Proposal for a multiple-asteroid-flyby mission with sample return

Asteroid exploration provides a new approach to study the formation of the solar system and the planetary evolution. Choosing a suitable target and designing of feasible profile for asteroid mission are challenging due to constraints such as scientific value and technical feasibility. This paper investigates a feasible mission scenario among the potential candidates of multiple flybys and sample return missions. First, a group of potential candidates are selected by considering the physical properties and accessibility of asteroids, for the sample return missions. Second, the feasible mission scenarios for multiple flybys and sample return missions to various spectral-type asteroids are investigated. We present the optimized design of preliminary interplanetary transfer trajectory for two kinds of missions. One is the single sample return mission to asteroids with various spectral types. The other is the multiple flybys and sample return mission to several asteroids. In order to find the optimal profiles, the planetary swing-by technique and Differential Evolution algorithm are used.     

基于累积差分图像和高斯背景统计模型的烟尘目标检测

根据烟尘目标灰度与天空背景灰度很接近,目标内部灰度分布不均匀,且形状和面积会随着时间不停变化等特点,提出了一种由粗到精的目标检测算法。首先,通过累积差分图像序列得到烟尘目标出现的大致区域,再通过构造高斯背景统计模型得到每一个可能目标点的精确分割阈值,用该阈值在上一步操作得到的目标区域内部进行逐帧精细分割,得到烟尘目标出现的位置信息和时间信息。实验结果表明,该方法抗干扰能力强,能够可靠、快速地检测出烟尘目标。     

由地面宇宙线中子强度反演空间质子和重离子的分布

采用线性回归的方法研究了太阳活动平静时期空间高能质子和重离子微分通量与地面OULU宇宙线台站中子强度之间的相关性,利用地面中子强度数据来反演空间高能质子和重离子通量.从质子和重离子的能谱出发,结合OULU台站中子强度的数据,提出了由地面中子强度数据反演空间高能质子和重离子微分通量的新方法.文中以GOES卫星上350～420 MeV,420～510 MeV,510～700 MeV,＞700 MeV(P8～P11)四能道的高能质子和ACE卫星上的元素C为例,并将反演的数据与测量结果比较,二者符合较好.为了探索这种反演方法在空间辐射环境描述中的应用,同时利用2006年11月和12月质子通量的反演结果对反演方法进行了验证,证明利用这一反演方法可以从地面中子强度的数据很好地反演出空间质子和重离子的微分通量.     

南极地区电离层总电子含量分布特征的初步探讨

通过对微分多普勒数据处理后得到的电离层总电子含量的分析, 探讨了南极地区总电子含量随纬度的分布变化特征及规律。     

Effects of space flight exposure on cell growth,tumorigenicity and gene expression in cancer cells

It is well recognized that harsh outer space environment, consisting of microgravity and radiation, poses significant health risks for human cells. To investigate potential effects of the space environment exposure on cancer cells we examined the biological changes in Caski cells carried by the “Shen Zhou IV” spaceship. After exposure for 7 days in spaceflight, 1440 survival subclonal cell lines were established and 4 cell lines were screened. 44F10 and 17E3 were selected because of their increased cell proliferation and tumorigenesis, while 48A9 and 31F2 had slower cytological events. Experiments with cell proliferation assay, flow cytometry, soft agar assay, tumorigenesis assay and DNA microarray analysis have shown that selected cell lines presented multiple biological changes in cell morphology, cell growth, tumorigenicity and gene expression. These results suggest that space environment exposure can make significant biological impact on cancer cells and provide an entry point to find the immunological target of tumorigenesis.     

Optimal trajectory planning of free-floating space manipulator using differential evolution algorithm

The existence of the path dependent dynamic singularities limits the volume of available workspace of free-floating space robot and induces enormous joint velocities when such singularities are met. In order to overcome this demerit, this paper presents an optimal joint trajectory planning method using forward kinematics equations of free-floating space robot, while joint motion laws are delineated with application of the concept of reaction null-space. Bézier curve, in conjunction with the null-space column vectors, are applied to describe the joint trajectories. Considering the forward kinematics equations of the free-floating space robot, the trajectory planning issue is consequently transferred to an optimization issue while the control points to construct the Bézier curve are the design variables. A constrained differential evolution (DE) scheme with premature handling strategy is implemented to find the optimal solution of the design variables while specific objectives and imposed constraints are satisfied. Differ from traditional methods, we synthesize null-space and specialized curve to provide a novel viewpoint for trajectory planning of free-floating space robot. Simulation results are presented for trajectory planning of 7 degree-of-freedom (DOF) kinematically redundant manipulator mounted on a free-floating spacecraft and demonstrate the feasibility and effectiveness of the proposed method.     

Estimation of QZSS differential code biases using QZSS/GPS combined observations from MGEX

As an important error source in Global Navigation Satellite System (GNSS) positioning and ionospheric modeling, the differential code biases (DCB) need to be estimated accurately, e.g., the regional Quasi-Zenith satellite system (QZSS). In this paper, the DCB of QZSS is estimated by adopting the global ionospheric modeling method based on QZSS/GPS combined observations from Multi-GNSS experiment (MGEX). The performance of QZSS satellite and receiver DCB is analyzed with observations from day of year (DOY) 275–364, 2018. Good agreement between our estimated QZSS satellite DCB and the products from DLR and CAS is obtained. The bias and root mean square (RMS) of DCB are mostly within ±0.3 ns. The day-to-day fluctuation of the DCB time series is less than 0.5 ns with about 96% of the cases for all satellites. However, the receiver DCB is a little less stable than satellite DCB, and their standard deviations (STDs) are within 1.9 ns. The result shows that the stability of the receiver DCBs is not significantly related to the types of receiver or antenna.     

Fuel-optimal and Energy-optimal guidance schemes for lunar soft landing at a desired location

Two guidance schemes (i) fuel-optimal (ii) energy-optimal to realize soft landing at a desired location on the moon are developed using the optimal control laws. The optimal control laws are obtained by solving a two-point boundary value problem formulated based on Pontryagin’s principle. The guidance laws, adapted from the optimal control laws, are obtained as a function of unknown co-state variables. Differential Transformation (DT) technique is employed to determine the unknown co-states at each time instant of landing trajectory using the information on the current vehicle state, target landing site (loaded on-board apriori) and the time-to-go. The numerical integration of co-state dynamics is avoided due to the DT based approach. The time-to-go, a critical parameter for any guidance scheme, is computed and updated real time using a simple strategy which uses the current and end states. The simple strategy for time-to-go works well even when the shape of the trajectory is nonlinear. Extensive analysis is carried out to evaluate and compare the proposed guidance schemes. Further, the proposed schemes are compared with other popular guidance schemes. The DT based proposed schemes help quantify the landing masses for fuel-optimal and energy-optimal objectives. Other features of the proposed schemes are that they do not assume constant gravity field and independent of reference trajectory.     

一种关节式人机合作机器人运动学及动力学建模

Cobot（Collaborative Robot）是一种可与操作者在同一作业空间实现直接物理合作的新型机器人。根据差动轮系的小完伞约束特性，提出了基于差动轮系的关节式人机合作机器人的模型。根据差动机构与关节、差动机构与差动机构之间的耦合关系，建专了并联Cobot的运动学模型，以及由行星轮系实现的差动机构的动力学模型和关节式并联Cobot的动力学模型。这种关节式Cobot模型具有不完全约束特性，可以实现人与机器人在同一作业空间合作，而不会伤害操作者。这种Cobot模型可推广应用于多关节Cobot，主要应用在大规模零件的装配生产线、外科手术以及一些需要人机合作的场合。     

基于火箭弹非线性动力学系统的解耦控制

为消除火箭弹在倾斜转弯（BTT）时俯仰与偏航通道的强耦合,根据建立的火箭弹非线性动力学模型,采用微分几何方法和二次Gauss/回路传函恢复（LQG/LTR）设计了一控制系统,给出了控制器的设计。仿真结果表明：侧滑角近似为零,滚转命令能快速响应,设计的解耦控制器有效。