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Acta Astronautica
Journal Prestige (SJR): 0.758
Citation Impact (citeScore): 2
Number of Followers: 446  
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0094-5765
Published by Elsevier Homepage  [3161 journals]
  • Real Data-based Thermal Environment Definition for the Ascent Phase of
           Polar-Summer Long Duration Balloon Missions from Esrange (Sweden)
    • Abstract: Publication date: Available online 20 January 2020Source: Acta AstronauticaAuthor(s): David González-Bárcena, Alejandro Fernández-Soler, Isabel Pérez-Grande, Ángel Sanz-AndrésAbstractLong Duration Balloon missions are key platforms for scientific research and space technology development. Thermal analyses of this kind of systems are crucial for the success of the mission. Even though the science is usually performed at float altitude, the ascent phase, usually non-operational, is where the extreme cold conditions occur, due to the convective effects caused by relative wind speed together with the low temperatures found in the tropopause, making this scenario a dimensioning case. In this paper, a thorough study of the thermal environmental conditions during the ascent is carried out, in particular winds, temperature, and radiative thermal loads have been obtained as a function of the altitude. The study is based on real data obtained from different sources, including atmospheric soundings, radar and satellite, and a meticulous statistical treatment. The study is focussed on one of the main stratospheric balloon launch sites in Europe, Esrange (Sweden), a centre of the Swedish Space Corporation, and the analyses are performed for the summer period. However, the methodology can be extended to any other location and epoch. As an example, the convective effect of the horizontal winds on a plate has been studied, and the heat transfer during the ascent phase has been quantified. A subcooling of around 7 ºC was found in this case, which make worth the dedicated analysis.
  • Dynamics and potential applications of a lunar space tethered system
    • Abstract: Publication date: Available online 17 January 2020Source: Acta AstronauticaAuthor(s): Liu JiaFu, Liu Bin, Wu ZhiGang, Jiang JianPing, Tian LiFengAbstractNonlinear dynamics and potential applications of a lunar space tether system, with one end connected to the Moon’s surface and the other with a large floating counterweight, are investigated in the paper. Dynamical equations of the system with a massless viscoelastic tether considering the planar libration and elastic elongation within the elliptical Earth-Moon restricted three-body (EEMRTB) system are established. The equilibria and stability of the dynamical system are explored for the system at L1 side without considering small perturbations caused by eccentricity to facilitate the rough selection of the length and elastic coefficient of the tether. The potential applications including harvesting the Rayleigh Damping Dissipation power and accessible regions within the Earth-Moon system will be studied based on the dynamic analysis of the full nonlinear dynamics. The allowed parameter regions (the tether system will neither collide the Moon/Earth nor rotate about the Moon) are identified exactly using numerical analysis, moreover, the performance of the potential applications and other related references for building a tether system are explored at L1 and L2 numerically. It is suggested that one should design a space tether based energy harvester at L1 side, release an unpowered spacecraft with high mechanical energy at L2 side respectively. Some conclusions on selecting the parameters and evaluating the performance of the space tether based platform are obtained based on numerical calculations. The research will be useful for the Moon infrastructure constructions.
  • Design and testing of a microelectromechanical-system-based high heat flux
           vaporizing liquid microthruster
    • Abstract: Publication date: Available online 16 January 2020Source: Acta AstronauticaAuthor(s): Pok-Wang Kwan, Xun Huang, Xin ZhangAbstractThis paper presents the design of a low power (8W) water-fed vaporizing liquid microthruster that operates in the Leidenfrost boiling regime. The direct thrust measurements show the proposed design is able to produce one of the best specific impulse amongst all similar microthrusters reported in the literature. One of the important features that enables the superior performance is the high heat flux miniature molybdenum heating elements fabricated inside the vaporization chamber in a single silicon device package of dimensions 35mm×35mm×1.05mm. The molybdenum heating elements are capable of producing a heat flux output of 370kW/m2 resulting in a sustained operational pressure of 2bar and temperature of 446K. The specific design details, such as choice of configurations and sizing, are given in this paper. In particular, the choice of material and the fabrication process carried out at the in-house nanosystem fabrication facility are described. The experimental setup and uncertainty analysis of the mN-range hanging pendulum direct thrust measurement stand are presented. Then, the evaporation of liquid water propellant is investigated in detail. The occurrence of Leidenfrost effect inside the vaporization chamber is captured with a high-speed camera at a frame rate of 5000Hz. It can be seen that the rapid vaporization of propellant in the Leidenfrost boiling regime results in a high specific impulse amongst other microelectromechanical-system-scale vaporizing liquid microthrusters. The direct thrust measurements show the current design is capable of producing a specific impulse ranging between 25.9–51.1s at a continuous thrust level of 1.00–2.00mN; considering contemporary energy storage technologies, the estimated thrust per device dry mass and specific impulse per device dry mass levels are 4.0-8.0 mN/kg and 103.6-204.0 s/kg respectively.
  • Damping device to reduce the risk of injection-coupled combustion
           instabilities in liquid propellant rocket engines
    • Abstract: Publication date: Available online 15 January 2020Source: Acta AstronauticaAuthor(s): Wolfgang Armbruster, Justin S. Hardi, Yannik Miene, Dmitry Suslov, Michael OschwaldAbstractA new countermeasure against injection-coupled combustion instabilities in liquid propellant rocket engines is presented. Whereas the problem is usually addressed by adding damping elements such as baffles or resonators to the combustion chamber, this approach directly damps the acoustic eigenmodes of the injector instead. The principle of the damping method is described in this article, as well as the implementation of such a device in a sub-scale rocket thrust chamber operated with liquid oxygen and hydrogen at conditions representative of upper stage engines. Test results are presented which show that flame and pressure oscillations were successfully reduced by the modification. The absorbers had no measurable influence on thrust chamber performance, and so the solution lends itself to retrofitting in existing engines, as well as integration during the design phase.
  • Real-Time Optimal Control for Irregular Asteroid Landings Using Deep
           Neural Networks
    • Abstract: Publication date: Available online 15 January 2020Source: Acta AstronauticaAuthor(s): Lin Cheng, Zhenbo Wang, Yu Song, Fanghua JiangAbstractTo improve the autonomy and intelligence of asteroid landing control, a real-time optimal control approach is proposed using deep neural networks (DNN) to achieve precise and robust soft landings on asteroids with irregular gravitational fields. First, to reduce the time consumption of gravity calculation, DNNs are used to approximate the irregular gravitational fields of asteroids based on the samples calculated by a polyhedral method. Second, an approximate indirect method is presented to solve the time-optimal landing problems with high computational efficiency by taking advantage of the trained DNN-based gravity model and a homotopic technique. Then, five DNNs are developed to learn the functional relationship between the state and optimal actions obtained by the approximate indirect method, The resulting DNN-based landing controller can generate the optimal control instructions according to the flight state and achieve the real-time optimal control for asteroid landings. Finally, simulation results of the time-optimal landings for Eros are given to substantiate the effectiveness of these techniques and illustrate the real-time performance, control optimality, and robustness of the developed DNN-based optimal landing controller.
  • A Multiple-Shooting Differential Dynamic Programming Algorithm. Part 1:
    • Abstract: Publication date: Available online 14 January 2020Source: Acta AstronauticaAuthor(s): Etienne Pellegrini, Ryan P. RussellAbstractMultiple-shooting benefits a wide variety of optimal control algorithms by alleviating large sensitivities present in highly nonlinear problems, improving robustness to initial guesses, and increasing the potential for parallel implementation. In this paper series, motivated by the challenges of optimizing highly sensitive spacecraft trajectories, the multiple-shooting approach is embedded for the first time in the formulation of a Differential Dynamic Programming algorithm. Contrary to traditional nonlinear programming methods which necessitate minimal modification of the formulation in order to incorporate multiple-shooting principles, DDP requires novel non-trivial derivations, in order to include the initial conditions of the multiple-shooting subintervals and track their sensitivities. The initial conditions are updated in a necessary additional algorithmic step. A null-space trust-region method is used for the solution of the quadratic subproblems, and equality and inequality path and terminal constraints are handled through a general augmented Lagrangian approach. The propagation of the trajectory and the optimization of its controls are decoupled through the use of State-Transition Matrices. Part 1 of the paper series provides the necessary theoretical developments and implementation details for the algorithm. Part 2 contains validation and application cases.
  • A Serial High-Speed Satellite Communication CODEC: Design and
           Implementation of a SpaceFibre Interface
    • Abstract: Publication date: Available online 13 January 2020Source: Acta AstronauticaAuthor(s): Pietro Nannipieri, Gianmarco Dinelli, Antonino Marino, Luca Dello Sterpaio, Alessandro Leoni, Luca Fanucci, Daniele DavalleAbstractIn the last few years, satellite on-board data handling bandwidth requirements grew significantly, as well as production volume of these systems. A series of different protocols currently try to answer this need. In particular, the European Space Agency developed an open protocol solution: SpaceFibre. The SpaceFibre protocol can sustain a line rate of 6.25 Gb/s per lane (up to 16 lanes). It offers advanced and flexible Quality-of-Service features, as well as Fault Detection Isolation and Recovery services. The protocol structure has been developed so that full hardware implementation of its core layers is straightforward, granting high performances at low price in terms of complexity and power consumption, one of the most stringent requirements in space applications. In this paper, a FPGA implementation on both rad-hardened (RTAX2000, RTG4, Virtex-5) and commercial (ZYNQ 7000) devices of the SpaceFibre CODEC is presented together with its verification environment and a hardware validation set-up. Particular attention is given to the trade-off between resources utilisation, power consumption and CODEC configurations, in order to enable future system adopters to efficiently explore the design space.
  • The Small Orbital Debris Population and its Impact on Space Activities and
           Ecological Safety
    • Abstract: Publication date: Available online 12 January 2020Source: Acta AstronauticaAuthor(s): V.V. Adushkin, O.Yu Aksenov, S.S. Veniaminov, S.I. Kozlov, V.V. TyurenkovaAbstractWhen it is said about the danger of orbital debris for space activities and the ecology of the Earth, it most often means large orbital debris. In contrast to large orbital debris, the influence of small ones to space activities and ecology of the Earth and near-Earth space is often underestimated. As will be shown in this paper, it is unfair. New data on the dynamics of contamination of near-Earth space with small debris in low Earth orbit were obtained. The number, mass, and dynamics of the small orbital debris population in low Earth orbit are estimated as well as the consequences of the deployment of multi-satellite communication satellite systems are estimated. It makes the study of this area particularly relevant. The various aspects of the consequences of technogenic contamination of near-Earth space are considered. The comparison of the danger of small orbital particles and large satellite fragments for space activity and the ecology of the Earth and near-Earth space is also provided. А significant lack of reliable information on small space debris is proved to be one of the main limiting factors for our knowledge about the population of space debris in low Earth orbits.
  • Hydrodynamic processes determining the silica fracture under the action of
           high-intense laser
    • Abstract: Publication date: Available online 11 January 2020Source: Acta AstronauticaAuthor(s): V.P. Efremov, A.D. KiverinAbstractIn this paper hydrodynamic processes arisen in the silica under laser action are analyzed numerically. Exactly these processes determine the development of fracture of optical fiber under the action of high-intense laser beams. The mathematical model describing the wave processes inside the core and cover of an optical fiber is proposed. It is shown that the basic mechanism of high-speed fracture wave propagation is related to the plasma expansion into the cold silica. At the same time, the transverse waves define the development of the plasma bubble and as a result the destruction of the optical fiber core. Obtained hydrodynamic mechanisms are basic for a wide class of scenarios related to the interaction of high-energy fluxes with solid medium.
  • Identification of Shoulder Joint Clearance in Space Suit Using
           Electromagnetic Resonant Spiral Proximity Sensor for Injury Prevention
    • Abstract: Publication date: Available online 10 January 2020Source: Acta AstronauticaAuthor(s): Benjamin Loflin, Kim Cluff, Jacob Griffith, Noor MohammedAbstractShoulder injury is one of the most common phenomena that occurs for astronauts when they are training for space flight. During training, astronauts are required to wear a full space suit, known as the extravehicular mobility unit (EMU). The major component of the EMU that attributes to shoulder injury is the hard upper torso (HUT). This component is primarily comprised of a rigid fiberglass shell with metal scye bearing joints. Placement of the scye bearing joints for the shoulders does not allow for enough range of motion, which can lead to rotator cuff tears. Additionally, shoulder injury also occurs when donning the suit and training in the Neutral Buoyancy Laboratory (NBL). The EMU currently does not contain any provision to account for this biomechanical interference to adjust for optimum range of motion. The objective of this paper is to propose a novel detection scheme using a wearable electromagnetic resonant spiral sensor that could allow for a quantitative value of proximity between the shoulder and the metallic scye bearing joint of the HUT. The presence of the liquid cooling and ventilation garment (LCVG) is also investigated in the environment to validate that accuracy of proximity detection is still achieved. Optimal location for the wearable proximity sensor would be on top the LCVG around the shoulder joint where the scye bearing joints are more likely to meet the shoulder. The first study investigated the ability of the wearable proximity sensor to detect the distance from an aluminum sheet (representing the scye bearing joint) with no LCVG present, while the second study incorporated the wearable proximity sensor on top of the LCVG for a simulated suit environment. Four scenarios were performed with two wearable proximity sensors, resonating at different frequencies, placed in an environment with and without the LCVG. Ten repeated tests were used to train and an additional ten tests to validate a regression learning algorithm to predict the distance for each scenario. Experimental results indicated that the wearable proximity sensors in both the open air and with the LCVG have enough accuracy to provide a root mean square error (RMSE) of approximately 1 mm or less. This accuracy is sufficient for use in the space suit to provide quantitative information for suit fit. The use of this proximity detection scheme incorporated into the suit will offer previously unknown information regarding suit fit, while also influencing optimum fit for future suit generations.
  • Dynamic analysis of space robot manipulator considering clearance joint
           and parameter uncertainty: Modeling, analysis and quantification
    • Abstract: Publication date: Available online 10 January 2020Source: Acta AstronauticaAuthor(s): Wuweikai Xiang, Shaoze YanAbstractClearance joint as an inevitable nonlinear factor in space robot manipulator modifies dynamic response of the mechanism, justifies deviations between predictions and measurements, and enhances sensitivity of mechanism response to parameter variation. The coupling of clearance joint and parameter uncertainty, therefore, would further significantly influence the kinematic accuracy and dynamic response of a space robot manipulator. In this paper, the dynamic performance of space robot manipulator with consideration of joint clearance and parameter uncertainty is analyzed. Quantification of parameter effect on the dynamic response is also presented. In the analysis, joint elements are modelled as colliding bodies, where the nonlinear contact force model and hybrid friction model are employed to describe the impact-contact phenomena. Motion equations of the mechanism are derived in which nonlinear forces are considered as external forces. Then, the Chebyshev polynomial method is introduced to explicate the relation between the mechanism response and parameters. Based on the Chebyshev polynomial method, dynamic response of the uncertain mechanism could be calculated through the use of interval algorithm, and a sensitivity analysis method is introduced to quantify the parameter effect. The dynamics of a space robot manipulator with joint clearance and parameter uncertainty is further investigated, where the clearance size and friction coefficients are taken as single and multiple uncertain parameters, and effects of the uncertainties on the manipulator response are quantified. This study could help for the design, analysis and test of a space robot manipulator with consideration of both clearance and uncertainty.
  • Design and Optimization of a Multifunctional 3D-Printed Structure for an
           Inspector Cubesat
    • Abstract: Publication date: Available online 10 January 2020Source: Acta AstronauticaAuthor(s): Terry H. Stevenson, E. Glenn LightseyAbstractA design has been developed for a 3D-printed aluminum Cubesat structure that incorporates a cold-gas ACS propulsion system into hollow spaces within the structure. The propellant tanks, feed pipes, and thruster nozzles are all incorporated into a single piece of printed aluminum that also contains PPOD-compatible rails and connection points for avionics, solar panels, and a payload. This multifunctional structure, called the Structural Propulsion Unit Demonstrator (SPUD), makes efficient use of its available volume, and delivers superior impulse per unit volume compared to existing commercial cold gas thrusters. Since many Cubesat missions are more limited by volume allocation than by mass allocation, volumetric efficiency of a propulsion system is crucial. In addition, the flexibility of additive manufacturing allows the exact location and angles of the nozzles to be tailored to a specific trajectory or set of trajectories. The SPUD nozzles were optimized for an inspector satellite role, although the optimization methods could be used for any mission profile.
  • Least-squares solution of a class of optimal space guidance problems via
           Theory of Connections
    • Abstract: Publication date: Available online 18 June 2019Source: Acta AstronauticaAuthor(s): Roberto Furfaro, Daniele MortariAbstractIn this paper, we apply a newly developed method to solve boundary value problems for differential equations to solve optimal space guidance problems in a fast and accurate fashion. The method relies on the least-squares solution of differential equations via orthogonal polynomials expansion and constrained expression as derived via Theory of Connection (ToC). The application of the optimal control theory to derive the first order necessary conditions for optimality, yields a Two-Point Boundary Value Problem (TPBVP) that must be solved to find state and costate. Combining orthogonal polynomials expansion and ToC, we solve the TPBVP for a class of optimal guidance problems including energy-optimal landing on planetary bodies and fixed-time optimal intercept for a target-interceptor scenario. The performance analysis in terms of accuracy shows the potential of the proposed methodology as applied to optimal guidance problems.
  • A techno-economic analysis of asteroid mining
    • Abstract: Publication date: Available online 10 May 2019Source: Acta AstronauticaAuthor(s): Andreas M. Hein, Robert Matheson, Dan FriesAbstractAsteroid mining has been proposed as an approach to complement Earth-based supplies of rare earth metals and supplying resources in space, such as water. However, existing studies on the economic viability of asteroid mining have remained rather simplistic and do not provide much guidance on which technological improvements would be needed for increasing its economic viability. This paper develops a techno-economic analysis of asteroid mining with the objective of providing recommendations for future technology development and performance improvements. Both, in-space resource provision such as water and return of platinum to Earth are considered. Starting from first principles of techno-economic analysis, gradually additional economic and technological factors are added to the analysis model. Applied to mining missions involving spacecraft reuse, learning curve effect, and multiple spacecraft, their economic viability is assessed. A sensitivity analysis with respect to throughput rate, spacecraft mass, and resource price is performed. Furthermore, a sample asteroid volatile mining architecture based on small CubeSat-class spacecraft is presented. It is concluded that key technological drivers for asteroid mining missions are throughput rate, number of spacecraft per mission, and the rate in which successive missions are conducted. Furthermore, for returning platinum to Earth, market reaction strongly influences its economic viability.
  • Adaptive Guidance and Integrated Navigation with Reinforcement
    • Abstract: Publication date: Available online 8 January 2020Source: Acta AstronauticaAuthor(s): Brian Gaudet, Richard Linares, Roberto FurfaroAbstractThis paper proposes a novel adaptive guidance system developed using reinforcement meta-learning with a recurrent policy and value function approximator. The use of recurrent network layers allows the deployed policy to adapt in real time to environmental forces acting on the agent. We compare the performance of the DR/DV guidance law, an RL agent with a non-recurrent policy, and an RL agent with a recurrent policy in four challenging environments with unknown but highly variable dynamics. These tasks include a safe Mars landing with random engine failure and a landing on an asteroid with unknown environmental dynamics. We also demonstrate the ability of a RL meta-learning optimized policy to implement a guidance law using observations consisting of only Doppler radar altimeter readings in a Mars landing environment, and LIDAR altimeter readings in an asteroid landing environment, thus integrating guidance and navigation.
  • Design and analysis of a cable-winding device driving large deployable
           mechanisms in astrophysics missions
    • Abstract: Publication date: Available online 8 January 2020Source: Acta AstronauticaAuthor(s): Xilun Ding, Hang Xiao, Qiaolong Yang, Long Li, Kun XuAbstractCables are widely used because of their light weight and wide range of arrangement. To guarantee successful deployment and retraction of cable-driven mechanisms, this paper proposes a novel cable-winding device to fulfil particular requirements of a space mission, such as a large driving force output, large cable displacement, and high reliability. The device consists of three parts: the transmission assembly, cable arrangement assembly, and redundancy motor assembly. The transmission assembly transforms the torque of a motor into a large driving force. Cables can be wound layer-by-layer on a winch with the cable arrangement assembly. The redundancy motor assembly ensures normal movement of the mechanism if one motor fails, and can offer greater torque than a single motor. A prototype of the proposed cable-winding device is fabricated, and experiments are conducted to verify the performance of the device. The device has also been used in a large telescopic boom, which further validates its feasibility for actuating deployable mechanisms.
  • Numerical study of hypersonic surface heat flux with different air species
    • Abstract: Publication date: Available online 7 January 2020Source: Acta AstronauticaAuthor(s): Yipu Zhao, Haiming HuangAbstractThe chemical nonequilibrium mathematical model is built to investigate the effect of the air species model on the heat flux, based on Navier-Stokes equations, the Gupta chemical kinetics model and air species models, including the five-species model, the seven-species model and the eleven-species model. The code is programmed in FORTRAN, and verified by making a comparison with the data in the literature. A good deal of calculations under different cases are completed to obtain differences among three air species models by taking the heat flux as an example. Results demonstrate that the heat flux computed by the seven-species model is largest among three air species models, meanwhile, the difference of the heat flux enlarges with the enhance of Mach number, which proves the necessity of using the seven-species model at higher Mach number.
  • Autonomous In-Orbit Satellite Assembly from a Modular Heterogeneous Swarm
    • Abstract: Publication date: Available online 7 January 2020Source: Acta AstronauticaAuthor(s): Rebecca C. Foust, E. Sorina Lupu, Yashwanth K. Nakka, Soon-Jo Chung, Fred Y. HadaeghAbstractThis paper presents a decentralized, distributed guidance and control scheme to combine a heterogeneous swarm of component satellites into a large satellite structure. The component satellites for the heterogeneous swarm are chosen to promote flexibility in final shape inspired by crystal structures and Islamic tile art. After the ideal fundamental building blocks are selected, basic nanosatellite-class satellite designs are made to assist in simulations involving attitude control. The Swarm Orbital Construction Algorithm (SOCA) is a guidance and control algorithm to allow for the limited type heterogeneity and docking ability required for in-orbit assembly. The algorithm consists of two parts, a distributed auction which uses barrier functions to ensure the proper agent selection for each target, and a trajectory generation portion which leverages model predictive control and sequential convex programming to achieve optimal collision-free trajectories to the desired target point even with nonlinear system dynamics. The optimization constraints use a boundary layer to determine whether the collision avoidance or the docking constraints should be applied. The algorithm was tested in a simulated perturbed 6-DOF spacecraft dynamic environment for planar and out-of-plane final structures and on two robotic platforms, including a swarm of frictionless spacecraft simulation robots.
  • Experimental investigation on the ignition and combustion characteristics
           of moving micron-sized Mg particles in CO2
    • Abstract: Publication date: Available online 7 January 2020Source: Acta AstronauticaAuthor(s): Xiaofei Zhu, Chao Li, Yu Guo, Wen Ao, Shining Liu, Chunbo HuAbstractFew databases exist for the research on the ignition or combustion of moving micron-sized Mg particles in CO2. In this study, the ignition and combustion characteristics of moving micron-sized Mg particles in CO2 were examined with a closed high-temperature furnace and a pneumatic ejection device. The ignition and combustion processes were captured and recorded with a high-speed camera. The condensed products were collected with a water-cooled probe and analyzed with a transmission electron microscope (TEM) or scanning electron microscope (SEM). The results showed that an uneven protective shell forms around a particle because of the heterogeneous reaction during the ignition stage. Ignition occurs when the weakest point of the shell ruptures because of the large pressure difference. The partial ejection of Mg vapor on the particle surface leads to a skewed distribution of the flame around the burning Mg particle in CO2. During the combustion process, the particle may spin at speeds of 0.4–1.5 rotations per millisecond. Empirical formulas were derived for the ignition delay and burning time. No bright flame was observed around the particles when the ambient pressure dropped below 0.025 MPa, which was concluded to be the ignition pressure limit of Mg in CO2. These results should be useful for the structural design and optimization of Mg/CO2 powder rocket engines intended for Mars exploration.
  • Optimal transfer schemes between space debris objects in geostationary
    • Abstract: Publication date: Available online 7 January 2020Source: Acta AstronauticaAuthor(s): A.A. Baranov, D.A. Grishko, О.I. Khukhrina, Danhe ChenAbstractThe paper compares two variants of re-orbiting space debris objects from the geosynchronous (GEO) region. Under the first re-orbiting variant, a spacecraft-collector transfers between target objects (87 upper stages). Each object is re-orbited into a disposal orbit (DO) using special thruster de-orbiting kits (TDK) which are placed on space debris objects by the collector. Under the second variant, the object is pushed to a DO by the collector itself, which then moves to a new space debris object from the previous object’s DO. It is shown that due to the slow evolution of the orbital parameters in the GEO region, the same transfer schemes can be used for both re-orbiting variants. We describe orbits in the near-equatorial region and consider two transfer schemes between objects. Under the first scheme, a transfer is executed when the orbits have the same inclination near the equator, and under the second scheme, when the orbit of the next object has the smallest inclination. Calculations show that both schemes are practically equivalent in terms of both the averaged ΔV for a transfer and the duration — however, not all objects under consideration can be covered under the first scheme. Hence, priority should be given to the second scheme. It can be calculated, that 6 collectors are required to clean the GEO protected region from spent upper stages. The service of each is expected to be at most 8 years and its required ΔV budget is at most 0.7 km/s. A re-orbiting of one object to a DO requires on average 10 m/s; the return to a new object from the DO of the previous object is nearly energetically equal to a sequential transfer between the objects. In this regard, as distinct from low orbits (in which it is preferable to use TDKs), it is more beneficial to follow the second variant for re-orbiting space debris objects from the GEO region (i.e., using the collector itself).
  • Hypersonic aerodynamic interference investigation for a two-stage-to-orbit
    • Abstract: Publication date: March 2020Source: Acta Astronautica, Volume 168Author(s): Juhong Jia, Debin Fu, Zepeng He, Junfan Yang, Lijie HuAbstractTo investigate the aerodynamic interference challenges for hypersonic vehicles, a new type of conceptual TSTO model is considered, which consists of a trapezoid wing as the booster and a hemisphere-cone-cylinder wing as the orbiter. Based on the three-dimensional hybrid LES/RANS numerical simulation method, the mechanism of high surface heat flux and the effect of stage separation between booster and aircraft in hypersonic flight are studied in detail. The results show that the oblique shock generated by the booster impinges on the bow shock in a three-dimensional region around the orbiter nose. Obviously, this interaction brings about a steep temperature gradient and high peak values of pressure and heat flux. When the bow shock under the orbiter is incident to the upper surface of the booster, it will trigger a shock-wave/boundary-layer interaction, which gives rise to the peak pressure and heat flux. When the reflected bow shock impacts the lower surface of the orbiter, it will initiate another interaction. When the two stages separate from each other, the increase in the normal distance between two stages results in a decrease in pressure and heat flux. When the vertical distance is large enough, the reflected bow shock impinges on the rear of the orbiter without producing an interaction. At that moment, the pressure and heat flux maintain low values.
  • The partial weight-bearing rat model using a pelvic harness does not
           impact stress or hindlimb blood flow
    • Abstract: Publication date: March 2020Source: Acta Astronautica, Volume 168Author(s): Marie Mortreux, Daniela Riveros, Carson Semple, Mary L. Bouxsein, Seward B. RutkoveAbstractAimFuture space missions will send humans to the Moon and Mars, where gravity is greatly reduced compared to Earth. The recent development of a rat partial weight-bearing (PWB) model allowed for a better understanding of the changes induced by reduced loading.MethodWe exposed animals to 28 days of PWB including: normal loading without apparatus (PWB100 N), normal loading with full apparatus (PWB100 FH), 70%, 40%, and 20% of normal loading (PWB70, PWB40, and PWB20, respectively). We assessed physiological parameters weekly (i.e.: tail blood pressure, hindlimb oxygen saturation, plasma corticosterone) to measure the impact of the apparatus during normal loading, and to determine if PWB resulted in a dose-dependent modification of stress and/or hindlimb blood pressure. In addition, we sought to determine if forelimb muscle atrophy could be detected.ResultsThe use of the full apparatus did not impact any parameters compared to the control group during normal loading, except for a reduced weight gain. PWB did not lead to significant modifications of animals’ blood pressure, blood oxygenation, or stress markers. Indeed, after 28 days of PWB, plasmatic corticosterone levels were of 39.8 ± 12.0, 47.0 ± 16.9, 69.5 ± 14.4 and 55.9 ± 17.7 ng/mL in animals exposed to PWB100, PWB70, PWB40 and PWB20, respectively (p = 0.7577).ConclusionThese results support our hypothesis that our rat PWB system using a pelvic harness is well tolerated by the animals and does not initiate a chronic-stress state that could mask other physiological alterations.
  • On the rapid breakdown of supersonic streamwise vortices with opposite
           sign double annular vorticity
    • Abstract: Publication date: March 2020Source: Acta Astronautica, Volume 168Author(s): Toshihiko HiejimaAbstractThe spatial development of supersonic streamwise vortices with opposite-sign double annular vorticity is investigated using direct numerical simulation at Mach number 2.5. The results show that the unstable modes originate from inside or outside the vortex depending on the ratio of vorticity thicknesses. Their initial development depends strongly on azimuthal shear and centrifugal instabilities arising on a plane perpendicular to the streamwise direction. When the ratio of vorticity thicknesses is small, spiral structures develop in the outer annular vorticity and give rise to multiple vortex pairs owing to curling on an interface between the positive and negative vorticities. As plural vortex pairs and small-scale eddies are rapidly generated from around the spiral structures, the streamwise vortices with the specific vorticity collapse at a fairly short distance. This mechanism differs from transitional structures of jets associated with hairpin vortex structures at small scales and those of swirls without annular flows. Thus, opposite-sign annular vorticity plays an important role in the rapid breakdown of supersonic streamwise vortices.
  • Collision probability of composite cubesats hovering in leader-follower
    • Abstract: Publication date: March 2020Source: Acta Astronautica, Volume 168Author(s): Yuchen Xie, Ken Chan, Jingrui ZhangAbstractAnalytical expressions are obtained for computing the collision probability of a large Composite CubeSats hovering in the close vicinity of another large Composite CubeSats in a Leader-Follower configuration. The composite is constructed from a large number of Unitary CubeSats arranged in a cuboid volume. The study involves the modeling of the growth of a time-dependent probability density function over a period of time and the effects of that growth on the collision probability. Studies of collision probability as a function of time are performed in terms of the parameters: separation between neighboring orbiters, covariance size (different in three directions) and the size of the two cuboid CubeSat Composites. It was found that certain combinations of parameters resulted in collision probability curves which intersected and others did not. This curve-crossing phenomenon cannot be predicted in advance but must be demonstrated quantitatively by performing detailed computations. This knowledge may be used to advantage in the design of distributed systems and in the orbital maintenance of their configuration. Moreover, the Principle of Scaling is used to obtain collision probabilities using the results obtained from a relatively small number of case studies so as to circumvent the effort to perform copious computer runs when the input parameters are changed.
  • The variability of urine proteome and coupled biochemical blood indicators
           in cosmonauts with different preflight autonomic status
    • Abstract: Publication date: March 2020Source: Acta Astronautica, Volume 168Author(s): L.H. Pastushkova, V.B. Rusanov, O.I. Orlov, A.G. Goncharova, A.G. Chernikova, D.N. Kashirina, A.R. Kussmaul, A.G. Brzhozovskiy, A.S. Kononikhin, K.S. Kireev, A.M. Nosovsky, E.N. Nikolaev, I.M. LarinaAbstractThe purpose of this work was to reveal the intra- and inter-individual variability of the urine proteomic composition and of biochemical blood parameters in cosmonauts with different preflight autonomic status when they are back to Earth (on the 1st and 7th day after space flight). The objects of the study were 5-min samples of electrocardiogram (ECG) at rest and urine and venous blood samples, obtained in the same timeline from twelve male cosmonauts (age 46.5 ± 3.4 years), who performed space flights (SF) with duration 169–199 days onboard the Russian segment of the International Space Station (ISS). Two groups with different sympathetic-parasympathetic balance were identified (each consists of 6 cosmonauts) by the results of preflight heart rate variability (HRV) analysis. We have revealed in groups of cosmonauts with preflight predominance of sympathetic or parasympathetic tone the significant differences in the directionality of changes on days 1 and 7 after the SF as compared to the preflight values in three proteins (from total amount around 200): alpha-1 subunit of collagen type VI, Mucin 1, Cadherin-13. A set of biochemical parameters, unidirectionally changing with these proteins, was different in classified groups. Direct bilirubin, potassium and total calcium move unidirectionally with collagen, direct bilirubin, potassium – with mucin, and uric acid, ferrum, alpha-1, KFK, potassium - with cadherin in group with a sympathetic tone. Potassium, ferrum, alpha-1 move unidirectionally with collagen, amylase, KFK, AST, urea, inorganic phosphate, glucose, alkaline phosphatase, ionized calcium – with mucin, and total ferrum biding capacity, transferrin, glucose gamma globulin transferase - with cadherin in group with parasympathetic predominance. Probably, differences between groups in the concentration of these proteins and their different relationship with some biochemical parameters reflect different ways to achieve the same goal - adaptation to a complex of SF factors and re-adaptation after returning to Earth.
  • Planetary exploration of Saturn moons Enceladus and Dione
    • Abstract: Publication date: March 2020Source: Acta Astronautica, Volume 168Author(s): J.R. Sanmartín, J. PeláezAbstractSearch for habitability in Outer Planets moons, requires presence of proper chemistry, water, and energy. Dissipation from tidal forces is major energy source in evolution of Icy moon systems, generically exhibiting a multi-layer structure, with outer solid (ice) and intermediate liquid layers, and solid (rocky) core. Saturn moon Enceladus has been found to eject plumes of water vapour and ice, and very recently, hydrogen molecules, a tentative sign of chemistry supporting microbial life. Purpose of the present work is a preliminary design of a minor electrodynamic tether mission to visit Enceladus. Free tether capture and maneuvering would take the S/C to a Saturn orbit with periapsis very close to the planet and apoapsis at Enceladus orbit, the S/C proved to be then in a 1:2 resonance with the moon, allowing parallel, conveniently slow flybys. Such mission could also involve visiting Dione, the 4 th largest Saturn moon, Enceladus and Dione being in a natural 1:2 Laplace resonance; it was recently brought to light that Dione exhibits multiple, parallel color lines, hundred kilometers long.
  • Augmented Reality for the enhancement of space product assurance and
    • Abstract: Publication date: March 2020Source: Acta Astronautica, Volume 168Author(s): Raul Alarcon, Fridolin Wild, Christine Perey, Marc Marin Genescà, Josefa Gavaldà Martínez, Josep Xavier Ruiz Martí, Maria José Simon Olmos, Diana DubertAbstractA growing number of companies in the aerospace industry are already leading projects to deploy Augmented Reality (AR) to improve their workplace performance, knowledge transfer, as well as workforce productivity. In parallel, national and international agencies in aerospace, such as the European Space Agency (ESA), are running studies to evaluate the application of AR to enhance the quality and cost effectiveness of space missions.We hereby present the results of a study performed by ESA to assess the maturity and potential business value of AR for application to space product assurance and safety activities. For this purpose, we conduct an on-line survey and interviews with product assurance and safety professionals. Moreover, we provide a detailed review of space industry use case requirements and readiness levels of potentially involved technology components. Findings indicate that maturity of many components enabling AR may not fully satisfy the space industry's requirements, while, at the same time, there is great potential for impact and long-term benefits from AR introduction.
  • Ultra-high-molecular-weight polyethylene as a hypervelocity impact
           shielding material for space structures
    • Abstract: Publication date: March 2020Source: Acta Astronautica, Volume 168Author(s): Ji-Hun Cha, YunHo Kim, Sarath Kumar Sathish Kumar, Chunghyeon Choi, Chun-Gon KimAbstractSpace debris impacts at hypervelocity of several tens of km/s threaten the survival of space structures. In the case of International Space Station, the concept of Whipple shield is applied to protect the astronauts and the electronic devices from impact of space debris. In this study, a Whipple shield design comprising of ultra-high-molecular-weight polyethylene were proposed to improve the space debris impact shielding efficiency over conventional Whipple shields. Ballistic performance was evaluated by a two-stage lightweight gas gun capable of accelerating 5.56 mm diameter aluminum projectiles to 4 km/s. High-temperature impact tests and outgassing tests were performed for space environment application. Through the test, ultra-high-molecular-weight polyethylene was better ballistic performance and outgassing properties than Kevlar used in conventional Whipple shield. Ultra-high-molecular-weight polyethylene can be an effective way to provide cosmic radiation shielding and ballistic capability for future spacecraft designs.
  • Effects of flow-field structures on the stability of rotating detonation
           ramjet engine
    • Abstract: Publication date: March 2020Source: Acta Astronautica, Volume 168Author(s): Kevin Wu, Shujie Zhang, Mingyi Luan, Jianping WangAbstractDue to less attention received by rotating detonation ramjet engine (RDRE), the three-dimensional flow-field structures and their influence on stability are less understood than rocket-mode rotating detonation engine (RDE). This paper presents three-dimensional numerical investigations on the RDRE model with a Laval inlet. The computations are based on detailed H2/air chemistry. The simulation shows that, unlike rocket-mode RDEs, an upstream oblique shock wave is induced by detonation. This oblique shock wave is then prevented from propagating upstream further by the normal shock wave in the inlet. In addition, two instabilities in RDREs, namely, backflow and strip-type fresh fuel layer, are analyzed for the first time. Results indicate that the backflow is related to reflected shock waves and the upstream oblique shock wave that induced by detonation. While the strip-type fresh fuel distribution is formed due to the unstable propagation of detonation. Detonation waves interact with fresh fuel layer, transverse waves, and the normal shock waves, making the irregular fresh fuel layer remains in the combustion chamber.
  • Experiment for pose estimation of uncooperative space debris using stereo
    • Abstract: Publication date: March 2020Source: Acta Astronautica, Volume 168Author(s): W.C. De Jongh, H.W. Jordaan, C.E. Van DaalenAbstractAcquiring the relative pose between an uncooperative target and a chaser satellite poses a unique problem for any active debris removal mission. A lack of prior knowledge regarding the target's motion, mass distribution and shape limits the possibilities for accurately tracking the target. In this paper, a stereo-camera pair, mounted on a chaser satellite, is used to extract unique features on the surface of an unknown, uncooperative target using the scale invariant feature transform (SIFT). The features are used as measurement input to an extended Kalman Filter (EKF) that makes use of the simultaneous localisation and mapping (SLAM) approach. The orientation and position of the target relative to the chaser is estimated, along with the target's linear and angular velocities. This motion is estimated relative to the camera reference frame (CRF) while the system simultaneously calculates the shape and size of the target. A simulation environment is created to test and verify the estimation algorithm. The integration of the feature extractor with the EKF is tested using real camera data. A laboratory experiment was conducted to capture image sequences of a moving target. A number of practical considerations is highlighted when such a system is to be applied to a mission. Results show that stereo cameras, along with the EKF-SLAM approach is a viable method for fully autonomous space debris mitigation systems.
  • She Space: A multi-disciplinary, project-based learning program for high
           school girls
    • Abstract: Publication date: March 2020Source: Acta Astronautica, Volume 168Author(s): Sivan Isaacson, Lonia Friedlander, Chen Meged, Shiran Havivi, Aviv Lee Cohen-Zada, Inbal Ronay, D.G. Blumberg, Shimrit MamanAbstractPrevious research investigating the under-representation of women in science and technology fields has identified various causes. These include, a lack of inspiring female role-models, limited exposure of girls to science, technology, engineering, and mathematics (STEM) subjects, gender-biased stereotypes, and preferences for different learning styles between genders. Dedicated to the ideas of women and space, the “She Space” research project for high school girls was a joint effort of the Earth and Planetary Image Facility (EPIF) at Ben-Gurion University in the Negev and Beit Yatziv. The participants included 20 high-school aged female students and a predominantly female staff of up to eight university researchers and advanced degree students. The goal of this project was to advance and support female students engaging with various scientific fields and, in particular, the field of space science. The project emphasized the quality and development of the research process and used project-based learning to help participants learn to use a research-based approach when encountering challenging scientific concepts or subjects. This, together with active learning and teamwork was set as the educational framework to meet the different learning styles and motivational needs of girls. Furthermore, special attention was given to the suppression of gender stereotypes by 1) introducing women role models 2) overcoming self-induced prejudices related to STEM abilities by introducing new and unknown subjects (remote sensing), about which participants lack preconceptions. Using participant surveys, we found that self-reported confidence with and interest in STEM subjects increased after the project. We also found that participants’ feelings about participating in an all-female program did not noticeably change after the program. However, the vast majority (87%) of participants did report that having a majority female staff was very important to them.
  • Electric sails are potentially more effective than light sails near most
    • Abstract: Publication date: March 2020Source: Acta Astronautica, Volume 168Author(s): Manasvi Lingam, Abraham LoebAbstractElectric sails are propulsion systems that generate momentum via the deflection of stellar wind particles through electric forces. Here, we investigate the relative merits of electric sails and light sails driven by stellar radiation pressure for F-, G-, K- and M-type stellar systems. We show that electric sails originating near M-dwarfs could attain terminal speeds of ~500 km/s for minimal payload masses. In contrast, light sails are typically rendered ineffective for late-type M-dwarfs because the radiation pressure is not sufficiently high to overcome the gravitational acceleration. Our analysis indicates that electric sails are better propulsion systems for interplanetary travel than light sails in proximity to most stars. We also delineate a method by which repeated encounters with stars might cumulatively boost the speeds of light sails to ≳0.1c, thereby making them more suitable for interstellar travel. This strategy can be effectuated by reaching ~105 stars over the span of ~10 Myr.
  • Nonlinear predictive filter based fault diagnosis of oxygen generation
           system by using electrolytic water in space station
    • Abstract: Publication date: March 2020Source: Acta Astronautica, Volume 168Author(s): Rui Guo, Yunhua Li, Mingbo LvAbstractThe oxygen generation system using electrolytic water is one of the important systems in space station which supplies the oxygen for the astronauts from the condensate water, i.e., Sabatier reduction reaction water and urine treated water. During the operation of the space station, the normal operation of the system directly affects the safety of astronauts and the operating costs of the space station, so the fault diagnosis of the system has become a research hotspot. This paper systematically describes the fault diagnosis method of the oxygen generation system using electrolytic water, including the establishment of the fault mode and effects analysis, mathematical model of the key components and the estimation algorithm of unmeasured parameters. For the two direct discriminant indicators of the oxygen production and hydrogen production, because they are unmeasurable and their dynamic models are difficult to be established, this paper proposes a cascade algorithm of nonlinear predictive filtering and low-pass filter to solve the problem. Firstly, the oxygen and hydrogen production are estimated by the predictive filter. And then, the high frequency noise introduced by measurement error is eliminated when the oxygen and hydrogen production signals entered in a low-pass filter. Through the simulation analysis of the normal and fault mode, the correctness and effectiveness of the estimation algorithm are illustrated.
  • Design and experiment of a noncontact electromagnetic vibration isolator
           with controllable stiffness
    • Abstract: Publication date: March 2020Source: Acta Astronautica, Volume 168Author(s): Yu Chen, Hao Wen, Dongping JinAbstractIsolating low-frequency vibration in current satellites that has a negative effect on the performance of precise payloads has increasing demand. In this work, a simplified model of a noncontact electromagnetic isolator for low-frequency vibration, which has a controllable stiffness with a minimum of zero, is proposed. Starting with the designing process of the vibration isolator, a series of ground-based experiments are carried out to verify the controllable stiffness. Two typical operating scenarios, the vibration isolation and rapid maneuver modes, are experimentally demonstrated. The experimental results indicate that the stiffness has a practically proportional relationship with the input current and the proposed design works well for both of the operation modes.
  • Pattern recognition in time series for space missions: A rosetta magnetic
           field case study
    • Abstract: Publication date: March 2020Source: Acta Astronautica, Volume 168Author(s): K. Ostaszewski, P. Heinisch, I. Richter, H. Kroll, W.-T. Balke, D. Fraga, K.-H. GlassmeierAbstractTime series analysis is a technique widely employed in space science. In unpredictable environments like space, scientific analysis relies on large data sets to enable interpretation of observations. Artificial signal interferences caused by the spacecraft itself further impede this process. The most time consuming part of these studies is the efficient identification of recurrent pattern in observations, both of artificial and natural origin, often forcing researchers to limit their analysis to a reduced set of observations. While pattern recognition techniques for time series are well known, their application is discussed and evaluated primarily on purpose built or heavily preprocessed data sets. The aim of this paper is to evaluate the performance of state of the art pattern recognition techniques in terms of computational efficiency and validity on a real-life testcase. For this purpose the most suitable techniques for different types of pattern are discussed and subsequently evaluated on various hardware in comparison to manual identification. Using magnetic field observations of the ESA Rosetta mission as a representative example, both disturbances and natural patterns are identified. Compared to manual selection a speed-up of a factor up to 100 is achieved, with values for recall and precision above 80%. Moreover, the detection process is fully automated and reproducible. Using the presented method it was possible to detect and correct artificial interference. Finally, the feasibility of onboard deployment is briefly discussed.
  • Systemic redox biomarkers suggest non-redox mediated processes in the
           prevention of bed rest-induced muscle atrophy after exercise training: The
           Cologne RSL study
    • Abstract: Publication date: March 2020Source: Acta Astronautica, Volume 168Author(s): C.F. Dolopikou, I.A. Kourtzidis, A.N. Tsiftsis, N.V. Margaritelis, A.A. Theodorou, V. Paschalis, C.A. Frantzidis, M.G. Nikolaidis, C. Kourtidou-Papadeli, A. KyparosAbstractIt has been previously reported that eccentric-biased exercise training prevents the decreases in lean body mass after 60 days of head tilt down bed rest (“Cologne RSL Study”). The aim of the present study, as a part of Cologne RSL Study, was to investigate whether these anti-atrophy effects of exercise training are regulated by redox processes, as assessed indirectly via redox biomarkers in blood and urine. Twenty-four volunteers (N = 24) participated in a randomized controlled study and were randomly divided into two groups: a jump training group (JUMP, n = 12) that performed a specific eccentric-biased training protocol on a Sledge Jump System and a control group (CON, n = 11; one drop-out) that did not perform any exercise. All participants maintained a 6° head tilt down position for 24 h/day for 60 days. Redox measurements in plasma, erythrocytes and urine were performed at several time points throughout the study (i.e., baseline, intervention and recovery phases). A main effect of time was found for all dependent variables (P  .05). In conclusion, our findings in systemic redox biomarkers indicate that the anti-atrophy effects of exercise training during a 60-day bed rest protocol are not regulated by redox processes.
  • Impact probability computation for NEO resonant returns through a
           polynomial representation of the Line of Variations
    • Abstract: Publication date: March 2020Source: Acta Astronautica, Volume 168Author(s): Marcello Sciarra, Matteo Losacco, Daniele Antonio Santeramo, Pierluigi Di LiziaAbstractA differential algebra based representation and propagation of the Line of Variations for Near Earth Objects impact monitoring is presented in this paper. The Line of Variations is described at the initial epoch by a high-order polynomial that is propagated forward in time. An Automatic Domain Splitting algorithm is embedded in the numerical integrator, in such a way that when the polynomials truncation error becomes too large, the line is split as many times as necessary to meet accuracy requirements. The Line of Variations is propagated forward in time until an intersection with a properly defined target plane occurs for all the generated subdomains. The subdomains are then projected onto the target plane to compute the impact probability by numerically integrating an associated one-dimensional probability density function. The proposed approach is applied to several test-cases to assess the performance of the method for the different possible shapes of the initial confidence region. Starting from a case of direct encounter, the technique is tested up to the case of a resonant return, which features critical nonlinearities.
  • Composite weighted average consensus filtering for space object tracking
    • Abstract: Publication date: March 2020Source: Acta Astronautica, Volume 168Author(s): Hao Chen, Jianan Wang, Chunyan Wang, Jiayuan Shan, Ming XinAbstractIn this paper, a composite weighted average consensus filtering (CWACF) algorithm is proposed for space object tracking by combining two distributed heterogeneous nonlinear filters. In light of the sensors' different sensing accuracy and computational capability, extended Kalman filter (EKF) and sparse-grid quadrature filter (SGQF) are compositely adopted on different sensors as local filters. Then, estimates from neighbours are fused based on the weighted average consensus framework to attain better estimation performance. Moreover, it is proved that the estimation error is exponentially bounded in mean square. The performances of the proposed algorithm, the distributed extended Kalman filtering (DEKF) and the distributed sparse-grid quadrature filter (DSGQF) are compared in a space object tracking problem.
  • DLR Reusability Flight Experiment ReFEx
    • Abstract: Publication date: March 2020Source: Acta Astronautica, Volume 168Author(s): Waldemar Bauer, Peter Rickmers, Alexander Kallenbach, Sven Stappert, Viola Wartemann, Clemens Hans-Joachim Merrem, René Schwarz, Marco Sagliano, Jan Thimo Grundmann, Andreas Flock, Thomas Thiele, Daniel Kiehn, Andreas Bierig, Jens Windelberg, Eugen Ksenik, Thorben Bruns, Tobias Ruhe, Henning ElsäßerAbstractThe German Aerospace Center (DLR) is currently developing the Reusability Flight Experiment (ReFEx). The successor of the already performed hypersonic flight experiments SHEFEX I and II shall be launched on a Brazilian VSB-30 sounding rocket in 2022 and shall achieve a re-entry velocity of more than Mach 5. The main goals of the project are the demonstration of a controlled autonomous re-entry flight from hypersonic velocity down to subsonic range and the testing of the key technologies required for future reusable first stage systems. Utilizing Concurrent Engineering (CE) approach the fundamental feasibility of this sophisticated flight experiment has been investigated by the entire ReFEx team. All required systems, including sensors and actuators as well as their interfaces have been defined and different options were assessed regarding matters such as the scientific output, complexity, risk and cost. The current configuration of ReFEx has a re-entry mass of about 400 kg, a length of 2.7 m and a wingspan of 1.1 m. This paper provides a system overview and addresses the Reusable Launch Vehicles (RLV) technologies Guidance, Navigation and Control as well as Flight Instrumentation. Furthermore the mission design (launch & re-entry) and the main challenges regarding the mission realization are addressed.
  • General relativistic impact on the precision of BepiColombo
    • Abstract: Publication date: March 2020Source: Acta Astronautica, Volume 168Author(s): Alexander P. YefremovAbstractThe general relativistic (GR) impact is assessed on the precision of the announced BepiColombo (BC) space positions at the Earth, Venus and Mercury flyby points providing planned gravity-assists. Apart of the known elliptic orbit precession, another recently specified for the Schwarzschild-Kerr metric effect of the ellipse axes contraction is considered in the thoroughly built model of BC motion from the launch point to the first assigned flyby point at Venus. The intermediate Earth gravity-assist act is shown to serve as an amplifier of the GR effects, so that the total GR-caused position shift at Venus can reach great distances, exceeding the accuracy of the assigned lengths thousands of times. Similar factors entailing possible GR deviation from BC-Mercury expected flyby points are also analysed.
  • Fostering innovation via ambidexterity in aerospace organizations
    • Abstract: Publication date: March 2020Source: Acta Astronautica, Volume 168Author(s): Christine Joseph, Danielle WoodAbstractThis paper discusses an on-going study that examines the role of organizational ambidexterity associated with the pursuit of Disruptive Innovation by incumbent organizations in the space sector. The study pursues evidence of the approaches used by organizations to pursue balance between the paradoxical tensions of exploration versus exploitation, and integration versus differentiation. Many authors have theorized how organizations might achieve such balance and some have produced empirical data to show how rare firms have survived a disruption. This study analyzes cases from the space sector as an example of a public service sector in which government agencies or regulators play a strong role. It is theorized that the unique interaction between firms and government within public service sectors may lead to different empirical patterns regarding innovation dynamics. Furthermore, well-established organizations may harness ambidexterity to simultaneously explore and exploit or to integrate and differentiate. The research question asks, how do well-established organizations in the space sector harness ambidexterity as part of their innovation strategy' This study reviews literature from organizational studies and innovation theory and proposes a framework by which to analyze the innovation behavior of incumbent organizations in the space sector. Specifically, the framework asks how organizations exercise ambidexterity in the areas of organizational architecture, culture, technology, policies, processes and communication.
  • Dust Storm: The cost-saving benefits of a compute cloud on Mars
    • Abstract: Publication date: March 2020Source: Acta Astronautica, Volume 168Author(s): Benjamin H. March, James G. CaslerAbstractAs more missions to Mars require greater autonomy of both rovers and humans, more sophisticated computer technology in close proximity will be necessary to sustain operations. On Earth, cloud technology has provided significant cost-saving benefits to companies that require heavy compute resources due to the pay-per-use pricing model. The same could be true on Mars, assuming that there is enough demand for high-capacity, on-demand compute and data storage resources. The concept of a compute cloud about Mars (“Dust Storm”) was developed to determine a basic pricing model for compute, and other Platform as a Service (PaaS) features. Existing mission concepts were re-evaluated under the assumption of using Dust Storm versus developing and deploying an in-house solution. Additionally, a sensitivity analysis was conducted to control for inaccurate assumptions and estimates. It was determined that five-year multi-agent missions would cost significantly less (48.6%) when renting time from Dust Storm. It was also determined that the greatest effects on cost savings are the cost of building and deploying Dust Storm, the maximum data transfer rate between Earth and Mars, and the length of time expected to recoup initial investments. Future research will be required to reduce hardware costs, and increase data transfer rates.
  • A spent upper stage removal mission aimed to reduce debris impact
           footprint size
    • Abstract: Publication date: March 2020Source: Acta Astronautica, Volume 168Author(s): Vladimir S. Aslanov, Dmitry A. SizovAbstractA process of a spent upper stage removal from low Earth orbit is considered, which consists of three phases: towing of the stage using a tether; descent of the stage into the low-density atmosphere; motion of its debris fragments after the breakup caused by the aerodynamic and thermal loads. It is shown that the attitude motion of the stage during its descent largely affects its breakup altitude and consequently the size of debris impact footprint and its position on the surface of the Earth. A certain number of ways to reduce the footprint extent are proposed. As an example of using the proposed method, a numerical simulation of the removal of a spent Ariane 4 upper stage H10 was performed. The results of the study can be used for planning missions to clean up space debris from low Earth orbit.
  • Vibration suppression for post-capture spacecraft via a novel bio-inspired
           Stewart isolation system
    • Abstract: Publication date: March 2020Source: Acta Astronautica, Volume 168Author(s): Xin Wang, Xiaokui Yue, Honghua Dai, Jianping YuanAbstractIn the process of on-orbit capture mission, some undesirable vibrations arising from the relative motions between the servicing spacecraft and the target are inevitable, which can make the post-capture combined spacecraft unstable or even tumbling. Therefore, suppressing post-capture vibrations is critical to mission success. In this work, a novel bio-inspired X-shape structure-based Stewart isolation platform (XSSIP) system is first proposed to install between the satellite platform and the capture mechanism. It can suppress the post-capture vibrations of a free-floating spacecraft subjected to the impulsive or periodic external forces. Beneficial nonlinear stiffness and nonlinear damping characteristics with the existence of X-shape structure can be acquired, which is helpful to achieve much better vibration isolation performance in multiple directions. Different from the traditional ground vibration isolation system, the dynamic equations of the 6-DOF under-constrained system in the weightless environment of space are established by Lagrange's principle. Influences on vibration isolation performance of the XSSIP system incurred by different structural parameters are systematically studied under either periodic or impulsive excitations. In addition, ADAMS simulation is conducted to verify the accuracy and feasibility of the theoretical model. Compared with the traditional spring-mass-damper (SMD)-based Stewart isolation platform system, the XSSIP system possesses an obvious advantage and offers a highly efficient passive way for suppressing post-capture vibrations of the floating spacecraft.
  • Experimental study of parallel injections with different distances into a
           supersonic crossflow
    • Abstract: Publication date: March 2020Source: Acta Astronautica, Volume 168Author(s): Chang-hai Liang, Ming-bo Sun, Qian-cheng Wang, Yuan Liu, Yi-xin Yang, Yong-chao Sun, Guang-xin LiAbstractThe flow physics aspects of parallel sonic transverse gaseous injections in a Ma = 2.95 supersonic crossflow are experimentally investigated in this study. NPLS (Nanoparticle-based Planar Laser Scattering) and oil flow techniques are employed for qualitative comparison. Under the supersonic crossflow with jet-to-crossflow momentum flux ratio (J) of 7.7, the NPLS images reveal the shock structures, K–H vortex and slip lines on different spanwise planes of each of the experimental conditions, and the oil flow experiments illustrate the bow shocks, separation zones and other interactions in the near-wall region. Furthermore, the fractal dimensions of the jets mainstream region are given to analyze the turbulent intensity. The interaction mechanism of the flow field is completely different with the distances of the orifices growing. As the orifices are close together, the flow structures of three orifices, including bow shocks, separation zone, horseshoe vortex and jet mainstreams, almost merge into one. With the distances between jets growth, the bow shocks would merge into a normal shock and the separation zones interact with each other. When the distances between jets are large enough, the jet mainstreams are independent, while the bow shocks interact with each other forming a complex shock system. The interactions between jets promote the development of turbulence in general, while the interactions between too close jets would restrict the development of turbulence. In addition, the horseshoe vortex and the shedding vortex are analyzed.
  • Numerical Investigation of Upstream Cavity Enhanced Fuel Mixing in
           Scramjet Combustors
    • Abstract: Publication date: Available online 2 January 2020Source: Acta AstronauticaAuthor(s): Tim Roos, Adrian Pudsey, Mathew Bricalli, Hideaki OgawaAbstractCavities are commonly used to provide flame-holding in scramjets. While the injector is generally placed inside or upstream of the cavity, placement of the cavity behind the injector limits the influence of the cavity on the jet interaction and limits cavity-induced mixing enhancement. The current study investigates a geometry in which the cavity is placed directly upstream of the injector and examines its effect on scramjet combustor mixing performance. Specifically, enhancement in jet mixing and penetration is considered using chemically frozen hydrogen fuel. The influence of three different thermal boundary conditions (isothermal 300 K, isothermal 1800 K and adiabatic) on the flowfield and mixing was also examined. The upstream cavities are found to improve mixing efficiency and jet penetration relative to a baseline flat plate configuration for most configurations, while they do incur a total pressure loss up to 2% higher than in the baseline. The magnitude of these effects is found to depend on the cavity geometry and wall thermal model. The primary mechanism behind the performance improvement is the shielding of the barrel shock by the cavity recirculation, which introduces extra vorticity into the flowfield and reduces the strength of the bow shock. Increased shielding provided by the cavity is found to enhance mixing by up to 9%. An optimum cavity aspect ratio is observed to exist at a cavity length-to-depth ratio of L/D=15, for which performance is maximum compared to the baseline for all wall treatments. Wall heat flux increases in configurations with cavities, particularly on the aft wall of the cavity, while fuel drawn into the cavity is seen to contribute to wall cooling in case of high wall temperatures. This can reduce wall cooling requirements and simplify combustor design. In general the enhanced mixing and jet penetration induced by the cavity could allow for shorter combustor designs, which in turn allows for more compact flight vehicle design.
  • Diffraction of cellular detonation wave over a cylindrical convex wall
    • Abstract: Publication date: Available online 31 December 2019Source: Acta AstronauticaAuthor(s): Xueqiang Yuan, Jin Zhou, Shijie Liu, Zhiyong LinAbstractNumerical simulations were performed to study diffraction of a cellular detonation wave over a 90∘ cylindrical convex wall. The dynamics of this diffraction phenomenon was described by the two-dimensional reactive Euler equations with a detailed hydrogen/oxygen chemistry model and solved numerically by using the adaptive mesh refinement code AMROC. The present numerical observations indicate that the continuous variation trend of area divergence ratio caused by the curved convex wall can make detonation transverse wave reflect on the wall and sustain the coupling of the diffracted detonation wave for a certain distance. The reflection of the transverse waves can also enhance the energy to promote the re-intiation of the diffracted detonation. As the wall curvature radius increases to a certain value, the detonation wave can even propagate stably without decoupling in the expansion area. The critical wall curvature radius for re-initiation is found to have negative correlation with the contained detonation cell number in the exit, while the critical radius for stable propagation is mainly determined by the initial pressure. The critical re-initiation criterion for the detonation diffraction is further explored by introducing two different re-initiation mechanisms and considering the width of an “equivalent exit” calculated by the Chester-Chisnell-Whitham theory to satisfy the re-initiation condition. Meanwhile the critical criterion of stable propagation is described quantitatively by applying the Dn−κ theory to confirm the relation between the propagation velocity and the curvature of the diffracted detonation wave front, and calculating the minimum curvature radius of the curved detonation wave front theoretically. The accuracy of the criterions are verified by compared with the numerical results.
  • Analysis of a Three-extensible-rod Tracker Based on 3-RPS Parallel
           Manipulator for Space Large Deployable Paraboloid Structure with Power and
           Communication Integration
    • Abstract: Publication date: Available online 28 December 2019Source: Acta AstronauticaAuthor(s): Tao Zheng, Fei Zheng, Xi Rui, Lide Yan, Kui Niu, Fengbin ZhangAbstractThe combination of a solar array and a communication antenna can reduce the entire mass, physical size, and cost in space applications. Currently, related studies mainly focus on the combination of the two structures on one flat plate structure (FPS). Compared with the FPS, a paraboloid structure has lower surface density and higher conversion efficiency. Therefore, the novel design of a space large deployable paraboloid structure with power and communication integration (SSPCI) is proposed for spacecraft on a sun synchronous earth orbit. A novel three-extensible-rod (TER) tracker is studied in detail for the SSPCI to track the sun for power in the sunshine region or turn to face the ground station for communication in the earth’s shadow region. The proposed TER tracker includes three extensible rods, where one end of each rod is connected to the base platform by a rotary joint, and the other end is connected to the mobile platform by a smart compound joint as a substitute for a spherical joint; this is known in the literature as a 3-RPS parallel mechanism. In contrast to existing serial mechanisms, it provides a simple and lightweight structure, high structural stiffness, low inertia, and more accurate positioning and pointing of the mobile platform. Meanwhile, the linear extensible rods used in the TER tracker help to reduce energy consumption, and do not require the use of large and heavy speed reducers. A kinematic model of the TER tracker is also established. Based on this kinematic model, a dynamic model is then derived by using Newton−Euler formulation. The motion trajectory of the TER tracker is planned for the SSPCI to track the sun or turn to face the ground station. By setting related parameters, the workspace and pointing accuracy of the TER tracker are analyzed and found to be satisfactory for the SSPCI, and the motion process of tracking the sun or turning to face the ground station is simulated to test the theoretical analysis. The driving force and consumed energy of the TER tracker are obtained; the results shows that the TER tracker is able to drive the SSPCI to track the sun or turn to face the ground station with the aforementioned advantages and small energy consumption. By using finite element analysis, the SSPCI supported by the TER tracker is found to have satisfactory structural performance at different orientations in a zero gravity state. Meanwhile, the TER tracker has a satisfactory operation life and can adapt well to the space thermal environment. Finally, preliminary sun tracking experiments on the TER tracker are performed on the ground successfully, indirectly proving its feasibility of the TER tracker from the mechanism principle and control mode in space applications.
  • Magnetic control without attitude determination for spinning spacecraft
    • Abstract: Publication date: Available online 26 December 2019Source: Acta AstronauticaAuthor(s): Javier Cubas, Anton de RuiterAbstractIn this article, a magnetic control without attitude determination for spinning spacecraft is presented. The control only uses magnetorquers as actuators and sun-sensors and magnetometers as sensors. An equilibrium angular velocity is reached by using two magnetic moments at the same time; the first one is a B-dot control that produces a despinning torque based in magnetic measurements; the second one produces a spinning torque using an inertial reference, such as the sun’s direction as viewed from the spacecraft. The final orientation of the spin is normal to the orbit, parallel to sun direction or an intermediate angle between them. This orientation is controlled by setting different dissipation gains or using gravitational gradient. Control performance has been analyzed mathematically and demonstrated with Monte Carlo tests for Sun-synchronous orbits. A methodology to estimate adequate control gains is also presented.
  • Advection diffusion model for gas transport within a packed bed of JSC-1A
           regolith simulant
    • Abstract: Publication date: Available online 26 December 2019Source: Acta AstronauticaAuthor(s): Garrett L. Schieber, Brant Jones, Thomas M. Orlando, Peter G. LoutzenhiserAbstractThe advection diffusion model was evaluated for gas transport within a packed bed of lunar JSC-1A regolith simulant at low to medium total pressures over three flow regimes: (1) the slip flow regime (2) the transition regime and (3) the Knudsen regime. These regimes are pertinent to the design of H2O extraction devices for in-situ resource utilization, sampling missions, and surface science. Experimentation was conducted over a range of average pressures of 100 to 25,000 Pa, corresponding to Knudsen numbers between 0.01 and 100 at ambient temperature with Ar and N2. Non-condensing, gases with ideal behavior were evaluated to isolate key flow properties as first step towards evaluating more complex H2O flows. Experimental results were coupled to physical models, and key properties were evaluated to assess the model fit. The experimental results in the transition regime followed the expected behavior based on similar works for microchannel flow and showed that advection is not negligible for transition regime flows. The advection diffusion model in the transition regime fit the results for Knudsen numbers less than unity, and showed the need to further develop gas slip models for Knudsen numbers greater than unity. Key parameters necessary to define were the porosity, tortuosity, wall diameter of the regolith medium, and the gas slip parameter was key in determining the gas-specific transport rate.
  • Experimental study on thermal ignition and combustion of droplet of
           ammonium dinitramide based liquid propellant in different oxidizing gas
    • Abstract: Publication date: Available online 25 December 2019Source: Acta AstronauticaAuthor(s): Hong-Meng Li, Guo-Xiu Li, Lei Li, Zhao-Pu YaoAbstractAn experimental study was conducted to investigate the thermal ignition and combustion characteristics of liquid droplet of ammonium dinitramide based liquid propellant in different oxidizing gas atmospheres under different on-load voltages. The oxidizing gases included air, O2, N2O and NO. The ignition and combustion processes were recorded synchronously by two high speed cameras to catch the directly recorded images and schlieren images respectively. In order to explore the ignition and combustion process quantitatively, the ignition delay time, burning duration and the development of the droplets were analyzed.
  • Structural shock verification by numerical analysis of the EPD payload
           units on board Solar Orbiter spacecraft
    • Abstract: Publication date: Available online 24 December 2019Source: Acta AstronauticaAuthor(s): Andrés García-Pérez, Ali Ravanbakhsh, Félix Sorribes-Palmer, Gustavo AlonsoAbstractElectronic components can be seriously damaged during the launch of spacecraft due to the intense shock loads, which are generated by the launch operations such as the separations of the launcher stages and the release of the spacecraft. A shock verification program should be carried out in the development phase of space instruments to guarantee that the parts most susceptible to shock damage, including electronic components, can withstand the severe shock environment. A new shock verification methodology is described in this paper, where the novelty is the utilization of the numerical simulations to verify the capability of space instruments to withstand the specified shock loads. The proposed procedure has been applied to the units of the Energetic Particle Detector (EPD) payload of the Solar Orbiter mission. The selected approach is not the usual method in the space systems for shock verification, where the preferred method is by testing. Therefore, this work represents one of the few documented cases where numerical simulations have achieved the demonstration of the shock capability of space structures without the need to perform a complete shock test campaign. The application of the numerical analyses for the shock verification of one of the EPD units is explained in detail, where the calculated responses such as maximum expected stresses, accelerations and relative displacements are compared to the allowable limits to demonstrate that this instrument and its sensitive electronic components can adequately support the intense shock loads during the launch phase.
  • Integrated Power and Vibration Control of Gyroelastic Body with
           Variable-Speed Control Moment Gyros
    • Abstract: Publication date: Available online 23 December 2019Source: Acta AstronauticaAuthor(s): Chuandong Guo, Quan Hu, Yao Zhang, Jun ZhangAbstractThe gyroelastic body refers to a flexible structure with distributed angular momentum exchange devices (AMEDs), such as the momentum wheels (MWs) or the control moment gyros (CMGs). The amplitude or the direction of the angular momentum of the rotors in the AMEDs can be changed to produce torques for vibration suppression of the flexible structure. In order to take full advantage of the AMEDs on the flexible structure, the AMEDs are also used for energy storage in this study, thus, an integrated power and vibration control system (IPVCS) is obtained. In this paper, the single-gimbal variable speeds control momentum gyros (VSCMGs) are chosen as the distributed AMEDs mounting on a constrained flexible structure. It can work in a “CMG & MW” mode and a “VSCMG” mode for simultaneous vibration suppression and energy storage. First, the dynamics of a constrained gyroelastic body is established, whereas the power equation of the rotors is deduced. Second, the feedback control laws are designed when the VSCMGs work in the CMG & MW mode and the VSCMG mode, respectively. Finally, numerical examples are presented for a flexible truss with distributed VSCMGs to verify the effectiveness of the proposed feedback control strategies.
  • Adaptive Sliding Mode Control for Deployment of Electro-dynamic Tether via
           Limited Tension and Current
    • Abstract: Publication date: Available online 23 December 2019Source: Acta AstronauticaAuthor(s): Shumin Chen, Aijun Li, Changqing Wang, Chenguang LiuAbstractThis paper studies the deployment control of the electrodynamic tether system by means of tether tension and electric current regulation. Design of the control strategy has been implemented based on the simplified dumbbell model. In order to improve the robustness of the control system to the possible external disturbances, an adaptive sliding mode control is proposed to deploy the tether to the local vertical with the consideration of input limitations, which are introduced by a pair of saturation functions to ensure that the tether tension is always non-negative and the current is within limits. In addition, the proposed adaptive law is intended to estimate the mass parameter of the model, which is with uncertainty caused by the difficulty in accurately determining the masses of the end-bodies. The stability characteristic of the system under the proposed hybrid controller is studied based on the Lyapunov theory. Numerical case studies in the different orbital inclinations are conducted to illustrate the effectiveness of the proposed control strategy. Moreover, the performance of the controller is presented in the presence of the initial perturbations, the external disturbances and the uncertainty of mass parameter of the system.
  • Uncertainty and sensitivity analysis of inflow parameters for HyShot II
           scramjet numerical simulaiton
    • Abstract: Publication date: Available online 18 December 2019Source: Acta AstronauticaAuthor(s): Yongkang Zheng, Chao Yan, Yatian ZhaoAbstractThe flowfield inside a combustor of scramjet such as Hyshot II system is highly complicated and many factors have effect on its numerical prediction. Uncertainty and sensitivity analysis of aerodynamics prediction on Hyshot II intake configuration is performed in this work. The inflow conditions of intake configuration are of vital crucial since they directly determine the inflow conditions of combustor configuration, which in turn have a remarkable influence on the combustion and mixing process. Meanwhile, the varied flight conditions may also introduce great and direct impact on the performance in actual flight tests. It is significant to evaluate the uncertainties and sensitivities and to identify the critical factors of inflow conditions for the intake configuration. Five input parameters are selected as the epistemic uncertain variables. The flowfield prediction is conducted via using Reynolds-averaged Navier-Stokes simulations as the numerical study approach with standard Menter’s shear stress transport turbulence model and species transport process for Hyshot II configuration. Stochastic expansions based on point collocation non-intrusive polynomial chaos, which require 42 deterministic simulations in this study, are employed to propagate and estimate the uncertainties. Meanwhile, Sobol indices are adopted to rank and indicate the individual contribution and to identify the critical inflow parameters. The results demonstrate that freestream Mach number and temperature are the dominated contributing parameters among the performance parameters. In addition, as observed from the wall-normal profile of related variables extracted at 355 millimetre in x coordinate direction in the simulation results, the freestream pressure plays a dominant role in determining the pressure distribution and the freestream temperature is the most prominent contributor to the distribution of temperature and velocity.
  • Direct Multiple Shooting Transcription with Polynomial Algebra for Optimal
           Control Problems Under Uncertainty
    • Abstract: Publication date: Available online 16 December 2019Source: Acta AstronauticaAuthor(s): Cristian Greco, Marilena Di Carlo, Massimiliano Vasile, Richard EpenoyAbstractThis paper proposes a novel approach to the solution of optimal control problems under uncertainty (OCPUUs). OCPUUs are first cast in a general formulation that allows the treatment of uncertainties of different nature, and then solved with a new direct transcription method that combines multiple shooting with generalised polynomial algebra to model and propagate extended sets. The continuity conditions on extended sets at the boundary of two adjacent segments are directly satisfied by a bounding approach. The Intrusive Polynomial Algebra aNd Multiple shooting Approach (IPANeMA) developed in this work can handle optimal control problems under a wide range of uncertainty models, including nonparametric, epistemic, and imprecise probability ones. In this paper, the approach is applied to the design of a robust low-thrust trajectory to a Near-Earth Object with uncertain initial conditions. It is shown that the new method provides more robust and reliable trajectories than the solution of an analogous deterministic optimal control problem.
  • Mission Architecture Analysis for Manned NEA Exploration Using MAM Method
    • Abstract: Publication date: Available online 14 December 2019Source: Acta AstronauticaAuthor(s): Yuxian Yue, Xiaohui Wang, Haoran Gu, Liheng MaoAbstractNear Earth Asteroids (NEAs) have become a hot topic these years for their scientific interests and technological accessibility. Manned NEA mission is a good choice for asteroid on-site exploration as well as a stepping stone for future manned deep space missions. Focusing on manned NEAs mission architecture analyzing, this paper uses the mission architecture matrix (MAM) method to reduce mission mass scale, for available studies show that simple mission architectures achieving NEAs all require LEO launching mass exceeding available space carrying capacity. By developing a series of mission architectures based on manned spacecraft system design method, the mass scale is estimated according to mission data of 63 most accessible NEA targets. It is discovered that with advanced mission architectures, maximum LEO launching mass can be significantly reduced by separate launching, rendezvous, and docking. The original on-orbit mass about 300-400 metric tons (mT) is reduced to 200-250 mTs, and the maximum launching mass is reduced to only about 70-100 mTs in several cases. This provides us a high possibility to launch manned NEA missions in the near future. In addition, this method can be used in mission mass scale analysis to other deep space targets. Advanced mission architecture also brings challenges on reliability, which plays another key role in mission design. The balance between mass scale and reliability needs to be kept in future works.
  • Calibration of Atmospheric Density Model based on Gaussian Processes
    • Abstract: Publication date: Available online 13 December 2019Source: Acta AstronauticaAuthor(s): Tianyu Gao, Hao Peng, Xiaoli BaiAbstractNeutral mass density is presently the predominant uncertain term among all the factors affecting the atmospheric drag, which is the dominant perturbation force for space objects at low altitude. The current best density estimation performance is often achieved by empirical models that can be limited by their assumed, parametric formulations of regression. This paper presents a density estimation framework that integrates information from empirical models, environment conditions, and satellite measurement data. Different from existing frameworks, the new integration mechanism is based on Gaussian Processes (GPs) which are nonlinear, non-parametric regression methods. The method can estimate both current and future densities. Furthermore, it will provide uncertainty quantifications in its estimates through GPs’ underlying Bayesian inference. Simulations are designed to test the hypothesis that the new framework is valuable to improve the nowcast performance of the empirical models, and to predict future density. Empirical models including NRLMSISE-00 and JB2008 and accelerometer-inferred densities from satellite CHAMP are used for the study. The new method is shown to achieve better Pearson correlation coefficient (R), root mean squared error (RMSE), and mean ratio from the empirical models when the density estimation is tested on both the missing data and future densities, which are, respectively, within and following the GP’s training period. Together with providing quality uncertainty estimations, the proposed framework has the great potential to reduce the estimation errors from the empirical model and provide an effective means to estimate density for a satellite.
  • Tether attachment point stabilization of noncooperative debris captured by
           a tethered space system
    • Abstract: Publication date: Available online 12 December 2019Source: Acta AstronauticaAuthor(s): Xin Sun, Rui ZhongAbstractBefore an active debris removal process is carried out, the attitude stabilization of the debris needs to be executed to ensure security. Fortunately, for the tethered system, a full despun is not always necessary; a stabilization of the motion of the tether attachment point is usually sufficient. This paper discusses the way to stabilize the motion of the tether attachment point of a captured noncooperative space debris without any auxiliary mechanisms. The debris possesses unknown inertia information and states after capture, while the tether tension is the only input to manipulate its attitude. The direction and value of the tension is regulated based on the continuous dissipation of the rotational energy of the debris. Moreover, the range of the tether direction is restricted to a small conical region, in order to reduce the tether libration motion and the orbit maneuver of the main satellite. The motion of the tether attachment point is desired to be observed instead of measuring the attitude motion of the debris in the feedback loop, which might be easier to attain in practical applications. Numerical simulations are carried out to validate the effectiveness of the control method and to check the performance of the controller with different parameters.]
  • Electric sail phasing maneuvers for constellation deployment
    • Abstract: Publication date: Available online 6 December 2019Source: Acta AstronauticaAuthor(s): Lorenzo Niccolai, Andrea Caruso, Alessandro A. Quarta, Giovanni MengaliAbstractThe aim of this work is to investigate heliocentric phasing maneuvers performed by a spacecraft propelled by an Electric Solar Wind Sail, that is, an innovative propellantless propulsion system that consists of a spinning grid of charged tethers that uses solar wind momentum to produce thrust. It is assumed that the Electric Solar Wind Sail may be controlled by varying its attitude with respect to a classical orbital reference frame, and by switching the tether grid off to obtain Keplerian arcs along its phasing trajectory. The analysis is conducted within an optimal framework, the aim of which is to find both the optimal control law and the minimum-time phasing trajectory for a given angular drift along the (assigned) working orbit. A typical phasing scenario is analyzed, by considering either a drift ahead or a drift behind maneuver on a circular, heliocentric orbit of given radius. The paper also investigates the possibility of using an Electric Solar Wind Sail-based deployer to place a constellation of satellites on the same working orbit. In that case, the optimal flight time is obtained in a compact, semianalytical form as a function of both the propulsion system performance and the number of the sail-deployed satellites.
  • Electric power module for a bare electrodynamic tether
    • Abstract: Publication date: Available online 5 December 2019Source: Acta AstronauticaAuthor(s): José A. Carrasco, Francisco García de Quirós, Higinio Alavés, Moisés NavalónAbstractElectrodynamic tethers are proposed as propulsion and energy harvesters for space probes orbiting planets with a magnetic field and ionosphere, however there are no descriptions in the technical literature of the design of an electrical power system for such an application at subsystem and circuit detail. This paper presents a proposal for such a power system that extracts energy from the kinetic energy of a spacecraft using a bare electrodynamic tether, i.e. an unsheathed conductive wire or band, in low-Earth orbit. The application of the system is the powering of the spacecraft while in its final de-orbiting maneuvers at end-of-life with no reliance on the main spacecraft bus.
  • Coulomb drag propulsion experiments of ESTCube-2 and FORESAIL-1
    • Abstract: Publication date: Available online 29 November 2019Source: Acta AstronauticaAuthor(s): Iaroslav Iakubivskyi, Pekka Janhunen, Jaan Praks, Viljo Allik, Kadri Bussov, Bruce Clayhills, Janis Dalbins, Tõnis Eenmäe, Hendrik Ehrpais, Jouni Envall, Sean Haslam, Erik Ilbis, Nemanja Jovanovic, Emilia Kilpua, Joosep Kivastik, Jürgen Laks, Philipp Laufer, Maido Merisalu, Matias Meskanen, Robert MärkAbstractThis paper presents two technology experiments – the plasma brake for deorbiting and the electric solar wind sail for interplanetary propulsion – on board the ESTCube-2 and FORESAIL-1 satellites. Since both technologies employ the Coulomb interaction between a charged tether and a plasma flow, they are commonly referred to as Coulomb drag propulsion. The plasma brake operates in the ionosphere, where a negatively charged tether deorbits a satellite. The electric sail operates in the solar wind, where a positively charged tether propels a spacecraft, while an electron emitter removes trapped electrons. Both satellites will be launched in low Earth orbit carrying nearly identical Coulomb drag propulsion experiments, with the main difference being that ESTCube-2 has an electron emitter and it can operate in the positive mode. While solar-wind sailing is not possible in low Earth orbit, ESTCube-2 will space-qualify the components necessary for future electric sail experiments in its authentic environment. The plasma brake can be used on a range of satellite mass classes and orbits. On nanosatellites, the plasma brake is an enabler of deorbiting – a 300-m-long tether fits within half a cubesat unit, and, when charged with -1 kV, can deorbit a 4.5-kg satellite from between a 700- and 500-km altitude in approximately 9–13 months. This paper provides the design and detailed analysis of low-Earth-orbit experiments, as well as the overall mission design of ESTCube-2 and FORESAIL-1.
  • Mission analysis and optimal control for cislunar mission with spinning
           tether system in hyperbolic orbits
    • Abstract: Publication date: Available online 28 November 2019Source: Acta AstronauticaAuthor(s): C. Wang, T. Huan, A. Li, H. LuAbstractThis paper presents a concept of using spinning tether system for interstellar mission, and designs the optimal trajectory and the controller required for the interstellar mission. The interstellar mission carried out by a two-body spinning tether system relies on the momentum-exchange techniques, which equipped with ion thrusters can greatly economize the propellant. In order to ensure that the system can achieve a state of being able to complete the mission under the given optimal conditions, an optimal trajectory is designed by using hp-adaptive pseudospectral method. Then, an adaptive robust sliding mode controller is given based on radial basis function neural network to make the system with uncertainty reach the optimal trajectory. Finally, numerical simulations are presented to evaluate the effectiveness of the optimal trajectory and the controller.
  • Stability analysis and motion control of spinning electrodynamic tether
           system during transition into spin
    • Abstract: Publication date: Available online 27 November 2019Source: Acta AstronauticaAuthor(s): H. Lu, A. Li, C. Wang, Yu.M. ZabolotnovAbstractSpinning electrodynamic tether systems are considered one of the most promising potential applications of tethered satellite systems, which require little fuel and avoid the equilibrium limit of conventional vertical electrodynamic tether systems. Therefore, spinning electrodynamic tether systems have good prospects in debris removal, orbit reboost, payload transportation, and so on. It has been found that, if not carefully controlled, tethers easily become slack or sagging during the transition process from equilibrium state into spin. In this regard, this paper mainly focuses on the transition process of spinning electrodynamic tether systems from the initial equilibrium state into the final spinning state with expected angular velocities. Conditions of dynamic equilibrium position and minimum current for acceleration (critical current) are firstly derived in this paper, which provide references for future space tether experiments. The motion of spinning electrodynamic tether systems is described by the Lagrangian model, which takes orbital motion into consideration. By considering power limits of electrodynamic tether systems, this paper proposes two open-loop control methods for the safe transition into spinning state as nominal control algorithms with different mission objectives. The first method (direct transition) provides a near time-minimum solution, and the second method (swinging transition) provides a minimum current-energy solution for acceleration into spin. Considering perturbations in space, including inhomogeneous distribution of magnetic induction, varying mass distribution of the system and so on, an adaptive sliding mode controller is proposed to regulate the system and to track nominal trajectories of acceleration. The effectiveness of the proposed control methods is validated by numerical results.
  • Dynamics of a tethered satellite formation for space exploration modeled
           via ANCF
    • Abstract: Publication date: Available online 21 November 2019Source: Acta AstronauticaAuthor(s): C.Q. Luo, J.L. Sun, H. Wen, D.P. JinAbstractThis paper studies the dynamics of a spinning three-body tethered satellite formation by a flexible multibody dynamics method. The tethered system is specially designed to constitute a Space Infrared Interferometric Telescope for a space exploration mission. Two sub-satellites are deployed from the main-satellite by using long flexible tethers and moving along trajectories of Archimedes spirals. Both of the large displacement and large deformation of the variable-length tethers are described by utilizing the Absolute Nodal Coordinate Formulation method in a framework of Arbitrary Lagrange-Euler (ANCF-ALE) description. The Natural Coordinate Formulation (NCF) method is used for describing the overall rigid motions of the three satellites. Considering the mass flow of tether element, the dynamic equations of tether element are derived by using the D'Alembert's principle. The governing dynamic equations of the system are obtained with a method of Lagrange multipliers. The tether deployment is achieved by regulating deployed velocity and applied jet forces. Numerical case studies are presented for investigating the parametric influences on the deployment dynamics of the tethered system by comparisons.
  • A Model for Macro-performances Applied to Low Power Coaxial Pulsed Plasma
    • Abstract: Publication date: Available online 16 November 2019Source: Acta AstronauticaAuthor(s): Hang Li, Zhiwen Wu, Guorui Sun, Kangwu Zhu, Tiankun Huang, Xiangyang Liu, William Yeong Liang Ling, Ningfei WangAbstractPulsed plasma thrusters (PPT), as an important developing direction of micro-satellite propulsion system, are attracting more and more attention. Low power coaxial PPT has great advantages in miniaturization because of its coaxial structure, which is beneficial for micro-satellite applications. Since there are few macro-performances estimation model in low power coaxial PPT, this paper establishes a model based on one-dimensional electromechanical PPT model and gas dynamic pressure forces model to describe macro-performances of low power coaxial PPT. In this model, the electromechanical model describes the plasma electromagnetic acceleration process, current and voltage changes of the main circuit during the discharge process, and the gas dynamic pressure forces model describes the expansion and acceleration of the neutral gas group in the discharge channel. To verify the model, we compared the voltage and current obtained from model simulation with the experimental results, and compared the impulse bit measured in the experiment with the impulse bit calculated by the model. The results show that the model established in this paper can well simulate the variation of voltage and current during the working process of low power coaxial PPT, and can preliminarily estimate the macro performances of the thruster.
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