Convex optimization of asteroid landing trajectories driven by solar radiation pressure

High-area/mass ratio landers driven by Solar Radiation Pressure(SRP) have potential applications for future asteroid landing missions. This paper develops a new convex optimization-based method for planning trajectories driven by SRP. A Minimum Landing Error(MLE) control problem is formulated to enable planning SRP-controlled trajectories with different flight times. It is transformed into Second Order Cone Programming(SOCP) successfully by a series of different convexification technologies. A t...     

大型太阳帆板展开状态动态特性研究

利用有限元技术及自编的 FORTRAN程序计算了单翼太阳帆板约束模态的振型和频率 ,计算结果和实验结果比较表明 ,计算精度在工程上是可以接受的。在此基础上 ,以飞船带有双翼对称太阳帆板为模型 ,计算了太阳帆板在转动和不转动情况下非约束模态的振型和频率。上述计算结果为研究带有挠性太阳帆板的航天器的动力学与控制问题打下了基础     

基于混杂非对称复合材料的自适应对日定向器

提出并设计了一种基于混杂非对称复合材料层合板的新型自适应对日定向器。该对日定向器采用混杂非对称复合材料层合板作为驱动元件,利用在轨光照条件的变化引起复合材料层合板温度变化,进而使其产生热变形并驱动太阳翼发生偏转。提出的自适应对日定向器结合传统的单自由度对日定向机构,能够实现太阳能帆板的双自由度对日定向。介绍了自适应对日定向器的基本原理,并结合地球静止轨道的光照条件进行了具体设计。利用能量变分原理建立了混杂非对称复合材料的热变形模型,分析其热变形特点,并利用有限元方法对定向器在地球静止轨道上的温度场特性、热变形及对日定向转动角度进行分析。有限元分析结果表明,通过合理设计,自适应对日定向器的转角能够随太阳光入射角变化呈线性变化,定向精度可达±1°。     

不同密度弹丸对水冰的超高速撞击成坑实验

为了研究冰冻天体表面撞击坑的形成与演化,开展了水冰的超高速撞击成坑实验。使用二级轻气炮发射1.0 mm直径的球形弹丸,以3 km/s、5 km/s和7 km/s速度对圆柱状冰块进行撞击。弹丸材料包括聚碳酸酯和不锈钢两种,冰块温度为253 K。实验观察到了不同弹丸和不同速度条件下,冰块中撞击坑的形貌特征。对撞击坑直径、深度和剖面形状进行了测量,并与文献中铝弹丸对水冰的撞击坑进行了比较分析。获得了水冰撞击坑特征随撞击参数的变化规律,结果表明：撞击坑直径和深度的主导机制不同,坑深主要由弹丸侵彻作用形成,而坑径主要由冰块的剥落所致;坑深比坑径具有更强的对于弹丸密度的依赖性,高密度弹丸撞击坑直径具有比低密度弹丸更强的对于撞击速度的依赖性;撞击坑体积与撞击能量成正比,高密度弹丸形成的撞击坑直径表现出“能量缩比”行为,而低密度弹丸形成的撞击坑直径表现出“动量缩比”行为。     

电机变频控制实现换热器节能的应用研究

结合寒冷地区气候特点与通信机房温控的现状,针对50%浓度乙二醇溶液为工质的换热器,试验研究了自然冷源利用率与换热器自身变频节能的关系。结合乙二醇冷剂的特性,通过建立功率与频率关系模型、温差与功率和频率关系模型,实现了换热器循环泵和风机的变频控制策略。结果表明:在室内外温差、换热功率与循环泵、风机频率同时满足的条件下,以功率模型作为参数进行换热器自身的变频节能是可行的。通过对哈尔滨地区的气候数据与散热房控温试验分析,证明了乙二醇换热器的变频节能效果。     

宽马赫数路德维希管风洞及其关键技术

随着高马赫数飞行器研制需求的增加,急需脉冲型风洞运行范围向中低马赫数段扩展,特别是需要具有跨马赫数运行能力。以路德维希管原理运行的管风洞试验设备,由于建设及使用成本较低、参数调节方便、流场品质高等优点,已在亚/跨/超声速及高超声速领域得到了发展和应用,体现出了宽马赫数的应用潜力。本文分析了宽马赫数脉冲型风洞发展现状,重点介绍了路德维希管风洞及其在宽马赫数应用中急需解决的关键技术,包括宽马赫数喷管设计技术、高温管外加热技术以及高温高压隔离技术。     

Time-dependent cosmic ray modulation

Time-dependent cosmic ray modulation is calculated over multiple solar cycles using our well established two-dimensional time-dependent modulation model. Results are compared to Voyager 1, Ulysses and IMP cosmic ray observations to establish compatibility. A time-dependence in the diffusion and drift coefficients, implicitly contained in recent expressions derived by , ,  and , is incorporated into the cosmic ray modulation model. This results in calculations which are compatible with spacecraft observations on a global scale over consecutive solar cycles. This approach compares well to the successful compound approach of Ferreira and Potgieter (2004). For both these approaches the magnetic field magnitude, variance of the field and current sheet tilt angle values observed at Earth are transported time-dependently into the outer heliosphere. However, when results are compared to observations for extreme solar maximum, the computed step-like modulation is not as pronounced as observed. This indicates that some additional merging of these structures into more pronounced modulation barriers along the way is needed.     

大型双曲冷却塔表面脉动风压随机特性——风压极值探讨

针对风压信号呈现的非高斯特性和传统极限估计方法的局限,首次提出基于保证率和相关性的极值估计方法——全概率迭代法进行冷却塔表面脉动风荷载极值分析,并和传统的峰值因子法及改进的Sadek-Simiu法计算结果进行对比验证。结果表明：全概率迭代法避开了对随机过程的高斯分布假定,相比传统的极值估计方法其结果更加真实可靠;表达风压极值中脉动分量的峰值因子数值沿着环向和子午向变化显著,如取为同一数值则偏于危险或过于保守;采用全概率迭代法得到的表面风压系数极值分布曲线与规范取值相比,迎风面和负压峰值区域极值偏小,背风区域极值偏大,且最小值对应角度相差约10°。     

Quantifying the role of solar radiative forcing over the 20th century

The 20th century temperature anomaly record is reproduced using an energy balance model, with a diffusive deep ocean. The model takes into account all the standard radiative forcings, and in addition the possibility of a non-thermal solar component. The model is parameterized and then optimized to produce the most likely values for the climate parameters and radiative forcings which reproduce the 20th century global warming. We find that the best fit is obtained with a negligible net feedback. We also show that a non-thermal solar component is necessarily present, indicating that the total solar contribution to the 20th century global warming, of ΔT_solar = 0.27 ± 0.07 °C, is much larger than can be expected from variation in the total solar irradiance alone. However, we also find that the largest contribution to the 20th century warming comes from anthropogenic sources, with ΔT_man = 0.42 ± 0.11 °C.     

DORIS processing at the European Space Operations Centre

This paper gives an overview of the DORIS related activities at the Navigation Support Office of the European Space Operations Centre. The DORIS activities were started in 2002 because of the launch of the Envisat satellite where ESOC is responsible for the validation of the Envisat Precise Orbits and a brief overview of the key Envisat activities at ESOC is given. Typical orbit comparison RMS values between the CNES POE (GDR-C) and the ESOC POD solution is 6.5, 18.8 and 23.1 mm in radial-, along- and cross-track direction. In the framework of the generation of the ITRF2008 ESOC participated in the reprocessing of all three space geodetic techniques; DORIS, SLR, and GPS. Here the main results of our DORIS reprocessing, in the framework of the International DORIS Service (IDS), are given. The WRMS of the weekly ESOC solution (esawd03) for the 2004–2009 period compared to the IDS-1 combined solution is of the order of 12 mm. Based on the long time series of homogeneously processed data a closer look is taken at the estimated solar radiation pressure parameters of the different satellites used in this DORIS analysis. The main aim being the stabilization of the Z-component of the geocentre estimates. We conclude that the ESOC participation to the IDS ITRF2008 contribution has been beneficial for both ESOC and the IDS. ESOC has profited significantly from the very open and direct communications and comparisons that took place within the IDS during the reprocessing campaign.