Advanced technologies available for future solid propellant grains

Significant advances have been made during the last decade in several fields of solid propulsion: the advances have enabled new savings in the motor development phase and recurring costs, because they help limit the number of prototypes and tests.The purpose of the paper is to describe the improvements achieved by SNPE in solid grain technologies, making these technologies available for new developments in more efficient and reliable future SRMs: new energetic molecules, new solid propellants, new processes for grain manufacturing, quick response grain design tools associated with advanced models for grain performance predictions.Using its expertise in chemical synthesis, SNPE develops new molecules to fit new energetic material requirements.Tests based on new propellant formulations have produced good results in the propellant performance/safety behavior ratio. New processes have been developed simultaneously to reduce the manufacturing costs of the new propellants.In addition, the grain design has been optimized by using the latest generation of predictive theoretical tools supported by a large data bank of experimental parameters resulting from over 30 years' experience in solid propulsion:

• Computer-aided method for the preliminary grain design

• Advanced models for SRM operating and performance predictions

Acceleration and losses of energetic protons and electrons during magnetic storm on August 30–31, 2004

Variations of particle fluxes during a moderate magnetic storm on August 30–31, 2004 are analyzed in this paper using measurements on low-orbit polar satellites CORONAS-F and SERVIS-1. The Earth’s radiation belts were filled at this time by enhanced flux of energetic particles accelerated a month ago during magnetic storms on July 23–27. The analysis has shown that even during a moderate magnetic storm a set of several adiabatic and non-adiabatic processes is observed, which leads to acceleration or release of particles and acts selectively depending on the energy range and charge of particles.     

Gravitation effect on a flux of sporadic micrometeoroids in the vicinity of near-Earth orbits

The new approach to gravitation effect determination in calculating the flux of sporadic micrometeoroids in the near-Earth space is proposed. The technique is based on integration of the equations of motion of sporadic micrometeoroids with accounting for bending their trajectories when particles are approaching the Earth. The technique and results of calculation of the gravitational focusing factor k_g for various conditions are presented. The feature of the proposed technique for calculating coefficient k_g consists in the fact that this coefficient does not explicitly depend on the values of particles velocity at the last point. The results of investigation of coefficient k_g have shown that, for the given initial velocity of micrometeoroids, the values of this coefficient depend on deflection of its direction from the direction to the Earth center. It is shown that for low-altitude orbits the flux density can increase up to 60%. The distribution of probabilities of various directions of particles flying to spacecraft structural elements is found to be non-uniform.     

A diffusion model of radial distributions of plasma density from measurements on the Cassini spacecraft in the inner magnetosphere of Saturn

Equatorial radial distributions of plasma density in the 3 < L < 9 region of Saturn’s magnetosphere, obtained from measurements on the Cassini spacecraft, are considered on the basis of diffusion theory. The concentration of particles in the magnetic tubes is found to grow with L. The external source is located at L ? 9. The particles diffuse to Saturn. In the 5 < L < 9 interval the distribution is close to equilibrium. A relation between the diffusion coefficient and the densities of internal sources and losses is obtained in this interval. Prevalence of losses over sources is very probable. Estimates of the diffusion flux and its derivative are given. If the diffusion coefficient is expressed as D _LL = D _o L ³ and the contencentration of particles depends on L according to a power law, the diffusion rate is constant.     

Regularization of the Limit Problem of Satellite Librations in a Keplerian Orbit Taking Light Pressure into Account

The planar librations of a satellite whose center of mass moves along an elliptic orbit are considered. It is assumed that not only the gravitational moment but also the forces of light pressure act upon the satellite. Account is taken of the fact that the right-hand sides of the differential equations are nonanalytic functions of the phase variables. When e 1, e being the orbit's eccentricity, the deformations of solutions are considered for the case of a satellite moving along a highly elongated orbit. Such transformation of the initial system of differential equations is carried out so that the new system becomes regular up to the value e = 1. A limit problem corresponding to the case e = 1 is considered. When the azimuth angle of the light source coincides with the direction to the pericenter, the dynamical system is reversible. In this case, the known families of the periodic solutions to the problem can be continued up to the limit case.     

卫星磁力矩器磁场效应仿真分析

磁力矩器是卫星上磁性较大的部件之一,局部的强磁场是影响卫星周围带电粒子分布的主要原因。为了定量分析磁力矩器与等离子体相互作用,文章基于磁场与运动粒子的耦合模型,利用有限元数值分析软件仿真了典型轨道航天器上磁力矩器工作时周围带电粒子入射轨迹变化及电荷(粒子数)分布。结果表明,受磁场作用,带电粒子在接近磁力矩器本体时会发生偏转,且偏转幅度随电子能量降低而增大;由磁场引起的这种偏转效应导致带电粒子不均匀入射到卫星内。     

Sources and Losses of Energetic Electrons at Low Altitudes from Satellite Data

Fluxes and differential spectra of 0.04–2.0 MeV electrons at low altitudes in the Earth's magnetosphere are considered in comparison with the model spectra AE-8 MAX and AE-8 MIN. Possible causes of the discrepancy between the observational and model spectra are discussed. The coefficients of radial diffusion at various L-shells are estimated for the maximum of solar activity (using the Interkosmos-19 data) and for the minimum of solar activity (using the Kosmos-1686 data) and are derived from the model AE-8. A quantitative evaluation of the electron yield from radial diffusion at low L shells is derived. Ionization losses, Coulomb angle scattering, and resonant wave–particle interaction are considered as the loss mechanisms. A calculation of these losses at the low L-shells is given. The electron distribution at low L-shells is best fitted by a combination of dissipative terms from different models: Coulomb scattering dominates at the lower L-shells (L = 1.2–1.4) and the resonant wave–particle interaction controls the radiation belt maximum and the gap (L = 1.4–2.0).     

Application of LB-Planning for Designing the Programs of Trajectory Measurements

The LB-planning is a construction of the dependence between three variables k, m, and , where k is the number of parameters of the linear dynamic system (LDS) under study, m is the specified number of measurements (communication sessions), and (defect) is the maximum value of failure (set of all criterion functions) in a chosen m-point measurement program relative to the optimal program. The problem is reduced to the solution of an extremal problem, which, at m = k + 1, is found rather simply by maximization of the Tchebyshev determinant (TD-planning).     

A Diffusion Model of Radial Distributions of Energetic Protons in Saturn's Magnetosphere

A simple diffusion model of Saturn's radiation belts with a constant internal source and particle losses at the boundaries is considered. The radial diffusion coefficient is supposed to be D _LL L ⁴. The analytical solution to the stationary diffusion equation describes well the observed radial profiles of the distribution function of energetic protons in Saturn's magnetosphere.     

Theoretical prediction of thermal diffusion coefficients for ternary hydrocarbon mixtures based on the irreversible thermodynamics theory

An accurate thermodiffusion model is of paramount importance to the petroleum industry for the prediction of the compositional variation in hydrocarbon reservoirs. Several theoretical models have been developed. Kempers and Firoozabadi models are the latest two models, which are not only applicable for binary mixtures but also for multi-component mixtures. In this paper, we applied the Firoozabadi model to a ternary hydrocarbon mixture of n-Dodecane, n-Butane and Methane with different mass fraction. It reveals that the accuracy of the thermal diffusion coefficients for a specific mixture of interest relies on the accuracy of the thermodynamic properties from equations of state, corresponding Fick's diffusion coefficients, and the thermal diffusion modeling.     

Relaxation of electron and proton radiation belts of the earth after strong magnetic storms

During strong magnetic storms in July and November of 2004 the fluxes of trapped particles (protons and electrons of MeV energies) in the Earth’s radiation belts have increased by orders of magnitude and then decreased remaining on an enhanced level for several months. These enhancements allowed us to study the processes of relaxation of the radiation belts. Measurements of energetic particles by low-altitude satellites Coronas-F and Servis-1 have shown that predictions of the theory about the rate of pitch-angle diffusion are not always correct, giving both overestimated and underestimated values for the lifetime of energetic particles.     

射流推力矢量喷管中粒子运动轨迹的数值模拟

用颗粒轨道模型对基于激波控制的二维收缩-扩张(2-DCD)喷管中的气固两相流动进行了数值模拟,研究了1～60 μm不同直径颗粒的运动轨迹.研究表明,颗粒尺寸越小,粒子的随流性越好;颗粒尺寸越大,主流中的粒子与收缩段壁面碰撞越剧烈,无粒子区越大,二次流中的粒子对下壁面的碰撞越剧烈.     

Buoyancy effects on smoldering combustion

A theoretical and experimental study is carried out to determine the effect of buoyancy on the rate of spread of a cocurrent smolder reaction through a porous combustible material. Since buoyant forces are proportional to the product g(_gi − _g), they can be controlled experimentally by varying either the gravitational acceleration, g, or the density difference, _gi − _g. The latter approach was followed in the present work. Measurements are performed of the smolder spread rate through porous α-cellulose (0.83 void fraction) as a function of the ambient air pressure. The experiments are carried out in a pressure vessel for ambient pressures ranging from 0.5 to 1.2 atm. The rate of spread was obtained from the temperature histories of thermocouples placed at fixed intervals along the fuel centerline. The smolder velocity was found to increase as the ambient pressure was increased. Extinction was found to occur when the buoyancy forces could not overcome the drag forces, indicating that at least for the present experimental conditions transport by diffusion cannot, by itself, support the spread of a smolder reaction. This conclusion is particularly important for outer space conditions where gravity and consequently buoyancy could be negligible. In the analysis, which assumes one-dimensional processes, the transport equations are solved to give the smolder spread rate as a function of the inlet oxygen mass flux. This mass flux is then estimated by balancing buoyancy and drag forces. Assuming that the smolder chemical reaction is only weakly dependent on pressure, the analysis finally predicts a smolder velocity dependence of the form v Y_oig²_gi Pa², i.e. is proportional to the ambient pressure squared. Good qualitative agreement is found between the theoretical predictions and the experimental results.     

The Structure of Ion Spectra in Outer Regions of the Ring Current: The November 13, 1995 Event

We present the results on variations of ion spectra in the energy range from 1 keV to 3 MeV. The spectra measured onboard the INTERBALL Tail Probe satellite on November 13, 1995, during the satellite's passage from the dipole field lines to the lines stretched into the magnetotail are analyzed. The data of the CORALL, DOK-2, and SKA-2 instruments are used to reconstruct the ion spectra. It is shown that, when the ion spectrum along the satellite trajectory is averaged over 2-min intervals, it is smooth up to geocentric distances of 6R _E. With decreasing distances, the form of the particle spectra in the region under consideration remained virtually unchanged (region from L = 11R _E down to L= 6R _E) and only insignificant variations of the energy of the spectral maxima are observed. Possible reasons for the observed regularities are discussed.     

固体火箭发动机用C/SiC导流管烧蚀性能研究

采用地面试车试验考核了固体火箭发动机用C/SiC导流管的烧蚀性能,并对C/SiC导流管的烧蚀机理进行了探讨。结果表明:导流管轴向线烧蚀率变化较大,沿气流方向呈上升趋势。材料的线烧蚀率从进口处的0.018mm/s增至出口处的0.032mm/s,且导流管中间段烧蚀稳定性明显优于进口段和出口段。同时,C/SiC导流管的烧蚀机制主要是粒子冲刷和机械剥蚀共同作用的结果。     

Peculiarities of the formation of a thin current sheet in the Earth’s magnetosphere

We investigate the process of the self-consistent formation of a thin current sheet with a thickness close to the ion Larmor gyroradius in the presence of decreasing magnetic field’s normal component B_n. This behavior is typical of the current sheet of the Earth’s magnetospheric tail during geomagnetic substorms. It has been shown that, in a numerical model of the current sheet, based on the particle-in-cell method, the appearance of self-consistent electric field component E_y in the current sheet vicinity can lead to its significant thinning and, eventually, to the formation of a multiscale configuration with a thin current sheet (TCS) in the central region supported by transient particles. The structure of the resulting equilibrium is determined by the initial parameters of the model and by the particle dynamics during the sheet thinning. Under certain conditions, the particle drift in the crossed electric and magnetic fields leads to a significant portion of ions becoming trapped near the neutral sheet and, in this way, to the formation of a wider configuration with an embedded thin current sheet. The population of trapped particles produces diamagnetic negative currents that manifest in the form of negative wings at the periphery of the sheet. Correspondingly, in the direction perpendicular to the sheet, a nonmonotonic coordinate dependence of the magnetic field appears. The mechanisms of the evolution of the current sheet in the Earth’s magnetotail and the formation of a multiscale structure are discussed.     

Protons with energy of E P ≥ MeV under the earth’s radiation belts

Variations in fluxes of quasi-trapped energetic protons were studied on the basis of the data of the CORONAS-I satellite. These variations are characterized by an increase in the proton fluxes with E _P ≥ 1 MeV both in the vicinity of the geomagnetic equator and in the high-latitude region of the magnetosphere. The analysis of structural features of the proton distributions in the regions at L ～ 1–1.1; 3 < L < 4; and L > 4, was performed and made it possible to detect reliably the type of the proton flux increase in this region. The mechanisms of particle scattering leading to the precipitation of energetic protons under conditions of various types of geomagnetic disturbances are considered.     

Energy dependence of the characteristic decay time of proton fluxes in solar cosmic ray events

Energetic solar proton events within the energy interval 1–48 MeV at the stage of their decay are considered over the period of 1974–2001. The dependence of the characteristic decay time on the proton energy in the assumed power-law representation τ(E) =E ^?n is analyzed for the events with an exponential decay form. The dependence of n on the heliolongitude of the flare (the particles source on the Sun) is studied.