飞行器鼻锥凹腔-发散组合冷却数值模拟

尖锐鼻锥冷却方案是可复用式航天飞行器研究领域一个十分重要的课题。传统发散冷却虽然可以有效降低鼻锥结构温度,但是由于驻点外极高的热流、压力,会出现驻点冷却效果差的问题。迎风凹腔结构是一种针对鼻锥驻点区域的减阻防热方案,尖锐唇口的分流作用可以使附近压力、热流降低。因此,提出一种新型冷却结构——凹腔-发散组合冷却,利用迎风凹腔结构对驻点的强化冷却解决发散冷却中驻点难以冷却的问题。以楔形鼻锥为物理模型,对发散冷却、迎风凹腔结构和凹腔-发散冷却3种冷却结构进行数值模拟,并和无冷却的纯鼻锥结构进行对比。结果表明,与传统发散冷却相比,使用凹腔-发散组合冷却可以使结构温度峰值下降16.8%;与没有冷却的纯鼻锥模型相比,鼻锥头部圆弧段表面平均温度降幅可达64%,证实了这种新型冷却结构的可行性和高效性。     

一种模块化航空有源滤波器的研究

 航空有源滤波器(AAPF)是解决飞机供电系统中电能质量问题的一种先进方案,而模块化设计对航空有源滤波器灵活性、可维护性和可靠性的提升作用巨大。首先提出并研究了一种新型模块化航空有源滤波器,分析了主电路数学模型及其混合载波PWM(CH-PWM)调制方式;其次基于损耗对比分析进行了主电路拓扑优化,推导了模块均压控制律并给出了系统控制策略;最后进行了仿真和实验验证。结果表明,模块化航空有源滤波器能够有效补偿航空电网中由典型非线性负载产生的谐波和无功电流分量,三相电网电流的总谐波畸变率(THD)均在5%以下,补偿效果显著。     

基于FFT含有饱和环节的非线性等效系统的方法研究

基于快速傅里叶变换(FFT)方法,对系统的输入和输出信号进行快速傅里叶变换,对含有高次谐波的输出信号进行滤波,得到期望主频率的傅里叶频谱,然后进行傅里叶反变换,求得在各主频率下的幅值和相位.利用MATLAB中的非线性最小二乘拟配方法得到含有非线性环节的飞机纵向飞行控制系统的频域等效线性模型.这种方法也为含有非线性环节的飞机纵向飞行控制系统的飞行品质评估提供了一种可行的方法.     

Heliotropic dust rings for Earth climate engineering

This paper examines the concept of a Sun-pointing elliptical Earth ring comprised of dust grains to offset global warming. A new family of non-Keplerian periodic orbits, under the effects of solar radiation pressure and the Earth’s J₂ oblateness perturbation, is used to increase the lifetime of the passive cloud of particles and, thus, increase the efficiency of this geoengineering strategy. An analytical model is used to predict the orbit evolution of the dust ring due to solar-radiation pressure and the J₂ effect. The attenuation of the solar radiation can then be calculated from the ring model. In comparison to circular orbits, eccentric orbits yield a more stable environment for small grain sizes and therefore achieve higher efficiencies when the orbit decay of the material is considered. Moreover, the novel orbital dynamics experienced by high area-to-mass ratio objects, influenced by solar radiation pressure and the J₂ effect, ensure the ring will maintain a permanent heliotropic shape, with dust spending the largest portion of time on the Sun facing side of the orbit. It is envisaged that small dust grains can be released from a circular generator orbit with an initial impulse to enter an eccentric orbit with Sun-facing apogee. Finally, a lowest estimate of 1 × 10¹² kg of material is computed as the total mass required to offset the effects of global warming.     

小卫星高分辨率成像系统

对小卫星对地观测高分辨率成像系统进行了综述。介绍了国内外有极高分辨率（0．5～1．0m）、高分辨率（1．8～2．5m）和中高分辨率（4-10m）小卫星光学成像系统的性能,并与合成孔径雷达（SAR）成像系统进行了比较。给出了小卫星光学成像系统、SAR高分辨率成像系统和卫星平台的关键技术。讨论了未来小卫星及其高分辨率成像系统技术的发展趋势。     

双接口电子存储设备技术的研究

由于嵌入式设备应用的特定环境,在实时系统运行时产生的关键数据很难捕捉。为了更好地组织和分析系统参数,研发了一种既能挂载到嵌入式计算机系统总线,又能方便地支持调试设备下载数据的基于USB和PCI双接口电子存储设备,能使维护人员准确地把握设备的动态信息,从而进一步提高设备运行的稳定性。     

飞行器管理系统需求

飞行器管理系统(VMS)将飞行、推进控制与相关的公管系统综合.飞行器管理系统的概念为性能改善带来了巨大的好处,同时对可靠性、维修性和保障性有重大改善.未来高性能的飞机将具有多操纵面/效应器以保证机动性,利用飞行/推进综合控制实现性能收益.随着更多系统的参与,综合设计的难度会增加.为确保VMS的实际应用,需要明确其计算和...     

Feasibility of performing space surveillance tasks with a proposed space-based optical architecture

Under ESA contract an industrial consortium including Aboa Space Research Oy (ASRO), the Astronomical Institute of the University of Bern (AIUB), and the Dutch National Aerospace Laboratory (NLR), proposed the observation concept, developed a suitable sensor architecture, and assessed the performance of a space-based optical (SBO) telescope in 2005. The goal of the SBO study was to analyse how the existing knowledge gap in the space debris population in the millimetre and centimetre regime may be closed by means of a passive optical instrument. The SBO instrument was requested to provide statistical information on the space debris population in terms of number of objects and size distribution. The SBO instrument was considered to be a cost-efficient with 20 cm aperture and 6° field-of-view and having flexible integration requirements. It should be possible to integrate the SBO instrument easily as a secondary payload on satellites launched into low-Earth orbits (LEO), or into geostationary orbit (GEO). Thus the selected mission concept only allowed for fix-mounted telescopes, and the pointing direction could be requested freely. Since 2007 ESA focuses space surveillance and tracking activities in the Space Situational Awareness (SSA) preparatory program. Ground-based radars and optical telescopes are studied for the build-up and maintenance of a catalogue of objects. In this paper we analyse how the proposed SBO architecture could contribute to the space surveillance tasks survey and tracking. We assume that the SBO instrumentation is placed into a circular sun-synchronous orbit at 800 km altitude. We discuss the observation conditions of objects at higher altitude, and select an orbit close to the terminator plane. A pointing of the sensor orthogonal to the orbital plane with optimal elevation slightly in positive direction (0° and +5°) is found optimal for accessing the entire GEO regime within one day, implying a very good coverage of controlled objects in GEO, too. Simulations using ESA’s Program for Radar and Optical Observation Forecasting (PROOF) in the version 2005 and a GEO reference population extracted from DISCOS revealed that the proposed pointing scenario provides low phase angles together with low angular velocities of the objects crossing the field-of-view. Radiometric simulations show that the optimal exposure time is 1–2 s, and that spherical objects in GEO with a diameter of below 1 m can be detected. The GEO population can be covered under proper illumination nearly completely, but seasonal drops of the coverage are possible. Subsequent observations of objects are on average at least every 1.5 days, not exceeding 3 days at maximum. A single observation arc spans 3° to 5° on average. Using a simulation environment that connects PROOF to AIUB’s program system CelMech we verify the consistency of the initial orbit determination for five selected test objects on subsequent days as a function of realistic astrometric noise levels. The initial orbit determination is possible. We define requirements for a correlator process essential for catalogue build-up and maintenance. Each single observation should provide an astrometric accuracy of at least 1”–1.5” so that the initially determined orbits are consistent within a few hundred kilometres for the semi-major axis, 0.01 for the eccentricity, and 0.1° for the inclination.     

CubeSail: A low cost CubeSat based solar sail demonstration mission

CubeSail is a nano-solar sail mission based on the 3U CubeSat standard, which is currently being designed and built at the Surrey Space Centre, University of Surrey. CubeSail will have a total mass of around 3 kg and will deploy a 5 × 5 m sail in low Earth orbit. The primary aim of the mission is to demonstrate the concept of solar sailing and end-of-life de-orbiting using the sail membrane as a drag-sail. The spacecraft will have a compact 3-axis stabilised attitude control system, which uses three magnetic torquers aligned with the spacecraft principle axis as well as a novel two-dimensional translation stage separating the spacecraft bus from the sail. CubeSail’s deployment mechanism consists of four novel booms and four-quadrant sail membranes. The proposed booms are made from tape-spring blades and will deploy the sail membrane from a 2U CubeSat standard structure. This paper presents a systems level overview of the CubeSat mission, focusing on the mission orbit and de-orbiting, in addition to the deployment, attitude control and the satellite bus.     

卫星导航系统天线阵接收机波束指向误差分析

研究表明：卫星导航系统阵元几何位置误差是影响波束指向误差的主要因素,而卫星和接收机位置误差则影响甚微,其中千米级的卫星位置误差以及接收机位置误差导致的波束指向误差不超过0.1°,而毫米级的阵元几何位置随机误差可导致典型7阵元天线阵波束指向误差达到几度。该研究成果可为卫星导航系统天线阵接收机的设计提供依据。