Aluminum particle ignition behavior in open atmosphere rocket propellants fires is of particular interest for preventing accidents for rockets carrying high-value payloads. For nominal motor pressures, aluminum particles oxidize to aluminum oxide in the gas phase and release significant combustion energy while minimizing motor instability. During rocket abort or launch pad malfunction which occur under atmospheric or low pressure, behavior of aluminum particle combustion becomes complex and aluminum appears to melt, agglomerate or form a skeletal structure. Furthermore, an oxide shell of alumina instantly forms on any fresh aluminum surface which is exposed to an oxidizing environment. Aluminum combustion then strongly depends on the oxide layer growth, which is influenced by causative factors, including particle size, environmental gas composition, and heating rate. This work focuses on the effect of the oxide barrier which forms on the surface of aluminum that is recognized to impede combustion of aluminum in solid rocket propellants. Understanding the mechanism for breach of this barrier is deemed to be an important consideration in the overall process. In this discussion, results of various experiments will be discussed which have a bearing on this process. Basically, a recognized criterion is the melting of the oxide layer at 2350 K is sufficient. However, in other situations, depending on the mechanism of oxide formation, there will occur defects in the oxide shell which provide for aluminum ignition at lower temperatures. For slow heating in an oxidizing environment, where the oxide layer can grow thick, then ignition is more difficult. Because there is no uniform model to establish an ignition criterion due to the unknown history of an aluminum particle, this paper reports experimental findings involving oxyacetylene torch, thermogravimetric analysis with differential scanning calorimeter, aluminum particle heating, electric ignition and aluminum powder heating, to address the influence of the oxide layer on the aluminum particle ignition. Full article

To develop technologies for the stable operation of electric propulsion systems, the effects of charge exchange (CEX) on the exhaust plume of a Hall thruster were studied using the particle-in-cell direct simulation Monte Carlo (PIC-DSMC) method. For the numerical analysis, an OpenFOAM-based code, pdFOAM, with a simple electron fluid model was employed. In an example problem using the D55 Hall thruster exhaust plume, the results showed good agreement with experimental measurements of the plasma potential. In the results, CEX effects enhanced Xe⁺ particle scattering near the thruster exit. However, due to the increase in the plasma potential with CEX effects, fewer Xe²⁺ particles were near the thruster exit with CEX effects than without CEX effects. Full article

Stratospheric airships have much potential in military and commercial applications. Design, analysis and optimization of stratospheric airships involves complex trade-off of different disciplines, and hence a multidisciplinary approach is essential. This paper describes a methodology coupling several disciplines and involving seven design variables to obtain the optimal design of a stratospheric airship powered by solar arrays. A numerical method is established to calculate the output power of the solar array in the optimization process. The optimal solutions are obtained using hybrid algorithms. The methodology can obtain the optimal envelope shape, solar array layout and other general configurations of subsystems. Results show that the methodology was able to achieve a solution with a 19.2% reduction in airship volume compared to the value being part of an arbitrary initial set of airship parameters. In addition, a comparative study is carried out to highlight the importance of considerations of solar array layouts and array circumferential location. Furthermore, detailed sensitivity analysis shows that operating parameters of latitudes, heading angles and average resisting wind speeds have significant effects on the airship design and solar array layouts. Full article

Outgassing or thruster’s generated contaminants are critical for optical surfaces and optical payloads because scientific measurements and, in general, the performances can be degraded or jeopardized by uncontrolled contamination. This is a well-known issue in space technology that is demonstrated by the growing usage of quartz crystal microbalances as a solution for measuring material outgassing properties data and characterizing the on-orbit contamination environment. Operation in space requires compatibility with critical requirements, especially the mechanical and thermal environments to be faced throughout the mission. This work provides the design of a holding structure based on 3D printing technology conceived to meet the environmental characteristics of space application, and in particular, to face harsh mechanical and thermal environments. A kinematic mounting has been conceived to grant compatibility with a large temperature range, and it has been designed by finite element methods to overcome loading during the launch phases and cope with a temperature working range down to cryogenic temperatures. Qualification in such environments has been performed on a mockup by testing a prototype of the holding assembly between −110 ${}^{\circ }$C and 110 ${}^{\circ }$C and allowing verification of the mechanical resistance and stability of the electrical contacts for the embedded heater and sensor in that temperature range. Moreover, mechanical testing in a random environment characterized by an RMS acceleration level of 500 m/s² and excitation frequency from 20 to 2000 Hz was successfully performed. The testing activity allowed for validation of the proposed design and opened the road to the possible implementation of the proposed design for future flight opportunities, also onboard micro or nanosatellites. Moreover, exploiting the manufacturing technology, the proposed design can implement an easy assembling and mounting of the holding system. At the same time, 3D printing provides a cost-effective solution even for small series production for ground applications, like monitoring the contaminants in thermo-vacuum chambers or clean rooms, or depositions chambers. Full article

Ground-based optical observation of GEO space debris plays an essential role in tracking, identifying, cataloging, and classifying space debris. The factors that affect the brightness of space debris include size, surface material, illumination geometry, attitude, shape, position, and so on. In order to better understand the influence of the above factors on the brightness of space debris, the synthetic light curves are analyzed. The Ashikhmin–Shirley model is chosen to simulate the light curves of space debris. The effects of orbit, attitude, model parameters, and the location of the observation station on the synthetic light curves are analyzed by the control variable method. Based on the Markov Chain Monte Carlo method (MCMC), the optimal model parameters that characterize the surface material of space debris can be obtained by comparing the synthetic light curves with the observed light curves under certain shape, orbit, and attitude characteristics. The results are roughly in good agreement with those measured in the laboratory. Full article

In this work, the enhanced correction factor technique (ECFT) is modified for a subsonic wing–body interference model, which can consider the forces on both the lifting boxes and the body elements of an idealized airplane, termed the advanced ECFT method. A passenger aircraft model is chosen as the simulation model, and the longitudinal static aeroelasticity at the transonic situation for two-degree freedom, including the α (angle of attack) degree and ϕ (angle of horizontal tail) degree, is simulated in this paper. The corresponding CFD results are used to correct the aerodynamic influence coefficients (AIC) matrix, which is then simulated by MSC.NASTRAN. The pressure distribution results of different aircraft components received by the advanced ECFT method indicate that it is suitable for the subsonic wing–body interference model. Compared with the uncorrected linear method and the diagonal corrected method, it is generally more consistent with the CFD/CSD coupling method, not only for the lifting boxes, but also for the body elements. In addition, the aerodynamic derivative results also show good agreement with the flight test data, which solidly verifies the advance ECFT method. Full article

A formation flying control algorithm using the Lorentz force for Low Earth Orbits to achieve a trajectory with required shape and size is proposed in the paper. The Lorentz force is produced as a result of interaction between the Earth’s magnetic field and an electrically charged spacecraft. Achievement of the required trajectories represents a challenge since the control in three-dimensional space is a scalar value of the satellite’s charge. A Lyapunov-based control algorithm is developed for elimination of the initial relative drift after the launch. It also aims at reaching a required amplitudes for close relative trajectories for in-plane and out-of-plane motion. Due to the absence of full controllability, the algorithm is incapable of correcting all the parameters of the relative trajectory such as in-plane and out-of-plane phase angles. The proposed control allows to converge to the trajectory with required shape and size, though with some oscillating errors in the vicinity of the required trajectory parameters. Numerical simulation of the relative motion is used to study performance of the control algorithm for one case of one controlled satellite and two cases of five controlled satellites forming a nested ellipses and train formations. The convergence time and final trajectory accuracy are evaluated for different control parameters and orbits using Monte Carlo approach. Full article

Obtaining the inertia tensors of defunct space objects is essential in on-orbit missions. When the inertia tensor of the space object is non-diagonal, the problem becomes challenging. In this case, the system does not have enough information to estimate the six independent parameters of the inertia tensor. In this paper, the problem of estimating the inertial parameters of a defunct space object with non-diagonal inertia tensor is studied. An excitation method of ejecting an impact ball from the tracking spacecraft to the object is proposed to estimate the complete inertial parameters of the object. The impact ball rebounds after colliding with the object and crashes into the atmosphere finally. After the collision, the angular momentum of the space object changes. The change is used to construct the estimation model. This paper designs an estimation model which consists of two Unscented Kalman-based estimators to estimate the inertial parameters and the motion states of the object. The observability of the estimators is proved through the observability theorem of nonlinear systems. Numerical simulations show that the estimation model is effective in estimating the complete inertial parameters of defunct objects, as well as reducing the measurement errors of the position and attitude of the object. Full article

Wind is one of the main factors raising errors in the spacecraft’s landing phase. As a result, an accurate description of incoming wind conditions is supposed to be a prerequisite for reliable parafoil trajectory planning. This work utilizes the Weather Research Forecast (WRF) model system with efficient parameterization schemes to reproduce the wind field in the main landing area during the landing phase of the “Shen Zhou” series spacecraft mission. In comparison with observational data from several cases, it is validated that the WRF model has the potential to give an accurate imitation of wind behaviors and is expected to be an alternative technique for costly and time-consuming experimental undertakings. Based on the numerical results, a linear model is proposed in the current work, which is applicable to the altitude range, specifically for parafoil trajectory planning. It is validated by comparisons with observational wind properties from radio-sounding stations. In addition, a sixth-order polynomial model is introduced for comparison as well. The results show that the current proposed model has both the characteristics of a simple form and good accuracy. It shows overall better consistency with observational data than the sixth-order polynomial model. Full article

Complex network theory, in conjunction with metrics able to detect causality relationships from time series, has recently emerged as an effective and intuitive way of studying delay propagation in air transport. One important step in such analysis is converting the discrete set of landing events into a time series representing the average delay evolution. Most works have hitherto focused on fixed-size windows, whose size is defined based on a priori considerations. Here, we show that an optimal airport-dependent window size, which allows maximising the number of detected causality relationships, can be calculated. We further show how the macro-scale but not the micro-scale structure is modified by such a choice and how airport centrality, and hence its importance in the propagation process, is strongly affected. We finally discuss the implications of these results in terms of detecting the characteristic time scales of delay propagation. Full article

The effects of projectile rotation on the internal and external flow fields of the supersonic fluidic element are numerically studied using sliding grid technique and the RNG k-ε turbulence model. The effects of rotating speed on internal and external flow fields, switching time and output characteristics are studied. The results show that: for the external flow field, there is no obvious change in the flow field structure at low angular velocity; when the angular velocity increases to 20 r/s, the flow field structure becomes obviously asymmetric due to the Coriolis force; the flow field far away from the surface of the projectile body (more than 0.3 m) is much more affected than the flow field near the surface of the projectile body. The influence of projectile rotation on the internal flow field is much weaker than on the external flow field, and the change of internal flow field is not obvious when the rotational speed is less than 20 r/s. The switching time decreases with the increase in angular velocity, and within normal range of the angular velocity, the deviation of switching time from that without rotation is within 5%. The change of thrust distribution is not obvious when the rotational speed is less than 20 r/s. However, when the rotational speed reaches 50 r/s, the thrust of the middle part of the right nozzle increases by about 20 N. Full article

The maglev flight tunnel is a novel conceptual aerodynamics test facility, in which the complicated aerodynamic characteristics caused by the high-speed translation of a moving model in a long, straight, closed tunnel, and wave propagation and aero-structure single-way coupling problems can be investigated. The unsteady characteristics originating from a high-speed model in the maglev flight tunnel were investigated and evaluated with regard to aero–structure coupling. The new conservation element and solution element method was used to solve the 3-D compressible fluid surrounding a moving model in a tunnel, and the variations in the aerodynamic parameters, wave propagation characteristics, and pressure distribution in the tunnel were obtained. The results provide support for key technical problems, such as a wave-absorbing construction design of the maglev flight wind tunnel. Full article

This study designs a multistatic synthetic aperture radar (SAR) formation-flying system for very-high-resolution stripmap imaging (VHRSI) using manufacturable SAR microsatellites. Multistatic SAR formation specifications for VHRSI are derived based on the SAR image theory. For the simultaneous multi-satellite operation, the advantages of the autonomous orbit and attitude control are prominent in terms of the workload of the ground station or the efficient performance of missions. Therefore, the autonomous relative-orbit-control algorithm using relative orbital elements is developed to maintain the designed multistatic SAR formation. Additionally, an autonomous attitude-control algorithm for multistatic SAR imaging is designed by applying the optimal right-ascension of the descending node (RADN) sector concept. Finally, the resolution improvement of VHRSI is verified through multistatic SAR imaging simulations. The multistatic SAR formation is designed with three satellites separated by 7.5 km each in the along-track direction. Autonomous relative orbit control maintains the relative position error within 45 m (3σ). Additionally, the autonomous attitude control simulation verifies that the satellites perform attitude maneuvers suitable for the operation mode, and the pointing error is maintained within 0.0035° (3σ). The spatial resolution of the multistatic SAR system for VHRSI is 0.95 × 0.96 m, which satisfies the very-high-spatial-resolution requirement. Full article

A high-precision variable-thrust control method based on real-time measurement of pintle displacement and closed-loop feedback control is proposed to solve the technical problems of deep throttling variable-thrust regulation and control of pintle liquid rocket engines (LRE). By optimizing the system structure and control parameters, the closed-loop control of displacement with high precision and a fast response under a wide range of variable thrust can be realized, and thus the large-range, fast-response, and high-precision control of the chamber pressure, equivalent to thrust, can be indirectly realized. The chamber pressure response time is not more than 0.3 s, the overshoot is not more than ±3%, and the pulsation amplitude is not more than ±5%, which can meet the technical requirements of the large-range thrust adjustment and control of variable-thrust LRE of reusable launch rockets. The proposed variable-thrust LRE thrust control system is simple, reliable, and easy to use and maintain, which solves the problem of the large range, high precision, and fast response of thrust adjustment and control. The proposed system can provide important technical support for carrier rocket recycling and launch cost reduction. This is the first time a closed-loop control method of displacement of an integrated gas generator/flow regulator to achieve a 5:1 large-range continuous-variable-thrust control for the LRE of a reusable launch rocket has been proposed. Full article

Ice accretion on an aircraft affects the aerodynamic performance of the wings by disrupting the airflow, increasing drag, and altering its flight characteristics, leading to a main or tail wing-stall and altimetry to aircraft loss. The current generation of ice-detection systems relies on environmental parameters to determine icing conditions, with the sensors usually located on the nose of the aircraft, giving no information on the ice accreted on the wings. This work focuses on modeling and developing a fiber-optic-array ice sensor, which illuminates and detects the reflected and scattered light directly from the ice surface and volume, and measures the accretion rate and type of ice on the wings. The ice morphology is influenced by the rate of freezing of the super-cooled droplets impacting the wings, and partially or totally trapping the dissolved gasses. This leads to the formation of rugged surfaces and ice shapes, which can be transparent or opaque, a process which is dependent on the local Freezing Fraction (FF) of the impinging super cooled water. The detection method relies on the optical characteristics of ice, affected by density and the size of micro-cracks and micro-bubbles formed during freezing. By using high Numerical Aperture (NA) fibers, it was possible to accurately measure the ice thickness, and to investigate a proof-of-concept experiment, correlating the optical diffusion to the FF of the ice on a wing. Full article