Analysis of the data processing strategies of spherical harmonic expansion model on global ionosphere mapping for moderate solar activity

Spherical harmonic (SH) expansion is widely used to model the global ionosphere map (GIM) of vertical total electron content (VTEC). According to the impact of different data processing methods of the SH expansion model on the VTEC maps, we specifically performed comprehensive analysis in terms of the data sampling rate, the time resolution, the spherical harmonic degree, and the relative constraint. One month of GPS data (January in 2016) from the International GNSS (Global Navigation Satellite System) Service (IGS) network in a moderate ionospheric activity period at the descending phase of Solar Cycle 24 was processed. To improve the computational efficiency of the daily GIM generation, the data sampling rate of 5?min was recommended allowing the GIM precision loss within 0.10 TECU (total electron content unit). The global VTEC map could be better represented in temporal and spatial domains with higher time resolution and higher spherical harmonic degree, especially at low latitude bands and in the southern hemisphere. The GIM precision improvement was about 10.91% for 1-h and about 15.15% for 0.5-h compared with the commonly used 2-h time resolution. The use of spherical harmonic degree 17 or 20 instead of 15 could improve the precision by 3.19% or 6.06%. We also found that an optimal relative constraint had to be found experimentally considering both the GIM precision and the GIM root mean square (RMS) map.     

Multi-objective Optimization of Differential Steering System of Electric Vehicle with Motorized Wheels

A differential steering system is presented for electric vehicle with motorized wheels and a dynamic model of three-freedom car is built. Based on these models, the quantitative expressions of the road feel, sensitivity, and operation stability of the steering are derived. Then, according to the features of multi-constrained optimization of multi-objective function, a multi-island genetic algorithm （MIGA） is designed. Taking the road feel and the sensi- tivity of the steering as optimization objectives and the operation stability of the steering as a constraint, the system parameters are optimized. The simulation results show that the system optimized with MIGA can improve the steering road feel, and guarantee the operation stability and steering sensibility.     

Simulation analysis for effects of bone loss on acceleration tolerance of human lumbar vertebra

The purpose of the present study was to analyze and predict the changes in acceleration tolerance of human vertebra as a result of bone loss caused by long-term space flight. A human L3–L4 vertebra FEM model was constructed, in which the cancellous bone was separated, and surrounding ligaments were also taken into account. The simulation results demonstrated that bone loss has more of an effect on the acceleration tolerance in x-direction. The results serve to aid in the creation of new acceleration tolerance standards, ensuring astronauts return home safely after long-term space flight. This study shows that more attention should be focused on the bone degradation of crew members and to create new protective designs for space capsules in the future.     

Predicting performance in manually controlled rendezvous and docking through spatial abilities

Manually controlled rendezvous and docking (manual RVD) is a challenging space task for astronauts. This study aims to identify spatial abilities that are critical for accomplishing manual RVD. Based on task analysis, spatial abilities were deduced to be critical for accomplishing manual RVD. 15 Male participants performed manual RVD task simulations and spatial ability tests (the object-manipulation spatial ability and spatial orientation ability). Participants’ performance in the test of visualization of viewpoints (which measures the spatial orientation ability) was found to be significantly correlated with their manual RVD performance, indicating that the spatial orientation ability in the sense of perspective taking is particularly important for accomplishing manual RVD.     

Stability of relative equilibria of the full spacecraft dynamics around an asteroid with orbit–attitude coupling

The full dynamics of spacecraft around an asteroid, in which the spacecraft is considered as a rigid body and the gravitational orbit–attitude coupling is taken into account, is of great value and interest in the precise theories of the motion. The spectral stability of the classical relative equilibria of the full spacecraft dynamics around an asteroid is studied with the method of geometric mechanics. The stability conditions are given explicitly based on the characteristic equation of the linear system matrix. It is found that the linearized system decouples into two entirely independent subsystems, which correspond to the motions within and outside the equatorial plane of the asteroid respectively. The system parameters are divided into three groups that describe the traditional stationary orbit stability, the significance of the orbit–attitude coupling and the mass distribution of the spacecraft respectively. The spectral stability of the relative equilibria is investigated numerically with respect to the three groups of system parameters. The relations between the full spacecraft dynamics and the traditional spacecraft dynamics, as well as the effect of the orbit–attitude coupling, are assessed. We find that when the orbit–attitude coupling is strong, the mass distribution of the spacecraft dominates the stability of the relative equilibria; whereas when the orbit–attitude coupling is weak, both the mass distribution and the traditional stationary orbit stability have significant effects on the stability. We also give a criterion to determine whether the orbit–attitude coupling needs to be considered.     

The Kumtag meteorite strewn field

The Kumtag meteorite strewn field was found in the Kumtag desert, 132 km south of Hami city in the Xinjiang province, China. It is an ellipse of 2.5 × 7.9 km, with a long axis extending along the northeast-southwest direction. The largest individual meteorite of the strewn field weighs about 10 kg; the smallest individual has a mass of only 27 g. In total, more than 100 individuals with a total mass of more than 180 kg were collected. The location and the distribution of the fragments suggest that the Kumtag meteoroid entered the atmosphere in the direction Northeast-Southwest. All meteorites collected in this strewn field are samples from the same unique meteorite shower. The Kumtag meteorite is an H5 ordinary chondrite with a shock stage S2, and a weathering grade W2. The cosmic ray exposure age of Kumtag is 6.7 ± 0.8 Ma, which is rather typical for H chondrites and which indicates that Kumtag was derived from the massive impact event on its parent body ~7 Ma ago. A significant amount of He has been lost during certain unknown processe(s) before the Kumtag meteorite was ejected from its parent body.     

Electron density inversed by plasma lines induced by suprathermal electron in the ionospheric modification experiment

Incoherent scatter radar (ISR) is the most powerful ground-based measurement facility to study the ionosphere. The plasma lines are not routinely detected by the incoherent scatter radar due to the low intensity, which falls below the measured spectral noise level of the incoherent scatter radar. The plasma lines are occasionally enhanced by suprathermal electrons through the Landau damping process and detectable to the incoherent scatter radar. In this study, by using the European Incoherent Scatter Association (EISCAT) UHF incoherent scatter radar, the experiment observation presents that the enhanced plasma lines were observed. These plasma lines were considered as manifest of the suprathermal electrons generated by the high-frequency heating wave during the ionospheric modification. The electron density profile is also obtained from the enhanced plasma lines. This study can be a promising technique for obtaining the accurate electron density during ionospheric modification experiment.     

Assessment on critical technologies for conceptual design of blended-wing-body civil aircraft

Civil aviation faces great challenges because of its robust projected future growth and potential adverse environmental effects. The classical Tube-And-Wing(TAW) configuration following the Cayley's design principles has been optimized to the architecture's limit, which can hardly satisfy the further requirements on green aviation. By past decades' investigations the BlendedWing-Body(BWB) concept has emerged as a potential solution, which can simultaneously fulfill metrics of noise, emission and fuel burn. The purpose of the present work is to analyze the developments of critical technologies for BWB conceptual design from a historical perspective of technology progress. It was found that the high aerodynamic efficiency of BWB aircraft can be well scaled by the mean aerodynamic chord and wetted aspect ratio, and should be realized with the trade-offs among stability and control and low-speed performance. The structure concepts of non-cylinder pressurized cabin are of high risks on weight prediction and weight penalty. A static stability criterion is recommended and further clear and adequate criteria are required by the evaluations of flying and handling qualities. The difficulties of propulsion and airframe integration are analyzed. The energy to revenue work ratios of well-developed BWB configurations are compared,which are 31.5% and 40% better than that of TAW, using state-of-art engine technology and future engine technology, respectively. Finally, further study aspects are advocated.     

Distributed intelligent self-organized mission planning of multi-UAV for dynamic targets cooperative search-attack

This article studies the cooperative search-attack mission problem with dynamic targets and threats, and presents a Distributed Intelligent Self-Organized Mission Planning (DISOMP) algorithm for multiple Unmanned Aerial Vehicles (multi-UAV). The DISOMP algorithm can be divided into four modules: a search module designed based on the distributed Ant Colony Optimization (ACO) algorithm, an attack module designed based on the Parallel Approach (PA) scheme, a threat avoidance module designed based on the Dubins Curve (DC) and a communication module designed for information exchange among the multi-UAV system and the dynamic environment. A series of simulations of multi-UAV searching and attacking the moving targets are carried out, in which the search-attack mission completeness, execution efficiency and system suitability of the DISOMP algorithm are analyzed. The simulation results exhibit that the DISOMP algorithm based on online distributed down-top strategy is characterized by good flexibility, scalability and adaptability, in the dynamic targets searching and attacking problem.