Broad-search algorithms for the spacecraft trajectory design of Callisto–Ganymede–Io triple flyby sequences from 2024 to 2040, Part II: Lambert pathfinding and trajectory solutions

Triple-satellite-aided capture employs gravity-assist flybys of three of the Galilean moons of Jupiter in order to decrease the amount of ΔV$\mathrm{\Delta }V$ required to capture a spacecraft into Jupiter orbit. Similarly, triple flybys can be used within a Jupiter satellite tour to rapidly modify the orbital parameters of a Jovicentric orbit, or to increase the number of science flybys. In order to provide a nearly comprehensive search of the solution space of Callisto–Ganymede–Io triple flybys from 2024 to 2040, a third-order, Chebyshev's method variant of the p-iteration solution to Lambert's problem is paired with a second-order, Newton–Raphson method, time of flight iteration solution to the _V∞$V_{\infty }$-matching problem. The iterative solutions of these problems provide the orbital parameters of the Callisto–Ganymede transfer, the Ganymede flyby, and the Ganymede–Io transfer, but the characteristics of the Callisto and Io flybys are unconstrained, so they are permitted to vary in order to produce an even larger number of trajectory solutions. The vast amount of solution data is searched to find the best triple-satellite-aided capture window between 2024 and 2040.     

Determination of the mean dynamic ocean topography model through combining multi-source gravity data and DTU15 MSS around China's coast

Mean dynamic ocean topography (or MDT) is closely related to ocean circulation and global climate change. It has important scientific significance and application value for the development and utilization of marine resources in China's coastal areas. Based on the terrain gravity, marine gravity, and SRTM 3?s data, an algorithm to reduce the problem of gravity data gaps between land and sea is proposed. A consistent land-sea gravity model is established based on point-mass fusion method. Then geoid model, which accuracy was estimated to be 8.5?cm through the verification of 348 GNSS/level data from the coastal provinces, of China's coastal areas was calculated through remove-restore technique. Connecting the above geoid model with DTU15 MSS model to establish a MDT model in China's coastal areas using the direct method in space domain. The effect of gravity field model, dominant factors of sea surface topography, and low pass filter are analyzed. Taking Bohai Sea and Yellow Sea as an example, and comparing MDT with the two international models CNES_2013_MDT and DTU15_MDT. The results show that the MDT has the potential to construct a vertical datum of the ocean and carry out related scientific research and application.     

基于强跟踪UPF的重力梯度辅助定位方法

针对重力梯度辅助定位中,存在重力梯度的强非线性分布及系统模型偏差等问题,将STUPF引入匹配定位过程。该方法根据残差信息实时调节系统状态跟踪能力,有效应对模型偏差对定位的影响。基于真实INS数据的仿真实验结果表明,STUPF可达到较好的定位效果,且与标准PF、GPF算法相比,其在定位的精度、稳定性及运算量上具有一定优势。     

Simulation-based evaluation of a cold atom interferometry gradiometer concept for gravity field recovery

The prospects of future satellite gravimetry missions to sustain a continuous and improved observation of the gravitational field have stimulated studies of new concepts of space inertial sensors with potentially improved precision and stability. This is in particular the case for cold-atom interferometry (CAI) gradiometry which is the object of this paper. The performance of a specific CAI gradiometer design is studied here in terms of quality of the recovered gravity field through a closed-loop numerical simulation of the measurement and processing workflow. First we show that mapping the time-variable field on a monthly basis would require a noise level below $5\text{mE}/\sqrt{\text{Hz}}$. The mission scenarios are therefore focused on the static field, like GOCE. Second, the stringent requirement on the angular velocity of a one-arm gradiometer, which must not exceed ${10}^{-6}$?rad/s, leads to two possible modes of operation of the CAI gradiometer: the nadir and the quasi-inertial mode. In the nadir mode, which corresponds to the usual Earth-pointing satellite attitude, only the gradient $V_{\mathit{yy}}$, along the cross-track direction, is measured. In the quasi-inertial mode, the satellite attitude is approximately constant in the inertial reference frame and the 3 diagonal gradients $V_{\mathit{xx}}\text{,}{V}_{\mathit{yy}}$ and $V_{\mathit{zz}}$ are measured. Both modes are successively simulated for a 239?km altitude orbit and the error on the recovered gravity models eventually compared to GOCE solutions. We conclude that for the specific CAI gradiometer design assumed in this paper, only the quasi-inertial mode scenario would be able to significantly outperform GOCE results at the cost of technically challenging requirements on the orbit and attitude control.     

急流与低层大气重力波能量的相关性研究

通过分析武汉(30.5oN, 114oE)上空2000至2004年的Radiosonde常规观测数据, 对当地对流层(1~10 km)与低平流层(18~25km)的某些惯性重力波特征进行了研究, 发现重力波能量与急流强度变化之间存在显著的相关. 同时分析了海口(20oN, 114oE)(2000至2004年)、北京(40oN, 116oE)(2001年12月至2003年2 月)的Radiosonde观测数据并进行了比较, 发现较高纬度地区的相关性明显大于低纬度地区. 通过对武汉地区2006年1月5天Radiosonde加密观测数据的分析, 讨论了重力波动能与势能的高度变化, 进一步发现纬向风的垂直剪切与急流中心的分布分别与重力波势能和动能的强弱分布相对应.      

叶轮式辅助心脏泵装置优化设计

叶轮式血液泵LAP-Ⅰ采用了航空叶轮机械中使用的设计思想方法,该装置是针对亚洲患者的临床应用而设计.综合航空叶轮机械技术和医学需求,采用整体转子和悬臂静子结构设计,并对其串列叶栅静子结构做了进一步的优化改进,得到叶轮式血液泵LAP-Ⅱ.计算流体动力学(CFD)模拟结果表明,血泵LAP-Ⅱ的压升性能达到医学需求,泵体内流动状况顺畅.最大比较剪切应力(S)值得到明显降低,流线显示血液通过泵体的最长时间得到减小,抗溶血应用性能得到提高.      

多用途重力梯度和磁控三轴稳定小型卫星公用平台

首先介绍重力梯度稳定小型卫星的突出特点：结构简单,可靠性高,成本低,研制周期短,质量轻;其次论述重力梯度小型卫星平台可能达到的技术性能指标;最后探讨了四种三轴姿态稳定小型卫星公用平台。     

重力波波包在可压大气中的非线性传播

本文采用二维全隐欧拉(FICE)格式对具有高斯分布的重力波波包在等温、可压大气中的非线性传播过程进行数值模拟和分析.数值分析结果表明:尽管存在非线性效应,在整个传播过程中,波动的等相面向下运动,波包和波相关能量向上传输.波相关扰动速度随高度增加指数增长,并且波与平流会发生非线性相互作用,最后导致平均流场增强.这与线性重力波理论完全一致.重力波波包的传播路径与重力波线性射线理论预言非常接近,但平均水平群速度和平均垂直群速度均明显小于线性射线理论给出的结果,可见波动的非线性过程会改变波相关能量的传输速度.模拟结果首次定量地展示出非线性效应对重力波波包传播的影响,表明建立在线性理论框架中的重力波运动学定义的合理性.      

重力波波包在传播过程中的参量激发

采用数值方法模拟了重力波波包在向上传播过程中的参量激发.结果表明,通过共振相互作用,两个次级波可由噪声水平发展到相当的强度,并拥有可观的空间范围,但两者获得能量的大小不同,说明在一个共振组中,主波的能量传递具有参数选择性.主波包只将部分能量用来激发次级波,在其能量衰减的同时,波包形状也发生强烈的畸变.波包之间的能量传递具有明显的局地性.由于波包能量交换不再具有可逆性,相互作用的特征时间具有特别重要的意义,它代表绝大多数能量传递发生的时间范围.在特征时间之外,波包之间净的能量传递已相当弱.由中间层向低热层传播的重力波,衰变过程和传播过程可以同步完成.共振相互作用不仅能够使波能量在谱空间扩散,而且能使波能量在物理空间扩展.      

重力波波包在剪切风场中的非线性传播

采用二维全隐欧拉格式,对具有高斯分布的重力波波包在剪切风场中的非线性传播过程进行数据模拟和分析,数值分析结果表明,在没有出现临界层的情况下,尽管存在非线性效应,在整个传播过程中,波动的等相面向下运动,波包和波相关能量仍然能够自由地向上传输。波相关扰动速度随高度增加而增加,并且垂直波长随高度增加而减小。