Launch Safety Research Articles

Active Learning Strategy for Surrogate-Based Quantile Estimation of Field Function

Uncertainty quantification is widely used in engineering domains to provide confidence measures on complex systems. It often requires to accurately estimate extreme statistics on computationally intensive black-box models. In case of spatially or temporally distributed model outputs, one valuable metric results in the estimation of extreme quantile of the output stochastic field. In this paper, a novel active learning surrogate-based method is proposed to determine the quantile of an unidimensional output stochastic process with a confidence measure. This allows to control the error on the estimation of a extreme quantile measure of a stochastic process. The proposed approach combines dimension reduction techniques, Gaussian process and an adaptive refinement strategy to enrich the surrogate model and control the accuracy of the quantile estimation. The proposed methodology is applied on an analytical test case and a realistic aerospace problem for which the estimation of a flight envelop is of prime importance for launch safety reasons in the space industry.

A test method for launch safety of explosive charge accurately simulating launch overload

ABSTRACT In this paper, the generalized Maxwell constitutive equation is embedded into LS-DYNA program by secondary development technology, the projectile launching process is numerically calculated, and the stress distribution of explosive charge in the launching process is described. According to the calculation results, the explosive charge launch safety simulator for the research of explosive charge launch safety is designed and developed. Then the experiment is carried out, and the dynamic behavior and ignition process of explosive charge were obtained. Finally, a quantitative evaluation method for the launch safety of explosive charge is established, and the launch safety of the PBX is evaluated.

Safe launch of a robotically assisted mitral valve repair program in a single center: experience of initial 20 cases under the Center for Minimally Invasive Surgery.

Robotically assisted mitral valve repair was approved by the Japanese government in April 2018. However, understanding robotic surgery involves steep learning curves of surgeons and dedicated cardiac teams. The Center for Minimally Invasive Surgery (CMIS) of Tottori University Hospital is a multidisciplinary organization established in 2011 with seven surgical departments. In this study, we report strategies for improving the safety of robotic surgery in the CMIS and early results of robotic mitral valve repair at our hospital. We reviewed the first 20 patients who underwent robotic primary mitral valve repair, including concomitant procedures, from October 2019 to September 2021 under the supervision of the CMIS. Before starting the program, the CMIS requires setting console time limit to 180min and implementing risk management strategies through simulation training for various mechanical failures. Mitral valve repair was completed in all patients. There was no in-hospital or 30-day mortality. No conversion to median sternotomy was necessary. The analysis of mitral pathology revealed 1 case of functional mitral regurgitation, 12 cases of posterior lesions, 3 cases of anterior lesions, 3 cases of bileaflet lesions, and 1 case of commissural lesion. The average cross-clamp time was 133 ± 27min. Sixteen cases had trace mitral regurgitation postoperatively, and 4 cases had mild mitral regurgitation. The median (interquartile range) postoperative hospital stay was 10 (8.5-12.5) days. Robotically assisted mitral valve repair was performed safely with assistance from the multidisciplinary CMIS, and the early results were satisfactory without compromising clinical outcomes.

Design and Performance of Armature Surface Coating for Electromagnetic Launcher

Armature is the key component of electromagnetic launcher (EML), but in the process of launching, its working environment is bad and the surface is seriously worn. Excessive wear will seriously weaken the mechanical properties of armature and affect the launching safety. Therefore, it is necessary to deal with the surface state of armature to reduce wear and improve the performance of armature. First, the properties of the candidate materials are analyzed. According to the principle of maximum current carrying capacity per unit mass, aluminum is the most suitable material for armature manufacturing. At the same time, the defects of material selection in single material system are pointed out. Second, based on the above problems, the surface coating design scheme is proposed. From the point of view of material melting point and hardness, it is proposed that tungsten can be used as the coating material for armature surface. According to the wear amount of armature tail under launch condition, the coating shape and thickness are designed. The best coating forming process is determined by calculating the shear force between coating and substrate; finally, the effect of the coating on the electric contact performance, system efficiency, and projectile gouging threshold velocity is analyzed. The results show that the maximum shear force between the coating and the substrate is above 171 MPa under the launching condition, and the laser cladding technology can meet the process requirements. After coating treatment, the contact resistance between the armature and rail (AR) increases by 6%, which has little effect on the system efficiency. Although it will affect the projectile gouging threshold velocity, it can be improved by modifying the tungsten coating or rail surface treatment. The analysis results are of great significance to reduce the armature wear, improve the contact performance between the AR, and improve the launch safety.

Numerical study on jet noise suppression with water injection during one-nozzle launch vehicle lift-off

The launch vehicle will experience extreme acoustic environment at lift-off, which will cause the invalidation and destruction of the aerospace equipment, and reducing noise is of great significance for improving launch safety. In this paper, the numerical simulation of gas–liquid two-phase flow and its acoustic field is carried out, and the flow field is simulated by the discrete phase model (DPM), second-order Roe format, Scale-Adaptive Simulation (SAS) and three-dimensional Navier–Stokes. Based on the analysis of the flow field, the acoustic analogy integration method (FW-H) is used to predict the jet noise at the observation position. The influence of the water different injection angles and mass flow rate ratios are studied, and the results show that water injection not only reduces the temperature, velocity and vorticity at the gas–liquid interface, and the temperature at the bottom of the jet deflector, it also significantly reduces the jet noise. The total sound pressure level can be reduced to 6.92 dB by appropriate selection of the water injection angles and water injection mass flow rates. The numerical method established in this paper provides a useful tool for the design and analysis of water injection noise reduction for high-thrust multi-nozzle launch vehicle.

Evaluation of the Mechanical Failure Criterion to Consider the Triple Base Propellant Safety Life: Application of Sustainable Renewables for Environmental Hazards

Implementation of clean energy and renewables is essential for the consideration of environmental impact because it can be implemented in supply chain networks and sustainable management procedures for safety. In order to study the safety life failure criterion of a triple base propellant under the failure mode of mechanical properties, an accelerated aging test, an evaluation method for the launch safety test of gun propellant charge, and a compressive strength test were used. The failure criterion of mechanical properties was obtained by researching the correlation between launch safety change and mechanical property change of samples. Berthelot’s equation was used to predict the safety life of the triple base propellant. The results show that the mechanical failure criterion is “27% reduction of maximum compressive strength.” The safety life at 25°C and 75% humidity is 13.77 years.

Finite Volume Method for the Launch Safety of Energetic Materials

It is important to examine the ignition of energetic materials for launch safety. Given that there is a paucity of experimental tests, numerical simulations are important for analysing energetic materials. A computer program based on the finite volume method and viscoelastic statistical crack mechanics model is developed to study the ignition of energetic materials. The trends of temperature and stress of energetic materials subjected to projectile base pressure are studied by numerical examples. The results are compared with those in an extant study, which verified the correctness of the proposed method. Additionally, the relationships between the temperature increase and nonimpact ignition of energetic materials were analysed. The results show that when the temperature at the bottom of the explosive rises to a certain value, it will cause the explosive to ignite. This research has significance to the study of the base gap of explosives, and it provides a reference for launch safety evaluation of energetic materials.

Influences of the Random Stacking and Charge's Diameter on Compression and Fracture Process of Propellant Charge

AbstractAfter decades of unremitting research on the launch safety of propellant charge at home and abroad, it is gradually recognized that the fractured propellant charge generated by the compression process of propellant particles is the leading cause of chamber explosion. The large numbers of particles in propellant charge inevitably bring out the complexity in describing the fracture process under impact load in description. The discrete element method is applied to study the influences of the random stacking configurations of propellant charge and the charge diameter on the compression and fracture process of propellant charge in this paper. The results show that the random stacking of propellant bed influences little on the fracture process under the same impact load. When the diameter of propellant charge is larger than a certain value, the charge's diameter has little influence on the fracture process.

Research on parameter matching characteristics of pneumatic launch systems based on co-simulation

AbstractPneumatic launch systems for Unmanned Aerial Vehicles (UAVs), including mechanical and pneumatic systems, are complex and non-linear. They are subjected to system parameters during launch, which leads to difficulty in engineering research analysis. For example, the mismatch between the UAV parameters and the parameter design indices of the launch system as well as the unclear design indices of the launching speed and overload of UAVs have a great impact on launch safety. Considering this situation, some studies are presented in this paper. Taking the pneumatic launch system as a research object, a pneumatic launcher dynamic simulation model is built based on co-simulation considering the coupling characteristics of the mechanical structure and transmission system. Its accuracy was verified by laboratory test results. Based on this model, the paper shows the effects of the key parameters, including the mass of the UAV, cylinder volume, pressure and moment of inertia of the pulley block, on the performance of the dynamic characteristics of the launch process. Then, a method for matching the parameter characteristics between the UAV and launch system based on batch simulation is proposed. The set of matching parameter values of the UAV and launch system that satisfy the launch take-off safety criteria are calculated. Finally, the influence of the system parameters of the launch process on the launch performance was analysed in detail, and the design optimised. Meaningful conclusions were obtained. The analysis method and its results can provide a reference for engineering and theoretical research and development of pneumatic launch systems.

Research progress on explosives for naval gun shell and its launching safety

<p indent="0mm">To investigate the launch safety problems in the application of powerful naval gun ammunition, this paper analyzes and studies the development of domestic and foreign explosives and weaponry for naval gun ammunition, the research equipment for explosive charge launching safety, impact mechanism of explosive charge launching safety, and the design of numerical simulation and equivalent test for explosive charge launching safety. Results show that although the explosive charge of naval gun ammunition varies among countries, the principle of the test device used to study the explosive charge launching safety is basically the same. To verify whether the explosive charge meets the launch safety requirements, the recoil force stress and its response to explosives in the launching process is simulated. Additionally, the relevant test and research results prove that the launching safety performance of explosive charge can be effectively enhanced by improving the charge quality and reducing the charge defects. By exploring the explosive formula design and charging technology, avoiding the hot spot of explosives in a complex stress launching environment, such as adiabatic compression and shear, is a crucial technical measure, as well as improving the launching safety of naval gun shell explosive charge.

Evaluation and prediction methods for launch safety of propellant charge based on support vector regression

In view of the consensus that the oversized initial combustion surface area of fractured propellant charge is the main cause of breech blow, the evaluation method for launch safety of propellant charge with initial dynamic vivacity ratio as the characterization parameter has drawn extensive attentions and inspired many variants. However, the characterization of propellant charge stacking configuration and the prediction of initial dynamic vivacity ratio are still two unsolved problems. To fill the gaps, this study provides a novel evaluation method for the launch safety of propellant charge through applying the machine learning and the error analysis methods. A new description with three parameters is proposed for dynamic compression and fracture process, and verified more accurate than the previous method with maximum compression stress as the single parameter. In addition, it identifies that the support vector regression is more suitable than back propagation neural network and least squares support vector machine in small sample training. And the corresponding model has been demonstrated by experiments to be of convinced accuracy and superior generalization capability. Through determining the model error distribution, this study makes it feasible to predict initial dynamic vivacity ratio and give an upper limit value with high confidence.

A Concept Study on Advanced Radioisotope Solid Solutions and Mixed-Oxide Fuel Forms for Future Space Nuclear Power Systems

Radioisotope power systems (RPSs) have transformed our ability to explore the solar system. RPSs have been in existence for almost seven decades. Most missions have utilized 238Pu as the radioisotope of choice to generate electrical power and to produce heat for the operation and thermal management of spacecraft systems. In Europe, for the past decade 241Am has been selected for RPS research programs. This paper hypothesizes that the inclusion of small quantities of relatively short-lived radioisotopes such as 232U and 244Cm, particularly when dealing with long-lived radioisotope 241Am, could have beneficial implications for future RPS designs. This paper focuses on the thermal output implications and impact on system-level design. The authors recognize that the selection of any new or modified radioisotope heat source material will require extensive research on fuel form stability, the radiological impact, cost of production, containment, and launch safety considerations.

Fatigue failure and launch safety assessment of gun barrel

Hundreds or thousands of projectiles have been fired through a gun barrel. Catastrophic fatigue failure of gun barrel due to cyclic loadings by the stresses induced by the combination of high pressure and temperature combustion gas, and projectile with the rotating band interaction with the bore surface, has not yet been understood. In this paper, laboratory hydraulic fatigue tests on simulated gun barrel were performed on MTS Land. The experimental results show that there is an inherent relation between crack propagation in thick-walled tube and the external surface hoop and axial strains. This fact suggests that fatigue failure of gun barrel should be likely prevented by monitoring the external surface strains of the gun barrel and stopping continued firing before a major crack growing up to the critical size.

A calculation method of interior ballistic two-phase flow considering the recoil of gun barrel

The theory of interior ballistic two-phase flow (IBTPF) is the primary means to study the distributions of physical quantities in gun chamber. In previous calculations, the gun breech is usually simplified as a fixed wall boundary, totally ignoring the effect of gun barrel recoil on interior ballistic processes. Thus to truly describe the interior ballistic process of the self-propelled gun (SPG), the transfer matrix method of multibody system (MSTMM) is combined with the theory of IBTPF in this paper. By simultaneously solving the generalized coordinate equations of multibody system and the conservation equations of IBTPF, the gun barrel recoil is converted to the moving boundary of the gun breech, and a more accurate calculation method of IBTPF is established. The results show that the simulated vibration characteristics, dynamic response during launch as well as interior ballistic performance of the SPG are all in good agreement with test values. Compared with no recoil, the gun barrel motion affects the growth regularity of the chamber volume behind the projectile, and eventually results in the changes of interior ballistic performance indexes such as maximum breech pressure and muzzle velocity. Overall, this study provides a more accurate prediction and simulation tool to enable better insight into such complicated interior ballistic processes, which is of great significance to the launch safety analysis and subsequent ballistic calculations.

A Hotspot Model for PBX Explosive Charge Ignition in a Launch Environment.

ABSTRACT The research of explosive ignition mechanisms in the launch environment is significant to determine the launch safety of explosive charge. Based on the two-phase flow theory, the internal ballistic process and the projectile base pressures are calculated accurately. The stress history of PBX explosive during the 155 mm howitzer launching process is obtained based on the finite element method, and then the 1D hollow sphere pore-collapse model considering explosive chemical reaction, heat conduction, phase transition, and viscoplastic deformation processes can be developed, to describe the hot spot formation in explosive charge. Finally, a quantitative determination method with initial porosity as the index for explosive ignition is proposed, contributing to the launch safety determination and performance evaluation of explosive change.

Dynamics Analysis of Carrier-based UAVs with Ski-jump Launch

Sinking has a direct influence on launch safety of carrier-based UAVs, occurred just while leaving carrier board caused of disappearance of ground effect. A dynamics model of an UAV was developed and some mechanical and dynamics analysis were given out to build its dynamics simulation model of ski-jump launch. Based on the simulation results, some important parameters were analyzed, such as trace, velocity and loadings of landing gears. By changing the values of engine thrust and mass of the UAV, it was validated that decreasing the mass properly or increasing thrust would reduce the sinking and improve launch trace to make it safer.

Study on Interior Ballistic Characteristics of the Multi-gas Sources Ejection Power System

In this paper, the internal ballistics model of the multi-gas sources ejection power system is established, the internal ballistics characteristics are studied, and the launch process of a certain missile is calculated by using the internal ballistics equation, and the important parameters such as velocity and acceleration of the missile, pressure and temperature in the launch cylinder are obtained. Compared with the pure gas single power launch scheme, the multi-gas sources ejection power system can effectively reduce the missile overload, reduce the pressure in the launching cylinder and improve the energy utilization efficiency. The maximum acceleration of the missile is reduced by more than 50%, which makes the movement process of the missile more stable and the interior ballistic trajectory more accurate; the maximum pressure in the launch cylinder is reduced by more than 45%, which greatly improves the launch safety, and also provides conditions for the lightweight of the launch device.

United States Air Force radioisotope material launch approval requirements

National Security Presidential Memorandum #20 [1] recently superseded National Security Council, Presidential Directive #25 [2] both of which require evaluation of risks associated with launch of radioactive sources into space. This evaluation is conducted by the Interagency Nuclear Safety Review Board (INSRB)*⁎The Interagency Nuclear Safety Review Panel (INSRP) consisted of the Department of Defense (DoD), charged with national security and the US Armed Forces; Department of Energy (DOE), concerned with US policies regarding energy and safety in handling and use of nuclear material; Environmental Protection Agency (EPA), responsible for human health and preservation of the environment; National Aeronautical and Space Administration (NASA), responsible for the civilian space program; and the Nuclear Regulatory Commission; (NRC), tasked with protecting public health and safety related to nuclear energy. The INSRP was replaced by the INSRB per NSPM-20 in August, 2019, adding two new organizations to the board, the Department of Transportation (DOT) responsible for transportation safety and the Department of State (DOS) responsible for international agreements.. The Air Force (AF) Chief of Space Safety is a co-chair on the Board representing the Department of Defense. There have historically existed no regulated acceptable risk thresholds within US Government or AF guidance specific to the potential for radioisotope exposure should a launch of this nature fail. To this end, the AF rewrote its existing policy to establish launch safety criteria for use by the AF Launch Decision Authority when approving launches that use radioactive sources. This paper outlines the thought process used while developing launch safety criteria specifically, with regard to when a risk evaluation should be accomplished and what the acceptable risk threshold should be.

A calculation method of interior ballistic two-phase flow considering the compression and fracture process of propellant bed

The fracture degree of propellant charge on the projectile base before it is ignited is the key to study the launch safety of propellant charge and simulate the breech-blow phenomenon of the gun. In this paper, by solving the difficult problem of calculating the gas generation law of fractured propellant charge, an interior ballistic two-phase flow calculation method with mixed-charge considering the fractured propellant charge is established. Through the test method for mechanical situation of propellant charge, the time history of compression stress of propellant charge near the projectile base is acquired, which is loaded into the propellant bed model based on discrete element method(DEM). The compression and fracture process of propellant charge in the 30 mm area near the projectile base at low temperature is simulated. Then the corresponding fractured propellant charge is obtained, and next setting it as the initial condition of the interior ballistic two-phase flow calculation; moreover, the simulation of interior ballistic two-phase flow with mixed-charge considering fractured propellant charge is carried out. And the simulation results are in good agreement with the ballistic performance test results. The research in this paper provides a precise calculation method for the abnormal pressure in chamber caused by fractured propellant charge, which can be used to predict the breech-blow phenomenon of the gun and to guide the design of gun charge structure.

Impact Temperature Determination for GPHS Safety Testing

Impact testing of general purpose heat sources (GPHSs) and their component GPHS clads is done to benchmark extensive safety calculations quantifying launch safety. Impact testing is done in the Isotope Fuels Impact Tester (IFIT), a large-bore gas gun at Los Alamos National Laboratory. Efforts to conduct an impact test at the extreme low end of the temperature range for launch have highlighted uncertainties in determining the GPHS clad temperature during impact tests. In IFIT impact tests, the GPHS clad temperature is inferred from the temperature of the radiological confinement. Heating tests have been done in the IFIT to determine the fueled clad surface temperature as a function of the surface temperature of the tantalum radiological confinement can. Direct measurement of clad temperatures in the impact configuration are described and the effect of emissivity of the various components indicated. The analytical model used to predict clad temperatures is seen to work well at temperatures above 625°C. Appropriate values of emissivity for use in the model were measured in the experiment. Calculation of the experimental clad impact temperature using the ANSYS thermal transport model is necessary at clad temperatures below 625°C. ANSYS modeling indicates that the clad temperature in a recent low-temperature impact was outside the relevant range for launch safety modeling of GPHS clad behavior.