Life test research of a high specific impulse Hall thruster HEP-140MF

In this study,a high specific impulse Hall thruster,HEP-140 MF,having a high discharge voltage,was used to accelerate ions.We aimed to obtain a high specific impulse and an acceleration zone moving downstream toward the channel exit to reduce wall sputtering erosion of the walls of the discharge channel,hence ensuring an enhanced lifetime.To study the lifetime characteristics of the high specific impulse Hall thruster,a life test was performed on the HEP-140 MF thruster for the first time,and performance parameters,such as thrust,specific impulse,and efficiency,were measured.Changes in the performance parameters and evolutions in the surface profiles of the discharge channel wall were summarized.The reasons contributing to these changes during the life test were analyzed.Moreover,the accelerated life test method was validated on the HEP-140 MF.

Experimental and numerical investigation on alternatives to sandy gravel

The NATO agreement STANAG 4569 defines the protection levels for the occupants of logistic and light armored vehicle.The Allied Engineering Publication,AEP-55,Volume 2 document outlines the test conditions for underbelly improvised explosive device(IEDs),which must be buried in water-saturated sandy gravel.The use of sandy gravel has some drawbacks,for instance reproducibility,time consumption,and cost.This paper focuses on the investigation of four alternatives to sandy gravel,which could produce similar specific and cumulative impulses:a concrete pot filled with water,a concrete pot filled with quartz sand,a steel pot without filling and a concrete pot filled with glass spheres(diameter 200μm—300μm)and different water contents.The impulses are measured with a ring technology developed at the Fraunhofer EMI.A numerical soil model based on the work of Marrs,2014 and Fi serov a,2006 and considering the soil moisture was used to simulate the experiments with glass spheres at different water contents,showing much better agreement with the experiments than the classical Laine&Sandvik model,even for high saturation levels.These results can be used to create new test conditions at original scale that are more cost-effective,more reproducible and simpler to manage in comparison to the current tests carried out with STANAG sandy gravel.

Modification of SDOF model for reinforced concrete beams under close-in explosion

In this paper,a modified single-degree-of-freedom(SDOF)model of reinforced concrete(RC)beams under close-in explosion is proposed by developing the specific impulse equivalent method and flexural resistance calculation method.The equivalent uniform specific impulse was obtained based on the local conservation of momentum and global conservation of kinetic energy.Additionally,the influence of load uniformity,boundary condition and complex material behaviors(e.g.strain rate effect,hardening/softening and hoop-confined effect)was considered in the resistance calculation process by establishing a novel relationship between external force,bending moment,curvature and deflection successively.The accuracy of the proposed model was verified by carrying out field explosion tests on four RC beams with the scaled distances of 0.5 m/kg~(1/3)and 0.75 m/kg~(1/3).The test data in other literatures were also used for validation.As a result,the equivalent load implies that the blast load near the mid-span of beams would contribute more to the maximum displacement,which was also observed in the tests.Moreover,both the resistance model and test results declare that when the blast load becomes more concentrated,the ultimate resistance would become lower,and the compressive concrete would be more prone to softening and crushing.Finally,based on the modified SDOF model,the calculated maximum displacements agreed well with the test data in this paper and other literatures.This work fully proves the rationality of the modified SDOF method,which will contribute to a more accurate damage assessment of RC structures under close-in explosion.

High-energy Metal Fuels for Rocket Propulsion： Characterization and Performance

A joint international effort to improve solid propellant performance within the framework of a FP7European Project was described.Several metallized solid rocket propellants,of the broad family AP/HTPB/Metal in the ratio 68/14/18,were experimentally analyzed seeking to optimize the delivered specific impulse by identifying the most suitable high-energy fuel.Keeping the same nominal composition,different metallic fuels(including micrometric and nanometric Al,AlH3,and a variety of dual metal compositions)were characterized,tested,and contrasted to a conventional micrometric aluminum(30μm average grain size)certified for space flights.In order to overcome the intrinsic performance limitations of the matrix AP/HTPB,a new matrix consisting of ADN/GAP satisfying also the need for environmentally benign propellant formulation was considered as well.A comparative analysis between the two solid propellant systems in terms of ideal thermochemistry and experimental combustion properties reveals advantages and disadvantages of both.Overall,it is judged worthwhile to develop ADN/GAP propellants,with or without metallic fuels,to enhance the current status of solid rocket propulsion.Controlling morphology and mechanical properties of ADN/GAP compositions and understanding their flame structure and aggregation/agglomeration properties are the main issues still challenging industrial users.

Innovative Metallized Formulations for Solid Rocket Propulsion

Several metallized solid rocket propellants,AP/Metal/HTPB in the ratio 68/18/14,were experimentally analyzed at the Space Propulsion Laboratory of Politecnico di Milano.Effects of the metals(micrometric and nanometric Al,B,Mg,and a variety of dual metals) on the performance of the propellant were studied and contrasted to a conventional micrometric aluminum(30 μm average grain size) taken as reference.It is shown that the propellant microstructure plays a fundamental role in controlling the critical aggregation/agglomeration phenomena occurring below and near the burning surface.Two specific effects of microstructure in terms of steady burning rate and average agglomerate size are illustrated.

Solid-like ablation propulsion generation in nanosecond pulsed laser interaction with carbon-doped glycerol

A solid-like propellant of carbon-doped glycerol ablated by a nanosecond pulsed laser is investigated. The results show that the specific impulse increases with increasing carbon content, and a maximum value of 228 s is obtained. The high specific impulse is attributed to the low ablated mass loss that occurs at high carbon content. More importantly, with increasing carbon content, the properties of the doped glycerol approach to those of a solid. These results indicate that propulsion at the required coupling coefficient and specific impulse can be realized by doping a liquid propellant with an absorber.

Impacts of laser pulse width and target thickness on laser micro-propulsion performance

In order to optimize the laser ablation performance of a micro-thruster with 1U dimensions,which employs a micro semiconductor laser,the impacts of pulse width and glycidyl azide polymer(GAP)thickness on thrust performance were researched.The results showed that with a GAP thickness of 200μm,the single-pulse impulse(I)increased gradually with the increase in the laser pulse width from 50 to 800μs,while the specific impulse(I_(sp)),impulse coupling coefficient(Cm)and ablation efficiency(η)all reached optimal values with a 200μs pulse width.It is worth noting that the optimal pulse width is identical to the ignition delay time.Both Cmandηpeaked with a pulse width of 200μs,reaching 242.22μN W^(-1)and 35.4%,respectively.With the increase in GAP thickness,I and Cmincreased gradually.GAP of different thicknesses corresponded to different optimal laser pulse widths.Under a certain laser pulse width,the optimal GAP thickness should be the most vertical thickness of the ablation pit,and the various propulsion performance parameters at this time were also optimal.With the current laser parameters,the optimal GAP thickness was approximately 150μm,I_(sp)was approximately 322.22 s,andηwas approximately 34.94%.

An improved constant volume cycle model for performance analysis and shape design of PDRE nozzle

An improved constant volume cycle （CVC） model is developed to analyze the nozzle effects on the thrust and specific impulse of pulse detonation rocket engine （PDRE）. Theoretically, this model shows that the thrust coefficient/specific impulse of PDRE is a function of the nozzle contraction/expansion ratio and the operating frequency. The relationship between the nozzle contraction ratio and the operation frequency is obtained by introducing the duty ratio, by which the key problem in the theoretical design can be solved. Therefore, the performance of PDRE can be accessed to guide the preliminary shape design of nozzle conveniently and quickly. The higher the operating frequency of PDRE is, the smaller the nozzle contraction ratio should be. Besides, the lower the ambient pressure is, the larger the expansion ratio of the nozzle should be. When the ambient pressure is 1.013 × 105 Pa, the optimal expansion ratio will be less than 2.26. When the ambient pressure is reduced to vacuum, the extremum of the optimal thrust coefficient is 2.236 9, and the extremum of the specific impulse is 321.01 s. The results of the improved model are verified by numerical simulation.

Energetic Opportunities of Solid Composite Propellants Containing Some Hypothetic Furazano-[3,4-d]-pyridazine-based Derivatives

Six furazano-[3,4-d]-pyridazine-based derivatives as main compounds in solid composite propellants have been investigated.It was shown that the use of some furazano-[3,4-d]-pyridazine-based derivatives as main compounds in solid composite propellants can considerably increase ballistic parameters compared with HMX if the compounds under consideration contain difluoramine groups.And the use of the compounds under consideration may be successful only in the presence of an active binder and 10%-30% of AP or ADN as additional oxidizers.

Systematic Direct Approach for Optimizing Continuous-thrust Earth-orbit Transfers

This article presents a systematic direct approach to carry out effective optimization of a wide range of continuous-thrust Earth-orbit transfers with intermediate-level thrust acceleration,including minimum-time (with a single burn arc) and mini-mum-fuel (with multiple burn arcs) transfers. With direct control parameterization,in which the control steering programs of burn arcs are interpolated through a finite number of nodes,the optimal control problem is converted into the parameter optimi-zation proble...

Theoretical investigation on water/metal fuel ramjet motor-thermodynamic cycle and thermodynamic calculation

For achieving high-speed requirement of underwater vehicle,a conceptual engine,which utilizes the hydroreactive characteristic of several metals under supercavitation environment,has been put forward. Especially,in order to obtain specific impulse as great as possible,a dual water injection system is taken into account. Then thermodynamic cycle model,which lead the improvement of power plant and energy system,is introduced in detail,and thermal efficiency is also analyzed. Furthermore,for investigating the performance of this kind of engine system,detailed thermodynamic calculation and analysis are achieved. Especially,regarding hydroreactive metal fuel Mg/AP/HTPB as our target fuel-rich propellant,considering its obvious deficient oxygen property and the energy property of magnesium/water reaction,theoretical calculation method is established by integrating chemical non-equilibrium with chemical equilibrium. Accordingly,low limit of primary water/fuel ratio is determined. In addition,the qualitative and quantitative relationship of performance parameters,such as theoretical specific impulse,nozzle exit temperature,characteristic velocity,etc.,versus water/fuel ratio is investigated respectively.

Investigation on plume interference effect of solid propellant micro-thruster

The three-dimensional numerical simulation of two-phase plume flow of solid propellant micro-thrusters was developed.Then it was used to investigate the plume interference effect by combining the direct simulation Monte Carlo(DSMC) method for multi-component gas flow with the two-way coupling model for two-phase rarefied flow.At different space between the two micro-thrusters and different wall temperature,the plume interference effect was analyzed specifically.The results show that under the plume interference effect the gas is compressed and the flow direction is changed,which resulted in the increasing of gas pressure and temperature;solid phase made no significant effect on the flow parameters of gas phase;with the rising of the space between the two micro-thrusters,the maximum pressure decreased and the maximum temperature increased in the domain under the plume interference effect;the wall temperature could influence the temperature of the gas which is extremely close to the wall,but not the gas pressure.

Ground and flight tests of AlSat-1B butane propulsion system

On September 26,2016 Algerian Space Agency launched AlSat-1B,the second in a series of medium resolution earth observation satellites mission.AlSat-1B electro-thermal propulsion system follows the classic design principle that has been used on previous SSTL-100 missions.With a total dry weight of 5.17 kg,the system is filled with 2.35 L selfpressurized butane.The thruster assembly is designed to use 15 W(at 28 V)redundant heater elements,it is designed to have an average mission thrust of 50 mN.With a warm up time of 10 min,the temperature of the butane will be increased by over 250℃.This is the equivalent of about 35%gain in specific impulse over ambient temperature butane.The spacecraft dry weigh at launch site was 107 kg,the propulsion system is designed to provide at least 19 m/s Delta-v to meet the spacecraft’s mission requirement.To investigate the system readiness for flight,a series of performance tests have been completed at the Surrey Satellite Technology Ltd laboratories(United Kingdom),Satellite Development Centre(Algeria)and Satish Dhawan Space Centre rocket launch site(India),the results of these tests as well as initial flight test results are presented in this paper.

Computational Study of Azide-oxirane as High-energy-density Materials

The azide oxiranes were studied at the CCSD(T)/cc-PVDZ//MP2/cc-PVDZ level in this paper.The sublimation enthalpies and heats of formation both in gas phase and solid state were calculated.The thermodynamics stability was predicted by using the bond dissociation energy and characteristic height,through which all title compounds are confirmed to be more stable than hexanitrohexaazaisowurtzitane(CL-20)and A,B1 and D are less sensitive than hexahydro-1,3,5,-trinitro-1,3,5-triazine(RDX).Furthermore,the detonation property was measured by the specific impulse.The detonation performance of the title compounds is comparable to that of RDX.Our results can provide basic information for the molecular design of novel high-energy-density compounds.

Numerical modelling of the hybrid rocket engine performance

The purpose of this paper is to present method of the numerical modeling of the hybrid rocket engine's work as a tool for designing engines of this type.The model is intended as an accurate and simple to use development tool for use in preliminary design stages of hybrid rocket engines,improving the effectiveness and quality of this process.General assumptions underlying the use of a model are presented,together with an analysis of past work in this field.Results of an extensive experimental campaign are presented and compared with the results of numerical modelling in order to calibrate the proposed model and evaluate its accuracy.Parameter variation and optimization were conducted,proving functionality of the methodology.Presented numerical calculations show that the adopted approach to reduce the analysis time and complexity was correct.This method of numerical calculation of hybrid engine working parameters combines aspects of accuracy and simplicity at the early design stage to avoid timeconsuming and costly changes in subsequent detailed stages of design.