Deorbiter CubeSat mission design

This paper presents the mission design for a CubeSat-based active debris removal approach intended for transferring sizable debris objects from low-Earth orbit to a deorbit altitude of 100 km. The mission consists of a mothership spacecraft that carries and deploys several debris-removing nanosatellites, called Deorbiter CubeSats. Each Deorbiter is designed based on the utilization of an eight-unit CubeSat form factor and commercially-available components with significant flight heritage. The mothership spacecraft delivers Deorbiter CubeSats to the vicinity of a predetermined target debris, through performing a long-range rendezvous maneuver. Through a formation flying maneuver, the mothership then performs in-situ measurements of debris shape and orbital state. Upon release from the mothership, each Deorbiter CubeSat proceeds to performing a rendezvous and attachment maneuver with a debris object. Once attached to the debris, the CubeSat performs a detumbling maneuver, by which the residual angular momentum of the CubeSat-debris system is dumped using Deorbiter’s onboard reaction wheels. After stabilizing the attitude motion of the combined Deorbiter-debris system, the CubeSat proceeds to performing a deorbiting maneuver, i.e., reducing system’s altitude so much so that the bodies disintegrate and burn up due to atmospheric drag, typically at around 100 km above the Earth surface. The attitude and orbital maneuvers that are planned for the mission are described, both for the mothership and Deorbiter CubeSat. The performance of each spacecraft during their operations is investigated, using the actual performance specifications of the onboard components. The viability of the proposed debris removal approach is discussed in light of the results.     

A multi-stage regulation strategy of space manipulators with a free-swinging joint failure

To ensure tasks can be completed after a free-swinging joint failure occurs, a multi-stage regulation strategy of space manipulators is proposed. Considering all terms of the dynamics equation, an evaluation model of the regulation ability (EMRA) of active joints over the fault joint is established based on the fuzzy entropy. And then a multi-stage regulation strategy based on the EMRA is designed to regulate the fault joint. The strategy divides the regulation process into several stages, and select a certain active joint to regulative the fault joint in every stage. With this multi-stage regulation strategy, the fault joint can be regulated to the desired angle without huge torque on regulative joints. The simulation is carried out with a 7-DOF space manipulator, verifying the correctness and effectiveness of the multi-stage regulation strategy. The strategy has three advantages: Coriolis and centrifugal terms are both considered for the first time in selecting the regulative joint, making the selection result more in line with the actual regulation process; The influence of the model uncertainty is eliminated in establishing the EMRA, making the evaluation of regulative ability more precise; The fault joint is successfully regulated to the desired angle without huge torque on regulative joints.     

中国空间探测领域40年发展

中国空间科学学会成立的40年，是中国空间探测逐渐走进世界舞台的40年，空间探测极大推动了空间科学和相邻学科的发展，也影响到经济、军事和日常生活诸多方面.本文简要回顾了从空间探测专业委员会成立的1980年至今，中国空间探测领域的主要发展历程，包括探空火箭、高空气球、科学卫星、月球与行星探测、载人航天空间探测、遥感卫星地面站等主要项目、进展和所取得的成果，对未来若干年空间探测的发展进行了展望.      

面向建筑空间的OFDM信号定位性能分析

针对利用OFDM信号进行定位时信号非连续性问题,提出一种粗检测和精细检测结合的测距方法,将距离测量转换为不同尺度的时延样点,采用时域粗检测快速估算接收OFDM信号的最大相关峰值,然后对传输时延进行频域精细测量,提升了小数倍采样周期时延测量的精度。在此基础上,分析了OFDM信号的定位性能,仿真结果表明,当OFDM信号在信噪比-11dB的情况下测距误差由3m左右(子载波数512)降至1m(子载波数4096)。     

Midlatitude ionospheric F2-layer response to eruptive solar events-caused geomagnetic disturbances over Hungary during the maximum of the solar cycle 24: A case study

In our study we analyze and compare the response and behavior of the ionospheric F2 and of the sporadic E-layer during three strong (i.e., Dst?<??100nT) individual geomagnetic storms from years 2012, 2013 and 2015, winter time period. The data was provided by the state-of the art digital ionosonde of the Széchenyi István Geophysical Observatory located at midlatitude, Nagycenk, Hungary (IAGA code: NCK, geomagnetic latitude: 46.17° geomagnetic longitude: 98.85°). The local time of the sudden commencement (SC) was used to characterize the type of the ionospheric storm (after Mendillo and Narvaez, 2010). This way two regular positive phase (RPP) ionospheric storms and one no-positive phase (NPP) storm have been analyzed. In all three cases a significant increase in electron density of the foF2 layer can be observed at dawn/early morning (around 6:00 UT, 07:00 LT). Also we can observe the fade-out of the ionospheric layers at night during the geomagnetically disturbed time periods. Our results suggest that the fade-out effect is not connected to the occurrence of the sporadic E-layers.     

Adaptive fuzzy terminal sliding mode control for the free-floating space manipulator with free-swinging joint failure

Space manipulator with free-swinging joint failure simultaneously contains kinematic and dynamic coupling relationships, so it belongs to a new underactuated system. To allow the manipulator to carry on tasks, an effective robust underactuated control method for the space manipulator with free-swinging joint failure is studied in this paper. Considering the effect of model uncertainty and joint torque disturbance, a robust underactuated control system based on the Terminal Sliding Mode Controller (TSMC) is designed, but two drawbacks are discussed: (A) Robustness depraves with eliminating chattering. (B) Control parameters are difficult to be determined under unknown uncertainty and disturbance. To improve the TSMC, the adaptive fuzzy controller is introduced to estimate the real effect of unknown uncertainty and disturbance according to deviations of sliding mode and its reaching law. The estimated result is directly compensated into active joints torque. In simulation, the space manipulator with free-swinging joint executes tasks based on the TSMC and the Adaptive Fuzzy Terminal Sliding Mode Controller (AFTSMC) respectively. Same tasks can be finished with smaller joints torque and stronger robustness based on the AFTSMC. Therefore, AFTSMC can serve as an effective robust control method for the space manipulator with free-swinging joint failure under unknown model uncertainty and torque disturbance.     

Packaging of thick membranes using a multi-spiral folding approach: Flat and curved surfaces

Elucidating versatile configurations of spiral folding, and investigating the deployment performance is of relevant interest to extend the applicability of deployable membranes towards large-scale and functional configurations.In this paper we propose new schemes to package flat and curved membranes of finite thickness by using multiple spirals, whose governing equations render folding lines by juxtaposing spirals and by accommodating membrane thickness. Our experiments using a set of topologically distinct flat and curved membranes deployed by tensile forces applied in the radial and circumferential directions have shown that (1) the multi-spiral approach with prismatic folding lines offered the improved deployment performance, and (2) the deployment of curved surfaces progresses rapidly within a finite load domain. Furthermore, we confirmed the high efficiency of membranes folded by multi-spiral patterns.From viewpoints of configuration and deployment performance, the multi-spiral approach is potential to extend the versatility and maneuverability of spiral folding mechanisms.     

首颗自主地月转移微卫星“龙江二号”

本文对世界首颗独立完成地月转移、近月制动、环月飞行的微卫星“龙江二号”进行了介绍。首先阐述了龙江二号的任务目标和总体方案；然后重点分析了轨道设计与控制、复杂电磁干扰的标定与抑制、宽视场三维基线干涉测量等关键技术难点；接着回顾了任务的实施过程；最后详细介绍了低频射电探测仪、沙特光学相机和VHF/UHF通信模块与学生微型CMOS相机等有效载荷，并展示了上述载荷获取的初步成果。     

空间激光通信系统中的信道纠错编码技术

由于空间激光通信系统的信道状态和链路捕获跟踪的不确定性,多种形式的信道纠错编码技术正被广泛发展研究。结合空间激光通信链路中误码性能的主要影响因素,分别选择合适的编码方案进行分析。通过仿真实验可知,对于在大气结构参数为1.5×10~(-14) m~(-2/3)、风速为20 m/s的空地激光链路的环境下,在系统数据速率为2 Gbit/s、要求误码率为10~(-6)时,LDPC码结合交织码相对未编码系统有3 dB的等效编码增益,LT码相对未编码系统有3.8 dB的等效编码增益。提供了一种能快速生成、扩展和校验的编码和交织实现方法,以抵抗大气湍流的快速变化对系统性能产生的影响。