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Acta Astronautica
Journal Prestige (SJR): 0.758
Citation Impact (citeScore): 2
Number of Followers: 441  
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0094-5765
Published by Elsevier Homepage  [3182 journals]
  • Design and optimisation of a space net capture system based on a
           multi-objective evolutionary algorithm
    • Abstract: Publication date: Available online 9 November 2019Source: Acta AstronauticaAuthor(s): Qingquan Chen, Qingbin Zhang, Qingyu Gao, Zhiwei Feng, Qiangang Tang, Guobin Zhang Space net capture is an innovative concept for active debris removal that provides a prospective method for the removal of large, non-cooperative space targets. The design of a space net capture system must meet two basic requirements: maximizing the capture ability and minimizing the system cost. This paper presents an inexpensive multi-objective optimization framework to solve this design problem. In this framework, a design optimization approach using a lumped parameter modelling method as well as an improved inexpensive multi-objective optimization algorithm is proposed. The system mass and effective distance are chosen as objectives of this optimization problem. The simulation results reveal that the multi-objective optimization framework is feasible and effective for the design of a space net capture system, and the designer preferred solutions that enhance system design are reliably identified.
  • Multi-objective Configuration Optimization for Coordinated Capture of
           Dual-arm Space Robot
    • Abstract: Publication date: Available online 9 November 2019Source: Acta AstronauticaAuthor(s): Lei Yan, Wenfu Xu, Zhonghua Hu, Bin Liang Dual-arm space robot is a promising autonomous system to remove the increasing space debris actively. Due to its limited on-orbit energy, dual-arm space robot should approach and capture the target with minimum time and base disturbance. In this paper, the multi-objective configuration optimization is proposed for maximizing manipulability and minimizing base disturbance of dual-arm space robot during the pre-contact phase. Based on virtual base modelling and coordinated planning, the free-floating dual-arm space robots can be controlled to track and approach the target satellite. In addition, in the null-space of tracking motion, the configuration optimization of dual-arm space robot can be realized by arm-angle adjustment of 7 DOF redundant manipulator. Therefore, the expressions of arm angle and arm-angle Jacobian are first derived. Then the arm-angle trajectory is parameterized by adopting 5th order polynomial interpolation. The optimal arm-angle trajectory can be obtained by Multiple Objective Particle Swarm Optimization (MOPSO), in which the objective function of configuration optimization is set to the vector consisted of base disturbance and manipulability. Therefore, in the null space of dual-arm space robot approaching the tumbling target satellite, the configuration optimization is realized through following the optimal arm-angle trajectory. Finally, several single-objective and multi-objective optimization simulations are carried out to verify the proposed method.
  • A Feasibility Study of Using Pintle Injector as Sole-Throttling Device for
           Shallow Throttling Condition
    • Abstract: Publication date: Available online 9 November 2019Source: Acta AstronauticaAuthor(s): Hyuntak Kim, Hongjae Kang, Sejin Kwon Feasibility of using the pintle injector as a sole-throttling device was tested with a focus on the acquisition of sufficient injector orifice areas for uniform liquid injection considering the maximum throttling ratio of 4 to 1. Cold flow tests using 95 wt% hydrogen peroxide were performed with a relatively long and a short variable-area continuous-radial orifice of an average surface roughness condition of 1.6 μm to explore hydraulic and liquid injection characteristics of the sole-throttling concept device. The required orifice gap size in the long orifice case was always larger than that in the short orifice case based on the same throttling ratio owing to lowered discharge coefficients. The transition from the uniform annular sheet injection to injection of jets with the sheet was observed as the decreased orifice gap size reached approximately 0.2 mm in both cases. The liquid injection in the short orifice case was more uniform compared to the long orifice case in the jet-sheet injection region. The feasibility of attaining the uniform annular sheet injection for the shallow throttling level was discussed from the test results.
  • Novel design methodology of integrated waverider with drip-like intake
           based on planform leading-edge definition method
    • Abstract: Publication date: Available online 9 November 2019Source: Acta AstronauticaAuthor(s): Shao-Hua Chen, Jun Liu, Feng Ding, Wei Huang Based on the planform leading-edge definition method, a novel methodology for designing an inlet-airframe integrated waverider vehicle, has been proposed and the resulting intake owns the superiority of the drip-like shape. In this study, the design of the vehicle contour relies on the axisymmetric basic flowfield and leading-edge planform curves, namely the former is presently generated by a shock wave curve, and the latter produces a drip-like intake, on account of the 3D cowl lip curve. Importantly, defining the leading edge on the horizontal projection plane facilitates to adjust the planform shape of the integrated waverider and the sweep angle of the wing. At last, the new design methodology is proved to be effective to design an integrated hypersonic waverider vehicle. This study provides more options for designing novel inlet-airframe integrated hypersonic vehicles.
  • Study of reducing the congregating effect of honeycomb structure on debris
    • Abstract: Publication date: Available online 9 November 2019Source: Acta AstronauticaAuthor(s): Ke Fa-wei, Jie Huang, Wen Xue-zhong, Zou Sheng-yu, Ma Zhao-xia, Liu Sen Aluminum honeycomb has been used widely on the spacecraft, as it has high strength mass ratio and good designability. In order to reduce the channel effect of honeycomb core, the multiple “Y” structures are proposed as the stuffing of the sandwich structure and the bracing structure of fabric layer respectively, and the compression tests are finished. The congregating effect of the “Y” structures on the debris cloud is validated by the hypervelocity impact test. The projectile diameter is 5 mm, and the impact velocities range from 3.9 km/s to 4.3 km/s. According to the test results, the “Y” structures adhered on the plate have certain stability and could play the bracing role, and they can reduce even eliminate the congregating effect on the debris cloud, however, their yield strength is lower compared with the aluminum honeycomb structure of equivalent areal density, which could be solved by structure optimum. The study results provide the reference for the improving the honeycomb structure used on spacecraft shield.
  • Experimental investigation on transpiration cooling for porous ceramic
           with liquid water
    • Abstract: Publication date: Available online 9 November 2019Source: Acta AstronauticaAuthor(s): Bo Zhang, Haiming Huang, Xueling Lu, Jinlong Peng Experiments are conducted in the arc-heated wind tunnel to investigate the transpiration cooling performances for SiC porous ceramic (0.98 g/cm3) with liquid water. It is experimentally found a new phenomenon that the ice beard forms on the specimen in the high enthalpy environment (15000 kJ/kg). Besides, the shape and size of ice beard are related to the uniformity of pores distribution on the surface of porous ceramic. At mainstream with specific enthalpy 5500 kJ/kg, heat flux 1900 kW/m2 and pressure 7800 Pa, the surface temperature of SiC porous ceramic with a coolant liquid water rate of 0.2 g/s just climbs to 360 K from 271 K, while its surface temperature without coolant permeating from the ceramic sharply increases to 1025 K. Therefore, transpiration cooling of SiC porous ceramic with liquid water is found to be effective. This work can provide a relatively useful reference for the design of active thermal protection system in hypersonic vehicles.
  • Transfers+from+near-rectilinear+halo+orbits+to+low-perilune+orbits+and+the+MOON’S+surface&rft.title=Acta+Astronautica&rft.issn=0094-5765&">Transfers from near-rectilinear halo orbits to low-perilune orbits and the
           MOON’S surface
    • Abstract: Publication date: Available online 9 November 2019Source: Acta AstronauticaAuthor(s): Sergey Trofimov, Maksim Shirobokov, Anastasia Tselousova, Mikhail Ovchinnikov Near-rectilinear halo orbits (NRHOs) are periodic orbits that belong to the families of halo orbits around the L1/L2 points in a three-body system and have low minimum distances to the smaller primary. NRHOs possess some good dynamical and geometrical properties and are now considered as potential orbits for a near-future crewed deep space station. Recently, intensive investigations have been performed with regard to different aspects of a lunar NRHO mission: Earth-NRHO transfers, station keeping, shadow avoidance, and ground station visibility conditions are deeply studied. At the same time, the important operation of soft lunar landing from the working NRHO is still poorly covered in literature. In this research, we analyze both the direct landing scenario and the option of a transfer from the working NRHO to the intermediate low-perilune orbit (LPO). This kind of orbit can serve as a platform for transport communication between the lunar surface and the working NRHO. Lunar regions attainable after a one-impulse NRHO departure maneuver are identified, and the costs required for the soft landing are analytically estimated based on the classical gravity-turn landing strategy. In the scenario of a two-impulse transfer to the intermediate LPO, a wide range of perilune distances and inclinations is proved to be available. Several resonant NRHOs have been considered as a working orbit: the 4:1 and 9:2 L2 orbits, and the 11:3 L1 orbit. The calculations are performed in a high-fidelity model of motion that includes the JPL’s DE430 ephemeris model of the Solar system and solar radiation pressure. The lunar gravitational field is evaluated based on the GRGM1200A spherical harmonic model truncated to degree and order 8.
  • Fast Solution Continuation of Time-Optimal Asteroid Landing Trajectories
           Using Deep Neural Networks
    • Abstract: Publication date: Available online 9 November 2019Source: Acta AstronauticaAuthor(s): Lin Cheng, Hengnian Li, Zhaowei Wang, Fanghua Jiang To improve the autonomy and reliability of asteroid landing control, a fast solution continuation approach for time-optimal asteroid landing trajectories is presented in this study. The contributions of this study are threefold. First, a deep neural network (DNN) is developed to approximate the gravitational field of asteroids, and the corresponding time consumption of gravity calculation in trajectory propagation is significantly reduced. Second, the original 3-dimensional (3D) landing control problem is connected to a simplified 2D one according to the continuation relationship between these model dynamics. Third, the 2D control problem is further transformed into a multi-variable root-finding problem with analytical shooting equations with the help of a Gauss-Legendre integral method and could be quickly solved by shooting methods. Taking the solution of this root-finding problem as an initial guess, the accurate solution of the original time-optimal landing problem can be quickly obtained through a backward solution continuation process. Finally, numerical simulations of landings on 443 Eros are given to verify the effectiveness of the proposed techniques and thus to illustrate the excellent performance on rapidity, convergence and solution accuracy of the developed algorithm for the generation of time-optimal landing trajectories.
  • Mining beyond Earth for sustainable development: Will humanity benefit
           from resource extraction in outer space'
    • Abstract: Publication date: Available online 9 November 2019Source: Acta AstronauticaAuthor(s): J.A. Dallas, S. Raval, J.P. Alvarez Gaitan, S. Saydam, A.G. Dempster The concept of sustainable development has been at the forefront of conversations around humankind’s shared future for several decades. With expansion into outer space likely to be a prominent feature of that future, it is important to consider how our actions in outer space may impact sustainable development. Definitions of sustainable development share the idea that we must work to preserve our environment, lift people from poverty, and reduce economic and social inequalities, all while looking to ensure inter-generational equality. With many resources becoming increasingly scarce on Earth, providing resources for future generations may mean looking to extraterrestrial bodies such as asteroids, the Moon and Mars to top up our dwindling supplies. There are numerous studies exploring the technical and economic considerations necessary to make resource extraction in outer space a reality; however it is important to also consider the social, socio-economic, and environmental impacts of such an undertaking. This paper discusses whether mining resources from celestial bodies is compatible with the international goal of achieving sustainable development. Mining in space has not yet begun in earnest, providing us with the unique opportunity to establish sustainable mining practices before any resource extraction takes place. As such, we make suggestions for a sustainable off-Earth mining framework, emphasising space mining practices that are environmentally, economically, and socially sustainable.
  • Spray characteristics of a pintle injector based on annular orifice area
    • Abstract: Publication date: Available online 9 November 2019Source: Acta AstronauticaAuthor(s): Suji Lee, Daehwan Kim, Jaye Koo, Youngbin Yoon As interest in low-cost reusable launch vehicles and extraterrestrial exploration has increased in recent years, soft-landing techniques have become important. A pintle injector can help realize this because it is capable of thrust control. However, research on this topic is very limited, and general optimization design procedures have not been completely established. In particular, no studies have examined orifice adjustment for annular flow, which is important in thrust control. In this study, a new design concept for a pintle injector is presented specifically to improve spray uniformity in a 400 N class engine; this maintains the concentricity of the pintle rod associated with the radial flow’s orifice size. The primary focus here was on spray tests that were conducted to obtain the control range of the orifice area for annular flow. Spray characteristics such as spray angle, spray uniformity, and droplet size were analyzed, from which empirical correlations were derived. Finally, the optimum control range for the annular flow’s orifice area was estimated from the perspective of atomization performance. This can be of reference to develop an enhanced thrust control system.
  • Collocated attitude and vibrations control for square solar sails with tip
    • Abstract: Publication date: January 2020Source: Acta Astronautica, Volume 166Author(s): Soroosh Hassanpour, Christopher J. Damaren This paper is devoted to developing collocated attitude and vibrations controllers for a square solar sail spacecraft containing four pre-tensioned triangular sails supported by flexible diagonal booms and four reflective control vanes at boom tips. Since the control torques for attitude control are created by the solar radiation pressure forces on the tip vanes, the attitude control problem is effectively non-collocated. The present work identifies collocated sensing for the tip vane forces which furnishes a passive input-output model. Various controllers are developed which furnish attitude and vibrations control. A finite-element-based linear structural model is used to evaluate the developed controllers and examine the controller-structure interactions.
  • Deep networks as approximators of optimal low-thrust and multi-impulse
           cost in multitarget missions
    • Abstract: Publication date: January 2020Source: Acta Astronautica, Volume 166Author(s): Haiyang Li, Shiyu Chen, Dario Izzo, Hexi Baoyin In the design of multitarget interplanetary missions, there are always many options available, making it often impractical to optimize in detail each transfer trajectory in a preliminary search phase. Fast and accurate estimation methods for optimal transfers are thus of great value. In this paper, deep feed-forward neural networks are employed to estimate optimal transfer costs to three types of optimization problems: the transfer time of time-optimal low-thrust transfers, the fuel consumption of fuel-optimal low-thrust transfers, and the total Δv of minimum-Δv J2-perturbed multi-impulse transfers. To generate the training data, both considered categories of low-thrust trajectories are optimized using the indirect method, and the J2-perturbed multi-impulse trajectories are optimized using J2 homotopy and particle swarm optimization. The hyper-parameters of deep networks are determined by grid search, random search, and the tree-structured Parzen estimators approach. Results show that deep networks are capable of estimating the final mass or time of optimal transfers with a mean relative error of less than 0.5% for low-thrust transfers and less than 4% for multi-impulse transfers. Our results are also compared with other off-the-shelf machine-learning algorithms and the generalization capabilities of the developed deep networks for predicting cases well outside the training data are investigated. Applications in multitarget mission design are also investigated.
  • Feasibility of quasi-frozen, near-polar and extremely low-altitude lunar
    • Abstract: Publication date: January 2020Source: Acta Astronautica, Volume 166Author(s): Sandeep Kumar Singh, Robyn Woollands, Ehsan Taheri, John Junkins Designing long-duration lunar orbiter missions is challenging due to the Moon's highly nonlinear gravity field and the third-body perturbations induced by the Earth, Sun and other large bodies. The absence of a Lunar atmosphere has offered the possibility for mission designers to search for extremely low-altitude, quasi-stable lunar orbits. In addition to the reduced amount of propellant required for station-keeping maneuvers, these orbits present great opportunities for unique scientific studies such as high resolution imaging and characterization of the polar ice deposits in deep craters. Prior to the GRAIL mission, mission planning for Lunar orbiters had suffered from inaccuracies, mainly due to the lack of an accurate Lunar gravity model, which resulted in severe deviations with respect to the spacecraft's nominal orbit.We study station-keeping feasibility for spacecraft in near-polar and extremely low-altitude, quasi-frozen orbits around the Moon, that are perturbed by a high-fidelity lunar gravity model and third-body effects from the Earth and Sun. For several candidate orbits, we compare the trade-space between mission duration and ΔV budget, considering impulsive maneuvers applied once every ‘N∈{2,6,10,14,18}’ orbits at periselene or aposelene. Additionally, we investigate the propulsive cost for different orbit insertion dates, the location of impulsive corrections for arresting argument of periselene (ω) drift, and controlling periselene altitude.
  • Quaternion-based adaptive attitude control of asteroid-orbiting spacecraft
           via immersion and invariance
    • Abstract: Publication date: Available online 6 November 2019Source: Acta AstronauticaAuthor(s): Keum W. Lee, Sahjendra N. Singh The design of an attitude control system for an asteroid-orbiting satellite via immersion and invariance is the subject of this paper. It is assumed that the asteroid is rotating with a constant rate, and that the inertia parameters of the satellite and the coefficients in the spherical harmonic gravitational potential of the asteroid are not known. The objective is to regulate the quaternion trajectory of the satellite orbiting in an equatorial orbit. Based on the immersion and invariance (I&I) theory, a noncertainty-equivalence adaptive (NCEA) attitude control law is derived. For the design, a backstepping design process involving two steps is used, and filtered signals are constructed to overcome the difficulty in solving certain matrix inequalities of the I&I methodology. The control law includes a stabilizer and an identifier - designed separately. Unlike the classical certainty-equivalence adaptive (CEA) systems, here the estimated parameters include not only the signals obtained from an integral type update law, but also judiciously chosen nonlinear algebraic signals that yield stronger stability properties. By the Lyapunov stability analysis, it is shown that the quaternion trajectories of the disturbance input-free closed-loop system asymptotically converge to the equilibrium point. The control law is effective in regulating the attitude to the equilibrium point with minimal rotation of spacecraft. Also, for the model with disturbance input, uniform ultimate boundedness of system trajectories is established. Simulation results for the attitude control of spacecraft in orbit around asteroid 433 Eros are presented for illustration. These results show that the spacecraft achieves nadir pointing attitude despite uncertainties in the system dynamics.
  • Micrometeoroid impact-induced damage of GLAss fiber REinforced aluminum
           fiber-metal laminates
    • Abstract: Publication date: Available online 5 November 2019Source: Acta AstronauticaAuthor(s): Md.Zahid Hasan Through several decades of development, engineers have made the GLAss fiber REinforced aluminum material mature for aviation structures, e.g., the fuselage of Airbus A380. A request like ‘GLARE + impact’ in a web search engine gives hundreds if not thousands of scientific articles address the high impact energy dissipation by GLAss fiber REinforced aluminum. GLAss fiber REinforced aluminum has a good prospect in the field of spacecraft protection against micrometeoroids and orbital debris. However, it is hard to comprehend a rational reason why a thorough search of the relevant literature yielded only a couple of articles concern with the ballistic impact of GLAss fiber REinforced aluminum. Handful of studies interrogated the GLAss fiber REinforced aluminum damage using analytical, numerical and experimental methods. No physical model, yet, has been proposed and validated to capture the GLAss fiber REinforced aluminum damage upon collision with micrometeoroids in the low Earth orbit environment. This study, therefore, introduces a new numerical model, based on the smoothed particle hydrodynamics and finite element methods, able to integrate the exorbitant strain rate of GLAss fiber REinforced aluminum constituents and approximate the cataclysmic amount of energy dissipates in the shockwave-induced collapse of GLAss fiber REinforced aluminum. The model assumed the S2-glass/FM94-epoxy composite to be orthotropic elastic prior to the onset of damage. Following the damage initiation, the energy-based orthotropic softening governed the damage accumulation of composite blocks. Using the model, an impact of a 2 mm 2024-T3 aluminum sphere on the GLAss fiber REinforced aluminum 5-6/5-0.4 target predicted pronounced petalling of the front face aluminum layer, spallation of the rear face aluminum layer, and buckling of the inner aluminum layers. By contrast, the composite blocks conserved the imparted energy through membrane stretching before being pierced. An experimental campaign, with the aid of a two-stage light-gas gun facility, was pursued to interrogate the model accuracy. It was found that the model predicted many of the experimental observations with a high degree of fidelity.
  • High-fidelity trajectory design to flyby near-Earth asteroids using
    • Abstract: Publication date: Available online 5 November 2019Source: Acta AstronauticaAuthor(s): P. Machuca, J.P. Sánchez, J.J. Masdemont, G. Gómez Fast development of CubeSat technology now enables the first interplanetary missions. The potential application of CubeSats to flyby near-Earth asteroids is explored in this paper in consideration of CubeSats’ limited propulsive capabilities and systems constraints. Low-energy asteroid flyby trajectories are designed assuming a CubeSat is initially parked around to the Sun-Earth Lagrange points. High-impulse and low-thrust trajectories with realistic thrusting models are computed first in the Circular Restricted Three-Body Problem (CR3BP), and then in a high-fidelity ephemeris model. Analysis in the ephemeris model is used to confirm that trajectories computed in the CR3BP model also exist in a more realistic dynamical model, and to verify the validity of the results obtained in CR3BP analysis. A catalogue of asteroid flyby opportunities between years 2019 and 2030 is provided, with 80 m/s of available ΔV and departure from halo orbits around the first and second Sun-Earth Lagrange points (of similar size to those typically used by scientific missions). Results show that the CR3BP model can serve as an effective tool to identify reachable asteroids and can provide an initial estimation of the ΔV cost in the ephemeris model (with ±15 m/s accuracy). An impulsive maneuver model can also provide an accurate estimation of the ΔV requirement for a CubeSat equipped with a high-impulse thruster (with 4 m/s accuracy), even if its thrust magnitude is small and requires duty cycling; low-thrust ΔV requirements, however, may differ significantly from the impulsive results (±15 m/s).
  • Development of a 6-kW-class Hall Thruster for Geostationary Missions
    • Abstract: Publication date: Available online 15 October 2019Source: Acta AstronauticaAuthor(s): Ikkoh Funaki, Shinatora Cho, Tadahiko Sano, Tsutomu Fukatsu, Yosuke Tashiro, Taizo Shiiki, Yoichiro Nakamura, Hiroki Watanabe, Kenichi Kubota, Yoshiki Matsunaga, Kenji Fuchigami To meet the growing demand for all-electric propulsion satellite, a 6-kW-class Hall thruster was newly fabricated and tested in laboratory. A Hall thruster that has an annular ceramic channel in 150-mm effective diameter and a centered hollow cathode was designed to optimize thrust performance with an appropriate channel-geometry and magnetic-field-topology combination. At an input power of 6 kW with xenon propellant, both high thrust (392 mN) and high specific impulse (1940s) was demonstrated for 300 V discharge voltage with xenon propellant. In this case a thrust efficiency of 62.7% was obtained. The thruster also worked in a low power mode at 1.8 kW, in which 92.7 mN and 1870s were available for 400 V operation. In comparison with existing thrusters, this thruster enables lower-power and higher-Isp operation for station keeping with satisfactory discharge stability, which will improve the all-electric propulsion satellite not only by reducing the propellant mass during station keeping but also by increasing the electric power available for mission payloads. Analysis in this study showed that the 6-kW operation is suitable for orbit raising maneuvers of geostationary satellites from a launch orbit to a geostationary orbit because a satellite from 3-ton to 10-ton can be transferred with two- or up to four-6kW-thrusters with a high payload ratio and a relatively short transfer time of 4- to 6-months. After transferred to a geostationary orbit, station keeping operation will be executed by a lower power mode. The Hall thruster will hence play an important role in the field of geostationary satellites.
  • Fostering Innovation via Ambidexterity in Aerospace Organizations
    • Abstract: Publication date: Available online 9 October 2019Source: Acta AstronauticaAuthor(s): Christine Joseph, Danielle Wood This 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.
  • Monocular-Based Pose Determination of Uncooperative Space Objects
    • Abstract: Publication date: Available online 1 October 2019Source: Acta AstronauticaAuthor(s): Vincenzo Capuano, Kyunam Kim, Alexei Harvard, Soon-Jo Chung Vision-based methods to determine the relative pose of an uncooperative orbiting object are investigated in applications to spacecraft proximity operations, such as on-orbit servicing, spacecraft formation flying, and small bodies exploration. Depending on whether the object is known or unknown, a shape model of the orbiting target object may have to be constructed autonomously in real-time by making use of only optical measurements. The Simultaneous Estimation of Pose and Shape (SEPS) algorithm that does not require a priori knowledge of the pose and shape of the target is presented. This makes use of a novel measurement equation and filter that can efficiently use optical flow information along with a star tracker to estimate the target’s angular rotational and translational relative velocity as well as its center of gravity. Depending on the mission constraints, SEPS can be augmented by a more accurate offline, on-board 3D reconstruction of the target shape, which allows for the estimation of the pose as a known target. The use of Structure from Motion (SfM) for this purpose is discussed. A model-based approach for pose estimation of known targets is also presented. The architecture and implementation of both the proposed approaches are elucidated and their performance metrics are evaluated through numerical simulations by using a dataset of images that are synthetically generated according to a chaser/target relative motion in Geosynchronous Orbit (GEO).
  • The active space debris removal mission RemoveDebris. Part 1: From concept
           to launch
    • Abstract: Publication date: Available online 6 September 2019Source: Acta AstronauticaAuthor(s): Jason L. Forshaw, Guglielmo S. Aglietti, Simon Fellowes, Thierry Salmon, Ingo Retat, Alexander Hall, Thomas Chabot, Aurélien Pisseloup, Daniel Tye, Cesar Bernal, François Chaumette, Alexandre Pollini, Willem H. Steyn This is the first of two companion papers that describe the development of the RemoveDEBRIS; mission. This first article focusses on the mission design and hardware development up to the delivery of the spacecraft to the launch authority. The Second article describes the in-orbit operations.The European Commission funded RemoveDebris mission has been the world's first Active Debris Removal (ADR) missions to demonstrate, in orbit, some cost effective key technologies, including net and harpoon capture; and elements of the whole sequence of operations, like the vision-based navigation, ultimately planning to terminate the mission with the deployment of the dragsail to de-orbit the craft. The mission has utilised two 2U CubeSats as artificial debris targets released from the main 100 kg satellite, to demonstrate the various technologies.This paper examines the design of the mission from initial concepts through to Manufacture, Assembly Integration and Testing of the payloads, up to launch, and apart from a general consideration of the mission, will focus on the elements of design and testing that differ from a conventional mission.
  • Sustainable space exploration and its relevance to the privatization of
           space ventures
    • Abstract: Publication date: Available online 5 November 2019Source: Acta AstronauticaAuthor(s): Nikolaos Iliopoulos, Miguel Esteban Although the majority of humanity’s current space programs are currently limited to the operation of the international space station and the deployment of probes to analyze distant planets, visions for future space exploration have long-duration missions in sight (such as manned missions to Mars and asteroid mining). According to contemporary literature these missions have the potential to provide tangible and intangible benefits, but they are also subject to public criticism given that increased awareness for environmental protection and preservation has ignited debates surrounding the socio-environmental and financial sustainability of space exploration. In hindsight of past advancements in outer space exploration, the authors follow the assumption that the commercial development will flourish and will provide auxiliary opportunities to overcome existing challenges. However, it is clear that the germination of private investment in the field of space exploration is contingent on the existence of unequivocal international space laws that permit and stimulate pro-profit decision making. Following this line of thought, this paper will explore the divergent definitions of sustainability that exist in the rhetoric of space exploration and will additionally expound on the privatization of space exploration and its relevance to the controversial legal rationales of international space laws.
  • Uncertainty and Sensitivity Study on Blunt Body’s Drag and Heat
           Reduction with Combination of Spike and Opposing Jet
    • Abstract: Publication date: Available online 5 November 2019Source: Acta AstronauticaAuthor(s): Sheng Wang, Wei Zhang, Fangjie Cai, Qiang Wang, Chao Yan Uncertainty and sensitivity study of three main parameters including length-to-diameter ratio, nozzle radius and total pressure ratio on the drag and heat reduction for the blunt body with spike and opposing jet is conducted. According to the simulation results obtained from the computational fluid dynamics, the relationship between input parameters and aerodynamic force/heat is established via the point-collocation non-intrusive polynomial chaos method. Uncertainties of pressure and heat flux caused by changes of input parameters are quantified. Sensitivity analysis is carried out to determine key parameters affecting pressure and heat flux changes. The results indicate that changes of peak pressure and peak heat flux are resulted from significant change in reattachment shock strength which varies with input parameters. Sensitivity analysis reveals that the length-to-diameter ratio has huge influence on the uncertainty in the recirculation zone, while the nozzle radius dominates the uncertainty in the reattachment zone. Moreover, it is found that the nozzle radius has an enormous effect on peak pressure and peak heat flux, and a significant negative correlation between them is identified.
  • Robust Adaptive Position and Attitude-Tracking Controller for Satellite
           Proximity Operations
    • Abstract: Publication date: Available online 5 November 2019Source: Acta AstronauticaAuthor(s): Bang-Zhao Zhou, Xiao-Feng Liu, Guo-Ping Cai This paper studies the pose tracking control problem for satellite proximity operations between a target and a chaser satellite, by which we mean that the chaser is required to track a desired time-varying trajectory given in advance with respect to the target. Firstly, by consulting an adaptive sliding-mode control method in literature developed for a class of nonlinear uncertain systems, an effective pose tracking controller is obtained. This controller requires no information about the mass and inertia matrix of the chaser, and takes into account the gravitational acceleration, the gravity-gradient torque, the J2 perturbing acceleration, and unknown bounded disturbance forces and torques. Then, an updated controller is proposed by combining the aforementioned controller and the unscented Kalman filter (UKF). This updated controller estimates the inertial parameters of the chaser through UKF, so it is of better adaptive ability to the initial estimation of the inertial parameters. Finally, numerical simulations are given to demonstrate the effectiveness of the proposed controllers. The simulation results show that the updated controller is more accurate.
  • Dynamics of a debris towing system with hierarchical tether architecture
    • Abstract: Publication date: Available online 2 November 2019Source: Acta AstronauticaAuthor(s): Keying Yang, Arun K. Misra, Jingrui Zhang, Rui Qi, Shan Lu, Yu Liu Use of a debris-tether-tug (DTT) system has been recognized as one of the most promising techniques for space debris removal. Attitude motion of the debris may give rise to severe disturbances to the debris removal system. In this case, a conventional DTT system with a single tether may no longer be capable of removing the debris in a stable manner. A hierarchical tether architecture is proposed to stabilize the debris with a main tether from the tug branched into multiple sub-tethers attached to the edges of the debris. The primary goal of this paper is to study the dynamics of a DTT system consisting of a tug, a rigid debris and the proposed tether architecture. First, a three-dimensional dynamics model is developed using Kane’s method. A simplified model is studied analytically to determine the equilibrium configurations and their stability, and the frequencies of oscillation about the stable equilibrium points. Numerical simulations are then conducted to verify the analytical results with both rigid and elastic tethers. Additionally, the stabilization effect of the branched tether system is investigated considering various debris angular velocities.
  • Validation of an Additively Manufactured Resistojet through Experimental
           and Computational Analysis
    • Abstract: Publication date: Available online 31 October 2019Source: Acta AstronauticaAuthor(s): F. Romei, A.N. Grubišić This paper presents the first proof of concept validation of the STAR thruster prototype. The device contains an innovative multifunctional monolithic heat exchanger, enabled by metal additive manufacturing processes. A 316L stainless steel printed thruster is characterized through a combination of dry heating and wet firing tests. This includes verification testing with argon in both cold and hot firing mode, at a range of electrical power inputs. Thrust measurements range from 9.7 mN ± 0.16 mN to 29.8 mN ± 0.16 mN, with a maximum measured specific impulse of 80.11 ± 1.49 s. Thrust performance is measured using a high-precision balance, and liquid-metal power transfer terminals to eliminate thermal drift. Highly coupled multiphysics computational models provide validation of the electro-thermal and thermo-fluidic characteristics of the prototype, including a prediction of the maximum propellant stagnation temperature and structural temperature, which were 649°C and 854°C.
  • Initial Orbit Determination with the Multibeam Radar Sensor BIRALES
    • Abstract: Publication date: Available online 31 October 2019Source: Acta AstronauticaAuthor(s): Matteo Losacco, Pierluigi Di Lizia, Mauro Massari, Giovanni Naldi, Giuseppe Pupillo, Germano Bianchi, Jan Siminski In this work we present a conceptual analysis of the use of the novel Italian multibeam radar sensor BIRALES for space surveillance. The dedicated orbit determination algorithm is described in detail. The algorithm is tailored to the peculiar configuration of the receiver gain pattern and is devoted to both reconstructing the track of the object transiting in the receiver field of view and estimating its state vector. The performance of the sensor is assessed with numerical simulations, offering an analysis on both pointing strategies and orbit determination accuracy for different survey configurations.
  • Multi-satellite scheduling framework and algorithm for very large area
    • Abstract: Publication date: Available online 31 October 2019Source: Acta AstronauticaAuthor(s): Yingjie Xu, Xiaolu Liu, Renjie He, Yingguo Chen This paper presents a multi-satellite scheduling problem for very large area observation with given specific constraints, derived from satellite capacity and customer requests. It is assumed that the profit was proportional to the coverage of acquired area, and the objective is therefore to maximize the total profits of generated observation schedule. To address the satellite scheduling problem, we first demonstrate a detailed problem description and then transform the problem into set covering problem within several criteria and constraints. Based on that, a mathematical model is established. In order to solve the multi-satellite scheduling problem for large area observation, a new solving framework is proposed. The framework is composed of three phases. In the discretizing phase, an area discretization method is adopted to establish the evaluation system. In the target decomposing phase, area target is decomposed into strips and corresponding visible time windows are calculated. In the scheduling phase, with crossover, mutation and feasibility operators, a genetic algorithm is introduced to generate an optimal observation schedule. Through extensive computational experiments on realistically generated problem with Chinese satellite platform, the effectiveness and reliability of the proposed solving framework are verified.
  • Optimization and Decision-making Framework for Multi-staged Asteroid
           Deflection Campaigns under Epistemic Uncertainties
    • Abstract: Publication date: Available online 31 October 2019Source: Acta AstronauticaAuthor(s): Sung Wook Paek, Olivier de Weck, Jeffrey Hoffman, Richard Binzel, David Miller In this study, we introduce a framework for planning and assessing multi-spacecraft asteroid deflection campaigns. In the scenario considered, a near-Earth asteroid (NEA) is nudged away from gravitational keyholes via a kinetic impactor (KI) technique, lest its passage should incur an Earth collision in the future. An asteroid orbiter or/and an impactor is/are used in the precursor stage to obtain uncertain information about the target asteroid, whose launch date and trajectory are optimized using Chebyshev’s method and a genetic algorithm. The KI mass is optimized through Monte Carlo simulations to improve the robustness of the method and achieve the minimum required probability of success (PoS). Case scenarios targeting Apophis and Bennu substantiate the utility of the framework in optimizing different deflection campaign architectures and making decisions amongst them via newly proposed visualization methods.
  • Parameterization and optimization for the axisymmetric forebody of
           hypersonic vehicle
    • Abstract: Publication date: Available online 31 October 2019Source: Acta AstronauticaAuthor(s): Jingfan Chen, Xaoqiang Fan, Bing Xiong, Zewei Meng, Yi Wang The axisymmetric hypersonic vehicle has attracted an increasing attention due to its simple structure and high volumetric efficiency. In order to find the optimal aerodynamic configuration of the axisymmetric hypersonic forebody, a novel parameterization method based on the theory of Non-uniform rational B-spline (NUBRS) curve and conical flows is proposed. Then, the optimization work which couples the global optimization algorithms NSGA-II with the computational fluid dynamics (CFD) fluid analysis is carried out. The optimization results show that configurations with higher lift-to-drag ratio as well as higher volumetric efficiency than the commonly used Von Karman Ogive configuration can be found. By analyzing flow structures of three different representative configurations, the reasons that lead to the different lift-to-drag ratios are found. Finally, the effects of angle of attack on the lift-to-drag ratio of three representative forebody configurations is studied.
  • Gravity Compensation System of Mesh Antennas for In-orbit Prediction of
           Deployment Dynamics
    • Abstract: Publication date: Available online 26 October 2019Source: Acta AstronauticaAuthor(s): Zhihua Zhao, Kangjia Fu, Meng Li, Jinyou Li, Yong Xiao Large deployable mesh antennas are central components of high gain satellites that are used for gathering electromagnetic signals. Deploying such antennas in-orbit is a delicate and precise process, and any failure in their unfolding can result in satellite malfunction. Thus, on-ground experiments have been used to attempt to predict the in-orbit deployment performance of mesh antennas. However, Earth’s gravitational field presents a great obstacle in achieving this goal, and how best to design a gravity compensation system for the flexible webs of mesh antennas remains unclear despite various proposed gravity compensation techniques. In this paper, we attempt to address this problem via flexible multibody simulations. The results first reveal that, if the webs are not offloaded at all, the weight of the webs causes the driving forces of the motors and the bending moments of the truss members obtained during on-ground tests to deviate from those experienced by the antenna in-orbit. To counteract this problem, two different gravity suspension systems for the webs of mesh antennas were designed and evaluated. In particular, the different numbers and positions of the suspension nodes were investigated. The results show that no matter which of the two proposed designs is adopted, the number and location of suspension nodes should be carefully selected to achieve well-behaved compensation performance. Furthermore, the proposed modeling and analysis methods can also be applied to other flexible mechanical systems requiring gravity compensation.
  • Augmented Reality for the Enhancement of Space Product Assurance and
    • Abstract: Publication date: Available online 25 October 2019Source: Acta AstronauticaAuthor(s): Raul Alarcon, Fridolin Wild, Christine Perey, Marc Marin Genescà, Josefa Gavaldà Martínez, Josep Xavier Ruiz Martí, Maria José Simon Olmos, Diana Dubert A 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.
  • Time Delay Prediction for Space Telerobot System with a Modified Sparse
           Multivariate Linear Regression Method
    • Abstract: Publication date: Available online 25 October 2019Source: Acta AstronauticaAuthor(s): Haifei Chen, Panfeng Huang, Zhengxiong Liu, Zhiqiang Ma Compared with general telerobot system, space telerobot system (STS) faces with more serious and complex time delay. In time delay prediction, the traditional sparse multivariate linear regressive (SMLR), auto regressive (AR), neural network (NN) and cubic polynomial model based (CBMB) approaches share lower efficiency or precision, when time delay is serious and complex. To solve this problem, time delay prediction for STS is discussed in this paper. Through analysis, time delay in STS can be divided to three parts: a) communication time delay; b) transmission time delay; c) processing time delay. Then, detailed varying rule and accurate statistics analysis are given for each parts of time delay. Based on the previous work, a modified SMLR is proposed and realizes the prediction of time delay. Compared with previous SMLR, AR, NN and CBMB approaches, the modified SMLR method shares more higher prediction efficiency or precision. Finally, a simulation example is given and the simulation results show the superiorities.
  • Integrated control method for spacecraft considering the flexibility of
           the spacecraft bus
    • Abstract: Publication date: Available online 25 October 2019Source: Acta AstronauticaAuthor(s): Liang Tang, Zixi Guo, Xin Guan, Youyi Wang, Kebei Zhang This paper presents an integrated control method for an extremely large spacecraft, such as the space interferometry telescope, to achieve control task with high accuracy and high stability. The flexibility of the spacecraft bus would be more obvious when their size gets larger, so the vibration reduction for this kind of spacecraft would be more challenging. This paper presented a dynamic model of the spacecraft with flexible central body, and with flexible appendages and CMG (Control Moment Gyroscope) with disturbances at the same time. Then the integrated control method is presented to make the relative attitude of the two payloads on the spacecraft bus track with each other. The vibration isolation techniques are adopted to reduce the high frequency vibrations, and the nonlinear feedback control is presented to achieve the relative attitude convergence to 0 with high accuracy and high stability. Finally numerical simulations are carried out to verify the performance of the integrated control method.
  • Distribution of stress intensity ratio in canonical turbulent flows and
           converging-diverging channel
    • Abstract: Publication date: Available online 24 October 2019Source: Acta AstronauticaAuthor(s): Jinglei Xu, Guopu Sun, Ding Xu The understanding and prediction of wall-bounded turbulence are of great importance for industrial flows. The stress intensity ratio, Rb, is recognized as one key parameter, and its value was known as being around 0.3 in the wake layer of wall-bounded turbulence and the mixing layer. In this work, Rb is studied using Direct Numerical Simulation data extracted from the canonical flows (channel, pipe, flat plate boundary layer at various Reynolds numbers) and converging-diverging channel flow. It is found that in canonical flows and the converging-diverging channel flow, the stress intensity ratio exhibits a certain pattern if the stress intensity ratio varies with the eddy viscosity ratio r or turbulent Reynolds number Rek. Moreover, the r-Rb distribution shows advanced similarity against the Rek-Rb distribution, which is due to that r is consist of transport variables. The similarity is evidenced by the fact that the r-Rb distribution is insensitive to zero pressure gradient, positive pressure gradient, and geometric effects. The r-Rb distribution seems to be mainly sensitive to the friction Reynolds number. This priori study shows that the r-Rb distribution is of universality in flows of different geometric configurations, and it offers information for the construction and improvement of turbulence models.
  • New Space and Agile Innovation: Understanding Transition to Open
           Innovation by Examining Innovation Networks and Moments
    • Abstract: Publication date: Available online 24 October 2019Source: Acta AstronauticaAuthor(s): Matjaz Vidmar, Alessandro Rosiello, Niki Vermeulen, Robin Williams, Julian Dines This paper is building a detailed understanding of the organisational structures and practices in SMEs’ knowledge absorption from a network of innovation partners. In particular, it explores the relationship between the openness of innovation process through innovation networks and the development of organisational structures within firms, as well as its linkage to a regional sectoral environment. It proposes a new conceptual tool of “innovation moments”, to synthesise the key theoretical premises of knowledge management, organisational learning and absorptive capacity literatures. In order to study this vital nexus of phenomena, we propose to deploy a novel mixed methods approach of combining quantitative ego-centric Social Network Analysis (Ego-SNA) and qualitative derived narratives of product development experiences via a sensitising concept, to study the emergence and development of the New Space Sector in Scotland. The findings show that the type of the SME – “traditional” versus New Space and upstream versus downstream – is clearly related to the structure of the firms’ ego-centric innovation networks and their position in the composite whole network. Furthermore, by using qualitative case study data we show that the firms' typology is also closely related to internal organisational features, in particular flattening hierarchical structures and the formalisation and standardisation within NPD processes. This paper argues that the interlinking of these two elements is poised to describe a cultural shift in the approach to innovation networking and new product development (NPD) process management, understanding of which is a critical element of examining Open Innovation in SMEs.
  • Hygrothermal mechanical behaviors of axially functionally graded
           microbeams using a refined first order shear deformation theory
    • Abstract: Publication date: Available online 23 October 2019Source: Acta AstronauticaAuthor(s): Yuewu Wang, Haoyuan Ren, Tairan Fu, Congling Shi The present work discusses mechanical behaviors of an axially functionally graded (AFG) beam in micro scales subjected to a moving mass. The AFG microbeam is exposed to hygrothermal environments with a uniform temperature rise and a moisture concentration rise. The material properties of AFG microbeam are assumed to vary along the axial direction of the beam according to a power-law function and are temperature dependent. A microbeam modeling is developed based on a refined first order shear deformation theory (FSDT) in conjunction with the closed-form solution technique, in which the modified couple stress theory is implemented to account for size effect. The minimum energy strategy is applied to derive the eigenvalue equations associated to buckling and free vibrations of the microbeam, while the equations of motion related to the dynamic response are obtained by adoption of Lagrange method and solved using the Newmark-β method. A ceramic-metal AFG microbeam with simply-supported end constraints is taken as a numerical illustration to show the effects of hygrothermal environments, small scale on the mechanical behaviors of AFG microbeams subjected to a moving mass.
  • Sleep deprivation impairs affordance perception behavior during an action
           boundary accuracy assessment
    • Abstract: Publication date: Available online 22 October 2019Source: Acta AstronauticaAuthor(s): Christopher Connaboy, Alice D. LaGoy, Caleb D. Johnson, Aaron M. Sinnott, Shawn R. Eagle, Joanne L. Bower, Gert-Jan Pepping, Richard J. Simpson, Candice A. Alfano ObjectivesAstronauts must adapt behaviors to changing affordances (action possibilities) when exposed to operational stressors such as sleep deprivation. The inability to correctly perceive affordances may cause astronauts to attempt behaviors that place them at greater risk. This study investigated the effects of sleep deprivation on affordance perception performance during 30-day NASA Human Exploration Research Analog missions.MethodsSixteen participants completed a perception-action coupling task (PACT) over days 22-25 of the missions. Participants completed sessions on day 22 (1800) and 24 (1200 and 1730) under normal sleep conditions and sessions on day 25 (0430, 1200 and 1445) after a night of sleep deprivation. During PACT, participants judge whether virtual balls afford posting (can fit) through virtual apertures. The ratio of ball-to-aperture size ranges from 0.2-1.8 (afforded trials 1). A two-way repeated measures ANOVA was used to analyze the effect of time and trial type (afforded versus unafforded) on response time (RST) and accuracy (ACC).ResultsFor RST, significant main effects of time (F2.666, 39.984 = 7.685, p = .001) and trial type (F1, 15 = 17.554, p = .001) were observed. Afforded RST was greater than unafforded RST. ACC decreased across time (F2.724, 20.939 = 5.137, p = 0.005) but did not differ between trial types. No significant interaction effects were observed.ConclusionDecrements in affordance-based behaviors were observed under increasing levels of sleep deprivation and subjects responded slower to trials where the task-specific affordance was available. These decrements may relate to changes in operational performance.
  • Fast-swirl space non-cooperative target spin state measurements based on a
           monocular camera
    • Abstract: Publication date: January 2020Source: Acta Astronautica, Volume 166Author(s): Gu Yingying, Wang Li Measuring the motion state of space non-cooperative targets is in the fields of space on-orbit services and debris removal. This paper proposes a method for the measurements of the spin rate of fast-swirl non-cooperative targets through a monocular camera, for image features that have been degraded at a medium and long distance. First, the coordinate system between the tracking satellite and the target is established, and the relationship between the target spin period and its image projection angle is deduced. An image processing method which can extract the projection angle of the target image stably under complex illumination conditions is then proposed. Next, considering the characteristics of the sequence projection angle of the fast-spinning target at a long distance, the spin rate of the target is calculated using a sinusoidal polynomial fitting method. The proposed method is validated by simulated and on-orbit data. Experiment results show that the method has strong adaptability, measurement reliability and practical engineering application prospects.
  • Effects of a new-type inner-canopy illuminant and light quality on spring
           wheat growth in CELSS
    • Abstract: Publication date: January 2020Source: Acta Astronautica, Volume 166Author(s): Yunze Shen, Shuangsheng Guo, Gu Zeng Traditional plant illumination in Controlled Ecological Life Support System (CELSS) has been generally roof illumination (RI). In order to improve the utilization efficiency of light energy for cultivating plants, a new-type inner-canopy illuminant (ICI), which was embedded among the stems and leaves of spring wheat, was applied in the research. The experimental group was 50% ICI+ 50% RI, while the control group was 100% RI, both of which consumed the same total electric power. For each of the two groups, six different qualities of light were separately used to study the effects of red, blue and green light under simulated CELSS conditions. By comparing the two groups, it was found that the PPFD (Photosynthetic Photon Flux Density) on the leaf surface was increased in the experimental group, resulting in a shortened growth period, higher net photosynthetic rate (Pn), lower plant height, larger leaf area index (LAI), higher biomass and seed yield. The increased percent of PPFD across the leaf surface under the experimental group on average reached 8.6%–14.6% within 30 days, while PPFD increased by 3.9%–8.0% in 70 days after sowing. An increased seed yield as large as 19.6% per day was achieved in the experimental group. In addition, Red, blue and green light contributed differently to photosynthetic efficiency. Firstly, red light promoted the shortening of growth period, while blue and green light had no significant effect on it. For example, reducing 20% red light caused a 12- or 13-day prolongation of the growth period. Secondly, increasing the ratio of red/blue could increase Pn, plant height, leaf area index, total biomass and seed yield. Thirdly, it can be seen that the green light did not contribute to photosynthesis directly, but it still had an important role in spring wheat growth. Green light significantly increased the tiller number and LAI, as well as total biomass and seed yield, but daily seed yield was not increased under 10% or more green light. The total seed yield was the highest in combination of 80% red +10% blue +10% green light, but the highest daily seed yield was achieved under 90% red +10% blue light for a shorter growth period. The above results should provide a useful reference for choosing the suitable plant lighting method in CELSS.
  • Effect of titanium surface roughness on oxygen catalytic recombination in
           a shock tube
    • Abstract: Publication date: Available online 17 October 2019Source: Acta AstronauticaAuthor(s): Ikhyun Kim, Yosheph Yang, Gisu Park Surface roughness and microscopic morphology are key factors influencing oxygen catalytic recombination. Titanium is extensively used as a material for metallic thermal protection systems (TPS) in the design of hypersonic and reusable launch vehicles. In this study, the effect of titanium surface roughness on oxygen catalytic recombination is experimentally investigated. The efficiency of the oxygen recombination reaction is determined by evaluating the measured heat-transfer rates while considering the existing theory of binary gas mixtures. The surface of the test models was coated with either titanium or silicon diox-ide, and for each model, four different levels of surface roughness were prepared. It is shown that, with an increase in surface roughness, oxygen recombination efficiency increased on both the titanium and silicon dioxide surfaces. Surface topography was characterized in terms of the roughness factor (Ф = A/Ag), i.e., the ratio of the actual surface area (A) to the projected surface area (Ag) using an atomic force microscope. The relationship between the roughness factor and oxygen recombination efficiency was examined.
  • Solar Sail Cooperative Formation Flying Around L 2-Type Artificial
           Equilibrium Points
    • Abstract: Publication date: Available online 17 October 2019Source: Acta AstronauticaAuthor(s): Wei Wang, Hexi Baoyin, Giovanni Mengali, Alessandro A. Quarta The aim of this paper is to propose a distributed control architecture for a solar sail-based formation, flying around an L2-type artificial equilibrium point in the Sun-[Earth+Moon] circular restricted three-body problem. Two typical cases, depending on whether the formation structure is leaderless or includes a virtual leader, are investigated. In particular, the virtual leader case is further analyzed according to whether the state information of the virtual leader is available to all of the sails or to a part of the formation structure only. The protocols of the consensus-based algorithms are formulated on a general directed (unidirectional) communication topology, by exploring each available local neighbor-to-neighbor information interaction in a cooperative manner. In that case, a synchronized formation tracking may be achieved while increasing the reliability of the formation system. Illustrative examples show the effectiveness of the proposed approach in a typical mission scenario.
  • Star identification robust to angular rates and false objects with rolling
           shutter compensation
    • Abstract: Publication date: Available online 16 October 2019Source: Acta AstronauticaAuthor(s): Vincenzo Schiattarella, Dario Spiller, Fabio Curti This paper addresses the problem of star identification in the presence of high slew rates, false objects and image deformations introduced by the rolling shutter. These problems can affect the operating life of star trackers and worsen the nominal performances. The proposed methodology relies on a technique named Improved Multi-Poles Algorithm, especially designed for robustness to false objects and slew rates. Angular velocities up to five degrees per second are considered so that stars are seen no more as near-circular spots but appear as streaks. The image deformation due to the rolling shutter of modern active pixel sensor detectors is compensated by means of a mathematical model based on a first order approximation of the problem. A star tracker high fidelity simulator generates the input images considering typical noises due to the electronics and space environment. The reported results show that the proposed approach guarantees a reliable star identification and attitude determination with angular velocity from zero to five degrees per second.
  • Interference into Radio Broadcast Satellite Uplinks
    • Abstract: Publication date: Available online 16 October 2019Source: Acta AstronauticaAuthor(s): Robert Briskman, Riza Akturan
  • 3Dguidance for hypersonic reentry gliders based on analytical prediction
    • Abstract: Publication date: Available online 16 October 2019Source: Acta AstronauticaAuthor(s): Liang Pan, Shuangchun Peng, Yu Xie, Yang Liu, Jianhong Wang In order togive full play to the potentialof hypersonic gliders to strike a longrange of targets and perform large lateral maneuveringmissions, a three-dimensional guidance method is proposed on the basis of analytical predictions. We first construct an entry guidance model for a glider and derive the analytical solution for the trajectory based on Lyapunov's artificial small parameter method. Such anapproach ensures high accuracy in the theoreticalprediction of flight trajectory. Subsequently, we construct a three-dimensional(3D) flight corridor that satisfies multiple constraints including heat rate, dynamic pressure, overload, angle of attack, and bank angle. Furthermore, the flight profile and bank reversal strategy in the 3D flight corridor model are designed on the basis of the analytical solution of the flight trajectory considering both longitudinal flight range and lateral flight mobility requirements of the glider. In addition, the control commands of the angle of attack and bank angle are generated bytracking the profile of the flight. The method has been tested in three cases of guidance under short-, medium-, and long-range flights. The results show that it provides high prediction accuracy and strong self-adaptive capability for all the test cases.Our proposed method targets the design of a 3D flight profile in a 3D flight corridor.Furthermore, the method considers flight requirements in both the longitudinal and lateral directions,thus maximising the aircraft’s abilityto reach the target while maintaining high levels of flexibility and self-adaptive capability during the mission.
  • Protective effect of pyrolysis gases combustion against surface ablation
           under different Mach numbers
    • Abstract: Publication date: Available online 16 October 2019Source: Acta AstronauticaAuthor(s): Jin Guo, Haiming Huang, Xiaoliang Xu Whether pyrolysis gases combustion has effect on surface ablation of charring material is a key issue in the optimization design of thermal protection system for hypersonic vehicles. The coupled method considering combustion of pyrolysis gases in shock layer is presented, realized in MATLAB and validated by comparison with the arcjet experiments. Relationship between surface ablation and mole fraction of oxygen, mass injection rate of pyrolysis gases and surface temperature of charring material under different Mach numbers are predicted by this coupled method. Numerical results indicate that the protective effect of pyrolysis gases combustion on surface ablation is more and more obvious with increase of Mach number. This study is helpful to the optimization of thermal protection system for hypersonic vehicles.
  • Orbital Maneuvering of Electric Solar Wind Sail Based on an Advanced Solar
           Wind Force Model
    • Abstract: Publication date: Available online 16 October 2019Source: Acta AstronauticaAuthor(s): Kohei Yamaguchi, Kikuko Miyata The electric solar wind sail is a propulsion system that extracts the solar wind momentum for the thrust force of a spacecraft by using an interaction between solar wind protons and the electric potential structure around charged long thin conducting tethers. The system enables a spacecraft to generate a thrust force without consuming reaction mass. This paper investigates the capability of the electric solar wind sail as a propulsion system for deep space exploration missions. The shape of the conducting tether that is determined by the equilibrium of the solar wind force and centrifugal force is numerically calculated for formulating an advanced solar wind force model. The conducting tethers deviate from the ideal sail spin plane, and the maximum value of the thrust direction varies from 13∘ to 19∘. To estimate the spacecraft thrust vector, which is calculated as the sum of solar wind force vectors exerted on each tether, best-fit polynomial equations are proposed. We performed numerical simulations for a two-dimensional orbital transfer mission to investigate the capability of the electric solar wind sail. Results of numerical simulations show that the electric solar wind sail enables spacecraft to perform Earth–Venus, Earth–Mars, and Earth–Itokawa transfer missions. Additionally, this paper performs three-dimensional simulations for an Earth–Ryugu transfer mission. The electric solar wind sail achieves a more complicated orbital transfer in a reasonable mission time.
  • Analysis of length effect on thermodynamic characteristics in a Z-shaped
           evaporating flameholder
    • Abstract: Publication date: Available online 16 October 2019Source: Acta AstronauticaAuthor(s): Junjie Miao, Yuxin Fan, Tianchi Liu, Weiqiu Wu In this paper, the length effects on thermodynamic characteristics of a Z-shaped evaporating flameholder are studied to optimize the ignition and flame-holding performance. The characteristics of ignition kernel, flamelet propagation, and flame stability under the operating conditions of turbine-based combined cycle combustors are experimentally investigated. The numerical flow fields are performed to explain the experimental results. Furthermore, the droplet distribution and flame equivalence ratio are acquired using image-processing to interpret the length effects. The results indicate that optimizing the structure can achieve a better matching of flow pattern and fuel mist, and a more uniform spatial distribution of flame equivalence ratio, attributed to the improved fuel-air mixing. The optimization of the L/H ratio can reduce the ignition delay time and increase the premixed degree during the ignition process, thereby owning the superior ignition and blowout performance within the wide-range operation. Changing the L/H ratio alters the double-reaction-zone morphology, and the contribution of the second reaction zone to sustain flame rises with the reduced L/H ratio. The optimal structure can consequently decrease the lean ignition and blowout equivalence ratio by 29.3% and 39.0%, respectively. The results provide a theoretical basis for the optimization of pilot-ignition structure employed in afterburner/ramjet combustors.
  • Performance and Plume Characteristics of an 85 W Class Hall Thruster
    • Abstract: Publication date: Available online 15 October 2019Source: Acta AstronauticaAuthor(s): Hiroki Watanabe, Shinatora Cho, Kenichi Kubota An 85 W class Hall thruster with inner and outer electromagnetic coils was developed, and its thrust performance and plume characteristics were experimentally evaluated. The 85-W Hall thruster required a maximum magnetic flux density along the channel centerline above 24.3 mT to achieve stable and efficient operation above a discharge voltage of 225 V. A specific impulse of 1,050 s, thrust-to-power ratio of 59.5 mN/kW, and anode efficiency of 0.306 were achieved at a discharge voltage of 225 V and a discharge power of 88.9 W under a background pressure of 7.9 × 10-4 Pa. Moreover, the thruster achieved throttling at a discharge power of 47.6 to 118.5 W with stable operation. The low anode efficiency of the 85-W Hall thruster was due to low propellant utilization and a large beam divergence. The short effective length for the propellant ionization owing to the narrow channel is deduced to be the cause for the low anode efficiency in low-power Hall thrusters. The mass utilization efficiency of the 85-W Hall thruster improved as the anode mass flow density increased. Therefore, an increase in the anode mass flow density is required to improve the performance of the 85-W Hall thruster.
  • E-sail Attitude Control with Tether Voltage Modulation
    • Abstract: Publication date: Available online 15 October 2019Source: Acta AstronauticaAuthor(s): Marco Bassetto, Giovanni Mengali, Alessandro A. Quarta An Electric Solar Wind Sail is a propellantless propulsion system that gains thrust from the interaction of solar wind particles with a grid of long and charged tethers, which are deployed by spinning the spacecraft about its symmetry axis. In an ideal arrangement, the tethers are all stretched out and the sail takes the shape of a spoked wheel. Actually, the solar wind dynamic pressure warps the tethers and, therefore, the expressions of thrust and torque vectors are difficult to predict in analytical form. Recent works have shown that the bending of the tethers induces a disturbance torque, which can be counterbalanced through a modulation of the tether electrical voltage. Under the assumption that the Electric Solar Wind Sail behaves like an axially-symmetric rigid body, this paper proves that a modulation of the tether electrical voltage is also a feasible option for actively controlling and maintaining the spacecraft attitude. The proposed control law, which is analytically derived as a function of time and spacecraft attitude, is validated through numerical simulations.
  • Options and uncertainties in planetary defense: Impulse-dependent response
           and the physical properties of asteroids
    • Abstract: Publication date: Available online 15 October 2019Source: Acta AstronauticaAuthor(s): David S.P. Dearborn, Megan Bruck Syal, Brent W. Barbee, Galen Gisler, Kevin Greenaugh, Kirsten M. Howley, Ronald Leung, Joshua Lyzhoft, Paul L. Miller, Joseph A. Nuth, Catherine Plesko, Bernard D. Seery, Joseph Wasem, Robert P. Weaver, Melak Zebenay Though rare, asteroid impacts are inevitable, and with the current state of technology, kinetic impactors are the preferred but not the complete solution. If the time to impact is short, or the threatening body too large, nuclear deflection serves as a final option. This work is part of an integrated study by National Aeronautics and Space Administration (NASA) and the National Nuclear Security Administration (NNSA) to better determine the relative efficacy of these complimentary approaches. In particular, we examine the important material properties that affect each approach, to improve critical characterization efforts, and reduce uncertainty in the limits of the impactor technology.Impact speeds for kinetic impactors on Near-Earth Object (NEO) intercept trajectories commonly range from 5 to 20 km/s, resulting in significant crater ejecta and a momentum enhancement above that carried by the impactor. This enhancement depends substantially on the strength and porosity of the asteroid, as well as the impact speed. Here simulations from different codes are presented, along with constraints from experimental measurements. The uncertainties due to ignorance of the strength and porosity of the impact point are significant in determining the limits of impactor sufficiency.The nuclear approach is considered within the context of current capabilities, posing no need to test, as extant and well-understood devices are sufficient for the largest known Potentially Hazardous Objects (PHOs). Results of x-ray sources with realistic spectra as well as blackbody spectra are given, along with some assessment on composition dependence.
  • SPECTROModule: A modular in-situ spectroscopy platform for
           Exobiology and Space Sciences
    • Abstract: Publication date: Available online 15 October 2019Source: Acta AstronauticaAuthor(s): A. Sgambati, M. Deiml, A. Stettner, J. Kahrs, P. Brozek, P. Kapoun, V. Latini, M. Mariani, E. Rabbow, P. Manieri, R. Demets, A. ElsaesserThe evolution of the solar system and the origin of life remain some of the most intriguing questions for humankind. Addressing these questions experimentally is challenging due to the difficulty of mimicking environmental conditions representative for Early Earth and/or space conditions in general in ground-based laboratories. Performing experiments directly in space offers the great chance to overcome some of these obstacles and to possibly find answers to these questions. Exposure platforms in Low Earth Orbit (LEO) with the possibility for long-duration solar exposure are ideal for investigating the effects of solar and cosmic radiation on various biological and non-biological samples. Up to now, the Exobiology and space science research community has successfully made use of the International Space Station (ISS) via the EXPOSE facility to expose samples to the space environment with subsequent analyses after return to Earth. The emerging small and nanosatellite market represents another opportunity for astrobiology research as proven by the robotic O/OREOS mission, where samples were monitored in-situ, i.e. in Earth orbit. In this framework, the European Space Agency is developing a novel Exobiology facility outside the ISS. The new platform, which can host up to four different experiments, will combine the advantages of the ISS (long-term exposure, sample return capability) with near-real-time in-situ monitoring of the chemical/biological evolution in space. In particular, ultraviolet-visible (UV-Vis) and infrared (IR) spectroscopy were considered as key non-invasive methods to analyse the samples in situ. Changes in the absorption spectra of the samples developing over time will reveal the chemical consequences of exposure to solar radiation. Simultaneously, spectroscopy provides information on the growth rate or metabolic activities of biological cultures. The first quartet of experiments to be performed on-board consists of IceCold, OREOcube and Exocube (dual payload consisting of ExocubeChem and ExocubeBio). To prepare for the development of the Exobiology facility, ground units of the UV-Vis and IR spectrometers were studied, manufactured and tested as precursors of the flight units. The activity led to a modular in-situ spectroscopy platform able to perform different measurements (e.g. absorbance, optical density, fluorescence measurements) at the same time on different samples. We describe here the main features of the ground model platform, the verification steps, results and approach followed in the customization of commercial–off-the-shelf (COTS) modules to make them suitable for the space environment. The environmental tests included random and shock vibration, thermal vacuum cycles in the range −20°C to +40°C and irradiation of the components with a total dose of 1800 rad (18 Gy). The results of the test campaign consolidated the selection of the optical devices for the Exobiology Facility. The spectroscopic performance of the optical layout was tested and benchmarked in comparison with state-of-the-art laboratory equipment and calibration standards showing good correlation. This includes spectra of samples sets relevant for the flight experiments and a performance comparison between the SPECTROModule ground model and state-of-the-art laboratory spectrometers. Considering the large number of samples and different types of optical measurements planned on-board the ISS, the main outcome was the implementation of an LED-photodiode layout for the optical density and fluorescence measurements of IceCold (42 samples) and ExocubeBio (111 samples); while the UV-Vis spectrometer will be mainly focused on the change of the absorption spectra of the 48 samples of OREOcube.The ExocubeChem samples (in total 48) will be analysed by infrared spectroscopy. The ground platform supports the establishment of analogue research capabilities able to address the long-term objectives beyond the current application.
  • Potential application of X-ray communication in Martian dust storm
    • Abstract: Publication date: Available online 14 October 2019Source: Acta AstronauticaAuthor(s): Shuang Hang, Xiaobin Tang, Huan Li, Yunpeng Liu, Junxu Mu, Wei Zhou, Peng Dang, Sheng Lai X-ray communication (XCOM) is an advanced space-communication technology. The high penetration of X-ray enables XCOM to achieve lower signal attenuation than conventional optical communication in Martian dust storm. This study provided a demonstration of this approach based on simulation methods. The transmission properties of X-ray beams in Martian non-dust storm weather were evaluated based on the MCNP5 code. Results demonstrated that the X-ray beam can transmit through a long-distance in Martian atmosphere. Moreover, on the basis of the anomalous diffraction and Mie theory codes, the transmission properties of X-ray and optical links in Martian dust storm were evaluated. Results showed that the dust attenuation of the X-ray links were significantly lower than that of optical links. Moreover, the penetration and communication performance of X-ray links were evaluated and compared with the optical link, considering atmospheric and dust attenuation. Results indicated that XCOM can be used to establish a low-BER communication link between rovers, and from the rover to the orbiter, in Martian dust storm.
  • Inverse design method on scramjet nozzles based on maximum thrust theory
    • Abstract: Publication date: Available online 14 October 2019Source: Acta AstronauticaAuthor(s): Kaikai Yu, Yile Chen, Shuai Huang, Jinglei Xu An inverse nozzle design method based on maximum thrust theory and method of characteristics (MOC) is proposed to increase the aerodynamic performance and practicality of scramjet nozzles. In comparison with the general maximum thrust nozzle design method, the proposed method not only utilizes maximum thrust theory but also demonstrates additional flexibility under geometrical constraints. The main characteristic of the proposed method is that the key point in the maximum thrust nozzle can become the target and be manually determined in advance in accordance with the actual requirements, rather than through an iteration method based on the flow conditions of the nozzle inlet and flight in the general design method. The proposed method is implemented using MOC, which is a universal mathematical method in solving partial differential equations. First, a brief introduction of maximum thrust theory and MOC are provided to comprehend the background. Second, the application of maximum thrust theory in the inverse design method is discussed, including the specific design procedure. Third, the feasibility and effectiveness of the proposed method are verified in an actual design case using computational fluid dynamic approaches. Then, the influence of cowl lengths on the aerodynamic performance of the nozzle is analyzed. Results show that the proposed method can provide different solutions to obtain high thrust coefficient or high lift and pitching moments, which offers flexibility and operability for the engineers. Finally, a nozzle named nozzle B is designed using the traditional forward method. In terms of aerodynamic performance, the nozzle A designed by the proposed method shows evident advantages. The thrust coefficient of nozzle A obtains approximately 31.8% increment, and the lift and pitching moments improve with 201.0% and 56.6% increments, respectively. In conclusion, this study proposes a new inverse nozzle design method that utilizes maximum thrust theory and MOC, which can not only increase the aerodynamic performance but also provide further flexibility and operability in the scramjet nozzle design.
  • Theoretical Prediction on the Global Surface Temperature Map of the Moon
    • Abstract: Publication date: Available online 14 October 2019Source: Acta AstronauticaAuthor(s): Taig Young Kim Several studies on lunar surface temperature have been published using temperature measurements from the Diviner Lunar Radiometer Experiment (DLRE) mounted on the Lunar Reconnaissance Orbiter (LRO). The recent study by Williams et al. [1] has provided a detailed temperature map of the entire lunar surface and provides a good opportunity to utilize it. Theoretically, in order to predict the lunar surface temperature, thermophysical properties of the regolith layer are indispensable. However, since the data are limited to those taken at the landing site, a new method is necessary to generate the global temperature map. In this study, a theoretical method to calculate temperature on the global lunar surface was proposed with comparable accuracy to the DLRE measurements without utilizing such thermophysical properties. The energy equation of the Lumped System Model (LSM) for the very thin uppermost lunar regolith layer was established, and the mathematical formulation of the bottom conductive heat flux required to solve the LSM equation was proposed using the appropriate theory. Based on recent work on the DLRE, the LSM equation was analyzed, assuming that thermal mass per unit area, which is only one integral thermophysical property of the LSM, is globally homogeneous over the Moon. The thermal mass per unit area and the coefficients of the suggested bottom conductive heat flux were extracted from DLRE measurements and optimized through best curve fitting to DLRE measurements. The temperatures predicted by LSM are reasonably accurate, and the mean temperature difference from the DLRE measurements in latitudes equatorward of 70° is only 3.15 K. The global surface temperature map reproduced by the LSM analysis is a good match with the map extracted from DLRE measurements, except in anomalous temperature zones caused by surface topology and rock abundance.
  • Towards the Utilization of Optical Ground-to-Space Links for Low Earth
           Orbiting Spacecraft
    • Abstract: Publication date: Available online 12 October 2019Source: Acta AstronauticaAuthor(s): Marcus T. Knopp, Andreas Spoerl, Marcin Gnat, Gregor Rossmanith, Felix Huber, Christian Fuchs, Dirk Giggenbach The microwave spectrum has become a highly limited resource in satellite communications owing to an ever increasing demand for bandwidth and capacity. Therefore, a shift to the exploitation of optical carrier frequencies is currently underway. Focusing on high-rate transmissions of payload data from remote sensing satellites, operational systems, like the well-known European Data Relay Satellite system, are based on optical inter-satellite links. Besides, direct-to-earth free-space optical communications from low Earth orbiting spacecraft hold high potential for upcoming space missions through lower complexity. In that regard, we study the viability of the ground-to-space beacon laser signal of optical ground stations to be additionally modulated with tele-command tokens. Such an optical return channel could be variously put into use, for example to trigger automatic repeat requests of payload data downlinks, for jamming-free control of the spacecraft or for high-rate software uploads to its on-board processor. A particular challenge is posed by the unequal fading behavior of the optical channel regarding the down- and uplinks, which cover asymmetric optical pathways through the atmosphere.We define the end-to-end architecture of the communication chain including the transmitter on ground and the space-based receiver. Special attention is given to compatibility with established space data and system standards. Moreover, we examine the effects on the scheduling of satellite control, resulting from a constrained availability of the optical uplink due to cloud blockages. Our analysis aims at the employment of available space protocols for bidirectional optical communications with low earth orbiting spacecraft. Further on, we consider the adoption of upcoming standards to account for the optical fading channel. Certain applications like immediate automatic-repeat-requests for the downlink will require novel, optimized protocols.
  • ORACLE: A Mission Concept to Study Mars’ Climate, Surface and
    • Abstract: Publication date: Available online 11 October 2019Source: Acta AstronauticaAuthor(s): Antonio Genova A comprehensive knowledge of the Martian climate requires a better understanding of the formation and evolution of the polar caps. Accurate measurements of mass, volume, and composition of the seasonal polar deposits would enable a precise characterization of the surface-atmosphere interactions relevant to the CO2 cycle. The acquisition of these science data is only possible through a dedicated orbital mission at Mars. ORACLE (Orbital Radio science and Altimetry for CLimate Experiment) is a mission concept that enables the monitoring of the CO2 mass exchange between the polar caps and the atmosphere with a pair of spacecraft in a 250×320 km orbit about Mars. A preliminary design of the mission configuration is presented in this study including the scientific payload that consists of a radio science system for inter-satellite tracking, a laser altimeter, and an infra-red camera. These instruments also provide data that are fundamental to investigate Mars’ internal structure and atmosphere. ORACLE is, therefore, a multi-disciplinary mission that is conceived to fulfill the constraints of a medium-class mission.
  • Dual quaternion based dynamics modeling for electromagnetic collocated
           satellites of diffraction imaging on geostationary orbit
    • Abstract: Publication date: Available online 11 October 2019Source: Acta AstronauticaAuthor(s): Xinzhu Sun, Xiande Wu, Weidong Chen, Yong Hao, Kofi Akrofi Mantey, Han Zhao This paper proposes an innovated approach to model an electromagnetic force which is an ideal control force without plume and light pollution for optical imaging system. The main scope is modelling the 3-axis coupled electromagnetic force using dual quaternion for its advantages in describing spiral motion with translation and rotation motion simultaneously. The derivation procedure relies on a far field model of the electromagnetic force, and also, the force is re-formulized. Final equations show the dual quaternion dynamics can express the relative motion caused by the electromagnetic force acting on the position and attitude integrally. A new mission concept of diffraction imaging system in GEO is discussed as application scenario of the new dynamics model. Two cases with different mass were simulated to verify the new model, and the results display the electromagnetic force is significant for a small mass spacecraft in GEO.
  • Study on the behavior of sunk screw connection between cabins in the
    • Abstract: Publication date: Available online 10 October 2019Source: Acta AstronauticaAuthor(s): Xiaogang Li, Xiaotian Zhang, Ruiqing Wang, Wenlong Wang A finite element model is conducted to investigate the behavior of sunk screw connection between cabins in the rocket. The finite element model is compared with experiment by the displacement along cabin. The load distribution of sunk screw connection between cabins subjected to bending moment and axial force is studied by analytical approach and numerical approach. It is found that the analytical approach can predict the load distribution accurately when the connection subjected to bending moment only and the friction is ignored at the same time. The axial force has significant effect on load distribution. With the rise of axial force, the shear forces on screw-1 to screw-3 significantly increase and the shear forces on screw-11 to screw-13 significantly decrease. Then a qualitative parametric study is presented to investigate the influence of friction and pretension on load distribution and strength. It is shown that with the increase of friction coefficient, the shear forces on sunk screw and the slope of shear force curve decrease. Therefore, the average attenuation coefficient can be introduced to predict the load distribution more accurately. In addition, the shear forces on screws reduce approximately linearly with the rise of pretension and the optimum pretension force can be predicted by finite element method.
  • Effect of exercise on brain function as assessed by functional
           near-infrared spectroscopy during a verbal fluency test in a simulated
           International Space Station environment: a single-case, experimental ABA
           study in Japan
    • Abstract: Publication date: Available online 9 October 2019Source: Acta AstronauticaAuthor(s): Shin-ichiro Sasahara, Christina-Sylvia Andrea, Go Suzuki, Yuichi Oi, Shotaro Doki, Daisuke Hori, Takashi Ohira, Chie Matsuda, Natsuhiko Inoue, Tsukasa Takahashi, Yuh Ohtaki, Tamaki Saito, Satoshi Furukawa, Katsuhiko Ogata, Ichiyo Matsuzaki Over the past few years, the number of Japanese astronauts recruited for a long-term stay in the International Space Station (ISS) has increased. However, no consensus has been reached on a standardized method for measuring psychosocial stress triggered under such confined environment conditions, and on methods to effectively minimize the detrimental effects of such stress. To address this matter, we aimed to inspect stress-related index measurements of frontal brain function in experiments simulating long-term space confinement environment at the Japan Aerospace Exploration Agency (JAXA). Study participants (N=8, all adult men) were confined in the “confinement environment adaptation training facilities” of the Tsukuba Space Centre for 15 days, in a controlled, confined environment that attempted to closely simulate the conditions experienced by astronauts during the astronaut selection examination and inside the ISS. Frontal brain activation of the prefrontal cortex during a verbal fluency test (VFT) was evaluated as a confinement-related stress index, measured by functional near-infrared spectroscopy (fNIRS), a non-invasive brain-imaging method. An exercise intervention was additionally applied, using a single-case experimental ABA design (Intervention period (B): 5 days, 15 min aerobike daily exercise; Control periods (A): 5 days before and 5 days after intervention period, prohibition of any type of exercise), to observe whether exercise could have an ameliorating effect on the confinement-induced stress. The fNIRS values showed a significant decrease at the beginning of confinement when compared with the before-confinement values, remaining stable during confinement and thus showing no difference between the exercise intervention and control periods, ultimately returning to pre-confinement levels a week after confinement (analyzed using a generalized linear mixed model). The fNIRS-measured initial decrease in prefrontal cortex activity indicates that fNIRS can efficiently detect the confinement-triggered stress. Importantly, the stable fNIRS values during confinement suggest that exercise can maintain the frontal brain function assisting against further deterioration under confinement environment stress. Our results support that exercise can facilitate better prefrontal cortex activity combating the negative effects of confinement-induced stress, and therefore should be beneficial for maintaining good frontal brain function among astronauts in the ISS.
  • A small spacecraft to probe the interior of the Jovian moon Europa: Europa
           Tomography Probe (ETP) system design
    • Abstract: Publication date: Available online 9 October 2019Source: Acta AstronauticaAuthor(s): Virginia Notaro, Mauro Di Benedetto, Guido Colasurdo, Daniele Durante, Paolo Gaudenzi, Luigi Imperi, Mirco J. Mariani, Armando Marotta, Gianluca Palermo, Luciano Pollice, Paolo Racioppa, Alessandro Zavoli, Luciano Iess We propose the system design of a small orbiter of the Jovian moon Europa (Europa Tomography Probe, ETP in short) aimed at unveiling its interior structure. ETP is conceived as a piggyback probe of a larger spacecraft to the Jovian system (such as Europa Clipper). Its payload comprises only a magnetometer and transponder. The former will be used to measure the time-varying, induction magnetic field of the moon at different orbital and rotational frequencies, a measurement inaccessible to a flyby spacecraft. An Inter-Satellite Link (ISL) between ETP and the main spacecraft, enabled by the on-board transponder, will be used to accurately determine Europa’s gravity field, rotational state and tidal deformation. By combining magnetic and gravity field measurements, ETP could characterize the interior structure of Europa with an accuracy only attainable by a low-altitude orbiter, thus constraining the thickness and conductivity of the subsurface ocean. Following the announcement that a 250-300-kg mass allowance was available on the upcoming NASA Europa Clipper spacecraft, we propose ETP’s mission and spacecraft design assuming Clipper’s nominal trajectory as a baseline. The concept can be adapted to a class of missions to the Jovian and Saturnian systems based upon a mother-daughter spacecraft system. The spacecraft design has been pursued under the philosophy of determining the minimum required total mass and volume that allows to meet the scientific requirements, rather than finding out what science return could be obtained with pre-assigned system constraints. Since ETP shall autonomously reach its final orbit, the propulsion system has been one of the primary focuses. The radiation analysis has also been essential because the shielding structure affects both the mission duration and the mass budget. We show that the ETP concept could be, indeed, technically feasible with an overall system mass budget just above 250 kg, thus providing a valuable yet affordable augmentation to a larger flyby mission to Europa.
  • DRAG on a spacecraft produced by the interaction of its magnetic field
           with the EARTH’S ionosphere. Physical modelling
    • Abstract: Publication date: Available online 9 October 2019Source: Acta AstronauticaAuthor(s): Valentin A. Shuvalov, Nikolai B. Gorev, Nikolai A. Tokmak, Yuri P. Kuchugurnyi The dynamic interaction of a “magnetized” sphere (a sphere with a magnetic field source) with a hypersonic rarefied plasma flow was studied experimentally to model the interaction of a “magnetized” spacecraft with the ionospheric plasma. The experiments were conducted at the plasma flow velocity parallel and normal to the sphere’s magnetic field. The electromagnetic drag coefficient was determined as a function of the ratio of the magnetic pressure to the dynamic pressure and the ratio of the mini-magnetosphere dimension to the spacecraft dimension (sphere radius). It was shown that a spacecraft’s magnetic field of about 0.8–1.5 T produces an electromagnetic drag comparable with the drag produced using ion beam technologies of space debris removal, which require dedicated spacecraft with plasma accelerators. Energy-efficient compact sources of a 0.8–1.5 Т magnetic field for space debris objects may be made using special arrangements of small-size permanent magnets – Halbach arrays.
  • Fast simulation of X-ray pulsar signals at a spacecraft
    • Abstract: Publication date: Available online 9 October 2019Source: Acta AstronauticaAuthor(s): Jianyu Su, Haiyan Fang, Weimin Bao, Haifeng Sun, Lirong Shen, Liang Zhao Existing methods for simulating pulsar signals at a spacecraft are inapplicable for large flux or high frequency because of their low efficiency, hindering research on X-ray pulsar-based navigation. To solve the problem, we propose a fast method based on the relation derivation between the photon arrival time and corresponding photon phase at the spacecraft. The absolute differences of searched frequencies between simulated data and observational data for the Crab pulsar are less than10-4, which sufficiently validates the method. Furthermore, the proposed method is up to 3 orders of magnitude faster than other methods, which shows that it is more efficient and better satisfies the needs of real-time navigation verification.
  • Numerical study of flow structures and mixing characteristics of a sonic
           jet in supersonic crossflow
    • Abstract: Publication date: Available online 9 October 2019Source: Acta AstronauticaAuthor(s): Chang-hai Liang, Ming-bo Sun, Yuan Liu, Guang-xin Li, Jiang-fei Yu This study numerically investigated the influence of flow structures on the mixing characteristics of a sonic transverse gaseous ethylene jet in a supersonic crossflow with a Mach number of 2.95. RANS (Reynolds Average Navier-Stokes) simulations were employed to reveal the transport mechanism of jet fluid. The influencing factors, the jet-to-crossflow momentum flux ratio (J) and the nondimensional thickness of the turbulent boundary layer in the mixing characteristics of the sonic transverse gaseous jet are investigated. In the near-wall field, there is a V-shaped region in the front of the separation bubble that contains more jet gas under a lower momentum flux ratio (J) condition, which is caused by the collision of different inflow streamlines. As the turbulent boundary layer grows, there is more space for the jet gas to expand so that the penetration of the jet is much higher.
  • Integration of energy storage functionalities into fiber reinforced
           spacecraft structures
    • Abstract: Publication date: Available online 9 October 2019Source: Acta AstronauticaAuthor(s): Benjamin Grzesik, Guangyue Liao, Daniel Vogt, Linus Froböse, Arno Kwade, Stefan Linke, Enrico Stoll One of the common challenges of spaceflight and e-mobility is the energy storage. The operational ranges of spacecraft or electric cars as well as operational usability is strongly dependent on the capacity of the energy storage, which is usually constrained by the mass and volume of the vehicle. For example, the battery mass of large communication satellites ranges from 6 % to 9 % of the dry mass. This amount increases for smaller satellites like CubeSats up to 13 % without accounting wiring harnesses and subsystem volume. Thus, a system can benefit from a reduction in mass and volume by combining multifunctional use of the components and materials. In the presented research, energy storage is integrated into lightweight carbon fiber materials. Carbon fibers have a distinct mass advantage compared to metal structures. In addition, they have very low thermal expansions that can reduce thermal stresses during the operation of a satellite. Fiber composites or laminates consist of two components, the fibers and the matrix material. In laminates, the typically resin based matrix content is 30 to 40 % of the component volume and could be substituted with novel solid state battery materials. Latter have the advantage that they have nearly similar physical properties as usually used resins and are also able to store energy electrochemically. Thus, about 25 % of the volume can be used for electrochemical energy storage without compromising structure integrity. To reach such electrochemical functions the host structures have to be infiltrated with anode, cathode, and separator materials. Using the developed recipes and a component thickness of 5 millimeters, an energy amount per component area of 1130 Wh/m2 can be reached depending on the applied battery active material.This article will give an overview of how fiber composite materials, which are increasingly being used in lightweight construction processes, can be combined with energy storage materials to be used in spacecraft structures. The goal of the research on this topic at the Technische Universtät Braunschweig is a structure battery for a spacecraft. However the article addresses as a first step the characterization and manufacturing of structural battery composite negative half-cells from carbon fiber reinforced PEO/LiTFSI. An estimation of the expected performance is carried out. The initial material evaluation and the manufacturing process as well as mechanical and electrical result will be discussed.
  • Changes in the cellular component of the human innate immunity system in
           short-term isolation
    • Abstract: Publication date: Available online 9 October 2019Source: Acta AstronauticaAuthor(s): Sergey Ponomarev, Olga Kutko, Marina Rykova, Sergey Kalinin, Evgenya Antropova, Anastasiya Sadova, Kseniya Orlova, Sofiya Shulgina A systemic approach in the evaluation of the various components of the immune system gave an opportunity to identify a number of characteristics of adaptive changes, including the quantitative and functional changes in both innate and adaptive immunity in response to space flight. Among them the most important are the changes in the system of Toll like receptors (TLRs), namely, the decrease in the content of circulating monocytes and granulocytes expressing TLR2, TLR4, TLR6, and inhibition of T-cells functional potential. However, a fundamentally important problem of revealing the complex of intermolecular and intercellular interactions during the immune response development under space fight conditions in an organism as a whole still remains unsolved. By now there exists quite strong evidence that dendritic cells (DCs) play the important role in linking the innate and adaptive immunity through their characteristic expression patterns of TLRs and cytokine production. In this study we examined the number of circulating plasmacytoid DCs (pDCs) and monocytes expressing signaling PRRs in 6 healthy participants of the “SIRIUS-17" project. Whole blood was collected at prior, during and post isolation periods from three male and three female volunteers aged 27 to 43 who spent 17 days in permanent isolation in an enclosed habitat consisting of hermetically sealed interconnecting modules at the Institute for Biomedical Problems (IBMP) in Moscow. Results of the investigation showed a distinct effect of short-term isolation on the immune system ability to mobilize. Although no significant changes in the percentages of cells which expressed surface TLRs (TLR1, TLR2, TLR4, TLR5 and TLR6) and endosomal TLRs (TLR3, TLR8 and TLR9) were noted, the percentage of pDCs (CD14-/CD16-CD123+CD85k+) significantly increased on day 7 of the experiment compared with the baseline. These changes were independent of gender of volunteers. On the first day of recovery period the levels of TLRs and pDCs were lower than before the isolation almost in all volunteers, however observed changes in pDCs were not statistically significant. These data suggest that, unfavorable factors of a space flight make immune system function differently compared to the normal conditions. This mobility of the immune system allows adaptation to the constantly fluctuating environment. However, the adaptive restructuring requires mobilization of functional resources at an early stage of adaptation, which can lead to depletion of reserve capabilities of the immune system.
  • An optimization dust-removing electrode design method aiming at improving
           dust mitigation efficiency in lunar exploration
    • Abstract: Publication date: Available online 9 October 2019Source: Acta AstronauticaAuthor(s): Jing Jiang, Yifan Lu, Xiaoteng Yan, Lei Wang The photovoltaic lunar dust removal technology has proved to own potential application for future space exploration. In this new technology, based on the high voltage characteristics of the photoelectric material lanthanum-modified lead zirconate titanate (PLZT), a dust-removing electrode is used to polarize and remove the lunar dust. The influence of the area and the shape of the dust-removing electrode on the dust removal performance is analyzed in this paper. An optimization of dust-removing electrode design method is proposed and comb-shaped electrodes are designed to improve the dust mitigation efficiency of the system. The configuration of the comb-shaped electrode is optimized by theoretical analysis. A series of experiments are performed to reveal the influence of different factors, such as electrode area, electrode shape, light intensity, copper foil thickness, insulation film and geometric parameters of electrode, etc. on the dust removal performance. Research results of this work can serve as guidelines for optimization electrode design to maximize the efficiency of this photovoltaic lunar dust removal system for future lunar exploration.
  • Heuristic Search via Graphical Structure in Temporal Interval-based
           Planning for Deep Space Exploration
    • Abstract: Publication date: Available online 8 October 2019Source: Acta AstronauticaAuthor(s): Hao Jin, Rui Xu, Pingyuan Cui, Shengying Zhu, Feng Zhou Operations of conventional spacecraft used to be planned on ground and are uploaded as telecommands and executed on board at due time. However, because of difficulties in communicating with distant spacecraft, direct human control for the spacecraft is infeasible. Therefore, great hopes are placed on automated planning techniques to enhance the security of the spacecraft. By deciding a complex set of activities or states, an onboard planner is able to effectively arrange the daily tasks on a spacecraft. In addition, as to support opportunistic science, the planner is also required to respond in the shortest possible time. Typically, to better characterize the spacecraft, the timeline-based knowledge representation benefits from its powerful ability to describe time and temporal behaviors, which is essential to effectively address real world problems. Compliant with the representation method, an elegant approach is devised for search guidance and solving problems efficiently in space-like contexts. Specifically, the key technique we build on is the heuristic estimate strategy based on a graphical structure defined in the model. Furthermore, a search algorithm joint with the heuristic function is proposed to avoid redundant work. By evaluating the branching nodes, this approach is able to prune irrelevant search space and make improvements in onboard planning efficiency. Our experiments exhibit an excellent performance on tested instances compared to Europa2.
  • Estimation of a reliability range for the area-to-mass ratio of orbiters
           at the geostationary ring
    • Abstract: Publication date: Available online 7 October 2019Source: Acta AstronauticaAuthor(s): Elvis Lacruz, Daniel Casanova, Alberto Abad This paper shows the precise relative motion of different orbiters located at the geostationary region thanks to high precision astrometric coordinates, which are calculated thanks to different accurate observations taken from the Venezuelan National Observatory. These orbiters are close to each-other and present different relative motions although the magnitude of the distribution forces that act over them is the same. Thus, these orbiters must posses other intrinsic physic parameters which provokes the different observed morphological dynamic. In particular, the area-to-mass ratio could be one of them, and consequently, the main goal of this paper is to determine a reliability range for the area-to-mass ratio, that justifies the relative motion of these objects. Since a complete relative motion of the orbit is not feasible, we use realistic models to simulate the real motion of these orbiters, and we associate them an invented value for the area-to-mass ratio. Then, we use an analytical reduced model to compute the evolution of the eccentricity, considering different values for the area-to-mass ratio. Consequently, we are able to recover a reliability range for this invented parameter. In this work, it is also possible to consider the real ephemerides of objects listed in the CelesTrack database, and estimate its corresponding value for the area-to-mass ratio. Thus, this paper provides an innovative way to obtain a physical property of a space object just by observational information.
  • Parameter analysis of on-orbit volumetric measurement using cavity
    • Abstract: Publication date: Available online 7 October 2019Source: Acta AstronauticaAuthor(s): Zhen Li, Yong Chen, Xin Li, Xiang Zhang, Xiaoqian Chen Propellant volumetric measurement based on the cavity acoustic resonance may be a promising alternate in space microgravity environment. The present paper concentrates on the influences of the hemispherical structure of the tank, steady/unsteady non-flat continuous propellant-gas interface, and propellant’s compressibility on the acoustic resonant frequency of the system. A one dimensional mathematical acoustic resonant model, where acoustic perturbation dynamics only in the axial coordinate is considered, based on conservations of mass and momentum is provided and compared with numerical simulations by COMSOL software and experiments conducted by the previous research. Results show that analytical predictions by the present model keep consistent with numerical simulations and experiments. While the structure of a hemispherical tank can influence the resonant frequency, the present model can optimizationally compensate such effect. The continuous non-flat propellant-gas interface changes the resonant frequency. A flatter interface leads to smaller influence. On the other hand, the unsteady low-frequency low-amplitude wave-like movement of the propellant-gas interface imposes negligible effluence on the resonant frequency of the tank. Finally, the propellant compressibility is quantitatively shown to be negligible for most propellants.
  • Influences of wall vibration on shock train structures and performance of
           two-dimensional rectangular isolators in scramjet engine
    • Abstract: Publication date: Available online 4 October 2019Source: Acta AstronauticaAuthor(s): Xianzong Meng, Zhengyin Ye, Zheng Hong, Kun Ye Shock trains are formed by shock wave boundary layer interaction in isolator to match the pressure between inlet and combustor. However, the complexity of this problem has primarily restricted to rigid isolators without deformation. A little is known regarding the impact of wall vibration, due to structural elasticity, on the flow in isolator. The current study focuses on this problem by comparing changes of 13 parameters regarding separation zone, shock structure, flow asymmetry and isolator performance. Results examine the differences due to one-wall vibration, two-wall vibration and short panel vibration. Analyses indicate that one-wall vibration will cause the upstream movement and length decrease of separation zone, upstream movement and length growth of shock trains, increase of flow asymmetry with large transient side loads and decrease of performance. Moreover, compared to one-wall vibration, two walls vibrating in opposite direction leads to a larger influence on flow structures and isolator performance, while the effect of two-wall vibration in the same direction is relative minor on flow structures and significant on flow asymmetry as well as isolator performance. Furthermore, by placing vibrating panels at different locations, analyses identify that the influence of upstream and midstream vibrations is stronger than downstream vibration in wall vibration. The upstream vibration has a greater impact on flow structures while the midstream vibration has a greater effect on flow asymmetry and isolator performance. The current study emphasizes the importance of future investigations on aeroelastic problem in isolator and provides primary knowledge for flow control by considering flexible or vibrating panel.
  • Effects of Cavity Depth on the Ethylene-air Continuous Rotating Detonation
    • Abstract: Publication date: Available online 3 October 2019Source: Acta AstronauticaAuthor(s): Shi-Jie Liu, Hao-Yang Peng, Wei-Dong Liu, Hai-Long Zhang Continuous Rotating Detonation (CRD) is a promising combustion mode for aerospace propulsion, with high heat release rate and thermodynamic efficiency, but it exhibits realization difficulty for fuels with low chemical activity. To settle this issue, a cavity-based annular combustor scheme has been proposed in our previous study, and its feasibility has been well demonstrated. A series of ethylene-air tests under different cavity configurations have been carried out in this paper, and the effects of cavity depth are revealed. For CRD mode, traditional isobaric combustion also exists at the contact surface between the high temperature burnt products and combustible mixture. Increasing the cavity depth can improve its isobaric combustion holding ability, but excessive isobaric combustion could destroy the foundation of CRD. For fuels with low chemical activity, appropriately improving the isobaric combustion can help the CRD realization. This paper reveals the cavity depth effects on the competitive relationship between isobaric combustion and CRD, and it can be used as a guideline for the CRD combustor design.
  • Unistellar eVscopes: Smart, Portable, And Easy-To-Use Telescopes For
           Exploration, Interactive Learning, and Citizen Astronomy
    • Abstract: Publication date: Available online 27 September 2019Source: Acta AstronauticaAuthor(s): Franck Marchis, Arnaud Malvache, Laurent Marfisi, Antonin Borot, Emmanuel Arbouch Unistellar has created the Enhanced Vision Telescope (eVscope), a compact telescope that amplifies light so users can see hundreds of nebulae and galaxies directly through its electronics eyepiece. It can also pinpoint and identify objects in the sky, making amateur astronomy fun and more accessible to the public. Thanks to its sensitivity and accuracy, the eVscope is a powerful tool able to generate data that can be used by scientists to search for transient events like supernovae, near-Earth asteroids, and comets. This constellation of small, & smart telescopes could also enhance and supplement data generated by the small number of large telescopes operating today. Unistellar initiated a partnership with the SETI Institute to identify and implement scientific applications for a network of eVscopes. We summarize in this article the technology behind the eVscope and its real-time data processing (Enhanced Vision, Automatic Field Detection), then show several applications accessible to future users, including asteroid occultations, the detection of the atmosphere of Pluto and observations of near-Earth asteroids. The Unistellar network has the potential to make citizen astronomy a popular reality by offering all users (new or experienced) a tool to explore the night sky with a powerful and reliable instrument while they contribute to scientific investigations.
  • Behavior and flow mechanism of shock train self-excited oscillation
           influenced by background waves
    • Abstract: Publication date: Available online 27 September 2019Source: Acta AstronauticaAuthor(s): Wenxin Hou, Juntao Chang, Zongqi Xie, Youyin Wang, Linke Wu, Wen Bao This study investigates shock train self-excited oscillation—influenced by background waves—occurring within an isolator in a direct-connect wind tunnel. The experimental data were obtained using high-speed Schlieren technique and high-frequency pressure measurements. Three oscillation modes of shock train self-excited oscillations were studied and have been presented in detail. These include Top-Large-Separation, Bottom-Large-Separation, and transition modes. The observed shock train with background waves conformed to one of the three modes, whereas the oscillation mode appeared randomly within a uniform incoming flow. To understand the differences of shock train unsteady behaviors in different modes, the distributions of intermittent region and zero-crossing frequency were compared. Furthermore, the mode and approximate location of the oscillations were judged by the distribution of wall pressure standard deviation. The influence of background waves on the shock train self-excited oscillation was then analyzed. For the shock train in a uniform incoming flow, the Strouhal number always lies in the range of 0.01–0.03, and the Strouhal number at both side walls is substantially equal. However, for the shock train influenced by background waves, the Strouhal number may fall outside the range of 0.01–0.03, and Strouhal number at the top and bottom walls is different. It was found that the wall pressure gradient caused by background waves affects the instability in the separation zone after the shock train leading edge, thereby influencing the unsteadiness of shock train self-excited oscillation.
  • Blind Validation Study of Parametric Cost Estimation Tool SEER-H for NASA
           Space Missions
    • Abstract: Publication date: Available online 25 September 2019Source: Acta AstronauticaAuthor(s): Paul D. Friz, Serhat Hosder, Benjamin B. Leser, Benjamin C. Towle One of the primary parametric cost modeling tools used by NASA and the aerospace industry to estimate the development and production cost of future spacecraft hardware is SEER-H by Galorath. To date, no independent validation of this tool for cost estimation of space missions has been reported in the literature. In the present validation study, cost estimators used SEER-H to estimate the cost of twelve different past NASA science missions. The estimators were prevented from knowing the actual cost of the missions in an effort to minimize cognitive biases. The point estimates of SEER-H had an average error of 23%, median error of -0.3%, and a standard deviation of 43%. Nine of the twelve mission’s actual costs fell within the 80% confidence interval of SEER’s probabilistic estimates. Several factors independent of SEER that may have affected the accuracy of the results have been identified and are discussed; these include: uncertainty in the technical data used for the estimates, the methods used to estimate uncertainty in spacecraft component mass and numbers of prototypes, and the experience of the estimators.
  • 3D inverse method of characteristics for hypersonic bump-inlet integration
    • Abstract: Publication date: Available online 24 September 2019Source: Acta AstronauticaAuthor(s): Zonghan Yu, Guoping Huang, Chen Xia Waverider-inlet integration design is an important approach to realize hypersonic flight. The inlet lip is the key factor for internal/external flow field coupling. This paper proposes a novel 3D inverse method of characteristics (MOC) to design the inlet lip with generalized 3D shock. The unit process and marching procedure of the inverse MOC in 2D and 3D focus on obtaining the unique coordinates of the solution points. The accuracy of inverse MOC is verified through its comparison with the analytical solution of a conical flow field. The approach is then applied for a hypersonic bump-inlet integration (The freestream Mach number M∞=6.0), where the inlet lip is inversely generated by a prescribed elliptic-conical shock wave. Inviscid results reveal good performance (The mass capturing ratio φ=0.813, the Mach number of inlet exit Mexit=3.71, the total pressure recovery coefficientσ=0.752). The incident shock is well attached on the inlet lip, which is of high ϕ. Viscous results show relatively low performance (φ=0.738, Mexit=2.94, σ=0.471), which indicates that the new method is a promising solution for the hypersonic internal/external coupling flow. Although the viscous effects should be further considered to improve the design, the proposed method can be applied to 3D surface design with generalized shock shapes.
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