propellant combination LOX/hydrogen at temperatures of $$T_{{{\text{H}}_{ 2} }}$$  = 120–282 K and $$T_{{{\text{O}}_{ 2} }}$$  = 110–281 K.
PubDate: 2017-06-19
DOI: 10.1007/s12567-017-0163-7

• Laser ignition of an experimental combustion chamber with a multi-injector
configuration at low pressure conditions
• Authors: Michael Börner; Chiara Manfletti; Gerhard Kroupa; Michael Oschwald
Abstract: In search of reliable and light-weight ignition systems for re-ignitable upper stage engines, a laser ignition system was adapted and tested on an experimental combustion chamber for propellant injection into low combustion chamber pressures at 50–80 mbar. The injector head pattern consisted of five coaxial injector elements. Both, laser-ablation-driven ignition and laser-plasma-driven ignition were tested for the propellant combination liquid oxygen and gaseous hydrogen. The 122 test runs demonstrated the reliability of the ignition system for different ignition configurations and negligible degradation due to testing. For the laser-plasma-driven scheme, minimum laser pulse energies needed for 100% ignition probability were found to decrease when increasing the distance of the ignition location from the injector faceplate with a minimum of 2.6 mJ. For laser-ablation-driven ignition, the minimum pulse energy was found to be independent of the ablation material tested and was about 1.7 mJ. The ignition process was characterized using both high-speed Schlieren and OH* emission diagnostics. Based on these findings and on the increased fiber-based pulse transport capabilities recently published, new ignition system configurations for space propulsion systems relying on fiber-based pulse delivery are formulated. If the laser ignition system delivers enough pulse energy, the laser-plasma-driven configuration represents the more versatile configuration. If the laser ignition pulse power is limited, the application of laser-ablation-driven ignition is an option to realize ignition, but implies restrictions concerning the location of ignition.
PubDate: 2017-06-19
DOI: 10.1007/s12567-017-0161-9

JournalTOCs
School of Mathematical and Computer Sciences
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