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Acta Astronautica
Journal Prestige (SJR): 0.758
Citation Impact (citeScore): 2
Number of Followers: 413  
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0094-5765
Published by Elsevier Homepage  [3155 journals]
  • Space-native construction materials for earth-independent and sustainable
    • Abstract: Publication date: Available online 10 December 2018Source: Acta AstronauticaAuthor(s): M.Z. Naser A successful space exploration requires establishing permanent and earth-independent infrastructure that are not only resilient to the extreme environment of space but also preferably made of sustainable and indigenous “space-native” construction materials. This review covers feasibility of exploiting in-situ lunar and Martian resources as well as harvesting of elements and compounds, from near Earth objects (NEOs), to produce extraterrestrial materials suitable for construction of space-based infrastructure. This review also details material features and characteristics required to withstand the unique, and harsh, effects of space environment. In essence, this paper reviews past and recent advancements in construction-based materials that could be used in the design and development of space human bases and highlights design consideration for sustainable human settlements. Towards the end of this review, practical and technological challenges associated with development of lunar and Martian indigenous construction materials are identified and examined.
  • Design exploration of combinational spike and opposing jet concept in
           hypersonic flows based on CFD calculation and surrogate model
    • Abstract: Publication date: Available online 10 December 2018Source: Acta AstronauticaAuthor(s): Min Ou, Li Yan, Wei Huang, Tian-tian Zhang The combined thermal protection system has led the drag and heat reduction of hypersonic reentry vehicles to a new developing direction. In order to obtain better resistance to aerodynamic drag and heat while maintain the work stability of the aircraft at the same time, the optimization design of the combined thermal protection system is indispensable. In this paper, a CFD numerical simulation method is combined with a surrogate model based multi-objective optimization algorithm to optimize the configuration of a combinatorial spike and opposing jet thermal protection system in a hypersonic flow with the freestream Mach number of 5.75. The obtained results show that when the total drag coefficient (Cd) and the heat fluxes on the head of the blunt body (Q) are the objective functions, the diameter ratio of the aerodisk to the blunt body bottom (d/D) has no significant effect on the drag and heat flux reduction, and it can be neglected in the optimization process. While the objective functions Cd and Q are affected by the three variables the length-to-diameter ratio of the aerospike (L/D), the jet pressure ratio (PR), and the nozzle radius (r0) in similar ways. Therefore, in this case, the optimization problem can be transformed into a single-objective optimization problem. The quadratic response surface model established by sample points obtained by the orthogonal experimental design method is of high simulation accuracy, with the determination coefficients of Cd and Q are 0.964 and 0.965 respectively, and there is only a difference of −6.96% in the objective function Cd, −0.93% in Q between the optimization results and the CFD results. The combined thermal protection system has better performance in both drag and heat reduction than the single spike or opposing jet systems. Compared with the pure blunt body, the total drag coefficient and heat flux on the head of the blunt body with the combined thermal protection system have significantly decreased, with the Cd goes down 86.66%, and the wall heat flux Q drops off 96.37%.
  • Photosynthetic response of Scenedesmus quadricauda to carbon ions
    • Abstract: Publication date: Available online 10 December 2018Source: Acta AstronauticaAuthor(s): Jie Wang, Jufang Wang, Wenjian Li, Guanghong Luo, Songqi Yang, Yan Du, Wei Wei, Wenjie Jin, Shanwei Luo, Xin Li Plants and algae are one of the key components in Controlled Ecological Life Support System (CELSS) in long-term manned space exploration. However, the biological effects of high linear energy transfer (LET) cosmic radiation on algae are even less well characterized. The photosynthetic apparatus is one of the most sensitive targets after radiation. In this study we analyzed the chlorophyll fluorescent parameters (Fv/Fm, φPSII, and NPQ), the photoprotective pigment lutein, and the transcriptional expression of Lhcb1 and Lhcb2 in a green microalgae, Scenedesmus quadricauda after exposure to 12C6+ ions that were provided by the Heavy- Ion Research Facility in Lanzhou (HIRFL), China. Scenedesmus quadricauda has rapid growth rate and is rich in high-value products which are essential for CELSS development. The results showed that low photosynthetic efficiency of Scenedesmus quadricauda was found in the 60 Gy group within 2 h after radiation. The thermal dissipation abilities of Scenedesmus quadricauda were stronger after exposure to 20 Gy and 60 Gy group within 2 h. Meanwhile, the transcriptional expressions of Lhcb1 and Lhcb2 were up-regulated after exposure to 20 Gy of carbon ions within 4 h. Therefore, 20 Gy of carbon ions radiation could cause stimulative effects on the photoprotective ability and transcriptional regulation of the major LHCII antenna proteins in Scenedesmus quadricauda. Our findings provide the first insight into the biological effects involved in heavy ions radiation on the photosynthetic activity of Scenedesmus quadricauda.
  • Method of heating of the separated parts of launch vehicle during the
           atmospheric phase of the descent trajectory
    • Abstract: Publication date: Available online 10 December 2018Source: Acta AstronauticaAuthor(s): V. Trushlyakov, A. Panichkin, D. Lempert, Ya Shatrov, D. Davydovich A new method for heating the structure of separated parts (like aft interstage, made of a polymer composite material) of launch vehicle up to its ignition temperature is developed, including the physico-mathematical model of heat- and mass transfer based on Navier-Stokes equations and a simplified methodology for implementing the difference scheme for numerical solution of these equations. The source of necessary amount of heat release for heating aft interstage (AIS) up to the ignition temperature is the combustion heat of an energetic material (EM) installed directly inside AIS. Energetic materials can be substances that emit heat during combustion. An example of energetic material can be pyrotechnic compositions, rocket fuels, etc.It is assumed that as soon the temperature of the AIS reaches its ignition temperature, the AIS begins to burn in oncoming airflow with the release of the heat amount enough for the rest mass of the AIS ignition. As an example of the implementation of the method, the results of the estimated temperatures of the AIS structures (made of CFRP) at the EM (oxygen + propane) burning are represented for the fixed point of the flight time at the atmospheric phase of the descent trajectory. The AIS of the launch vehicle "Soyuz" has been considered using two codes: ANSYS FLUENT and the developed code for the numerical solution the difference scheme of the Navier-Stokes equations. The results obtained with the both of these codes are in an acceptable error zone for calculations of the conjugate heat transfer, and the dispersion between these two methods is less than 20%.
  • The mechanism of bystander effect induced by different irradiation in
           human neuroblastoma cells
    • Abstract: Publication date: Available online 9 December 2018Source: Acta AstronauticaAuthor(s): Bo Chen, Peng Zhang, Feiyi Sun, Bo Li, Yu Chen, Sizhu Pei, Ziyin Zhang, Robina Manzoor, Yifan Deng, Chunli Sun, Li Sui, Fuquan Kong, Hong Ma Cells exposed with irradiation can induce different biological effects in non-irradiated cells due to the cell-cell interactions. Herein, we investigated the bystander effect of different types of irradiation including gamma irradiation (GR) and lithium heavy ion irradiation (LR) on the model human neuroblastoma cell line (SH-SY5Y). The gamma and lithium ion irradiation induced different bystander effects on the SH-SY5Y cell line. The bystander effect induced by gamma irradiation promoted the cell proliferation through activating the ERK and AKT signaling pathways, but it could slightly influence the cell cycle of non-irradiated SH-SY5Y cells. Whereas, the bystander effect induced by lithium heavy ion irradiation inhibited the cell proliferation, arrested the cell cycle and activated the process of pro-apoptosis. The findings of this study confirm the diversified bystander effects of various irradiation on the non-irradiated cells, therefore it highlights the importance of revised strategy for clinical radiotherapy and radioprotection to reduce the damages caused by bystander effects. Further, the in-depth mechanism research on the cell proliferation influenced by the bystander effect of radiation will also be useful to understand the biological effects of radiation.
  • Experimental investigations of cavity parameters leading to combustion
           oscillation in a supersonic crossflow
    • Abstract: Publication date: Available online 8 December 2018Source: Acta AstronauticaAuthor(s): Guo-Yan Zhao, Ming-Bo Sun, Xi-Liang Song, Xi-Peng Li, Hong-Bo Wang The effects of cavity parameters on combustion oscillation inside an ethylene-fueled scramjet combustor equipped with a cavity flameholder are experimentally investigated for Mach 5.5 flight conditions. Three certain cases, such as i) longer length-to-depth ratio, ii) sharper aft degree of cavity, iii) closer air throttling downstream of the cavity, exhibit quasi-periodic combustion oscillation, which can be separately attributed to i) larger recirculation volume in the cavity and more mass and heat exchange between cavity shear layer and the core flow, ii) the stronger impinging shock wave in the cavity acting on shear layer, iii) improved fuel/air mixing owing to the interaction between separated boundary layer and combustion. High-speed and schlieren images demonstrate that the cavity and downstream of it act as the most sensitive areas, at the same time, the factors mentioned above can form a thermal throat further triggering flame flashback, which is an indispensable key sub-process of combustion oscillation. The quantitative analysis results obtained from iso-luminosity contour have shown the different distribution trends of flame front and distinct differences of quasi-periodic oscillation frequencies, whereas similar flame propagation speed distributions. In addition, a simplified combustion opening system model has been established to analyze combustion oscillation mechanisms, which theoretically demonstrates that above factors can destroy the balance of heat release and dissipation, causing the system cannot self-stabilize once certain temperature fluctuation thresholds in sensitive areas are exceeded.
  • Simple solution to optimal cotangential transfer between coplanar elliptic
    • Abstract: Publication date: Available online 7 December 2018Source: Acta AstronauticaAuthor(s): Alessandro A. Quarta, Giovanni Mengali The aim of this paper is to propose a semi-analytical method for the analysis of a two-impulse transfer between two coplanar elliptic orbits, assuming each maneuver to change the magnitude of the spacecraft velocity only, without affecting its direction. Using a recent mathematical model that describes the spacecraft dynamics in a compact analytical form within a two-dimensional multiple-impulse scenario, this work proposes an algorithm to calculate the global minimum velocity variation required to complete the transfer. The characteristics of the optimal transfer trajectory, which is tangent to both the parking and the target orbit, are obtained as a function of a single variable, which defines the angular position of the first maneuver. This feature allows the designer to analyze the cotangential transfer in a parametric form, thus obtaining a trade-off solution between the total velocity variation and the desired characteristics of the transfer orbit.
  • Reliability modeling and analysis of environmental control and life
           support systems of space stations: A literature survey
    • Abstract: Publication date: Available online 7 December 2018Source: Acta AstronauticaAuthor(s): Garima Sharma, Rajiv Nandan Rai Ultra reliable life support is needed for environmental control and life support systems (ECLSS) of space stations (SS) because provisioning of spare parts or a speedy crew recovery may not be a feasible option. There is limited work on the reliability modeling and analysis (RMA) of ECLSS of a SS. In addition, presently the literature review on RMA of space stations which is the central theme of the paper is not organized in a formalized manner and the ideas presented are spread out and limited in developing a consolidated literature review in a sequential manner. The paper presents a detailed literature survey on the RMA of SS ECLSS. The paper also highlights the research gaps and an overview of latest RMA models that can be applied for the reliability analysis of SS ECLSS. The paper contributes by providing sufficient insights into the complete development of RMA of the SS ECLSS comprehensively for better understanding of the readers.
  • Mars atmospheric entry guidance for optimal terminal altitude
    • Abstract: Publication date: Available online 6 December 2018Source: Acta AstronauticaAuthor(s): Jiateng Long, Ai Gao, Pingyuan Cui, Yang Liu Maximizing the terminal altitude for Mars atmospheric entry has long been investigated on trajectory design to allow a sufficient timeline margin for subsequent operations and the scientific requirements of exploring Mars ancient highland. The purpose of this paper is to design an onboard Mars atmospheric entry guidance algorithm, which can achieve the optimal terminal altitude at the predetermined terminal flight range. Two important characters that the optimal bank angle profile are revealed in this paper, offering the gateway to the application of the optimal guidance by onboard parameter searching, which will be accomplished by the numerical predictor-corrector strategy. Moreover, suboptimal situations are also investigated considering the performance restriction of reactive control system (RCS). Effectiveness of the proposed guidance algorithm is demonstrated using scenarios of the Mars Science Laboratory (MSL) mission.
  • Power system analysis and optimization of a modular experiment Carrier
           during an analog lunar demo mission on a volcanic environment
    • Abstract: Publication date: Available online 5 December 2018Source: Acta AstronauticaAuthor(s): Georgios Tsakyridis, Caroline Lange, Stephan Siegfried Jahnke, Lars Witte, Norbert Toth, Marco Scharringhausen, Nikolas I. Xiros The ROBEX (Robotic Exploration of Extreme Environments) alliance, as formed by the German Helmholtz association, aims to explore synergies and bring together technological challenges and scientific questions between two, up to now unrelated, fields: space and deep sea. The final goal of the alliance targets field tests for available and newly developed instrumentation for the deep sea and on a terrestrial lunar analogue. In this regard, two different test campaigns were conducted, one in the area of Svalbard, Norway and one on mount Etna in Sicily, Italy. The volcano environment served as a lunar analogue, enabling seismic scientific experiments and testing of robotic mobility algorithms. The complete field mission infrastructure consists of a stationary lander, a mobile element and instrument carriers. The modular instrument carrier, commonly referred as Remote Unit (RU), was developed accounting for two different mass requirements: 3 kg (RU3) and 10 kg (RU10). While developed in the frame of ROBEX resumes the idea of a lightweight instrument carrier as developed for the MASCOT (Mobile Asteroid surface scout) mission. The RU houses the instrument, shelters it and provides all essential support functions such as rudimentary thermal control (via foil covering), power provision, data acquisition and handling and data transmission to the control centre. This paper presents theoretical and experimental results of the RU3 power subsystem analysis during the mount Etna field campaign. Drawing upon this analysis, necessary adjustments and revisions to further develop the system towards a more power efficient structure for terrestrial and extraterrestrial usage can be concluded.
  • Finite time sliding sector control for spacecraft atmospheric entry
    • Abstract: Publication date: Available online 5 December 2018Source: Acta AstronauticaAuthor(s): Biao Xu, Jun Sun, Shuang Li, Tao Cao The paper presents a novel variable structure control with finite time sliding sector for spacecraft atmospheric entry guidance. The finite time convergence of tracking error in the presence of system uncertainty can be guaranteed. In contrast with the normally used notion of asymptotic stability in conventional sliding sector, a finite time sliding sector for the entry guidance is designed as a subset of state space in which the Lyapunov function candidate satisfies the finite time stability condition. Then, the finite time sliding sector controller is designed to guarantee the tracking error to converge to a small region of zero. The chattering existing on the boundary of the sliding sector is further reduced by introducing inner sector and outer sector which are the subsets of the proposed sector. Finally, numerical simulation results are given to demonstrate the effectiveness of the proposed method.
  • The satellite layout optimization design approach for minimizing the
           residual magnetic flux density of micro- and nano-satellites
    • Abstract: Publication date: Available online 5 December 2018Source: Acta AstronauticaAuthor(s): Xianqi Chen, Shucai Liu, Tao Sheng, Yong Zhao, Wen Yao With the rapid development of space technology, more and more complex micro- and nano-satellite missions have been proposed for more sophisticated objectives such as remote sensing and space astronomy. To meet these mission requirements, the satellites need to maintain a highly precise attitude control capability. However, the satellite residual magnetic moment, as the dominant disturbance torque, greatly limits the realization of the accurate attitude determination and control system. To minimize the influence of the residual magnetic field on satellite attitude determination, in this paper, a novel satellite layout optimization design (SLOD) approach is proposed. The determination method of satellite residual magnetic field is elaborated firstly and then the corresponding SLOD model concerning complex performance constraints is established. Moreover, the improved accelerated particle swarm optimization (IAPSO) algorithm is developed to search for the optimal layout solution. Finally, the feasibility and effectiveness of the proposed methodology are validated by a numerical layout example and a simplified nano-satellite layout case.
  • Cost estimating of commercial smallsat launch vehicles
    • Abstract: Publication date: Available online 4 December 2018Source: Acta AstronauticaAuthor(s): N.T. Drenthe, B.T.C. Zandbergen, R. Curran, M.O. Van Pelt Commercial launch service providers’ low-priced offerings have been a hotly debated topic. However, the strategies with which these firms reduce costs have seen little incorporation into the hardware Cost Estimating Methods (CEMs) and tools prevalent in the aerospace industry. This research changes this, by providing adaptations to agency-focused CEMs that befit a new commercial paradigm, with an emphasis on smallsat launch vehicles.A parametric model for estimating costs in an early phase of development was synthesized, with which it is possible to approximate the full life-cycle costs of small commercial liquid and solid propellant rockets, as well as their cost-based price per flight. Key elements included were reductions in cost achieved by commercial launch operators, by modeling reduced subcontractor management effort and profit retention experienced at lower subcontracting rates.Prices per flight of small commercial launch vehicles were approximated by combining a parametric cost estimating methodology used frequently in the context of space agencies such as ESA and NASA, called the T1 Equivalents method, with another parametric three-part estimate developed by Koelle for development, manufacture and operations phase costs. The first two phases were estimated through the T1 method, while the operations costs were modeled with TRANSCOST.Along with the newly developed methodologies, novel insights such as required launch rates have shone a light on small commercial launch systems’ cost feasibility in the age of public-private spaceflight partnerships.The model developed was able to approximate costs of development, manufacture and price per flight of three commercial rockets to within 20% of actual reported costs or prices. However, it is recommended the model is refined as more reference cost data, especially on a subsystem level, as well as pricing for these smaller rockets becomes available in the coming years.
  • Numerical simulation of gel fuel gas-phase ignition by a local source of
           limited heat content
    • Abstract: Publication date: Available online 4 December 2018Source: Acta AstronauticaAuthor(s): D.O. Glushkov, G.V. Kuznetsov, P.A. Strizhak, R.I. Taburchinov A mathematical model has been developed to predict the characteristics of interdependent physical and chemical processes taking place in a gel fuel ignition by a hot cylinder-shaped particle located on its surface. The density values have been established for the heat flux (60–950 kW/m2) from the local heating source to the fuel, that are required for its ignition in a wide range of various initial temperatures (840–1500 K), dimensions (radius 2.5–10 mm, height 5–20 mm), and particle materials (steel, copper, aluminum, ceramics, and carbon). Changes in these parameters were found to significantly affect the main characteristic of the process – ignition delay times – under the near-threshold ignition conditions. During local conductive heating, the delay times of the gas-phase ignition of the fuel vary between 0.02 and 0.8 s. At the initial fuel temperature of 80 K, the duration of the induction period rises by 40% as compared to the fuel ignition delay time at the initial temperature of 275 K in the conditions of ignition by a particle with a temperature of 1000 K. It has been established that regardless of the local heating source parameters and conditions of the process, the ignition of the fuel occurs near the base of the hot particle in the immediate vicinity of the gel fuel surface.Graphical abstractImage 1
  • Cosmopolitical bodies: An architecture of space
    • Abstract: Publication date: Available online 3 December 2018Source: Acta AstronauticaAuthor(s): Mikaela Patrick The project of ‘Cosmopolitical Bodies: An Architecture of Space’ is a design research project, where the relationship between Space exploration and its ideals, architecture and the environment are reimagined within the complexities of our planet's ecosystem. Tools of image production and architectural propositions are employed to argue that the encounter between people and the planet should be recomposed to form new alliances with nature; cosmopolitical bodies. research is loosely divided into two parts, research into prevailing imaginations of space and their counter-arguments and implications for creative practice; and a speculative design thesis titled ‘Dandal Kura’ exploring the potentials of space technologies on Earth. Based upon research around multispecies theory and critiques of scientific practice, the research does not propose a human agent being replaced by the environmental agent; but a balance or symbiosis of living, living with nature. Both real and imagined space exploration's influence on (ecological) architecture has historically been seen as an exercise in escaping environmental crisis and reinforcing dominant political narratives. In this context, an alternative imagination of space is considered to propose new architectures. An imagination of space that reflects multiplicities, is arguably female, and considers an ecological architecture that confronts the complexity of the social, environmental and political systems of the planet we inhabit; calling forth ideas of settling as an alternative to the mastery of nature. The project consists of a critique on the closed system conceptions of nature produced through imaginations of space exploration and locates Lake Chad as an ‘Earth site’ to test scales of ecological architectures: from the planetary system of the Lake as seen from space, to the microbiology of life-sustaining algaes growing in the wadis. The Lake Chad design project takes the name of Dandal Kura (meeting place) and speculates on the impact of series of interventions where space technologies allow women's cooperatives around Lake Chad to adapt to climate change. Through the intersection of scientific and indigenous knowledge, the project of Dandul Kura proposes that space technologies can become an emancipatory tool in the context of climatic crisis. The design proposal is conveyed through a series of images, reimagining modes of living in Lake Chad in this context of climate change and economic and environmental scarcity.
  • Application of a planar air-bearing microgravity simulator for
           demonstration of operations required for an orbital capture with a
    • Abstract: Publication date: Available online 3 December 2018Source: Acta AstronauticaAuthor(s): Tomasz Rybus, Karol Seweryn, Jakub Oleś, Fatina Liliana Basmadji, Kamil Tarenko, Radosław Moczydłowski, Tomasz Barciński, Jan Kindracki, Łukasz Mężyk, Przemysław Paszkiewicz, Piotr Wolański Microgravity is the aspect of space environment that is important for robotic technologies. One possible approach to simulate microgravity conditions on Earth is to use planar air-bearing microgravity simulators. In this study we have assessed the possible application of such simulator for demonstration of operations required for the orbital capture manoeuvre. In our experiments we have used mock-up of satellite equipped with a manipulator and a set of cold-gas thrusters. Results of two sets of experiments are presented. In both sets the manipulator end-effector followed a straight-line trajectory. In the first set the satellite mock-up was commanded to hold fixed position and orientation, while in the second set the satellite mock-up was commanded to follow a pre-defined trajectory. Performed experiments show that the accuracy of the planar air-bearing microgravity simulator is sufficient to use this facility to validate control algorithms and control strategies. Presented analysis also shows that changes of the satellite-manipulator system parameters caused by the consumption of air and nitrogen from gas canisters located on the satellite mock-up have negligible influence on the dynamic behaviour of the system.
  • Station-keeping of libration point orbits by means of projecting to the
    • Abstract: Publication date: Available online 3 December 2018Source: Acta AstronauticaAuthor(s): Hanqing Zhang, Shuang Li There are many different types of (quasi)periodic orbits in the vicinity of collinear libration points. These libration point orbits (LPOs) are inherently unstable and must be controlled. This paper studies general station-keeping strategies that are suitable for various types of LPOs. Two complementary methods are proposed by exploiting the hyperbolic dynamics of the collinear libration points. One main advantage of these methods is that no information of the nominal orbit is needed in order to do the station-keeping. The first is a semi-analytical projection method which is based on the high order polynomial approximation of the center manifold. After the transformation from synodic coordinates to center manifold coordinates is derived, the error state can be projected to center manifold or its stable manifold by introducing a station-keeping Delta-V, effectively eliminating the unstable component. The second is a fully numerical method. An escape time algorithm is designed to find the intersection of stable and unstable manifolds, effectively projecting the error state to the center manifold. By applying these techniques to the collinear libration points of Earth–Moon system, it has been demonstrated that these proposed methods can achieve better maneuver cost performance and they can handle station-keeping problems of various types of LPOs in a unified manner.
  • Halo orbits construction based on invariant manifold technique
    • Abstract: Publication date: Available online 3 December 2018Source: Acta AstronauticaAuthor(s): Ying-Jing Qian, Jian-Yu Guo, Tian-Jun Yu, Xiao-Dong Yang, Dong-Mei Wang The current investigation applied the invariant manifold technique to study the halo orbits around the libration points in circular restricted three-body problem. Two dominant (leading) directions were considered as dominant motions for the construction of spatial halo orbits, the third direction motion being the slave (following) motion. The dominant motions correspond to four-dimensional invariant manifolds in the phase space. The invariant nonlinear asymptotic relations (i.e. INARs) between the two dominant motions and the slave motion were established, enabling a transformation from the 3-DOF problem into a 2-DOF problem. Application of the INARs are also discussed. Such invariant nonlinear relations in polynomial expansion form could be used as: (I) approximate analytical solutions; (II) topological constraints to obtain more exact numerical solutions with differential correction. General findings in the current research revealed that the nonlinear asymptotic relations among the directions provided an alternative point of view to explore the overall dynamics of halo orbits around libration points with general rules. The effectiveness of the proposed method was also verified by numerical simulations.
  • A high-accuracy autonomous navigation scheme for the Mars rover
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Yunan Zhao, Xinlong Wang, Qunsheng Li, Dun Wang, Yuanwen Cai High-accuracy, autonomous and reliable navigation systems are important foundations for Mars rovers to achieve exploration missions successfully. Based on the motion characteristics and working environment of the rover, the paper shows a high-accuracy strapdown inertial navigation system/visual navigation system/celestial navigation system (SINS/VNS/CNS) integrated navigation scheme suitable for the rover with long-time and long-distance motion. According to the feature point positions in the camera frame at adjacent time obtained by the binocular visual odometry, its velocity in the camera frame and the attitude are calculated, then a subsystem model of SINS/VNS integrated navigation is established. In addition, using the star vectors measured by the large field-of-view star sensor, a high-accuracy attitude matrix of the rover in the inertial frame can be obtained, and a SINS/CNS subsystem model is established. Furthermore, in order to make full use of the complementary advantages of the two subsystems in attitude and position estimation, an interacting multiple model filter is developed. By updating the model probabilities of the subsystems separately in real time, the filter can output accurate navigation information of the rover. Simulation results show that the proposed navigation scheme can significantly improve the estimation accuracy of attitude, position and velocity simultaneously.
  • Project Dragonfly: Sail to the stars
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Tobias Häfner, Manisha Kushwaha, Onur Celik, Filippo Bellizzi This paper aims to assess the feasibility of an interstellar mission to reach the Alpha Centauri star system and delivering scientific data, using current and near-future technology. The mission baseline uses 100 GW of laser power to accelerate a spacecraft of 2750 kg to 5% the speed of light with light sail technology, resulting in a travel time of about a century. This paper explores several aspects of the mission: Possible locations of the laser infrastructure and different sail materials to achieve the required acceleration are discussed. Deceleration using a magnetic sail in the interstellar medium and in the heliosphere of the target star, taking into account mathematical models from Zubrin [6], Freeman [22] and Gros [21], is studied. Potential orbits in the star system are considered for observation and data collection. Finally, a multi-spacecraft mission architecture is presented, as it would allow for the spacecraft to be launched sequentially, thus exploiting the possibility of continuously operating the laser infrastructure.
  • Developing predictive models: Individual and group breakdowns in long-term
           space travel
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Alires J. Almon It is inevitable that individuals and groups will experience stress and distress in the harsh and extreme environment of deep space. When these occur, we now have a mission in jeopardy -- not due to hardware failure, but because a psychological breaking point has been reached. It will happen. The question is when. This paper seeks to identify signs of impending breakdowns and suggests strategies for a crew to minimize its impact when it does. This paper begins to create definitions and qualities of breaking points, define the impact on group dynamics, and identify post-breakdown recovery strategies that will be used as a foundation for predictive model development.
  • Earth-Mars cyclers for a sustainable human exploration of Mars
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Stewart Pelle, Eugenio Gargioli, Marco Berga, Jacopo Pisacreta, Nicole Viola, Alessandro Dalla Sega, Michele Pagone Since the early history of Space Exploration, Mars conquest has been the most important target. After Apollo mission's Moon landing, several concepts and projects, concerning a mission on the Red Planet, were developed. One of the most important contributes was given by Buzz Aldrin, who theorized the use of particular kind of orbits, called cycler orbits, as baseline for an enduring Mars colonization.A cycler orbit is a kind of orbit which repeats every integer multiple of synodic period and which encounters two bodies with a precise schedule. In the case, the bodies considered are Earth and Mars. It is possible to inject a space station in the cycler orbit which allows a continuous transfer of a crew from Low Earth Orbit to Mars Low Orbit and vice-versa. Small taxi vehicles are used to rendezvous the cycler station from the two bodies, significantly reducing the amount of propellant.In this paper a mission architecture based on this new concept was analysed, in order to develop an alternative mission profile compared to the actual architectures proposed for human missions. The work starts with an analysis of several classes of cycler. Through a trade-off analysis an unique class of cycler was identified as baseline for a further mission analysis. The mission analysis consists of an evaluation of orbital perturbation, the computation of ΔV required for injection and rendezvous manoeuvres and an identification of close approach windows of the cycler with the two planets, allowing an evaluation of mission duration.Eventually, the presented mission concept was compared with more classical concepts, focusing on a key figure to enable Mars colonization, sustainability.Finally the proposed architecture should be seen as a preliminary assessment of an alternative solution to the currently proposed enabling architectures for the Martian exploration.
  • Optimal in-orbit repositioning of Sun-pointing Smart Dust
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Alessandro A. Quarta, Giovanni Mengali, Eugenio Denti A Smart Dust is a femto-spacecraft with an external surface coated with electrochromic material, which exploits the solar radiation pressure to produce a propulsive acceleration. As the optical properties of the electrochromic material change upon application of a suitable electric voltage, its propulsive acceleration may be modulated, within some limits, without the use of any propellant. This paper analyzes the optimal trajectories of a Sun-pointing Smart Dust, which provides a propulsive acceleration aligned with the Sun-spacecraft direction. In particular, the paper describes the relative motion of a Smart Dust with respect to a conventional spacecraft (the Mother Ship) that covers a heliocentric circular orbit of given radius. The Smart Dust is required to vary periodically its angular position with respect to the Mother Ship using an optimal (minimum time) strategy. This problem is addressed using an indirect approach and the optimal control law is obtained in a closed-form solution. The results discussed in this paper ensure interesting improvements over existing models from the recent literature, including the possibility of obtaining a generic phasing angle of the Smart Dust and to take into account an optimal number of on-off switchings of the electrochromic control system.
  • Thermal-structural analysis of a square solar sail
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Luisa Boni, Alessandro A. Quarta, Giovanni Mengali The aim of this work is to improve an efficient methodology, recently developed to study the structural response of a classical square solar sails in free flight, under the action of the solar radiation pressure. The new approach models the effect of thermal loads acting on the sail's reflective surface. In particular, a square solar sail with a side length of 20m at 1au distance from the Sun is analyzed for different values of incidence and clock angles. The thermal-structural analyses are carried out under the assumption that the stress-displacement solution depends on the temperature field, but there is no inverse dependency. The thermal loads, for some attitude conditions, are shown to have remarkable effects on the sail deformation.
  • Multiple solar sail formation flying around heliocentric displaced orbit
           via consensus
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Wei Wang, Alessandro A. Quarta, Giovanni Mengali, Jianping Yuan This paper investigates the problem of multiple solar sail-based spacecraft formation flying in which the chief follows a heliocentric displaced orbit, whereas each deputy adjusts the sail propulsive acceleration so as to track a desired (relative) trajectory with respect to the chief. In particular, coordinated control strategies are presented for both the full state feedback case and the relative velocity unavailability case, respectively. The developed consensus-based algorithms rely on the protocols formulated on an undirected communication topology with information link couplings, utilizing every available neighbor-to-neighbor information data such that the reliability of the formation system can be enhanced. Illustrative examples show the validity the proposed method.
  • Interplanetary CubeSats for asteroid exploration: Mission analysis and
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Gianluca Benedetti, Nicoletta Bloise, Davide Boi, Francesco Caruso, Andrea Civita, Sabrina Corpino, Erik Garofalo, Giuseppe Governale, Luigi Mascolo, Gianluca Mazzella, Mariangela Quarata, Dario Riccobono, Giulia Sacchiero, Domenico Teodonio, Pietro Maria Vernicari Recent advances in CubeSats technology are leading the transition from purely education tools to actual scientific missions. The small volumes and masses, the versatile purpose, as well as the fast development time associated with a potential high return-to-cost ratio are at the origin of the increasing number of new mission proposals, also beyond low Earth orbit (LEO). The purpose of this study is to assess the CubeSats ability to complement an interplanetary scientific mission. The proposed AIDA (Asteroid Impact and Deflection Assessment) mission, an ESA/NASA joint effort to demonstrate the kinetic impact technique to change the motion of an asteroid in space, has been selected as case study, having a mission context particularly suitable in showing CubeSats supporting capabilities. The feasibility study of a mission involving the use of CubeSats as secondaries for technology demonstration and science purposes was performed. Mission objectives and requirements were defined, followed by the development of concepts of operations and mission architectures proposals. Eventually, multiple trade-off tools were adopted to define the proposed mission baseline, which involves the deployment of two 3U CubeSats performing a detachment to achieve the final configuration of one 2U and four 1U CubeSats. The scientific campaign conducted by the CubeSats includes gravitational and magnetic field mapping, on-surface chemical-physical measurements via multiple wide chip-size-sensor nets deployed from orbit, on-surface seismic measurements via landing of the 2U CubeSat, direct observation of the impact from multiple viewpoints and evaluation of the asteroid's orbit deflection due to the impact. The mission proposed involves also some important technological demonstrators. The S-iEPS (Scalable-ion Electrospray Propulsion System) has been considered as propulsion system, while a potential landing system has been proposed to achieve the soft touchdown of the 2U CubeSat. Finally, an inter-satellite communication link via laser has been included as main communication system. The proposed mission baseline has shown that CubeSats can be successfully integrated as multi-platform systems to provide useful support to interplanetary missions. This solution may enable the capability to acquire more detailed information with the possibility to combine them to obtain better results with respect to single-platform systems. The proposed mission concept represents a valuable low-cost piggyback solution adaptable to several mission contexts, with a potential high return and a remarkable attitude for the implementation and testing of new technologies and operations. In this context, this study provides a useful framework for the design and development of interplanetary CubeSats missions.
  • Moon Farside Protection, Moon Village and PAC (Protected Antipode Circle)
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Claudio Maccone The Moon Farside is the only place in space, and not too far from the Earth, where radio transmissions and noises produced by Humanity on Earth may not reach since the spherical body of the Moon blocks them, acting like a shield. Thus, protecting the Moon Farside from all kinds of non-scientific future exploitations (e.g. real estate, tourism and military) has long been a concern for many far-sighted space scientists as well as for several IAA Academicians. We started facing this problem in the 1990s, when the French radio astronomer Jean Heidmann of the Paris Meudon Observatory first promoted an IAA Cosmic Study about which areas of the Moon Farside should be reserved for scientific uses only. But Heidmann passed away on July 3rd, 2000, and his work had to be continued by others. This author took over his IAA Cosmic study and a paper describing both the scientific and legal aspects of the problem was published in 2008 (see Ref. [1]), Later, on June 10, 2010, this author was the first scientist to present the case for the Moon Farside Protection at the United Nations Office of Outer Space Affairs in Vienna (see Ref. [2]) during a meeting of UN-COPUOS, the United Nations Committee on the Peaceful Uses of Outer Space. Unfortunately, the undeclared but quite real “current, new race to the Moon” complicates matters terribly. All the space–faring nations now keep their eyes on the Moon, and only the United Nations might have a sufficient authority to Protect the Farside and keep safe its unique “radio-noise free” environment. But time is money, and the “Moon Settlers” may well reach the Moon before the United Nations come to agree about any official decision concerning the Farside Protection. Quite an URGENT ISSUE. In this paper, we firstly define the PAC (= Protected Antipode Circle), i.e. a circular piece of land on the Farside having its center at the Antipode of the Earth and tangent to the +30° and -30° parallels. This turns out measuring about 1820 km in diameter on the surface of the Moon Farside. Then we propose that the new “Moon Village”, supported by the vision of the ESA Director General, Jan Woerner, be located OUTSIDE the PAC (obviously not to interfere with the detection of radiation coming from space) and also SOUTH OF THE PAC, to be “close” to the South Pole as much as needed in order to benefit of frozen water there. It thus appears that the best venue for the “Moon Village” would be on or around the 180° meridian and possibly quite close to the South Pole.
  • Access to Space: Capacity-building for development through experiment and
           payload opportunities
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Daniel García Yárnoz, Ayami Kojima, Simonetta Di Pippo The United Nations Office for Outer Space Affairs has developed a comprehensive set of capacity-building activities and associated partnerships providing access to experimental facilities on ground and to a wide range of Low Earth Orbit platforms. These opportunities are available to applicants from high-school to university level, as well as other research, governmental and inter-governmental institutions. This is a unique approach to space capacity-building, away from the traditional classroom or lecture methods, aimed at developing and emerging economies, as well as encouraging cooperation with agencies and institutions from developed nations. This paper summarizes the series of activities and related programmatic and roadmap of the Office.
  • A twofold mission to the moon: Objectives and payloads
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Y.G. Shkuratov, A.A. Konovalenko, V.V. Zakharenko, A.A. Stanislavsky, E.Y. Bannikova, V.G. Kaydash, D.G. Stankevich, V.V. Korokhin, D.M. Vavriv, V.G. Galushko, S.N. Yerin, I.N. Bubnov, P.L. Tokarsky, O.M. Ulyanov, S.V. Stepkin, L.N. Lytvynenko, Y.S. Yatskiv, G. Videen, P. Zarka, H.O. Rucker Ukraine has scientific and technical potential to construct a spacecraft and payloads for exploration of the Moon in collaboration with other interested countries. In this paper we propose a double mission that consists of two parts: (1) orbiter exploration from an elongated orbit with a pericenter over the north pole (100 km above the surface) and the apocenter over the south pole (altitude about 3000 km), and (2) exploration with a lander located on the lunar farside near the south pole in the surroundings of the crater Braude. The lander carries five antennas for radio astronomy observations from hundreds of KHz to 40 MHz. The farside landing is necessary to provide effective shielding electromagnetic noises from the Earth, including aurora and lighting radiation. The lander communicates with the relay satellite in a high portion of the orbit; the orbiter is equipped with scientific payloads for investigation of the lunar surface. In the mode of a radio spectrometer, the radio antennas may study solar flares of various types, coronal mass ejections, Jupiter radio emission (L and S bursts), and Saturn (lightning and kilometer radio emission). Overlapping frequencies in the range of 10–40 MHz will allow coordination with terrestrial radio telescopes of IRA NAS, Ukraine (UTR-2, GURT), whose operation is limited by the Earth ionosphere. The absence of terrestrial noise allows us to approach the solution of the problem of searching for cosmological effects associated with the line of neutral hydrogen at Z = 50 … 100. The lander panoramic camera equipped with color and polarization filters provides important observations of horizon glow caused by the effect of electrostatic levitation of the lunar dust. For the orbital module we suggest remote-sensing instruments, which had not previously been used in space exploration of the Moon. The expected spatial resolution of the data will be about 100 m for the northern hemisphere. The equipment should include instruments, prototypes of which are already available in science organizations of Ukraine. These include an infrared spectrometer to map the abundance of OH/H2O compounds in the lunar soil. A HiRes camera operating in two spectral bands is suggested for mapping structural and mineralogical characteristics of young surface formations. The 3-mm radar, working in a squint mode, will not only map the radio brightness of the surface, which characterizes its roughness, but also improve the lunar topographic model with a spatial resolution of 100 m.
  • Exploring the surface of the Moon and Mars: What kind of ground vehicles
           are required'
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): M. Baratta, G. Genta, D. Laurenzano, D. Misul On the surface of the Moon and Mars, the astronauts must have at their disposal means for exploring a suitable area of the planet. A ground vehicle was tested for the first time outside Earth during the Apollo program, but the longer stay and the wider extent of the exploration will make similar vehicles designed for Mars larger, faster and more complex. In later missions, transportation on the planet will possibly require aerial vehicles and finally the realization of a whole transportation infrastructure. Furthermore, robotic rovers will be required to assist the astronauts in their exploration duties.
  • Science on the lunar surface facilitated by low latency telerobotics from
           a Lunar Orbital Platform - Gateway
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Jack O. Burns, Benjamin Mellinkoff, Matthew Spydell, Terrence Fong, David A. Kring, William D. Pratt, Timothy Cichan, Christine M. Edwards NASA and ESA are preparing a series of human exploration missions using the four-person Orion crew vehicle, launched by NASA's Space Launch System, and a Lunar Orbital Platform - Gateway (LOP-G) that enable long duration (>30 days) operations in cis-lunar space. This will provide an opportunity for science and exploration from the lunar surface facilitated by low latency surface telerobotics. We describe two precursor experiments, using the International Space Station (ISS) and a student-built teleoperated rover, which are laying the groundwork for remote operation of rovers on the Moon by astronauts aboard the LOP-G. Such missions will open the lunar far side, among other sites, for exploration and scientific exploration. We describe examples of two high-priority, lunar science missions that can be conducted using low latency surface telerobotics including an astronaut-assisted far side sample return and the deployment/construction of a low frequency radio telescope array to observe the first stars and galaxies (Cosmic Dawn). The lessons learned from these lunar operations will feed-forward to future low latency telepresence missions on Mars.
  • How the Lunar Space Tug can support the cislunar station
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Martina Mammarella, Pietro M. Vernicari, Christopher A. Paissoni, Nicole Viola The Lunar Space Tug is a sustainable transportation system able to rendezvous with a target body in Low Earth Orbits environment, assess its current position, attitude and operational status, capture the target and move it to the Cislunar space where the Lunar Orbital Platform-Gateway will be settled. Thanks to the adoption of an electric Propulsion Subsystem based of Hall Effect Thruster clusters, the Lunar Space Tug can save fuel to the detriment of much longer transfer time to deliver the unmanned cargo to the cislunar Gateway. Since the Lunar Space Tug has been conceived to be reusable, one of the main issue is related to the on-orbit refueling to sustain the Lunar Space Tug during its operational lifetime. Each mission scenario shall take into account the effects related to refueling operations according to mission requirements and constraints. Considering the whole mission scenario in which the Lunar Space Tug will operate, this paper focuses on mission analysis and conceptual system design, including typical systems budgets, like transfer duration, Δv, mass and power. Moreover, according to the transfer duration and the needs of the Lunar Orbital Platform-Gateway, a preliminary trade-off analysis has been accomplished to investigate the possibility of using a fleet of Lunar Space Tug instead of a single tug, taking onto account safety, reliability, costs and operations issues. The identified optimal configuration is then compared with the current reference option, i.e. the NASA Space Launch System adopted as cislunar delivery vehicle.
  • Living in the Moon Village - Ethical and legal questions
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Irmgard Marboe The ethics of human beings living together depends on shared values and principles that are generally recognised and respected. These values and principles are reflected in legal rules and regulatory frameworks to provide safety, security and foreseeability for the members of the community. The same would be true for the Moon Village. While not being a programme or project, but a concept which may serve the development of ideas of future space activities, ethical principles and relevant legal rules already exist. Others will have to be developed in the future. The present paper addresses three steps towards an ethical and regulatory framework for a Moon Village.
  • Editorial
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Giancarlo Genta
  • Osteoclast-derived exosomes inhibit osteogenic differentiation through
           Wnt/β-catenin signaling pathway in simulated microgravity model
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Ting Huyan, Yongyong Du, Dandan Dong, Qi Li, Ruixue Zhang, Jiancheng Yang, Zhouqi Yang, Jingbao Li, Peng Shang In the microgravity environment of space, astronauts undergo osteoporosis due to an imbalance in bone remodeling. Recent studies have shown that exosomes derived from osteoclasts could mediate cell-to-cell communication in bone remodeling. However, the role of osteoclast-derived exosomes in bone remodeling in microgravity remains a mystery. Our objective is to investigate the cellular processes modulated by exosomes from RAW264.7 cell-derived osteoclasts and the underlying mechanism of action for the exosomes-mediated osteogenesis of osteoblast-like MC3T3-E1 cells in simulated microgravity. We took advantage of the random positioning machine (RPM) to simulate microgravity for the model and investigated the role of exosomes from RAW264.7 cell-derived osteoclasts in osteoclast-osteoblast communication. The results showed that this type of mature osteoclast-derived exosomes (OC-Exos) in the RPM evidently inhibited the cellular proliferation of osteoblasts via inducing cellular apoptosis and altering their cell cycle distribution. Alkaline phosphatase and mineralization activity of MC3T3-E1 cells were significantly lower after treatment with OC-Exos from RPM and mRNA expression of osteoblast-specific genes were down-regulated. Further study confirmed that OC-Exos in RPM obstructed the differentiation of MC3T3-E1 cells by interfering with Wnt/β-catenin signaling pathway. Together, these observations demonstrated that OC-Exos played an essential role in the regulation of bone remodeling in the microgravity environment. These results shed light on a novel pathway of cross-talk between osteoclasts and osteoblasts, which will be helpful to explain the possible mechanisms underlying osteoporosis in microgravity.Graphical abstractImage 1
  • Physics-based Gaussian process for the health monitoring for a rolling
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Seyed M.Mehdi Hassani.N, Xiaoning Jin, Jun Ni An improved Gaussian process regression (GPR) is presented to predict the remaining useful life (RUL) of a gyroscope being integral to its prognostics and health management, despite uncertainties in the mean and variance values. In our approach, the degradation model of the gyroscope innovatively serves as a global model in the GPR methodology to capture the actual trends of the RUL. Moreover, the ball bearing whose rolling contact wear is responsible for the drifting in the gyroscope is considered as an essential component for the gyroscope RUL estimation. Employing the GPR method and the physical degradation model, the prognosis for the ball bearing can successfully predicts the defect before it occurs. Compared to other data-driven algorithms, results obtained for a gyroscope in an inertial navigation system confirm that the proposed method can be applied for drift prognostics with significant efficiency.
  • LES of primary breakup of pulsed liquid jet in supersonic crossflow
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Y.H. Zhu, F. Xiao, Q.L. Li, R. Mo, C. Li, S. Lin The injection of a pulsed liquid jet into supersonic air flow is a promising approach to improving the fuel atomization performance in a Scramjet engine. Therefore, the primary breakup of a pulsed liquid jet in supersonic crossflow is numerically investigated in the present paper. A two-phase flow Large Eddy Simulation (LES) algorithm is developed for simulations of liquid jet atomization in supersonic gas flow. A coupled Level Set and Volume of Fluid (VOF) method is used to track the interface deformation and disintegration. The supersonic gas flow is solved using a compressible flow solver while the liquid phase is solved by an incompressible flow solver. Appropriate boundary conditions are specified at the interface for both solvers to correctly capture the interaction between the gas and liquid phases. The primary atomization of a steady liquid jet with the same average mass flow rate as the pulsed jet is also simulated as a benchmark test case. The liquid velocity pulsation produces a very different primary atomization morphology in comparison with the steady liquid jet, which significantly enhances the primary breakup process. It is observed that Rayleigh-Taylor instability dominates the development of surface waves for the steady liquid jet. For the pulsed liquid jet, the liquid column deformation induced by the liquid velocity pulsation determines the wavelength of the surface waves and thus the liquid jet breakup location. In comparison with the steady liquid jet, the penetration of the pulsed liquid jet increases by 20%, and the width of the wake zone expands by 25%, resulting in improved atomization and mixing performance.
  • BELA transmitter performance and pointing stability verification campaign
           at DLR-PF
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): C. Althaus, H. Michaelis, H. Hussmann, K. Lingenauber, R. Kallenbach, S. Del Togno, F. Lüdicke BELA is the first European planetary laser altimeter and shall be launched onboard of ESA's Mercury Planetary Orbiter (MPO) as part of the BepiColombo spacecraft in October 2018. The complete development of the instrument was done in collaboration with team members in Switzerland, Germany and Spain. The transmitter is also the first space-qualified laser system for a planetary mission built in Europe. Highly important for scientific performance is the transmitter's performance which is specified with demanding values. Thermo-optical pointing stability, alignment, pulse energy, wavelength, pulse profile and length have a direct impact on the signal quality and strength of the instrument and in consequence on the quality of science data. Furthermore for in-orbit operation the detailed knowledge of the transmitter behavior is required for the interpretation of measurement data. Therefore the transmitter, an encapsulated diode pumped pulsed Nd:YAG laser, was extensively tested at facilities at DLR in Berlin-Adlershof under various environmental conditions in all possible representative configurations. This is necessary because thermo-elastic and optical behavior are difficult to predict accurately only theoretically. Furthermore there are temperature dependent effects, e.g. for laser energy, which directly affect science measurements and can only be calibrated on-ground. An optical test bench was designed and set up for this particular task. This work describes the test bench and the measurement procedures. The measurement results for the Engineering Qualification Model and Flight Model are presented and discussed as well as lessons learned. The outcome of the tests shows that the BELA FM transmitter performs well with margins and BELA is expected to achieve its scientific goals.
  • A two-time scale control scheme for on-orbit manipulation of large
           flexible module
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Meibao Yao, Xueming Xiao, Yang Tian, Hutao Cui The key issue in on-orbit manipulation is to transport large flexible modules to pre-assembly position accurately. However, the cooperative manipulation by a team of space robots can induce large vibration in the robot-beam system. This paper presents a two-time scale control scheme for vibration minimization in trajectory tracking of the flexible module. The control scheme is composed of a slow controller ensuring precise tracking of the beam's rigid motion and a fast controller to minimize the systemic vibration. Our approach to the slow controller design is based on non-singular terminal sliding mode control, with which fast and finite-time convergence of tracking errors against disturbances is obtained. The fast controller guarantees minimum vibration induced during the manipulation by applying optimal control technique. Numerical results by comparison show that the two-time scale control scheme for cooperative manipulation demonstrates higher precision and finite-time convergence in tracking the rigid motion with robustness and minimizing the vibration simultaneously.
  • Response of inner flow and spray characteristics of a pressure swirl
           injector to pressure oscillation in supply system
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Peng Cheng, Qinglian Li, Zhongtao Kang, Huiyuan Chen The present work focused on the response of the two phase flow of a pressure swirl injector to pressure oscillation in supply system. A mechanical pulsator was used to generate pressure oscillation in supply system. The inner flow of the injector and spray were captured by backlit shadowgraph technique and the droplet size was recorded by laser diffraction technique. In addition, image processing and proper orthogonal decomposition were used to analyze the data. The results indicate that the inner flow, spray and droplet size oscillate along with pressure oscillation mainly at the driving frequency. The oscillation of air core was used to characterize the inner flow. The dynamics of air core center and air core diameter was analyzed and the modes of the inner flow were obtained. Then, the way the oscillation propagated inside the nozzle was identified as a long wave manner. When the liquid was emanated from the nozzle, thick film resulted from pressure peak was faster when compared with thin film resulted from the trough of pressure oscillation. This characteristic was found to be responsible for the sudden shrink of the spray, and changed the spray pattern from a hollow cone to a pagoda. Finally, the thick and fast film produced a dense spray and large droplets. The whole paper discussed the response of inner flow and spray characteristics of a pressure swirl injector to pressure oscillation, and revealed the way the pressure oscillation propagated from supply system to spray field.
  • Numerical investigation of transverse jet in supersonic crossflow using a
           high-order nonlinear filter scheme
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Yixin Yang, Hongbo Wang, Mingbo Sun, Zhenguo Wang, Yanan Wang We carried out a numerical study of a sonic transverse jet into a Ma = 2.0 crossflow based on a hybrid Reynolds-averaged Navier-Stokes (RANS)/large eddy simulation (LES) method. In order to enhance the calculation accuracy, an improved high-order finite-difference scheme is introduced. This scheme consists of an eighth-order central scheme and a nonlinear dissipation filter. The filter is derived from the explicit seventh-order weighted compact nonlinear scheme (WCNS-E−7). By incorporating a local smoothness indicator and a discontinuity sensor into the nonlinear filter, we further decrease the unnecessary dissipation and increase the resolution. With the proposed scheme, the key flow features, including shock structures, large-scale vortical structures and jet-crossflow shear/mixing layers, are well captured. The simulation shows a good agreement with the experiment data in jet penetration and diffusion.
  • Impact of pure favorable pressure gradient on a supersonic flat-plate
           turbulent boundary layer
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Qian-cheng Wang, Zhen-guo Wang, Yu-xin Zhao By employing the particle image velocimetry and Nanoparticle-based Planar Laser Scattering method, the impact of streamwise favorable pressure gradient on the mean and turbulent characteristics of a Mach 2.95 turbulent boundary layer is experimentally investigated. Through a careful arrangement of the experiment, the possible influence of streamline convex curvature is minimized to have a flat-plate streamwise favorable-pressure-gradient boundary layer. While the log law is found to be well preserved at all streamwise positions, the wake region is weakened by the pressure gradient. Different from the boundary layers formed over the convex wall and over the sudden expansion ramp, both principal strain rate and bulk dilatation in the near-wall region are found to be barely changed along the streamwise direction in the flat-plate favorable-pressure-gradient boundary layer. Because of this, the impact of the favorable pressure gradient on the near-wall turbulent fluctuation is also found to be insignificant, which differs from the supersonic convex boundary layer where the near-wall turbulence is found to be greatly suppressed.
  • The Evo-SETI unit of evolution is EE = Earth Evolution = 25.575 bit
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Claudio Maccone The discovery of a larger and larger number of exoplanets raises a question: where does a newly-discovered exoplanet stand in its capability to develop life as we know it on Earth'Our tentative answer to this question is our Evo-SETI Theory, a mathematical model aiming at casting Cladistics and the Evolution of Life on Earth over the last 3.5 billion years in terms of a few simple statistical equations based on lognormal probability distributions in the time, rather than in the amount of something else.The first new notion is that of a b-lognormal, i.e. a lognormal probability density function (pdf) starting at time b > 0 rather than at time zero. The lifetime of any living form may then be expressed as a b-lognormal starting at b, reaching puberty at the ascending inflexion point a (“adolescence (end)”), raising up to the peak time p, then starting to decline at the descending inflexion point s (“senility”) and finally going down along a straight line up to the intercept d with the time axis, that is the “death” of the individual. Based on all this, the author was able to derive several mathematical consequences like the Central Limit Theorem of Statistics re-cast in the language of Evo-SETI theory: from the lifetime of each individual to the lifetime of the “big b-lognormal” of the whole population itself to which the individual belongs (“E-Pluribus-Unum Theorem”).In addition, this author discovered the “Peak-Locus Theorem” translating Cladistics in term of Evo-SETI: each SPECIES created by Evolution over 3.5 billion years is a b-lognormal whose peak lies on the exponential in the number of alive Species. More correctly still, this exponential is not the exact curve telling us exactly how many Species were on Earth at a given time in the past: on the contrary the exponential is the mean value of a stochastic process called “Geometric Brownian Motion” (GBM) in the mathematics of finances, so that also the Mass Extinctions of the past are incorporated in Evo-SETI Theory as all-lows of the GBM.But then: what is the Shannon ENTROPY of each b-lognormal representing a Species' Answer: the Shannon ENTROPY (with a reversed sign) is the MEASURE OF HOW EVOLVED THAT SPECIES WAS, or is now, compared to other Species of the past and of the future. That means MEASURING EVOLUTION, at long last: i.e. just a number in bits, typical of Shannon's Information Theory, rather than a mountain of words!One more key point: what is the equivalent of the MOLECULAR CLOCK in Evo-SETI Theory' Answer: it is the STRAIGHT LINE behavior in time of the Shannon Entropy if the exponential is the Peak-Locus curve of all the b-lognormals representing the various Species (called “Evo-Entropy” in our papers).Concluding top remark: this author was able to GENERALIZE his Peak-Locus Theorem from the simple exponential case to the GENERAL CASE when the mean-value Peak-Locus is not just an exponential, but rather an ARBITRARY CURVE that you may chose at will: for instance it as a polynomial of the third degree in the time in the Markov-Korotayev (2007) model of evolution, leading then to a non-linear EvoEntropy. A neat mathematical tool for future biologists willing to understand Evolution by the statistically simple Evo-SETI Theory !And the Evo-SETI UNIT of evolution is 25.575 bits if life on Earth started 3.5 billion years ago. It should be given a name. We propose EE (Earth Evolution).
  • The effect of coolant injection from the tip of spike on aerodynamic
           heating of nose cone at supersonic flow
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): F. Pish, Rasoul Moradi, Amirhossein Edalatpour, M. Barzegar Gerdroodbary Aerodynamic heating is the main challenge for increasing the speed of hypervelocity vehicles. In this work, three-dimensional numerical simulations have been performed to investigate the influence of the cooling injection from the tip of the spike mounted on the nose cone. This work comprehensively focused on the effect of different types of gas injections (Air, He and CO2) on the flow feature and mechanism of cooling through three-dimensional simulations. Comprehensive parametric studies are performed to reveal the main effective parameters on the cooling performance along the nose cone. In order to perform numerical simulations, Reynolds-averaged Navier–Stokes equations with Menter's Shear Stress Transport (SST) turbulence model are applied. Our findings show that the injection of the CO2 jet from the tip of a spike is more efficient on the cooling of the nose cone due to the formation of larger circulation in the vicinity of the spike. In addition, the mass distribution of these two jets confirms that helium jets penetrate more in the upstream. Our results clearly show that the effect of the helium in low jet pressure is more significant on the cooling performance of the nose cone.
  • Characterization of heat release rate by OH* and CH* chemiluminescence
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Yao Liu, Jianguo Tan, Hao Wang, Liang Lv As single component chemiluminescence cannot accurately measure the distribution of heat release rate, this paper put forward the idea of employing OH* and CH* chemiluminescence for the measurement. However, it is difficult to characterize the relationship between chemiluminescence and heat release rate, so the method of deep learning was applied to process numerical simulation results of methane-air steady premixed flames and a deep neural network model was developed to determine the distribution of heat release rate with OH* and CH* chemiluminescence. The evaluation indexes of the model performed satisfactorily: root mean square error of the normalized heat release rate is less than 0.13, mean relative error of peak and opening distance is below 3%, and mean error of peak position less than 0.01 mm. The validation results showed that OH* and CH* chemiluminescence could properly measure the distribution of heat release rate: relative error of peak ranges from −6% to 6%; on test dataset, correlation coefficient between predictive results and simulation results is above 0.99 in terms of heat release rate peak, peak positions and opening distance.
  • Thermal-structural analysis for flexible spacecraft with single or double
           solar panels: A comparison study
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Lun Liu, Shupeng Sun, Dengqing Cao, Xiyu Liu The thermal-structural analysis for a flexible spacecraft with double solar panels is carried out in this paper through a comparison study with spacecraft having a single panel. The solar panels are composed of honeycomb panel and subjected to time-varying thermal loading. Taking into account the coupling effect among attitude motion, structural deformation and thermal loading, the rigid-flexible-thermal coupling dynamic model of the spacecraft is established by using the Hamiltonian Principle. Based on the finite difference method, an explicit algorithm is developed to solve the transient heat conduction problem of the solar panel. The coupled thermal-structural analysis reveals significant differences between the dynamic characteristics of thermally induced vibration of spacecraft with single and double solar panels. The thermally induced dynamic response significantly affects the attitude of spacecraft with a single solar panel, while it hardly affects the attitude of spacecraft with double solar panels. As the maneuver attitude or the initial incident angle of heat flux increase, the thermally induced vibration of spacecraft with a single solar panel changes from stable to unstable and thermal flutter occurs, while that of spacecraft with double solar panels always keeps stable.
  • A graphical tool to design two-ways human Mars missions
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): G. Genta, P.F. Maffione Human two-way missions to Mars may be of two types: long-stay and short-stay missions. Both require that the crew spends several months in space, with all the problems related with exposure to radiation and microgravity. Using advanced propulsion the travel time may be reduced, but this requires developing nuclear propulsion, either NTP or NEP. Short stay missions also require non-minimum energy trajectories and usually involve quite a short stay on the planet. The aim of the present paper is to develop a graphical tool allowing to choosing the most suitable travel dates for a two-ways planetary mission, in a quick and straightforward way. This tool, which can be applied to both impulsive and low thrust propulsion, combines together the well known pork-chop plot – or J-plot or, alternatively, the bacon plot – computed for the two legs of the travel and combines them together after stating the time the crew has to spend on the planet.
  • Optimization design of launch locking protective device (LLPD) based on
           carbon fiber bracket for magnetically suspended flywheel (MSFW)
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Liu Qiang, Wang Kun, Ren Yuan, Chen Xiaocen, Ma Limei, Zhao Yong Because of the launch vibration and shock, magnetically suspended flywheels (MSFWs) are equipped with an additional launch locking protective device (LLPD), and the LLPD performance has great influence on the attitude control precision of the flywheel system. In this paper, a LLPD that takes the carbon fiber bracket as the key clamped and releasable mechanism was presented. And the configuration, operating principle and functional performance requirements were introduced. The locking/unlocking force, maximum stress and contact force of the carbon fiber bracket were analyzed. The dynamic analysis of the single carbon fiber bracket equivalent to the cantilever beam model was carried out. Subsequently, the sensitivity of the constraint variables vs the structural parameters was calculated. The lower and upper parts of the carbon fiber bracket were separately optimized. The result shows that the mass of the carbon fiber bracket can reach to the minimum of 60.5 g when the number of the upper carbon fiber bracket slices is 12. Finally, the LLPD prototype was manufactured and its locking protection for the flywheel system was verified by the swept-sine vibration and the random vibration.
  • Velocity-free sliding mode control for spacecraft with input saturation
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Yong Guo, Bing Huang, Jin-hua Guo, Ai-jun Li, Chang-qing Wang This paper investigates the robust control for spacecraft without angular velocity measurement subject to the external disturbances and input saturation constraints. A novel integral sliding mode surface that is suitable to solve the problem of input saturation constraints is established based on the hyperbolic tangent function. Both controllers can deal with the actuator saturation and external disturbances simultaneously by using the sliding mode surface. The first controller is full state feedback, while the second one just contains attitude information, where the angular velocity is unnecessary due to the existence of a finite-time observer. Finally, Lyapunov theory and simulation results are provided to illustrate the effectiveness of the controllers.
  • IFC - Publication Information
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s):
  • Flow characteristics of a pintle injector element
    • Abstract: Publication date: January 2019Source: Acta Astronautica, Volume 154Author(s): Peng Cheng, Qinglian Li, Huiyuan Chen The flow characteristics of a pintle injector element were studied by theory and experiments. A spray angle model was firstly proposed based on our previous work, and then a model on the discharge coefficient of the orifice was also derived. Then, experiments were conducted by a pintle injector element which was simplified from pintle injectors with discrete radial orifices. Snapshots of the sprays were captured by using backlit photography technique. Results show that the pintle injector forms an arched cloak-like spray. The spray pattern and breakup are heavily related to the local momentum ratio and Reynolds numbers of jet and film. The spray angles obtained from the snapshots coincide with theory well. Meanwhile, a semi-empirical model of discharge coefficient of the orifice was proposed based on the experiments. It is found that the spray angle and discharge coefficient are dominated by the local momentum ratio. The spray angle and discharge coefficient increase along with local momentum ratio and tend to be stable for large local momentum ratios. Besides, discharge coefficient of the orifice is also found to be slightly affected by the ratio of jet diameter to film thickness.
  • Globally asymptotic three-axis attitude control for a two-wheeled small
    • Abstract: Publication date: Available online 2 December 2018Source: Acta AstronauticaAuthor(s): H. Sh Ousaloo This paper focuses on investigating and analyzing hybrid control strategies of onboard magnetic torque bars (MTs) and reaction wheels (RWs) for attitude stabilization on three-axis stabilized small satellites. The two reaction wheels are mounted on the spacecraft in three different configurations. The proposed attitude control algorithms in this study are based on Lyapunov design approach that almost globally and asymptotically stabilize the spacecraft attitude and this method is not restricted to zero angular momentum assumption that most existing two-wheeled control techniques exploit. Simulation and air bearing testing results presented in the paper demonstrate that the attitude control system can provide successful pointing and tracking in the presence of external disturbances and actuator constraints for a specified class of two-wheeled small satellite.
  • Optimization of aeroassisted rendezvous and interception trajectories
           between non-coplanar elliptical orbits
    • Abstract: Publication date: Available online 1 December 2018Source: Acta AstronauticaAuthor(s): Hongwei Han, Dong Qiao, Hongbo Chen Aeroassisted orbital maneuver can potentially reduce fuel consumption, compared with the traditional impulse maneuver. However, studies on aeroassisted orbital rendezvous and interception are limited to maneuvering between circular orbits. In this study, the optimal aeroassisted rendezvous and interception with elliptic initial and target orbits are investigated using the hp-adaptive pseudospectral method. Cases with minimum fuel and minimum time are considered. The initial state constraint at the deorbit position for an elliptical initial orbit is rederived first under the premise that the waiting time before the deorbit maneuver is an optimization variable. In addition, other interior constraints, including the constraints at the atmospheric entry and rendezvous/interception position, are derived. Considering the heating-rate and load factor constraints, numerical results demonstrate that the aeroassisted rendezvous and interception problems can be processed and easy to converge for optimization when elliptical initial and target orbits are considered. Moreover, comparative results with the traditional pure-impulse indicate that aeroassisted rendezvous and interception can reduce fuel consumption and adjust the rendezvous/interception time and phase with certain constraints.
  • Thermal protection characteristics for a combinational opposing jet and
           platelet transpiration cooling nose-tip
    • Abstract: Publication date: Available online 1 December 2018Source: Acta AstronauticaAuthor(s): BinXian Shen, Liang Yin, HongPeng Liu, Weiqiang Liu A combinational opposing jet and platelet transpiration cooling nose-tip is analyzed. Platelet transpiration is introduced to the opposing jet thermal protection system (TPS) in hypersonic vehicles to enhance the cooling efficiency in the reattachment region without increasing the overall cooling intensity, thereby saving the total coolant consumption. In this study, the combinational cooling nose-tip is simplified with a limited number of enlarged transpiration orifices instead of micro-pores. The two-equation shear stress transport k-w turbulence model is utilized to study the flow field and surface heat transfer in hypersonic flow, and the numerical method is validated against experimental data available in the literature. The peak heat flux reduces more than 6.6% of the combinational cooling nose-tip than that of the opposing jet TPS with the same total coolant consumption. Thus, platelet transpiration can help save the coolant consumption to reach a similar cooling efficiency. The transpiration gas can cover the surface to insulate heating. Results show that the cooling efficiency increases with increasing transpiration intensity. Finally, the peak heat flux of the four-orifice model reduces more than 3.7% than that of the two-orifice model. The cooling efficiency is improved as the number of orifices is increased. This result indicates that the cooling efficiency of the simplified model is underestimated than that of real structures with a large number of transpiration micro-pores.
  • Optical fragment tracking in hypervelocity impact experiments
    • Abstract: Publication date: Available online 1 December 2018Source: Acta AstronauticaAuthor(s): Erkai Watson, Max Gulde, Lukas Kortmann, Masumi Higashide, Frank Schaefer, Stefan Hiermaier In-orbit impacts between satellites and space debris lead to varying degrees of fragmentation, ranging anywhere from minor damage to complete breakups. In this paper, we describe an experimental measurement approach for studying fragmentation caused by hypervelocity impact in the laboratory. We investigate impacts on thin aluminum bumper plates with the goal of measuring individual fragment velocities and sizes generated by hypervelocity impact. The experimental setup, commonly used in fluid dynamics for Particle Tracking Velocimetry, consists of using a laser plane and high-speed video camera to track the motion of debris fragments. We describe the fragment tracking algorithm and demonstrate its ability to determine fragment velocity and sizes in specific hypervelocity impact experiments performed at Fraunhofer EMI. The measurement technique enables quantitative data, at an unprecedented level of detail, to be measured from hypervelocity impact fragmentation experiments in the lab, which can be applied to understanding the effects of satellite collisions and improving breakup models.
  • Formation flying along unstable Libration Point Orbits using switching
           Hamiltonian structure-preserving control
    • Abstract: Publication date: Available online 30 November 2018Source: Acta AstronauticaAuthor(s): Seungyun Jung, Youdan Kim Orbits for spacecraft formation flight along an unstable orbit are designed. The Hamiltonian structure-preserving (HSP) control is used to stabilize the motion of the spacecraft. Using a simple switching control strategy, the size of a circular orbit relative to a nominal trajectory can be systematically designed. To perform station-keeping of a spacecraft, the proposed HSP control is repeatedly applied. The nonlinear stability of the controller is also analyzed using Lagrange-Dirichlet criterion. To demonstrate the performance of the proposed switching HSP controller, a numerical simulation is performed for the formation flight of the spacecraft in Earth-Moon system's L2 halo orbit.
  • Numerical analysis of convergence property of heat flux next to the wall
    • Abstract: Publication date: Available online 30 November 2018Source: Acta AstronauticaAuthor(s): Yipu Zhao, Yumeng Hu, Haiming Huang The chemical nonequilibrium mathematical model is used to study the effect of the first grid spacing next to the wall on numerical calculation results of the surface heat flux and the stagnation heat flux. This model is composed of two-dimensional axisymmetric Navier–Stokes equations, the thermodynamic relations and the chemical reaction model. The solver is derived by implicit finite volume schemes and is validated by comparing the numerical calculation results with that in the literature. The surface heat flux and the stagnation heat flux are calculated under nine cases in which the cell Reynolds number next to the wall equals to 14.7, 7.3, 5.1, 2.9, 1.5, 1.0, 0.7, 0.5 and 0.25, respectively, and the results indicate that the surface heat flux and the stagnation heat flux gradually converge with the decrease of the cell Reynolds number next to the wall. To further verify the conclusion, the stagnation heat flux is also calculated by changing a single factor, which considers nine cases and the cell Reynolds numbers above are selected for each case, and the consistent result is obtained under nine cases.
  • `Using predictive Bayesian Monte Carlo- Markov Chain methods to provide a
           probablistic solution for the Drake equation
    • Abstract: Publication date: Available online 29 November 2018Source: Acta AstronauticaAuthor(s): Frederick Bloetscher Are we alone in the universe' It is an age-old question that continues to encourage interest and controversy among the public as well as academics. Development of explanations for life elsewhere ranges widely, but few mathematical models have been developed to measure the likelihood of concurrent, intelligent life, and those that exist are widely speculative due to the lack of information. However, with the addition of information from Kepler explorations for new solar systems within our galaxy, and calculation of the potential number of stars in the expanse of the universe, data for a useful probabilistic model to determine the likelihood of life beyond Earth may be possible with the use of predictive Bayesian statistics. Predictive Bayesian statistical methods are designed to use limited, uncertain data, to develop results. The result provides a probability curve of the likelihood of life in the universe that includes both uncertainty and potential variability within the result to provide a means to define the probability of life in the galaxy as well as life within proximity to earth. That said, the results indicate that the probability we are alone (
  • Integrated orbit determination and maintenance in Earth-Moon unstable
           dynamics environment
    • Abstract: Publication date: Available online 29 November 2018Source: Acta AstronauticaAuthor(s): Yang Zhou, Mai Bando, Shinji Hokamoto, Panlong Wu The hyperbolic instability of collinear libration point orbits dominates the distribution of orbit uncertainty, which is closely related with the unstable manifold of the local orbit. Exploiting the distribution of orbit uncertainty in an unstable orbital environment, an integrated orbit determination and maintenance approach is proposed. X-ray pulsar navigation embedded in the Kalman filtering architecture is adopted to determine the orbit of a spacecraft flying along the Earth-Moon L2 halo orbit. To keep the spacecraft in the vicinity of the nominal trajectory, the newly proposed orbit maintenance approach based on the covariance matrix is proposed to design the orbit maintenance maneuver. The numerical simulations show that the proposed approach has a good performance in orbit determination and maintenance.
  • Cortical connectivity analysis for assessing the impact of microgravity
           and the efficacy of reactive sledge jumps countermeasure to NREM 2 sleep
    • Abstract: Publication date: Available online 29 November 2018Source: Acta AstronauticaAuthor(s): Christos A. Frantzidis, Christina K. Dimitriadou, Panteleimon Chriskos, Sotiria C. Gilou, Christina S. Plomariti, Polyxeni T. Gkivogkli, Maria A. Karagianni, Lamprini P. Konstantara, Christiane Nday, Emmanouil K. Kostakis, Panagiotis D. Bamidis, Chrysoula Kourtidou-Papadeli Cognitive performance is crucial for long-term space missions, however, environments with zero gravity such as the International Space Station (ISS) or spacecrafts induce isolation and confinement. Many studies adapt the 6° head-down tilt bed rest (HDT) protocol in order to simulate the effects of weightlessness on sleep and psychophysiology in controlled environments. We investigated how weightlessness affects the sleep physiology and whether current countermeasures are efficient for sleep quality preservation by employing the head-down tilt (6°) bed rest protocol. We focused on NREM 2 sleep stage and we employed a 3-step analysis, which includes the estimation of the features that quantify the global functional organization of the cortical networks (mean cluster coefficient and characteristic path length), a local network analysis by estimating the connectivity strength of the various cortical regions with the thalamus and, quantifying changes in the functional importance (hub strength) for 22 cortical regions. The data were collected in the premises of the ENVIHAB Medical Research Facility of the Aerospace Centre in Cologne, Germany. The participants were 23 male individuals aged between 23 and 45 years old, assigned to either the control or experimental (sledge) group. Our design involved 60 days of HDT bed rest position (with the head tilted 6° downwards), with a two-week baseline and recovery period before and after the HDT duration. Our experimental design involved polysomnographic recordings (PSG) during sleep and we analysed the data collected 14 days before experiment onset (BDC-14) and during the 21st day of the HDT period (HDT21). Our results indicate that during N2 sleep in extreme environments, global networks characteristics and their feature connectivity are impaired. Degradation of N2 phase quality affects the declarative memory, especially for motor skills. The above finding highlights the importance of sleep quality regulation in astronauts in a way that enhances cognitive functions that is crucial in extreme environments.
  • A multi-channel polymerase chain reaction lab-on-a-chip and its
           application in spaceflight experiment for the study of gene mutation
    • Abstract: Publication date: Available online 29 November 2018Source: Acta AstronauticaAuthor(s): Chunhua Yang, Yulin Deng, Hao Ren, Rui Wang, Xiaoqiong Li Astronauts face serious health threats during spaceflight. The two major factors that may lead to an astronauts' physiological dysfunction are space radiation and microgravity. Heavy ion radiation, one of the important components of charged particles in orbit, can cause deoxyribonucleic acid (DNA) damage and gene mutations. Microgravity can also affect a series of cell physiology functions, including cytoskeleton remodeling, DNA modification, interactions between molecules, etc. Several ionizing radiation experiments performed in our previous study suggested the variation in the mutation across different selected immune genes. Here, we performed a further experiment (IGM-BIT-1) on board the International Space Station (ISS) to explore the molecule evolution rules of the selected DNA. To conduct the on-orbit amplification of the DNA fragments from the antibody encoding genes in the ISS, a self-developed portable and programmable PCR device was designed and produced. We developed a novel PCR chip that consists of a multi-channel optical adhesive reaction chamber and a miniature thermal cycler. The reaction chamber was cost effective and disposable. The thermal cycler was used to achieve both rapid heating and cooling. As the DNA amplification yield of IGM-BIT-1 PCR device was much similar or even higher than the commercial devices, the IGM-BIT-1 payload has been proven to be suitable for space life science research.
  • Seismic investigation of icy crust covering subsurface oceans of Europa
           and Ganymede: Preliminary assessment of hypothetical experiment using
    • Abstract: Publication date: Available online 28 November 2018Source: Acta AstronauticaAuthor(s): Aline Franqui, Spencer Seufert, Masakata Okutsu Jupiter's satellite Europa is believed to harbor a global ocean beneath its ice-covered surface. But the thickness of this ice, despite its significance to the habitability of this moon, is unknown: estimates range from as thin as hundreds of meters to as thick as tens of kilometers. In this paper, we investigate the feasibility of a hypothetical experiment in which the ice's thickness is measured via seismic analysis. The assumed scenario calls for a seismometer to be placed on the satellite's surface to detect the ice surface's seismic response induced by an artificial impact event. Our hypothetical experiment could be applied at Europa as well as at Ganymede. For both satellites two impact scenarios are considered: a low-energy-impact case, in which an orbiter probe impacts the ice at the end of the mission, and a high-energy-impact case, in which a spent upper rocket stage impacts the ice upon Jupiter arrival. We find that an impactor-induced seismic investigation is a promising add-on experiment in future missions to the icy moons of Jupiter.
  • Do astronauts benefit from autonomy' Investigating perceived
           autonomy-supportive communication by Mission Support, crew motivation and
           collaboration during HI-SEAS 1
    • Abstract: Publication date: Available online 28 November 2018Source: Acta AstronauticaAuthor(s): Sophie Goemaere, Katrijn Brenning, Wim Beyers, AngeloC.J. Vermeulen, Kim Binsted, Maarten Vansteenkiste The topic of astronaut autonomy has received increasing attention in recent spaceflight literature. However, the question of whether astronauts benefit from autonomy in space, and how autonomy can be fostered by Mission Control deserves further examination. The objective of the present research was to study how the experiences of autonomy relate to crew motivation (i.e., internalization, lack of defiance) and collaboration (i.e., crew-ground cooperation and irritation) during HI-SEAS mission 1, and how crew autonomy relates to Mission Support's perceived communication style in interacting with the crew. The study sample comprised all six volunteers, three women and three men, between 33 and 43 years of age (M = 39, SD = 4), who participated in the HI-SEAS 1 mission, which simulated a four-month-long stay on Mars. During the simulation, measures of Mission Support's perceived autonomy-supportive communication, crew members' autonomy, motivation and crew-ground interactions were taken on a weekly basis during eight weeks. Data were analyzed using multilevel analyses. Results indicated systematic week-to-week variation between constructs, such that greater experiences of autonomy during a given week related to more internalization and acceptance of instructions, less oppositional defiance, and a more fruitful collaboration with ground support that week. Additionally, weekly variations in crew autonomy were positively related to weekly variations in perceived autonomy-supportive communication by Mission Support. Implications for future studies and human spaceflight are discussed.
  • Complex numerical-experimental investigations of combustion in model
           high-speed combustor ducts
    • Abstract: Publication date: Available online 28 November 2018Source: Acta AstronauticaAuthor(s): Mikhail Ivankin, Alexey Nikolaev, Vladimir Sabelnikov, Anna Shiryaeva, Vadim Talyzin, Vladimir Vlasenko Fast technologies for numerical simulation of high-speed flows in ducts, developed in TsAGI, are described. The examples are presented of the application of experimental data, obtained at T-131 wind tunnel, for validation of the developed numerical technologies: 1) validation of 2.5D and 3D calculations of flow in the elliptic combustor with hydrogen supersonic combustion that was studied within HEXAFLY-INT international project; 2) validation of 2D and 2.5D calculations of flow in high-speed model combustor duct with step-like expansion. Preparation of new series of experiments, oriented on validation of turbulent combustion models, is described.
  • Numerical simulation of the high-speed collision of the ball and the
           spherical fluid-filled shell
    • Abstract: Publication date: Available online 27 November 2018Source: Acta AstronauticaAuthor(s): N.N. Smirnov, A.B. Kiselev, P.P. Zakharov Effectiveness of a honeycomb shield assembled of gas-filled containments is discussed. A numerical tool is developed aimed at investigating hypervelocity impact of a spherical projectile on thin-walled metallic containment filled in with gas or fluid. Variation of gas density inside the containment essentially affects perforation scenario and successive fragmentation of the projectile, while variation of gas properties – adiabatic index – does not affect fragmentation, but has a strong influence on shock wave generated by fragments in the containment.
  • Simulated microgravity led to increased brown adipose tissue activity in
    • Abstract: Publication date: Available online 27 November 2018Source: Acta AstronauticaAuthor(s): Yongjie Chen, Hongyu Zhang, Ji Xu, Chao Yang, Feng Wu, Xin Lu, Jian Chen, Kai Li, Hailong Wang, Yue Zhong, Huan Nie, Yu Li, Yinghui Li, Zhongquan Dai Long-term spaceflight has been proven to induce metabolic dysfunction. Brown adipose tissue (BAT) plays an important role in whole-body energy metabolism. We speculated that BAT function would change under microgravity. Here, we employed a tail suspension (TS) rat model to simulate the effects of microgravity and found that TS increased BAT activity including 1.79, 2.74, 2.69 folds upregulation of UCP1 mRNA at different TS time and induced a phenotypic switch from white adipose tissue (WAT) to brown fat. Furthermore, serum metabolomics revealed abnormal fatty acid metabolism pathway in TS rats. Additionally, we observed that TS led to higher levels of circulating epinephrine (1.28, 1.2, 1.26 folds), norepinephrine (1.12, 1.08, 1.26 folds), adiponectin (1.52, 1.36, 1.64 folds), and FGF21 (2.2, 1.9, 2.7 folds) in different TS rats groups respectively, which contributed to the metabolic disorder in TS rats. In summary, our results indicated that microgravity increased the activity of BAT which might contribute to metabolic dysfunction during long-term exposure to the space environment.
  • An active control strategy to suppress nonlinear vibrations of large space
    • Abstract: Publication date: Available online 27 November 2018Source: Acta AstronauticaAuthor(s): Hang Shi, Chao Wang, Lilan Liu, Zenggui Gao, Yangmin Xie Large space membranes have been widely used in many space projects to develop extremely large and lightweight SAR antennas, solar arrays and solar sails, and the nonlinear structural vibrations induced by on-orbit disturbances should be suppressed to satisfy the mission requirements. In this paper, the nonlinear dynamic behaviors of a typical large space membrane, which can not be accurately described by natural frequencies and mode shapes, are investigated by the trustworthy iterative membrane property modeling approach. Based on the discussions of the controller design challenges from such nonlinearity, this paper proposes a distributed control strategy to actively suppress the nonlinear membrane vibration, and comparatively evaluates three different actuating and sensing placements to obtain superior vibration suppression performance. Very promising results numerically demonstrate that the proposed control strategy is theoretically feasible and has great potential to be used in the design of active vibration suppression systems for large space membrane applications.
  • The motion of surface particles for the asteroid 101955 Bennu
    • Abstract: Publication date: Available online 27 November 2018Source: Acta AstronauticaAuthor(s): Yonglong Zhang, Xiangyuan Zeng, Christian Circi, Giovanni Vulpetti The asteroid 101955 Bennu is the target asteroid of the ongoing asteroid sample return mission OSIRIS-REx from NASA. In the mission, the spacecraft is scheduled to rendezvous with Bennu in August 2018. Investigating the dynamics of surface motion can offer guidance for further hopping landers or even sample return missions regarding Bennu or similarly irregular-shaped asteroids. This paper presents the free motion of sample particles on and above the surface of Bennu. The concepts and equations that govern the motion of a particle on and above the surface of an asteroid are briefly introduced. Trajectories of a number of particles' free motion are numerically calculated by considering four scenarios with different restitution coefficients. Initial positions of those particles are all randomly given on the surface of Bennu and their initial velocities are set as zero. The distribution of final locations of those sample particles is summarized and analyzed. Both the gravitational potential and its effective potential on the surface of Bennu are calculated to give a possible reason for the distributing characteristics.
  • A hybrid method based on invariant manifold and chaos control for
           earth-moon low-energy transfer
    • Abstract: Publication date: Available online 27 November 2018Source: Acta AstronauticaAuthor(s): Yue Zheng, Binfeng Pan, Shuo Tang In this paper, a new hybrid method based on invariant manifold and chaos control is presented to design Earth-Moon low-energy transfer trajectory in the planar circular restricted three-body problem. In the proposed method, one segment trajectory emanates from the period orbit around the Earth to Lyapunov orbit associated with the Lagrange points L1, which is designed by chaos control method to reduce the transfer time wandering in the chaotic region. Another segment starts from the Lyapunov orbit and reaches the Moon orbit, which is designed by the invariant manifold method. The two segments are patched with varying Jacobi constant by utilizing a Poincaré section, which is determined by the pericenter relative to the Earth. Several candidate low-energy transfer trajectories can be obtained by the proposed method, among which a suitable trajectory could be selected via the trade-off between fuel and flight time. Extensive numerical simulations are implemented to demonstrate the effectiveness of the proposed method.
  • Observability-based visual navigation using landmarks measuring angle for
           pinpoint landing
    • Abstract: Publication date: Available online 26 November 2018Source: Acta AstronauticaAuthor(s): Shengying Zhu, Dongchen Liu, Yang Liu, Pingyuan Cui Visual navigation by landmarks on the surface of the planet and small body is a potential main navigation method for pinpoint landing, which is a very challenging and necessary task in future Mars and asteroid exploration missions. In this paper, a method to reduce the complexity caused by nonlinear characteristic of six-degree-of-freedom (6-DOF) state estimation using pixel values of navigation landmark is proposed. Based on the invariance of angles in optical image, the position and attitude in pixel observation equations are decoupled by choosing angles between the line-of-sight (LoS) vectors of landmarks as observations, hence the solution can be obtained with high accuracy and low complexity. Then, the influence of landmark distribution on navigation accuracy can be analyzed, through evaluating the observable degree of landmark by LoS angle observation matrix. Based on the analysis, an optimal navigation landmarks selection method and the corresponding navigation algorithm are given. Finally, Monte Carlo simulations are used to verify the effectiveness of the proposed navigation algorithm, and evaluate the influence of related factors on navigation accuracy.
  • Effects of total pressure on mode transition in a dual-mode combustor
    • Abstract: Publication date: Available online 26 November 2018Source: Acta AstronauticaAuthor(s): Jianping Li, Guiqian Jiao, Jinyuan Luo, Wenyan Song The mode transition experiments of the dual-mode combustor were carried out under the conditions that the total pressure was 600 kPa, 700 kPa, 800 kPa and 900 kPa, the total temperature was 810 K, and the Mach number was 2.0. According to the wall pressure of the combustor measured in the experiment, the distribution of other airflow parameters of the combustor were obtained through the one-dimensional performance calculation method. The processes of mode transition of the combustor under different total pressures were studied. The study show that the dimensionless peak pressure of the combustor increased with the increase of the entrance total pressure under the same fuel equivalence ratio; the larger the total pressure, the smaller the fuel equivalence ratio required to reach the same dimensionless peak pressure. The results show that there were pure scramjet mode, dual-mode scramjet mode, dual-mode ramjet mode and the combustion state that the pressure disturbance had spread to the entrance of the isolator with the increase of the fuel equivalence ratio. The dimensionless peak pressures of the combustor when mode transition occurred were 0.25, 0.41, and 0.5, and did not change with the change of the total pressure of the incoming flow.
  • Numerical investigation on drag and heat reduction mechanism of combined
           spike and rear opposing jet configuration
    • Abstract: Publication date: Available online 26 November 2018Source: Acta AstronauticaAuthor(s): Jie Huang, Wei-Xing Yao, Xian-Yang Shan In order to reduce the hypersonic aerodynamic drag and heating, a combined spike and rear opposing jet configuration is proposed in this paper, and the CFD method is adopted to analyze the drag and heat reduction efficiency. The results show that the spike pushes the bow shock wave away from the blunt body, which translates the normal shock wave into the oblique shock wave and reduces the shock wave intensity. In addition, the low temperature jet gas is injected into the flow field, which reduces the temperature of the flow field after the shock wave. So the combined configuration reduces the aerodynamic drag and heating of the blunt body by the reconstruction of flow field, and the drag and heat reduction efficiency is better than the other configurations that already exist. The influences of the length of spike, total pressure of the opposing jet and jet gas on the drag and heat reduction efficiency are studied. The results show that increasing the length of the spike and the total pressure of the opposing jet can effectively improve the drag and heat reduction efficiency, and the decreasing rates of the aerodynamic drag and heating slow down gradually with the increase of above two parameters. In addition, the nitrogen has the best drag reduction efficiency and the carbon dioxide has the best heat reduction efficiency. The investigations in this paper verify the advantages and application in engineering of the combined configuration proposed in this paper.
  • Space collision probability computation based on on-board optical cues
    • Abstract: Publication date: Available online 23 November 2018Source: Acta AstronauticaAuthor(s): Meng Yu, Shuang Li, Shu Leng This paper presents a novel on-board space collision analysis method for space situational awareness. The framework is developed under the following assumptions: 1) A satellite can be equipped with on-board sensors for space object recognition. 2) No a–priori knowledge of the space objects is provided. A space object size and relative state estimation method is firstly proposed, wherein optical cues acquired from onboard sensors are utilized to achieve the estimation. Then, the unscented transform approach is employed to calculate the probability density function (PDF) of collision probability based on the estimate information. Monte Carlo simulations and an experimental test demonstrate that the proposed approach can achieve high-precision on-board collision probability estimation with an error less than 3%.
  • Arabidopsis flowering induced by photoperiod under 3-D clinostat
           rotational simulated microgravity
    • Abstract: Publication date: Available online 23 November 2018Source: Acta AstronauticaAuthor(s): Junyan Xie, Huiqiong Zheng The transition from vegetative growth to flowering is very important for the plant reproductive success. This process is delayed under microgravity conditions in space, but whether microgravity affects plant flowering at the molecular level is still unknown. Here, we studied the effects of altered gravity on photoperiod-controlled flowering induction by using a random positioning machine (RPM, 3-D clinostat). First, using transgenic plant pro FT:GFP in the Col-0 background and examining the expression of key genes in the photoperiod pathway, such as FT, CONSTANS (CO) and GIGANTEA (GI), we found that 3-D clinostat rotation affected the activity of the FLOWERING LOCUS T (FT) promoter under long-day conditions. Second, using a pro SUC2:FT CDS:GFP construct in the ft-10 mutant background, we observed that the transport of FT from the leaves to the shoot apical meristem was also delayed by simulated microgravity under 3-D clinostation conditions compared with the 1 g stationary control. These results indicate that photoperiod-controlled plant flowering is delayed by 3-D clinostat rotation.
  • Detecting migrant vessels in the Mediterranean Sea: Using Sentinel-2
           images to aid humanitarian actions
    • Abstract: Publication date: Available online 23 November 2018Source: Acta AstronauticaAuthor(s): Urška Kanjir The process of migration by sea is often accompanied by a great deal of risk for the migrants. The need for reliable and on time information on migrant movements is essential, especially as the available information is often limited or inconsistent. The aim of this paper is to show how freely available Sentinel-2 optical images over large areas can support humanitarian actions with timely and accurate geospatial information by providing the exact location of vessels at sea at the time of satellite acquisition. With the proposed detection method, we would like to distance ourselves from border surveillance and fight against clandestine migration as the first associations when dealing with movements of people using satellite technology. Instead, we would like to provide a better understanding of the situation for relieve authorities. Using Sentinel-2 data we have developed an automatic vessel detection and classification procedure. By first removing land from the images with the use of Modified Normalized Difference Water Index (MNDWI) we obtained a sea mask. We then applied a “vessel index”, which eliminates most of the atmospherics influences that can significantly weaken the detection results from optical images and binomial logistic regression on the sea mask to obtain segments of possible vessels. We calculated a group of geometrical and spectral attributes of detected segments and removed all the non-vessel segments based on the value of segments area. Later we implemented classification using decision tree classifier. Finally, we performed an accuracy assessment of vessel classification. The results demonstrate that the methodology gives a reliable outcome in a timely and consistent manner but can overlook smaller vessels (the length less than 20 m). Freely available satellite technology can, therefore, offer an efficient and effective solution for frequent monitoring and tracking of vessels in real time across large areas. This approach would give effective results when complementary with other methods for search and rescue of migrants to help reduce the intolerable death toll of refugees while crossing the sea.
  • Global fixed-time attitude tracking control for the rigid spacecraft with
           actuator saturation and faults
    • Abstract: Publication date: Available online 22 November 2018Source: Acta AstronauticaAuthor(s): Xiao-Ning Shi, Yong-An Zhang, Di Zhou, Zhi-Gang Zhou This paper investigates the global finite-time attitude tracking problem for the rigid spacecraft subject to inertial uncertainties, external disturbances, actuator faults, and input saturation constraints. The exponential coordinates vector in conjunction with a hysteretic-based jump condition is introduced to overcome the topological obstacles of global stability on the special orthogonal group. A novel nonsingular fixed-time-based sliding mode is designed, which not only avoids the singularity but also guarantees that the convergence time of tracking errors along the sliding surface is independent of the state value. Then, an adaptive fault-tolerant control law is constructed to enforce the system state to reach a neighborhood of the sliding surface in the sense of the fixed-time concept, which can accommodate actuator failures under limited control torque. The total convergence time is independent of the initial conditions information. A rigorous mathematical stability Proof is given. Numerical simulations are finally performed to demonstrate the effectiveness of the proposed finite-time controller.
  • Maneuver-free approach to range-only initial relative orbit determination
           for spacecraft proximity operations
    • Abstract: Publication date: Available online 22 November 2018Source: Acta AstronauticaAuthor(s): Baichun Gong, Shuang Li, Yang Yang, Junjie Shi, Wendan Li Range-only relative orbit determination for spacecraft proximity operations suffers from a well-known mirror solution problem in the context of Clohessy-Wiltshire dynamics during coasting flight. One approach proposed in previous work is to perform specific orbital maneuvers so as to avoid ambiguous relative state estimates. Alternatively, if the range-sensor offset from the spacecraft center-of-mass (COM) is considered, the relative orbit may be determined by using range-only measurements. This research developed a maneuver-free analytic solution to the range-only initial relative orbit determination (IROD) problem for close-in proximity operations by utilizing the range-sensor offsetting for enhanced observability to exclude mirror solutions. As a result, the initial relative orbit determination is reduced to a problem of solving linear equations. Based on these equations, the relative state observability is explored and observable conditions with respect to the range-sensor offset are obtained. The uncertainty of the relative orbit estimation is also derived, given as approximate analytic mean and covariance solutions. Overall, it has been strictly theoretically proven the range-only problem of non-periodic coasting close-in operations can be analytically solved. All these theoretical results are verified by a set of numerical simulation examples.
  • Research on the hydrolysis of human urine using biological activated
           carbon and its application in bioregenerative life support system
    • Abstract: Publication date: Available online 22 November 2018Source: Acta AstronauticaAuthor(s): Guorong Zhu, Guanghui Liu, Dianlei Liu, Haoxiang Chen, Chenhao Fang, Yue Yi, Ming Li, Beizhen Xie, Hong Liu The water and nitrogen recovery from human urine are the crucial issues for the water recycling in the bioregenerative life support system (BLSS). Most of the water in the urine could be recovered through physical/chemical methods, however the efficiency of recovering nitrogen remained unsatisfactory. In our previous work, immobilized urease catalysis followed by reduced pressure distillation has been utilized to purify the urine, and high recovery efficiency of both water and nitrogen has been gained. However, the source of the urease and the immobilization preparation method would limit its practical application. In this study, biological activated carbon (BAC) immobilizing urease-producing microorganisms was explored as the continuous provider of urease to hydrolyze urea existing in human urine. The batch experiment results illustrated that it is feasible to use BAC technology to hydrolyze urea in urine and the highest urea hydrolysis efficiency of 79.33% was gained in synthetic urine with the powder activated carbon dosage (PACD) of 100 g/L and the hydraulic retention time (HRT) of 5 d. Image results of scanning electron microscope and confocal laser scanning microscope presented that BAC succcessfully immobilized living bacteria, and 16S rRNA high throughput sequencing illustrated that the main urease-producing bacteria were genera of Bacillus, Sporosarcina, Pseudomonas and Paracoccus, and genera of Pseudomonas and Paracoccus possessed heterotrophic nitrification ability as well. A pilot-scale membrane biological reactor inoculated with urea-hydrolyzing BAC cultivated in batch experiment was applied to treat the crew's urine continuously inside an experimental facility for BLSS, and the urea hydrolysis efficiency could maintain at 99.84% during 203 d operation.Graphical abstractImage 1
  • Study on electrons conduction paths in Hall thruster ignition processes
           with the cathode located inside and outside the magnetic separatrix
    • Abstract: Publication date: Available online 22 November 2018Source: Acta AstronauticaAuthor(s): Wen-Bo Li, Hong Li, Yong-Jie Ding, Li-Qiu Wei, Qian Gao, Shi-Lin Yan, Tian-Hang Meng, Xi-ming Zhu, Da-Ren Yu A high speed charged coupled device (CCD) camera was used to examine the plume features over time when the cathode was located inside and outside the magnetic separatrix. Due to the different positions of the cathode, there are obvious differences in the electron impact excitation process, the characteristics of the plasma bridge, and the transition process from the end of ignition to the steady-state discharge process. The main reason for these differences may be due to the different conduction paths followed by emitted electrons into the acceleration channel. The CCD images method can be used as a technique to characterize the ignition process of Hall thruster.
  • CubeSat particle aggregation Collision Experiment (Q-PACE): Design of a 3U
           CubeSat mission to investigate planetesimal formation
    • Abstract: Publication date: Available online 22 November 2018Source: Acta AstronauticaAuthor(s): Stephanie Jarmak, Julie Brisset, Joshua Colwell, Adrienne Dove, Douglas Maukonen, Samir A. Rawashdeh, Jürgen Blum, Larry Roe Observations of the collisional evolution of particle ensembles in a microgravity environment are necessary to characterize the processes that lead to the formation of planetesimals, km-size and larger bodies, within the protoplanetary disk. The two current theories of planetesimal formation, namely growth through binary sticking collisions and gravitational instability within the protoplanetary disk, have difficulties in explaining how particles grow beyond a centimeter in size. In this paper we describe the CubeSat Particle Aggregation and Collision Experiment (Q-PACE), a Low Earth Orbit 3U CubeSat mission that will provide a high-quality, long duration microgravity environment in which we will observe collisions between particles under conditions relevant to planetesimal formation. We have designed a series of experiments involving a broad range of particle size, density, surface properties, and collision velocities to observe collisional outcomes from bouncing to sticking as well as aggregate disruption in tens of thousands of collisions.
  • Augmented unbiased minimum-variance input and state estimation for
           tracking a maneuvering satellite
    • Abstract: Publication date: Available online 20 November 2018Source: Acta AstronauticaAuthor(s): Yuzi Jiang, Hexi Baoyin, Pengbin Ma The technique of tracking a maneuvering satellite is significantly important for Space Situation Awareness (SSA). Traditional Kalman filters (KF) cannot robustly track unknown maneuvers. Motivated by the problem of tracking a non-cooperative maneuvering satellite, an augmented unbiased minimum-variance input and state estimation (AUMVISE) method is developed for estimating the state and the maneuver acceleration in this study. The maneuver acceleration estimate of the proposed method is proven to be more accurate than the original unbiased minimum-variance input and state estimation (UMVISE) method. Approaches based on the measurement residuals and the acceleration estimates are developed for maneuver start and end detection. The filter is switched between the AUMVISE method and the classical extended Kalman filter (EKF) to obtain an accurate tracking result during both the maneuver period and the non-maneuver period. Simulation results show that the proposed method has a suitable maneuver detection delay and outperforms the UMVISE method in estimating the state and maneuver acceleration.
  • On-board spacecraft relative pose estimation with high-order extended
           Kalman filter
    • Abstract: Publication date: Available online 20 November 2018Source: Acta AstronauticaAuthor(s): Francesco Cavenago, Pierluigi Di Lizia, Mauro Massari, Alexander Wittig This paper analyzes the real-time relative pose estimation and attitude prediction of a tumbling target spacecraft through a high-order numerical extended Kalman filter based on differential algebra. Indeed, in the differential algebra framework, the Taylor expansion of the phase flow is automatically available once the spacecraft dynamics is integrated and thus the need to write and integrate high-order variational equations is completely avoided making the presented solution easier to implement. To validate the technique, the ESA's e.deorbit mission, involving the Envisat satellite, is used as reference test case. The developed algorithms are implemented on a BeagleBone Black platform, as representative of the limited computational capability available on onboard processors. The performance is assessed by varying the measurement acquisition frequency and processor clock frequency, and considering various levels of uncertainties. A comparison among the different orders of the filter is carried out.
  • Cost analysis of solar thermal propulsion systems for microsatellite
    • Abstract: Publication date: Available online 20 November 2018Source: Acta AstronauticaAuthor(s): Fiona Leverone, Angelo Cervone, Eberhard Gill In recent years, satellite design has extended towards miniaturisation to reduce associated cost with launching and conducting space missions. Small satellites provide low-cost platforms for space missions. However, this lower cost comes at the expense of the removal of key sub-systems, such as the propulsion system, due to the small available onboard volume and mass restrictions. For this reason, small, lightweight, high-performing and affordable propulsion systems are necessary. However, there is limited research available on the comparison of propulsion technologies with regards to cost. Motivated by the above challenges the objective of this paper is to provide a comparison of propulsion technologies that are compatible with small satellites with respect to cost and application. The different propulsion systems are investigated for three mission scenarios, a small on-orbit manoeuvre, a station-keeping, and a lunar orbit transfer mission. Each system is evaluated in terms of a total figure of merit which incorporates nine variables such as propellant mass, safety, and hardware price, that affect the total cost of a propulsion system. This figure of merit is used to quantitatively compare the propulsion systems to identify cost-effective solutions as a function of various mission scenarios. Solar thermal propulsion has been proposed for small satellite applications, but information regarding the concepts are not available in a single report. Therefore, another objective of this paper is to provide the reader with a review of the current status of solar thermal propulsion. An important finding of this research is the classification of propulsion systems in terms of thrust, specific impulse, cost, and application.
  • Configuration optimization of multi-optical sensors with complex pointing
    • Abstract: Publication date: Available online 19 November 2018Source: Acta AstronauticaAuthor(s): Yuchen She, Shuang Li This paper investigates the pointing direction optimization problem of multi-optical sensors with complex pointing constraints. In the spacecraft design area, this problem is characterized as the optical-sensor configuration optimization. The complex pointing requirements and avoidance constraints of different types of optical sensors are taken into account, and a new optimization method is presented. The proposed combinatorial optimization algorithm is divided into three steps. First, an initial guess solution is generated by coordinate projection. The relative directions between all constraint objects and the spacecraft are projected into the spacecraft body-fixed coordinate system. Second, the density-of-presence analysis is conducted for relative directions by introducing the image processing concept into the optimization process. The morphological dilation approach is adopted with a new filter, and the high and low density regions are defined to reduce the dimension of the candidate solution group. Finally, the mathematical model of the optimization problem is developed and solved by the Genetic Algorithm (GA). The computer simulations show that the new method can properly handle the configuration optimization problem with complex requirements and constraints in a relatively short calculation time.
  • Towards increasing nanosatellite subsystem robustness
    • Abstract: Publication date: Available online 17 November 2018Source: Acta AstronauticaAuthor(s): Carlos Leandro Gomes Batista, Anderson Coelho Weller, Eliane Martins, Fátima Mattiello-Francisco Short development life cycle and low cost of cubesat-based mission have motivated the growing number of nanosatellite launched in the last decade around the world. Fast and cheaper space project do not guarantee success in orbit. The lack of good practices on design, assembly and tests has been pointed out as one of the major causes to nanosatellite mission failures. Efforts on the use of verification and validation techniques are required. Because the increased use of nanosatellites missions for technology qualification of payloads on orbit, faulty behavior of those payloads can be expected. However, such malfunction shall not represent a risk to the whole mission. Robustness is an important property of reactive critical system not addressed properly in the cubesat standardization. Although significant mitigation of the interface failures has been observed at hardware level in the integration phase of the payloads with the nanosatellite platform, behavior aspects of the communicating subsystems on the use of these interfaces shall be verified. The test systematization of CubeSat-based nanosatellites supported by proper tools is necessary to reduce the mission development cycle in terms of the time consumed by the verification & validation activities. In this paper we present a failure emulator mechanism framework, named FEM, for robustness testing of interoperable software-intensive subsystems onboard nanosatellite. FEM acts in the communication channel being part of the integration test workbench in two phases of nanosatellite design: (i) robustness requirement specification using model in the loop (MIL) and (ii) robustness validation using hardware in the loop (HIL). The architectural aspects of the proposed FEM framework support its instantiation to any communication channel of the CubeSat standard. As an example, FEM prototype was instantiated to I2C communication channel to support NanosatC-BR2 testing. NanosatC-BR2 is a Cubesat based scientific mission, under development and integration at Brazilian Institute for Space Research (INPE), which uses I2C communication channel for its payloads interactions with the On-Board Data Handling computer subsystem (OBC). FEM prototype was used to support OBC integration testing with each payload subsystem at MIL scenario aiming at anticipating the robustness requirement verification on the development lifecycle. Moreover, the FEM prototype was also validated at HIL scenario using Test Cases automatically generated. Results of these two scenarios executions are reported demonstrating in a case study the effectiveness of FEM framework in detecting the lack or noncompliance of robustness requirements by the interoperated subsystems under testing.
  • Experimental study on the thermodynamic characteristics of the high
           temperature hydrocarbon fuel in the cooling channel of the hypersonic
    • Abstract: Publication date: Available online 17 November 2018Source: Acta AstronauticaAuthor(s): Haowei Li, Jiang Qin, Yuguang Jiang, Weixing Zhou, Wen Bao, Hongyan Huang Cooling is one of the key technologies for the scramjet considering the enormous thermal load and the demand of reusable long-range mission. In the regenerative cooling process, hydrocarbon fuel flows through the cooling channel, gets heated and experiences severe thermal properties changes. The compressibility of fuel becomes non-negligible and possible dynamic process emerges, which affects both the characteristics of fuel cooling and fuel mass flow control. As a result, the dynamic characteristics of the high temperature hydrocarbon fuel within the cooling channel must be carefully studied. In this work, experiments are conducted at different simulated engine working conditions. The settling time of pipe pressure drop is used to characterize the dynamic process of the outlet fuel mass flow, because the outlet temperature of the fuel is too high to measure the fuel mass flow directly. In conditions of the variation of inlet fuel mass flow and backpressure disturbance, overshoot of the pressure drop is observed and the magnitude of which varies with the working conditions. The settling time of outlet fuel temperature and wall temperature channel firstly increases, then decreases with the increase of the outlet fuel temperature. The settling time of both outlet fuel temperature and wall temperature increases with the increase of the heating heat flux. The experimental results in this work are expected to provide supports to the engine control system design.
  • SiO 2 +crystal+structure+on+the+stability+of+polymer+composites+exposed+to+vacuum+ultraviolet+radiation&rft.title=Acta+Astronautica&rft.issn=0094-5765&">Effect of SiO 2 crystal structure on the stability of polymer composites
           exposed to vacuum ultraviolet radiation
    • Abstract: Publication date: Available online 16 November 2018Source: Acta AstronauticaAuthor(s): V.I. Pavlenko, N.I. Cherkashina Vacuum ultraviolet (VUV) radiation produced by the Sun in the space environment can cause degradation to thermoregulating coatings producing changes in optical, mechanical, and chemical properties. These effects are particularly important for polymers. The purpose of this study was to study the effect of VUV radiation on polymeric composites based on polyalkaneimide. Amorphous and crystalline SiO2 were used as the filler. A comparative characterization of physico-mechanical properties of composites is presented depending on the polymorphic structure of the filler being introduced. According to the microhardness of the surface of composites with amorphous and crystalline SiO2, an optimum filler content of 60–65 wt% is established. The exposure of VUV radiation to polymeric composites with SiO2 leads to a mass loss and a change in their near-surface layers, which leads to a deterioration in the optical properties. At an elevated temperature (125oC), the mass loss of all composites with amorphous crystalline SiO2 does not exceed 1.33%, and with crystalline SiO2, the maximum mass loss is 0.52%. The mass loss of composites with crystalline SiO2 of all compositions did not exceed the allowable value for spacecraft products of 1%. For high-filled (50 wt% filler or more) composites with amorphous SiO2, mass loss after VUV treatment is more than 1%, which does not allow them to be used in outer space. The change in the main optical characteristics of thermoregulating coatings after VUV treatment was studied. The smoothing of the surface of composites after VUV treatment is established.
  • Separation of proteins and DNA by microstructure-changed microfuidic free
           flow electrophoresis chips
    • Abstract: Publication date: Available online 14 November 2018Source: Acta AstronauticaAuthor(s): Wei-Wei Sun, Rong-Ji Dai, Yong-Rui Li, Guo-Xin Dai, Xiu-Jie Liu, Bo Li, Xue-fei Lv, Yu-Lin Deng, Ai-Qing Luo Microfuidic free-flow electrophoresis (μFFE) is a micro-separation analysis technology with continuity, no solid support medium and mild separation conditions. However, the bubble problem has limited its application for a long time. Here, we proposed a μFFE device that isolated the bubbles from the separation chamber with partitioning bars of ∼40 μm wide in ∼5 μm intervals effectively. Compared to the conventional chip form, the change of micro-structure assured the stability of the chips even after working for 150 min. Lysozyme, BSA and pepsin were separated from the μFFE with electric field intensity of 81.82 V/cm, sample flow rate of 3 μL/min and pH 5. The optimized chips successfully separated lysozyme BSA and calf thymus DNA, which demonstrated an excellent baseline-separation of protein and nucleic acid mixtures under milder separation condition. These results showed that optimized μFFE chips based integrated device can be potentially applied to prepare and analyze complex biological samples in the future for deep space exploration.
  • Mixing augmentation mechanism induced by the dual injection concept in
           shcramjet engines
    • Abstract: Publication date: Available online 14 November 2018Source: Acta AstronauticaAuthor(s): Zhao-bo Du, Wei Huang, Li Yan, Zheng Chen, R. Moradi As one of the key techniques, achieving adequate fuel/air mixing before combustion is a task that must be addressed seriously for shock-induced combustion ramjet (shcramjet) engines. In this paper, dual injectors which have been combined by a front hydrogen jet and a rear air jet with different aspect ratios are placed on the second ramp of a shcramjet inlet to promote mixing process between fuel and hypersonic crossflow. At the same time, dual injectors with pure hydrogen injection and the single hydrogen injection with the same injection area are studied as well for comparison. Flow field properties are investigated numerically based on grid independency analysis and code validation. Obtained results predicted by the three-dimensional Reynolds-average Navier-Stokes (RANS) equations coupled with the two equation SST κ-ω turbulence model show that the grid scale makes only a slight difference to wall pressure profiles for all cases studied in this article. The dual transverse injection system with a front hydrogen jet and a rear air jet is beneficial for improvement of the mixing efficiency between hydrogen and air. Mixing efficiency in the near field increases with increase of aspect ratio of the air porthole. The air porthole in dual transverse injections would accelerate mixing process when compared with the single injection strategy irrespective of aspect ratio of the air porthole.
  • Investigation on rat intestinal homeostasis alterations induced by 7-day
           simulated microgravity effect based on a proteomic approach
    • Abstract: Publication date: Available online 14 November 2018Source: Acta AstronauticaAuthor(s): Shibo Wang, Yushi Zhang, Jingjing Guo, Liting Kang, Yulin Deng, Yujuan Li The present study aims at investigating alterations of rat intestinal homeostasis induced by 7-day simulated microgravity (SMG) effect through a proteomic approach. Tail-suspension model was used to simulate microgravity effect and a label-free quantitative proteomic strategy was employed to determine proteins in rat intestine. As a result, 717 differently expressed proteins were identified and 29 proteins were down-regulated while 688 proteins were up-regulated. 283 out of 717 proteins were categorized into 7 clusters with DAVID (version 6.8). The three highest enrichment scores were annotation cluster I about cell-cell adhesion (46 proteins with enrichment score of 16.67), annotation cluster II about carbohydrate metabolism (32 proteins with enrichment score of 6.17) and annotation cluster III about activity of pepdtidase (17 proteins with enrichment score of 4.74). Results of rat intestine proteomics indicate that SMG might disrupt intestinal homeostasis, which possibly resulted in opening of intestinal epithelial barrier (IEB), potentially leading to risk of systemic inflammatory response (SIR) and inflammatory bowel diseases (IBD). The present results also provide some useful information for mechanism and countermeasures of intestine injuries induced by microgravity.
  • Characterization of flow mixing and structural topology in supersonic
           planar mixing layer
    • Abstract: Publication date: Available online 14 November 2018Source: Acta AstronauticaAuthor(s): Dongdong Zhang, Jianguo Tan, Liang Lv, Fei Li The investigations on mixing process and structural topology properties of supersonic planar mixing layer with different inflow conditions are conducted by employing direct numerical simulation. First, the present high-order accuracy numerical methods are validated by comparing the simulation results with the data gained from previous well characterized experimental and numerical cases. Then the high-resolved three-dimensional numerical visualizations of supersonic mixing layer are presented by utilizing Q-criterion. The visualization results show the full development and evolution process of mixing layer, including the shear action, the transition process populated sequentially by Λ-vortices, hairpin vortices and braid structures and the establishment of self-similar turbulence. The effects of density ratio, velocity ratio and convective Mach number between the two parallel streams on mixing layer growth rate are evaluated by examining the indexes including velocity thickness and momentum thickness represented the mixing process. The results indicate that for the only variation of density ratio, the velocity thickness growth rates do not significantly vary, while the momentum thickness becomes larger when the upper and lower streams possess the same density. With the increase of only velocity ratio, the mixing layer becomes more stable and the velocity and momentum thickness are both drastically depressed in the whole flow field. As only convective Mach number increases, the mixing layer growth is inhibited in the near field through the transition delay of the flow, while in the far field, the growth rates are nearly the same for different convective Mach numbers. The spatial correlation analysis of structural topology indicates that the effects of each of the three main flow parameters on vortex topology lead to different mean structure sizes and shapes. The present research is useful for evaluating the effects of different flow parameters on mixing properties, which is important for the future scramjet combustor design and evaluation in engineering.
  • Numerical and experimental study of the thermochemical erosion of a
           graphite nozzle in a hybrid rocket motor with a star grain
    • Abstract: Publication date: Available online 13 November 2018Source: Acta AstronauticaAuthor(s): Tian Hui, Yu Ruipeng, Li Chengen, Zhao Sheng, Zhu Hao Hybrid rocket motors is a promising propulsion system because of its intrinsic advantages over a conventional solid rocket motor and liquid rocket engine. However, serious nozzle erosion is a key problem that prevents hybrid rocket motors from being widely used, especially for propulsion systems with long operating times. In this paper, the erosion of a graphite-based nozzle coupled with a combustion flow field is studied in a hybrid rocket motor with a star grain. As the oxidizer and fuel, 90% hydrogen peroxide and hydroxide-terminated polybutadiene are adopted, respectively. The nozzle erosion was simulated coupled with the flow field in a typical hybrid rocket motor through three-dimensional numerical simulations. The simulations are based on a pure-gas steady numerical model considering turbulence, fuel pyrolysis, oxidizer/fuel reactions, thermal conduction and solid-gas boundary interactions on the fuel and nozzle surfaces. The results indicate that the nozzle erosion is greatly influenced by the inner flow field. The flame near the grain trough is thicker than that near the grain peak. Therefore, the maximum erosion rate (0.042 mm/s) occurs near the nozzle throat corresponding to the grain trough. The OH and H2O contribute 49.8% and 45.5% to the erosion rate, respectively, in this area. Furthermore, 56.6% and 31.9% contributions are made by OH and H2O, respectively, in the area corresponding to the grain peak. The O, CO2 and O2 make much lower contributions to the total erosion. In addition, a firing test is carried out to characterize the graphite nozzle erosion on a full-scale hybrid rocket motor with star grain. The nozzle inner profiles before and after test show that the erosion behavior of the graphite material is strictly related to the fuel shape.
  • Experimental study on combustion characteristics of powder magnesium and
           carbon dioxide in rocket engine
    • Abstract: Publication date: Available online 13 November 2018Source: Acta AstronauticaAuthor(s): Yue Li, Chunbo Hu, Xiaofei Zhu, Jiaming Hu, Xu Hu, Chao Li, Yupeng Cai Mechanisms of powder magnesium and carbon dioxide combustion are required for the concept of Mars propulsion based on the perspective of in-situ resource utilization. Most current characterizations are based on laboratory experiments conducted in stationary or simple flow configuration. However, the chamber condition in most applications of engine is very complicated with high pressure and multi-phase flow environment, and the combustion process in engine-scale has not been established. The burning efficiency, combustion stability and excessive deposition are the mainly primary issues that limit the combustion performance in rocket environment, the experimental study aims at combustion characteristics and the affection mechanism of powder magnesium and carbon dioxide in rocket engine. A new configuration of powder rocket system is established. Meanwhile, a multiple-inlet configuration of CO2 injection is designated to control the CO2 injection positions and parameters, such as global and local oxidant-fuel ratio. Ignition process is studied and an empirical model for ignition judgment is established according to the result of ignition tests. Mechanism for combustion deposition is studied by the analysis of morphology, composition and distribution, characteristics of combustion efficiency are estimated based on test pressure and thermodynamic calculation, and oscillation mechanism of combustion pressure is obtained by frequency domain analysis. The higher concentration of magnesium particle, the cool CO2 injection and the increasing of CO concentration is supposed to be the main reasons for the deposition in different areas along the axis of the combustion chamber. The allocation of gas injection is an important factor that affects the combustion sufficiency associated to the heterogeneous reaction. Raising the O/F ratio in chamber head is an effective way to improve combustion efficiency for rocket engine, and the efficiency is improved firstly and then is decreased with increasing flow rate of fluidization gas. The low frequency oscillation is supposed to be related to flame instability induced by the gas injection in chamber head. The influence caused by primary and secondary gas injection are further analyzed in the frequency domain, the related characteristic bands are classified and the fluctuation tendency is obtained.Graphical abstractImage 1
  • Design-build-launch: A hybrid project-based laboratory course for
           aerospace engineering education
    • Abstract: Publication date: Available online 13 November 2018Source: Acta AstronauticaAuthor(s): R.M. Spearrin, F.A. Bendana A project-based course involving the design, analysis, manufacturing, testing, and launching of mid-power solid-propellant rockets over a ten-week period has been developed and taught as an approach to enhance the education and preparation of aerospace engineers at the university level. The course consists of a sequence of structured laboratory assignments that expose students to common software tools, aerospace materials, manufacturing techniques, and testing methods that directly inform and run parallel to the project. Teams of four to five students complete the project (and portions of the labs) collaboratively within an engineering competition framework. Individual students within each team are assigned specific engineering roles (e.g. design engineer, manufacturing engineer) to create an interdependence that reflects a typical integrated product team in industry and exposes students to realistic social dynamics. Student teams conduct design reviews as progressive milestones for assessment, in addition to laboratory assignments. At a per-student cost on the same order as a textbook, the project-based course combines theoretical content from several subjects with a high-order learning approach (create, evaluate, analyze) to advance the engineering skills of university students.
  • Aluminum agglomeration of AP/HTPB composite propellant
    • Abstract: Publication date: Available online 12 November 2018Source: Acta AstronauticaAuthor(s): Jifei Yuan, Jianzhong Liu, Yunan Zhou, Jianru Wang, Tuanwei Xv Aluminum (Al) powder agglomeration is one of the main reasons for the degradation in the performance of aluminized solid propellant rockets and so, understanding the combustion behavior of aluminum in solid propellants is of great importance. In this work, a laser ignition test bench was used to study the behavior of Al on the burning surface of an aluminum/ammonium perchlorate/hydroxyl-terminated polybutadiene composite propellant, under atmospheric pressure. Based on the images captured by a high-speed camera, the agglomeration process and behavior of the agglomerates were analyzed in detail. The size distribution and speed of motion of the agglomerates away from the burning surface were also considered. Results show that the formation of an agglomerate on the burning surface from multiple aluminum particles include three stages: accumulation, aggregation, and agglomeration. Local ignition promotes the collapse of the aggregate into a spherical agglomerate. Before detachment, the agglomerates often roll around on the burning surface and pick up more aluminum, promoting self-growth. The interesting phenomenon of an agglomerate droplet rupturing and ejecting liquid alumina on the burning surface was clearly captured for the first time. This is believed to indicate the heterogeneous composition characteristics of the agglomerate. The transformation of the polar oxide cap on one part of the agglomerate surface into an alumina shell that fully covers the droplet surface was also captured for the first time. The agglomerates have different shapes, diameters, and velocities when they leave the burning surface. The formation of non-spherical agglomerates consisting of more than one aluminum droplet is ascribed to the propellant microstructure. The 400 agglomerates that were counted had diameters that ranged from 51 μm to 815 μm and the majority of them (nearly 98%) were below 400 μm. The velocities of motion of 176 agglomerates exhibited great dispersion, with the maximum and minimum velocity being 196 cm/s and 13 cm/s, respectively. In general, the moving velocities of the agglomerates decreased with increasing diameter.
  • Multiple-horizon multiple-model predictive control of electromagnetic
           tethered satellite system
    • Abstract: Publication date: Available online 11 November 2018Source: Acta AstronauticaAuthor(s): MohammadAmin AlandiHallaj, Nima Assadian This study aims to investigate the control of the electromagnetic tethered satellite system using a Model Predictive Control (MPC) scheme. The electromagnetic tethered satellite system is actuated by electromagnetic coils to generate controlling forces. The dynamical model of the system is described in high and low levels of accuracy, which are used to design the control framework. Multiple-Horizon Multiple-Model Predictive Control approach is employed to drive the formation to the desired state. Not only does the presented control law satisfy input and output constraints but also has appropriate characteristics in the sense of optimality. The main benefit of using Multiple-Horizon Multiple-Model Predictive Control is having lower computational burden than the classical MPC. The numerical simulation results are presented and compared with sliding mode control to demonstrate the effectiveness of the proposed control method and its advantage over both classical MPC and sliding mode control methods. The obtained results show dramatic reductions in computational time and consumed energy compared to the classical MPC and sliding model control methods, respectively.
  • Effects of fueling distance on combustion stabilization modes in a
           cavity-based scramjet combustor
    • Abstract: Publication date: Available online 10 November 2018Source: Acta AstronauticaAuthor(s): Yanan Wang, Zhenguo Wang, Mingbo Sun, Hongbo Wang, Zun Cai The effects of distance from the injector upstream to the cavity leading edge on combustion stabilization modes were investigated experimentally and numerically. High-speed flame luminosity and schlieren images were utilized to reveal the combustion characteristics. Under a Mach 2.52 supersonic inflow condition with a stagnation temperature of 1629 K, hydrogen was injected with injection distances of 30 mm, 100 mm and 160  mm at global equivalence ratios from 0.20 to 0.32. The flame in cavity stabilized mode is observed at a relatively low equivalence ratio. Increasing the global equivalence ratio, the combustion stabilization mode transfers to the jet-wake stabilized mode with injection distances of 100 mm and 160 mm. It is surprising that the mode transition is the easiest for the medium injection distance of 100 mm. Large eddy simulations were then performed to explain the easiest mode-transition. Mixing characteristics, jet-cavity interactions and the jet-wake features upstream of the cavity for three injection distances were analyzed. With the injection distance of 100 mm, the reflected shock wave impacts on the cavity shear layer, and the interactions of the shock wave structures and the cavity induce the beginning phase of the jet-wake stabilized flame and help the flame propagate upstream around the cavity. Relatively larger amount of the fuel, lower streamwise velocity and lower static pressure was also found in the jet wake upstream of the cavity, which further supports the flame to propagate upstream and stabilize in the jet wake.
  • Proximity scenario design for geostationary rendezvous with collocated
           satellite avoidance
    • Abstract: Publication date: Available online 7 November 2018Source: Acta AstronauticaAuthor(s): Ya-Zhong Luo, Zhen-Jiang Sun, Jin Zhang Proximity operation is one of the prerequisites for in-orbit service or debris removal. Especially for objects in geostationary orbit (GEO), there are certain challenges in rendezvous and proximity operations, such as perturbed relative dynamics and constraints from collocated satellites. In this study, a novel optimization model is built to design the GEO proximity scenario, including the keeping points and durations of each phase. First, as a prerequisite of proximity scenario design, relative dynamics considering solar radiation pressure effects and the corresponding two-point boundary value problem are analytically solved. Second, the concept of passive safety performance is introduced. The safety constraints from both the target satellite and the collocated satellites are considered. The optimization model is then built, and an improved differential evolution optimization algorithm is employed to seek the solution with minimal velocity increment. The numerical examples indicate that a GEO proximity scenario can be stably and effectively designed by the presented method. Moreover, in the scenarios without a collocated satellite, with a static collocated satellite, and with dynamic collocated satellites, the optimized proximity scenarios remain passively safe. If any impulse in the scenario ceases, the resulting free drift trajectory would diverge from the target and the collocated satellites, maintaining the safety index and satisfying the given threshold.
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