脉冲激光烧蚀推进技术的航天应用进展

脉冲激光烧蚀推进技术具有比冲高和推力可精确控制的特点,既可用于发射有效载荷也可用于星载动力,甚至可用小行星表面物质作为推进剂使其偏转轨道,因此,在航天领域得到越来越多关注。围绕激光单级入轨发射、同步轨道和火星轨道运输;激光微推力器用于航天器姿轨控,以及激光与电组合推进;激光烧蚀操控cm级空间碎片的轨道,以及激光烧蚀操控较大尺寸碎片的姿态;激光烧蚀偏转小行星轨道等方面,对脉冲激光烧蚀推进技术在航天领域研究现状和进展,进行了系统全面地归纳和总结,并对激光平均功率、波长、脉宽和推进剂选材等关键问题,进行了详细分析。     

A simplex method for the orbit determination of maneuvering satellites

A simplex method of orbit determination (SMOD) is presented to solve the problem of orbit determination for maneuvering satellites subject to small and continuous thrust. The objective function is established as the sum of the nth powers of the observation errors based on global positioning satellite (GPS) data. The convergence behavior of the proposed method is analyzed using a range of initial orbital parameter errors and n values to ensure the rapid and accurate convergence of the SMOD. For an uncontrolled satellite, the orbit obtained by the SMOD provides a position error compared with GPS data that is commensurate with that obtained by the least squares technique. For low Earth orbit satellite control, the precision of the acceleration produced by a small pulse thrust is less than 0.1% compared with the calibrated value. The orbit obtained by the SMOD is also compared with weak GPS data for a geostationary Earth orbit satellite over several days. The results show that the position accuracy is within 12.0 m. The working efficiency of the electric propulsion is about 67% compared with the designed value. The analyses provide the guidance for subsequent satellite control. The method is suitable for orbit determination of maneuvering satellites subject to small and continuous thrust.     

空间电推进技术发展及应用展望

我国空间电推进技术已进入成熟和全面应用的新阶段。为进一步促进电推进技术发展,加速推动空间动力领域技术进步,采用调研、对比分析的方法,以功率为划分标准,重点结合未来空间任务对电推进的应用需求,针对电推进各技术方向的特点,从“中、微、超”3个功率区间对空间电推进进行了分类综述。总结了国内外电推进技术的发展现状和存在的不足,提出了需要攻克的关键难点,研判了发展的主要趋势,归纳了存在的共性问题,提出了未来10年空间电推进技术的发展建议,供我国卫星用户、总体单位和空间电推进专业技术单位参考。     

Low-thrust trajectory optimization of asteroid sample return mission with multiple revolutions and moon gravity assists

Near-Earth asteroids have gained a lot of interest and the development in low-thrust propulsion technology makes complex deep space exploration missions possible. A mission from low-Earth orbit using low-thrust electric propulsion system to rendezvous with near-Earth asteroid and bring sample back is investigated. By dividing the mission into five segments, the complex mission is solved separately. Then different methods are used to find optimal trajectories for every segment. Multiple revolutions around the Earth and multiple Moon gravity assists are used to decrease the fuel consumption to escape from the Earth. To avoid possible numerical difficulty of indirect methods, a direct method to parameterize the switching moment and direction of thrust vector is proposed. To maximize the mass of sample, optimal control theory and homotopic approach are applied to find the optimal trajectory. Direct methods of finding proper time to brake the spacecraft using Moon gravity assist are also proposed. Practical techniques including both direct and indirect methods are investigated to optimize trajectories for different segments and they can be easily extended to other missions and more precise dynamic model.     

微小卫星贮箱内两相流界面变形定位及控制管理

液化气推进技术是微小伴随卫星在轨飞行采用的一种新型推进技术。微小伴星空间调姿、变轨过程需精确的推力控制,因此必须了解卫星推进系统中推进剂的形位分布。本文理论分析了空间微重力环境下液化气推进剂气/液界面的形位分布及变化,并通过落塔实验验证了微重力环境下有效控制液体推进剂的管理方法。     

太阳与地磁活动对超低轨重力卫星电推进系统工作的影响

面向当前第25太阳活动周,评估太阳与地磁活动对超低轨重力卫星电推进系统工作的影响。通过对超低轨道重力卫星进行轨道仿真和分析GOCE任务数据,得出大气阻力的变化规律,并获得了太阳活动极大年附近任务和极小年附近任务对携带工质量的影响、地磁暴对电推进系统保持“无拖曳”工作的影响。结果表明：其余情况相同下,卫星在太阳活动低年附近任务的工作轨道高度可较高年降低约20 km,有利于提高重力信号强度。强地磁暴通常引起超低轨道卫星阻力增加30%～90%,飞行控制需为克服地磁暴影响留足够的推力裕度。推力器设计应保证最大推力的10%～70%推力区间具有高比冲,且着重考虑此区间的寿命问题。     

Laser ablation in a running hall effect thruster for space propulsion

Hall Effect Thrusters (HETs) are promising electric propulsion devices for the station-keeping of geostationary satellites (more than 120 in orbit to date). Moreover, they can offer a cost-effective solution for interplanetary journey, as proved by the recent ESA SMART-1 mission to the Moon. The main limiting factor of the HETs lifetime is the erosion of the annular channel ceramics walls. In order to provide a better understanding of the energy deposition on the insulated walls, a laser irradiation study has been carried out on a PPS100-ML thruster during its run in the PIVOINE-2G ground test facility (CNRS Orléans, France). Two distinct approaches have been followed: continuous wave fiber laser irradiation (generation of thermal defects) and nanosecond pulsed laser ablation (generation of topological defects). The irradiated zones have been monitored in situ by IR thermography and optical emission spectroscopy and further investigated ex situ by scanning electron microscopy and profilometry.     

Modeling of a discharge in crossed fields with account of collisions and ionization

A one-dimensional mathematical model is proposed for calculating the characteristics of a discharge in crossed electric and magnetic fields. In particular, the model can be applied for calculating electric propulsion engines with closed (azimuthal) drift of electrons.     

Gate control of quantum dot-based electron spin–orbit qubits

We investigate theoretically the coherent spin dynamics of gate control of quantum dot-based electron spin–orbit qubits subjected to a tilted magnetic field under electric-dipole spin resonance (EDSR). Our results reveal that Rabi oscillation of qubit states can be manipulated electrically based on rapid gate control of SOC strength. The Rabi frequency is strongly dependent on the gate-induced electric field, the strength and orientation of the applied magnetic field. There are two major EDSR mechanisms. One arises from electric field-induced spin–orbit hybridization, and the other arises from magnetic field-induced energy-level crossing. The SOC introduced by the gate-induced electric field allows AC electric fields to drive coherent Rabi oscillations between spin-up and -down states. After the crossing of the energy-levels with the magnetic field, the spin-transfer crossing results in Rabi oscillation irrespective of whether or not the external electric field is present. The spin–orbit qubit is transferred into the orbit qubit. Rabi oscillation is anisotropic and periodic with respect to the tilted and in-plane orientation of the magnetic field originating from the interplay of the SOC, orbital, and Zeeman effects. The strong electrically-controlled SOC strength suggests the possibility for scalable applications of gate-controllable spin–orbit qubits.     

Sputter yields of Mo,Ti, W,Al, Ag under xenon ion incidence

The sputter yield is an important material parameter not only for various surface treatment techniques, but also for electric spacecraft propulsion. Many satellite or thruster components might be subject of erosion due to energetic and/or related secondary ions. In order to estimate the lifetime of these components the sputter yield under xenon ion incidence has to be known in dependence on ion energy and incidence angle, mainly in the low energy region (i.e. below 1500 eV). However, for many materials related to electric propulsion the supply of sputter yield data in literature is quite poor. Therefore, in this study the sputter yields of molybdenum, titanium, tungsten, silver and aluminium was investigated under xenon ion incidence.     

Field Emission Electric Propulsion: Emission Site Distribution of Slit Emitters

Field emission electric propulsion is the technological application of the principle of liquid metal ion sources as thrusters in electric space propulsion. Research work sponsored by the European Space Agency (ESA) on a slit-type field ion thruster is reported and discussed. The most significant new features of its emission performance are as follows: For the first time, a slit emitter with a closed propellant supply system was fired in any optional direction, requiring, in principle, no gravitational forces. Quantitative data relating the constituents of the residual gas atmosphere to the wetting behavior of the liquid metal propellant and the emission site distribution were obtained. A homogeneous distribution of equally spaced emission sites was observed; the measured spacing is in good agreement with a simple hydrostatic model of wavelike instabilities on electrically stressed surfaces of fluids.     

Theory of electronic light scattering in lateral superlattices with Rashba spin–orbit coupling under quantizing electric and magnetic fields

The influence of an in-plane electric and out-of-plane magnetic field on the electronic light scattering is calculated for a lateral semiconductor superlattice within Rashba spin–orbit interaction. Sharp resonances are predicted to appear when the Raman shift matches one frequency of the Wannier–Stark ladder. The spin–orbit interaction gives rise to a dispersion of the exact one-particle eigenstates and an associated finite width of the Raman line, which can be tuned by the electric and magnetic field. When the Bloch frequency is located in this Raman line, a Fano resonance is observed.     

Assessment of bilayer silicene to probe as quantum spin and valley Hall effect

Silicene takes precedence over graphene due to its buckling type structure and strong spin orbit coupling. Motivated by these properties, we study the silicene bilayer in the presence of applied perpendicular electric field and intrinsic spin orbit coupling to probe as quantum spin/valley Hall effect. Using analytical approach, we calculate the spin Chern-number of bilayer silicene and then compare it with monolayer silicene. We reveal that bilayer silicene hosts double spin Chern-number as compared to single layer silicene and therefore accordingly has twice as many edge states in contrast to single layer silicene. In addition, we investigate the combined effect of intrinsic spin orbit coupling and the external electric field, we find that bilayer silicene, likewise single layer silicene, goes through a phase transitions from a quantum spin Hall state to a quantum valley Hall state when the strength of the applied electric field exceeds the intrinsic spin orbit coupling strength. We believe that the results and outcomes obtained for bilayer silicene are experimentally more accessible as compared to bilayer graphene, because of strong SO coupling in bilayer silicene.     

Technical Report: Synchrotron Radiation from Outer Space and the Chandra X-ray Observatory

The Chandra X-ray Observatory began its journey into space on July 23, 1999, using the Space Shuttle Columbia for the initial ascent. An upper stage and integral propulsion then placed the observatory into an elliptical orbit with an initial apogee of 140,000 km (1/3 of the distance to the moon) and an initial perigee 10,000 km (about two earth radii). In this orbit, the satellite (Figure 1) is above the radiation belts for more than 75% of the 63.5 hour orbital period, allowing for uninterrupted observations up to more than two days.     

基于空间矢量脉宽调制策略的船用永磁同步电机控制仿真

随着船舶吊舱技术以及永磁电机及其控制技术的发展,永磁同步电动机开始迅速应用于船舶吊舱电力推进系统中。针对船用电机的转速和转矩在过渡过程中波动很大的现象,引入了空间矢量脉宽调制方案,结合永磁同步电机数学模型及船桨模型,搭建了基于空间矢量脉宽调制策略的船用永磁同步电机仿真模型。仿真结果表明空间矢量脉宽调制方式可有效减小转矩的脉动,电机推进系统有良好的动态响应效果。为船舶电力推进系统的研究提供了新的思路。     

氢负离子在梯度电场中光剥离的波包动力学研究

利用含时微扰论和闭合轨道理论相结合的方法, 给出了氢负离子在梯度电场中自关联函数的计算公式, 并且对体系的自关联函数进行了计算和分析. 重点探讨了激光脉冲的宽度、梯度电场中背景电场强度及电场梯度对氢负离子体系的自关联函数的影响. 研究结果表明, 当激光脉冲的脉冲宽度较短, 远小于剥离电子的闭合轨道的周期时, 量子波包的回归现象显著, 自关联函数中会出现一系列比较明显的回归峰, 这是由于沿闭合轨道返回的电子波包和出射的电子波包之间产生干涉形成的. 但是随着激光脉冲宽度的增加, 量子波包的回归现象减弱. 当脉冲宽度和闭合轨道的周期相差不是很大时, 自关联函数中的回归峰逐渐变宽, 振荡渐趋平缓, 相邻的峰之间发生相互干涉, 从而导致对应关系消失. 除此之外, 我们还发现梯度电场中背景电场强度和电场梯度对体系的自关联函数也会发生显著的影响. 随着背景电场强度和电场梯度的增加, 剥离电子的闭合轨道的周期变短, 自关联函数中回归峰的个数逐渐增加, 量子回归现象增强. 因此, 我们可以通过改变脉冲的宽度、外加电场强度的大小对氢负离子发生光剥离的自关联函数进行调控. 我们的结果对于实验研究原子或离子体系在外场中的波包动力学性质可以提供一定的参考价值.     

Global Numerical Model for the Assessment of the Effect of Geometry and Operation Conditions on Insert and Orifice Region Plasmas of a Thermionic Hollow Cathode Electron Source

Thermionic hollow cathodes have been widely used in wide variety of areas such as spacecraft electric propulsion systems, material processing and lasers for more than half a century as efficient electron sources. Especially in electric propulsion systems, hollow cathodes are being used as electron sources for propellant ionization and ion beam neutralization. Moreover, it is also a promising candidate for utilization as a stand‐alone propulsion system in microsatellites or nanosatellites due to its small physical size, low power consumption and ease of operation. On the other hand, the small geometry of the typical orificed hollow cathodes makes the plasma diagnostics difficult which is why numerical studies become important for understanding the driving physical processes behind their operation, and the effects of the geometry and the operation parameters on cathode performance. In this paper, a global numerical model for the insert and orifice plasma of a hollow cathode is presented where volume averaged plasma parameters are considered for both regions. The results of this study show that the developed model can be used for designing and sizing orificed hollow cathodes as comparisons with the results of experimental and other numerical studies are in good agreement with the ones obtained from the developed model. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

垂直电磁场中He原子的吸收谱和回归谱的理论计算

半经典闭合轨道理论已经成功地计算了在外加磁场和平行电磁场中的里德堡原子的回归谱.但对于垂直电磁场中的里德堡原子,理论和计算都变得更为复杂.本文把闭合轨道理论推广到三维情况,采用 B.Hüpper的模型势计算了ε=-0.03,主量子数n≈ 40,m=0下He原子在垂直电磁场中的光吸收谱和回归谱,并和H原子在垂直电磁场中的回归谱作比较,突出了实散射的贡献.计算中应用了离子实散射的分区自洽迭代方法,并考虑到轨道的多次重复和离子实的多次散射效应.这是对闭合轨道理论的验证和进一步推广.     

负径向电场对荷电粒子运动的影响及其数值模拟

从负径向电场产生的电漂移改变荷电粒子运动的极向运动速度着手,推导出在负径向电场存在时安全因子的表达式,分析了安全因子对荷电粒子漂移位移和运动轨迹的影响。建立了在负径向电场条件下,荷电粒子在梯度磁场和曲率磁场中运动数学模型。通过数值模拟,获得了通行粒子、香蕉粒子的漂移位移和运动轨迹所呈现出的新特点和规律:负径向电场改变了荷电粒子的最大漂移位移。当荷电粒子的极向运动速度增加时,最大漂移位移减小,反之增大;改变了荷电粒子的运动轨迹,通行粒子的轨亦可能变为香蕉粒子的轨迹,香蕉粒子的轨迹可能变为通行粒子的轨迹,当电场达到足够的强度时,均成为在极向上顺时针运动的通行粒子轨迹。     

Fluid Simulation of a Cusped Field Thruster

The cusped field thruster is a kind of newly developed electric propulsion device. The electric field at the channel exit and the low frequency oscillation were measured by former experiments. While the formation mechanism of them have not been fully interpreted yet. Through studying two distinguishing typical electron paths in the thrusters, a fluid model is built up along two electron paths, and then the model is completed by synthetically analyzing the effect of two electron paths. Time‐averaged electric potential distribution, anode current oscillation curve and time‐synchronized atom density and ion density distribution are obtained by simulation. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)