Descent Stage Research Articles

Mars 2020 Descent Stage Integrated Propulsion Subsystem: Changes and Flight Performance

On February 18, 2021, NASA’s Mars 2020 mission successfully landed the Perseverance rover in Jezero Crater, the heaviest interplanetary rover ever built, on the surface of Mars. Following up on the successful entry, descent, and landing of the Curiosity rover of the Mars Science Laboratory mission in August 2012, the Mars 2020 mission Descent Stage Propulsion System was a build-to-print sequel. The Mars 2020 Descent Stage Propulsion System had a few minor low risk changes based on the flight performance of the Mars Science Laboratory System to improve performance. The in-flight performance of the Descent Stage Propulsion System was consistent with expectations with the exception of apparent higher than expected delivered thrust from the Mars Lander Engines, which occurred on both the Mars 2020 and the Mars Science Laboratory missions. The Descent Stage Propulsion System completed its mission with significant capability margin with respect to thruster life, maximum delivered thrust, and available propellant at touchdown.

Improving the calculation module for estimating pollutant emission from conventional and hybrid regional aircraft

For the aviation sector, it is extremely important to devise revolutionary solutions in the field of technology to restrain the potential impact of civil aviation on the environment to the level of the established strategic goals of ACARE (FlightPath2050). The introduction of innovative technologies (improvement of the combustion chamber, the introduction of electric hybrid power plants on airplanes, and the use of alternative aviation fuel) will ensure the sustainable growth of air transportation. To assess the effectiveness of advanced technologies, it is extremely important to have a model for calculating global/local emissions that takes into account the parameters of the flight path of conventional and hybrid aircraft, operational characteristics of the aircraft engine and hybrid powerplant, and the features of sustainable fuel. The improved module for calculating emission indices by combining the module for calculating the parameters of the flight path and the results of calculating the thermogas-dynamic calculation of the aircraft engine makes it possible to detect the influence of fuel consumption (engine thrust) on the values of the emission indices. This feature is representative for evaluating the efficiency of hybrid powerplants because the electrification of the aircraft fleet is primarily aimed at reducing fuel consumption. The analysis of simulation results reveals that the fuel consumption and EINOx are significantly reduced (for the climb stage – 25 %; for the descent stage – 30 %) for the hybrid AN26 compared to the conventional AN26. The specified operational measure, in the part of the low-pitch descend, significantly reduces EICO for the hybrid AN26 by an average of 50 % compared to the descend stage for the conventional trajectory. The results of calculations for the entire flight path demonstrate that the use of a hybrid power plant for An26 contributes to an average reduction of fuel consumption by 10 %, NOx emissions by 25 %, water vapor emissions by 10 %, and CO2 by 10 %.

Effective metaheuristic and rescheduling strategies for the multi-AGV scheduling problem with sudden failure

This paper investigates a novel scheduling problem, the multi-AGV scheduling problem with sudden failure (MASP-SF), which is of great importance in modern intelligent manufacturing systems. The problem considers how to assign tasks to multiple AGVs with the objective of minimizing the total cost under two events of normal production and sudden failure in the workshop. In the event of normal production, a population-based variable neighborhood search (PVNS) algorithm with effective strategies such as rule-based stochastic method in the initialization stage, pancake flipping strategy in the shaking stage, improved neighborhood structures in the variable neighborhood descent stage is presented to solve the multi-AGV scheduling problem. In the event of sudden failure, a mixed-integer linear programming model and two rescheduling strategies are proposed to solve MASP-SF. The two rescheduling strategies are the rapid repair rescheduling strategy and a rescheduling strategy based on an improved NNH. To validate the above ideas, we conduct comprehensive and in-depth experiments on a practical plant and statistical analysis of the resulting data. The results show that the scheduling solutions generated by the rescheduling strategies are feasible, and the proposed PVNS algorithm has a superior performance compared to existing algorithms in multi-AGV scheduling problem.

Spatio-temporal distribution of aerodynamic forces and their associated vortex drift patterns around a closed-box girder during torsional vortex-induced vibration

Torsional vortex-induced vibrations (VIVs) pose potential risks to prototype bridges with increasing spans and lower damping levels. However, the underlying mechanism remains unclear. Wind tunnel tests revealed that torsional VIVs occurred at an initial attack angle of + 3°. To unravel the VIV mechanism throughout the lock-in range, encompassing the ascent stage, amplitude extremum, and descent stage, the spatio-temporal distribution of aerodynamic forces around the bridge girder was analyzed. The results demonstrated the presence of traveling pressure waves with approximately 2.5 wavelengths and three uniformly distributed separated vortices over the upper side throughout the lock-in range. The primary source of these travelling pressure waves stemmed from the vortex drift patterns, with the aerodynamic wave travelling velocity equating the vortex drift velocity. The formation of separated vortices, known as the “double-vortex model”, occurred at the windward barrier on the upper side and windward maintenance rail on the lower side. These vortices directly imposed travelling pressure waves on the girder, thereby inducing torsional VIVs. Among them, the former vortices contributed more to the VIVs than the latter. Therefore, the formation of separated vortices and their related aerodynamic waves in the windward edge with the 2nd SVM/AWM modes predominantly governed the occurrence of torsional VIVs. Furthermore, both the ratio of the wave travelling time to the vibration period and the mean value of the wave travelling velocity ratio exhibited an inverse relationship with the VIV responses. However, the actions exerted by the vortex drift patterns were proportional to the VIV responses on both the upper and lower sides. Therefore, there existed evolutionary characteristics of aerodynamic waves and their related vortex drift patterns throughout the lock-in range, which was responsible for the “lock-in” phenomena.

Experimentos de ruptura de barragens de terra homogêneas por galgamento

ABSTRACT This work physically simulates the effect of low and high flow rates and filling times of reservoirs and rupture due to overtopping (caused by intense rains) of small homogeneous silty-sand earthfill dams. The experiments seek to verify how input variations impact the formation of the breach and the rupture wave. The results show that different filling times, soil moisture and composition, and degree of compaction affect landfill saturation, failure time, and breach formation. The result confirms that smaller breaches with a higher degree of compaction led to a lower peak rupture flow compared to dams with low degree of compaction. The rupture hydrograph presents a faster descent stage than an exponential hydrograph. Simulations and models based on this law may minimize the effect of the dam-break wave, also impacting water resource decision-making for damage reduction. The results were extrapolated to a real prototype, providing information and a database for the studies of overtopping dam-break waves.

Microstructure and mechanical properties of T2 copper /316L stainless steel explosive welding composite with small size wavy interface

Copper/stainless steel composite is often used for preparation of superconducting busbar “double box” lap joints. However, it is a challenge for the large thickness T2 copper/316L stainless steel composite is fabricated by explosive welding, because of the bonding interface is always present many problems such as large ripple size, many microscopic defects, low bonding strength and poor sealing etc. In this paper, the big-thickness T2 copper/316L stainless steel composite with small size wavy interface was successfully fabricated by explosive welding. Microstructure of bonding interface indicated that the welding process could be divided into three stages: detonation growth stage, detonation stabilization stage, detonation descent stage. The morphology of bonding interface presented a regular wavy interface and no defects such as cracks, voids and intermetallic compound were formed in the stable stage, which was consistent with the results of ultrasonic and permeability quality inspection. The hardness of copper side and stainless steel side close to the bonding interface reached 131HV and 432HV, respectively. Dynamic recrystallization and fine grain generated in the bonding interface. The mechanical properties of tensile strength, pull-off strength and shear strength in the stable detonation stage is greater than 110 MPa, which is meeting the requirements of preparation of superconducting busbar “double box” lap joints. The deformation failure mainly occurred in the copper side near the bonding interface, which presented a higher bonding strength than copper. Some dimples and tearing edges with different sizes on the fracture surfaces, indicating that the fracture was a typical ductile fracture.

Mechanical and electrical responses of natural-cooled high-temperature granite of different grain sizes

In order to understand the effect of grain size on the mechanical and electrical responses of natural-cooled high-temperature granite, uniaxial compression tests were carried out on natural cooled coarse- and fine-grained granite samples subjected to thermal treatment at room temperature, 200 °C, 400 °C, and 600 °C respectively. The resistivity and acoustic emission (AE) during the compression were monitored and changes in physical and mechanical properties, the AE and resistivity characteristics in the loading process were analyzed. Results show that high temperature exerts a more significant effect on deteriorating the coarse-grained granite. Changes in resistivity can reflect the development of rock damage. Corresponding to the compaction stage, crack initiation and stable propagation stage, and crack rapid propagation stage of rock under compressive load, changes in resistivity can be divided into three stages accordingly, including the initial rapid descent stage, the gentle descent stage, and the secondary rapid descent stage for the thermal-treated rock at 25–400 °C. The secondary rapid descent stage of resistivity can be used as a precursor for rock entering into the failure stage. The resistivity change is more sensitive to the damage development in coarse-grained granite.

Identification of karst spring hydrographs using laboratory and numerical simulations considering combined discrete‐continuum approaches

AbstractThe quantitative analysis of karst spring hydrographs aids in characterizing the hydrodynamic properties of aquifer systems. However, the relationships between spring hydrographs and hydrologic functions of different media lack in‐depth research. This study detected the rainfall‐discharge processes of covered karst systems using two combined discrete‐continuum models (a coupled continuum‐pipe model and a hybrid model) developed based on laboratory experiments. An improved exponential function was used to decompose spring recession hydrographs with a great performance, and the results indicate that the slow drainage controlled by the porous medium dominates the whole recession process. There is a shift in the contribution of the matrix to karst discharge systems with the increase of its hydraulic conductivity. Although spring hydrographs have a great dependency on the hydraulic process of fracture networks, the variation in permeability of the matrix significantly changes the storage capacity of fractured rocks and spring discharge behaviours. The changing process of water storage rate of the matrix and fractures with spring hydrographs reveals three stages: a period of steep rise and fall, a period with slight fluctuations, and a gentle descent stage. The parameter sensitivity analysis in both models shows that the covering porous layer has a strong effect on the patterns of karst spring hydrographs, and the specific yield is more sensitive than hydraulic conductivity. While these simulations were conducted at the laboratory scale, the findings provide insights into practical applications of spring protection and water resources management.

Experimental and numerical investigation of the aircraft fuel tank inerting system

ABSTRACT The performance of the aircraft fuel tank inerting system is influenced by multiple factors which are strongly coupled. It is a time-consuming process to analyse and evaluate the performance of the system through experiments, and it is difficult to analyse the effects of various factors through limited experimental data. An efficient numerical method is significant for the preliminary design and optimisation of inerting products. In this paper, a generic mathematical model of the hollow-fibre-membrane module (HFMM) was established and the accuracy of the numerical results was verified using experimental data. Based on this mathematical model, a simulation model of the aircraft fuel tank inerting system was developed through cosimulation of AMESim and Matlab/Simulink. The accuracy and applicability of the simulation model for this inerting system were verified using experimental test data. Using this simulation model, the effect of nitrogen-enrich air (NEA) flow rate and aircraft flight altitude on the performance of the inerting system were investigated. The results show that increasing the NEA flow rate contributes to a shorter time for the oxygen concentration to reach a steady state while with a higher stabilised value. The use of a high NEA flow mode is effective in improving the inerting performance during the rapid descent stage.

Experimental study of interfacial adhesion performance of prefabricated UHPC-NC diagonal shear groove

The reinforced lining of the tunnel was carried out using a prefabricated composite structure consisting of Ultra-High Performance Concrete (UHPC) and Normal Concrete (NC), utilizing a semi-post-pouring method. The bond performance between UHPC and NC is crucial for enhancing the overall stability and safety of the tunnel. To investigate the influence of interface construction on the bond performance at the UHPC-NC interface, inclined shear tests were conducted with variations in groove density, groove morphology, groove aspect ratio, and interface angle. The results revealed four different failure modes of the grooved specimens, with over 80% exhibiting failure at the interface between UHPC and NC. The average interface bond strength of the grooved specimens was found to be 5.8 times higher than that of the untreated interface group, indicating a significant improvement in the bond performance of the UHPC-NC interface due to the presence of grooves. When the volume loss ratio was below 0.09, the interface bond strength of the UHPC-NC interface increased with an increase in groove density. The interface bond strength of the 60° trapezoidal grooves was 80% higher than that of the right-angle grooves, while the interface bond strength of the 40° trapezoidal grooves was 28% higher than that of the right-angle grooves. Furthermore, the interface bond strength decreased as the angle between the interface and the horizontal plane increased. The precast inclined shear grooves exhibited a bond-slip curve that consisted of an initial slow-rise stage, an elastic rise stage, a yield stage, and a failure descent stage, with some specimens not exhibiting a distinct yield stage. In this study, a bond-slip model for the precast UHPC-NC inclined shear grooves was proposed, and recommendations for bond stiffness were provided.

Automatic interval management for aircraft based on dynamic fuzzy speed control considering uncertainty

A novel real-time autonomous Interval Management System (IMS) is proposed to automate interval management, which considers the effect of wind uncertainty using the Dynamic Fuzzy Velocity Decision (DFVD) algorithm. The membership function can be generated dynamically based on the True Air Speed (TAS) limitation changes in real time and the interval criterion of the adjacent aircraft, and combined with human cognition to formulate fuzzy rules for speed adjusting decision-making. Three groups of experiments were conducted during the en-route descent stage to validate the proposed IMS and DFVD performances, and to analyze the impact factors of the algorithm. The verification experimental results show that compared with actual flight status data under controllers’ command, the IMS reduces the descent time by approaching 30% with favorable wind uncertainty suppression performance. Sensitivity analysis shows that the ability improvement of DFVD is mainly affected by the boundary value of the membership function. Additionally, the dynamic generation of the velocity membership function has greater advantages than the static method in terms of safety and stability. Through the analysis of influencing factors, we found that the interval criterion and aircraft category have no significant effect on the capability of IMS. In a higher initial altitude scenario, the initial interval should be appropriately increased to enhance safety and efficiency during the descent process. This prototype system could evolve into a real-time Flight-deck Interval Management (FIM) tool in the future.

Effects of dynamic prestress on silicon carbide ceramic against long rod impact

It is well known that silicon carbide (SiC) ceramic is a pressure dependent material, where the compressive strength increases as the pressure increases. So, it is an effective way to improve the ballistic performance of SiC ceramic by introducing prestress on ceramics surface. In this paper, the concept of dynamic prestress on SiC ceramic by energetic materials was proposed. Five key factors, including the time of projectiles contact targets, velocity of the long rod projectiles (V p), prestress rising stage time (T r), prestress descent stage time (T d) and peak pressure of prestress (P k), were selected to investigate the effect of dynamic prestress on SiC ceramic targets against long rod impact. The effect of dynamic prestress on the ballistic performance of SiC ceramic were investigated, and the dynamic prestress path which can increase the protection capability of SiC ceramic was given. The results indicated that, in most cases, the ballistic performance of the dynamic prestressed SiC ceramic targets against long rod projectiles impact was improved. However, it was also revealed that not all dynamic prestressing can improve the ballistic performance of SiC ceramic targets. It will be benefit to the ballistic performance of SiC ceramic by controlling the prestress time to make sure the moment of the long rod projectile impacts the target in between T 2 and T 4. The sequence of influence degree of each factor on the erosion length of long rod projectile is the velocity of long rod projectiles (V p), prestress descent stage time (T d), peak pressure of prestress (P k) and prestress rising stage time (T r). The erosion length of long rod projectile decreases with the increase of V p, and increases with the increase of prestress descent stage time (T d), peak pressure of prestress (P k) and prestress rising stage time (T r).

Visual characteristics of drivers in different directions and lengths of gradual landscape zones in extra-long highway tunnels

Owing to the tightness and monotonicity of the tunnels, the number of traffic accidents caused by driving through them for a long time is positively correlated to their length. To improve driving safety, a landscape zone with the function of awakening the driver and relieving their fatigue has been adopted in an increasing number of extra-long highway tunnels. However, the sharp contrast between the landscape and ordinary zones often makes drivers uncomfortable. Therefore, a gradual landscape zone is proposed in this study. Through driving simulation tests, the eye movement and pupil index were used to study the attractiveness, direction, and length of the gradual landscape zone in an extra-long highway tunnel. The results show that there is no risk of causing excessive distraction to drivers in the “blue sky and white clouds” landscape zone of the tunnel vault, and the gradual landscape zone in the approach direction has a significant influence on the change rate of the pupil diameter range of drivers. In contrast, the gradual landscape zone in the driving direction has little influence. For a longer length of the gradual landscape zone in the approach direction, drivers require a longer adaptation time at the descent stage of the pupil diameter, and the change rate of the pupil diameter range is smaller. Therefore, a longer gradual zone in the approach direction is helpful in improving the adaptability of drivers when passing through the landscape zone.

Multi-Objective, Multi-Disciplinary Design Optimization and Multi-Attribute Evaluation of Hybrid Rocket Motors Used for Manned Lunar Lander

This paper proposed a multi-objective, multi-disciplinary design optimization and multi-attribute evaluation method for the manned lunar lander descent stage. A system design model is established considering multiple disciplines such as propulsion, structure, trajectory and cost. With the goal of minimizing mass, minimizing cost and maximizing velocity increment, the overall scheme for hybrid rocket motors was optimized by altering various grain shapes and feed systems, acting as an alternative propulsion scheme for the manned lunar lander. Under the same design conditions, the optimal scheme of hybrid rocket motors considering continuous and discrete attributes was studied and compared with that of liquid rocket engines to elucidate the characteristics of the hybrid rocket motors for deep space exploration. The results showed that the evaluation results obtained by considering only continuous attributes were different from those by considering both continuous and discrete attributes. The liquid propulsion scheme with liquid oxygen/kerosene is superior to the hybrid propulsion schemes due to its excellent cost and specific impulse performance when only continuous attributes are considered. However, hybrid rocket motors have shown good performance in terms of operability, manufacturability, safety and environmental protection. So, after introducing discrete attributes, the hybrid propulsion schemes show greater potential. In brief, based on the multi-attribute evaluation method considering comprehensive attributes, the hybrid rocket motor provided with tube grain and gas pressure feed system was considered as the optimal propulsion system for the lunar lander. Furthermore, the parametric analysis showed that the fuel grain outside diameter, the initial design thrust and the initial oxygen-to-fuel ratio had a significant influence on the performance of the hybrid rocket motor for the lunar lander, and in particular, the effect of the fuel grain outside diameter was more than 50%.

Performance Analysis and Optimization of Fuel Tank Ground-Based Washing Inerting on Unmanned Aerial Vehicles

In this study, a ground-based washing inerting (GBWI) method was proposed, and the application of GBWI in the field of fire prevention and explosion suppression of unmanned aerial vehicle (UAV) fuel tanks was studied using a volume of fluid (VOF) two-phase flow model at a given typical flight envelope. The variation in oxygen concentration in tank ullage during flight was calculated considering the entrance of ambient air and the escape of dissolved oxygen from the fuel. The results indicate that the oxygen concentration in the ullage increases with increasing initial oxygen concentration in the ullage and the initial fuel load after GBWI. In the climb and cruise stages, the oxygen concentration in the ullage increases slowly, while in the tactical descent stage, the oxygen concentration in the ullage increases rapidly, easily exceeding the limiting oxygen concentration (LOC) of aviation fuel combustion. To expand the application range of GBWI, an optimization scheme of nitrogen filling protection was proposed so that the GBWI could meet the requirements of an inert tank at different fuel loads and initial oxygen concentrations in the ullage. Compared with a traditional on-board inert gas generation system (OBIGGS), the optimized GBWI method could greatly reduce the fuel compensation loss and improve the maneuverability of UAVs at the same time.

Braking and attitude control of lunar lander in active descent stage

Abstract China officially launched the lunar exploration project, named “Chang’e Project,” in 2004. Then, in 2013, Chang’e-3 completed the soft landing on the lunar surface, starting a series of studies on the soft landing of spacecraft. This study aims to optimize the dynamic flight guidance and attitude control of the lunar landing module represented by Chang’e-3 in the soft landing stage. After analyzing the attitude control requirements of the soft landing stage of the lunar landing module, this study designs the lunar soft landing process under a variable structure sliding mode (VSSM) control. The study also analyzes the influence of the pulse width modulator (PWM) on the soft landing process. The simulation model of the lunar soft landing guidance and control system is established by MATLAB/Simulink, and the traditional proportional–integral–derivative (PID) control mode is compared with the interference condition. Results show that VSSM + PWM is superior to PID in robustness and accuracy and has a theoretical reference value for future lunar landing exploration and even Mars landing exploration.

The Investigation of Plume-Regolith Interaction and Dust Dispersal during Chang’E-5 Descent Stage

The plume-surface interaction that occurs as a result of a variable-thrust engine exhaust plume impinging on soil during landings is critical for future lunar mission design. Unique lunar environmental properties, such as low gravity, high vacuum, and the regolith layer, make this study complex and challenging. In this paper, we build a reliable simulation model, with constraints based on landing photos, to characterize the erosion properties induced by a low-thrust engine plume. We focus on the low-thrust plume-surface erosion process and erosion properties during the Chang’E-5 mission, aiming to determine the erosion difference between high- and low-thrust conditions; this is a major concern, as the erosion process for a low-thrust lunar mission is rarely studied. First, to identify the entire erosion process and its relative effect on the flat lunar surface, a one-to-one rocket nozzle simulation model is built; ground experimental results are utilized to verify the simulated inlet parameters of the vacuum plume flow field. Following that, plume flow is considered using the finite volume method, and the Roberts erosion model, based on excess shear stress, is adopted to describe plume-surface interaction properties. Finally, a Lagrangian framework using the discrete phase model is selected to investigate the dynamic properties of lunar dust particles. Results show that erosion depth, total ejected mass, and the maximum particle incline angle during the Chang’E-5 landing period are approximately 0.2 cm, 335.95 kg, and 4.16°, respectively. These results are not only useful for the Chang’E-5 lunar sample analysis, but also for future lunar mission design.

Batteries for robotic spacecraft

Batteries for robotic spacecraft

Optimal guidance for lunar soft landing with dynamic low-resolution image sequences

To relieve the burden of obtaining high-precision lunar surface information during lunar soft landing, a new guidance algorithm based on dynamic low-resolution image sequences is proposed. The integrated procedure of dynamic descent stage considering obstacle-avoiding requirement without the hover measurement is designed, which enables the spacecraft to optimize the final landing site by rolling in orbit. A small number of points are used to obtain the variance, slope and roughness of the field of vision subarea, and the shortest distance spiral search algorithm is used to determine the safest landing point. In order to reduce unnecessary control, an acceptance domain algorithm of alternative landing sites is designed to judge whether or not to accept the change of landing sites in dynamic low-precision image sequences. Assuming that the control acceleration is adjustable, the non-singular fast terminal sliding mode (NFTSM) controller based on terminal attractor is adopted and improved, and the stability of the closed-loop system is also proved. The validity, reliability and effectiveness of the proposed guidance algorithm are verified by numerical simulation on the case with disturbance and large sample data. The results demonstrate that the image information required for stable lunar soft landing is far less than that of the traditional methods, which can greatly reduce the burden of the onboard computer.

Simulation of biogenic coalbed gas from anthracite in the south of Qinshui Basin, China

High-rank coal, such as anthracite, has been considered difficult to generate biogas because of the high coalification degree. Selecting anthracite from Sihe Coal Mine, Qinshui Basin, China, as substrate, this study carried out a simulation experiment of biogas generation for 80 days, the purpose of which was to verify whether anthracite could be biodegraded to produce biogas under laboratory conditions. The results showed that the selected anthracite can be utilized by methanogenic bacteria to produce biogas and the approximate production field was 1.79 mL/g, which was less than that of the lower rank coal of other published studies. The generation process can be divided into a rapid growth stage (0–30 days) and a slow descent stage (30–80 days). CO2 and CH4 are the main components of biogas, although some heavy hydrocarbons were also tested. The CO2 concentrations were low (< 30%), and the δ13C-CH4 values were positive (−39.9‰ to −45.8‰), which suggested that the main biogas generation pathway was acetic fermentation. But at the same time, the concentrations of CH4 and CO2 were mutually increasing and decreasing with the passage of experiment time, and δ13C-CH4 tends to be lighten in the later stage(40–80 days), suggesting that parts of biogenic CH4 were generated by way of CO2 reduction.