Fuzzy multi-criteria decision-making approach to prioritization of space debris for removal

As private companies and government space agencies begin to seriously consider the task of active space debris removal, it is becoming increasingly more important to determine the highest priority objects to deorbit. This work sets forth an approach for prioritization of space debris through the utilization of Multi-Criteria Decision-Making methodologies and fuzzy logic, as well as both quantitative and qualitative criteria. The proposed debris prioritization approach considers various criteria including the orbit, size, mass, pairwise and total collision probabilities, and decay timeframe of each debris object. The means of assigning attributes to each assessment criterion is discussed in detail. To determine the weighting scheme for the criteria, a questionnaire was prepared and shared with experts in the field of space situational awareness. The work examines over two thousand critical debris objects selected from the existing debris catalog with respect to these criteria. The quantified attributes for each debris object are then aggregated through the fuzzy versions of the Analytic Hierarchy Process and the Technique for Order Preference by Similarity to Ideal Solution. The results of the analysis identify high-priority debris objects for removal from Earth-bound orbits.     

Performance improvement of real-time PPP ambiguity resolution using a regional integer clock

Obtaining reliable GNSS uncalibrated phase delay (UPD) or integer clock products is the key to achieving ambiguity-fixed solutions for real-time (RT) precise point positioning (PPP) users. However, due to the influence of RT orbit errors, the quality of UPD/integer clock products estimated with a globally distributed GNSS network is difficult to ensure, thereby affecting the ambiguity resolution (AR) performance of RT-PPP. In this contribution, by fully utilising the consistency of orbital errors in regional GNSS network coverage areas, a method is proposed for estimating regional integer clock products to compensate for RT orbit errors. Based on Centre National d’Études Spatiales (CNES) RT precise products, the regional GPS/BDS integer clock was estimated with a CORS network in the west of China. Results showed that the difference between the estimated regional and CNES global integer clock/bias products was generally less than 5 cm for GPS, whereas clock differences of greater than 10 cm were observed for BDS due to the large RT orbit error. Compared with PPP using global integer clock/bias products, the AR performance of PPP using the regional integer clock was obviously improved for four rover stations. For single GPS, the horizontal and vertical accuracies of ambiguity-fixed PPP solutions were improved by 56.2% and 45.3% on average, respectively, whereas improvements of 67.5% and 50.5% in the horizontal and vertical directions, respectively, were observed for the combined GPS/BDS situation. Based on a regional integer clock, the RMS error of a kinematic ambiguity-fixed PPP solution in the horizontal direction could reach 0.5 cm. In terms of initialisation time, the average time to first fix (TTFF) in combined GPS/BDS PPP was shortened from 18.2 min to 12.7 min. In view of the high AR performance realised with the use of regional integer clocks, this method can be applied to scenarios that require high positioning accuracy, such as deformation monitoring.     

Preliminary analysis of the quality and positioning performance of BDS-3 global interoperable signal B1C&B2a

BeiDou-3 Navigation Satellite System (BDS-3) satellites are equipped with the new generation GNSS signals B1C and B2a, which support the interoperability with GPS and Galileo systems. In this study, the pseudo-range multipath error and carrier phase observation noise of the BDS-3 B1C and B2a signals were evaluated based on zero baseline measurements from the day of year (DOY) 113 to 116, 2020. Further, the precision and performance of the single point positioning (SPP) and precise point positioning (PPP) are assessed at 9 stations. This assessment manifests that the standard deviations (STDs) of the pseudo-range multipath error are about 0.09 ~ 0.22 m, while STDs of the carrier phase observation noise are about 0.075 mm. For the single-frequency SPP, its positioning precision is about 2.03 ~ 4.85 m and 3.29 ~ 10.73 m at the 99.99% confidence level in horizontal and vertical directions, respectively, while the dual-frequency SPP precision is about 1.92 ~ 8.02 m and 4.81 ~ 12.77 m in horizontal and vertical directions, respectively. For the daily static PPP, the convergence time is about 20 ~ 30 min, while the daily positioning precision can reach 1.38 ~ 4.42 cm and -1.31 ~ 4.34 cm in horizontal and vertical directions, respectively. In general, the quality and the SPP and PPP performance of the BDS-3 B1C&B2a signals are comparable to the GPS and Galileo.     

改善电压调节器调压精度的措施及其分析

晶体管型电压调节器具有结构简单、工作可靠及成本低等优点，但现有的电压调节器普遍存在稳态电压调节精度不高的问题。本文根据某型晶体管电压调节器的工作特点，分析造成稳态电压调节精度差的原因；并提出采用励磁电流反馈的改进方法，即按占空比变化调节参考电压。本文推导了反馈电阻的了值方法。对JF15发电机的电压调节实验证实；采用该方法可以有效地补偿稳态电压偏差，提高电压调节器的稳态精度。     

地球资源技术卫星地面轨迹控制原理及调轨周期的选择

1.引言 在整个任务执行期间,要求资源卫星在一个复盖周期里的地面轨迹中心线与另一个复     

力学环境试验测量不确定度分析

航天器力学环境试验数据的测量是完成试验的关键技术之一。任何测量过程都客观上存在测量误差,使测量结果带有不确定性,进行测量不确定度分析的目的是提供评价测量结果的可信度指标。力学环境试验一般需要动态测量,影响测量误差和数据不确定度的因素较多,进行全面准确的分析相对困难。文中通过介绍一些有关测量误差和测量不确定度的基本知识,针对固定的振动环境试验系统,综合所有客观存在的误差因素进行分析计算,给出目前力学环境试验数据测量误差和测量不确定度数值,提高试验数据判读的准确性,满足提供测量误差和测量不确定度指标的实际需求。     

复杂结构模态分析中的截断准则

在复杂结构的动态分析中，通常采用截断的主模态坐标变换方法，这种方法可以在保证足够计算精度的要求下，节省大量的计算机时，是一种十分有效而被普遍采用的方法，不过，在分析计算精度与系统的保留的低阶主模态数之间，至今未能找到一种一般的关系式作为“截断准则”，本文在模型加速度方法的基础上，建立了模态分析中的截断准则。     

Influence of Setting Error of Tool on Tooth Profile and Contact Point of Face Gear Drive

In order to analyze the influence of setting error of tool on both tooth profile and contact characteristic of orthogonal face gear drive,the coordinate systems with and without setting error are established.Moreover,the equations of tooth profile and contact points of face gear drive are derived by envelope principle.According to the equations,the change of tooth profile and the contact points position on face gear are analyzed.The tooth surface and contact points are obtained by numerical simulation.Results show that the tooth profile and contact characteristic of face gear drive are not sensitive to the setting error of tool.     

钛合金宽弦空心风扇叶片数控切削加工关键技术

数控切削加工是最终保证钛合金宽弦空心风扇叶片制造精度的重要技术手段。分析了采用超塑成形/扩散连接技术制作的钛合金宽弦空心风扇叶片结构特征以及毛坯状态,指出了后续的数控切削加工应突破复杂曲面结构测量、加工变形控制以及切削加工误差补偿等关键技术。提出了开发集测量、分析和加工为一体的数控切削加工集成系统的研究思路,可为实现钛合金宽弦空心风扇叶片加工精度的精确控制提供指导。     

硅酸盐细菌的分离及生理生化特性的鉴定

本实验通过一系列方法从采集的样品中分离出一株芽孢杆菌，并对其进行了表形特性、培养特性、生理生化特性的鉴定，确认该菌为一株硅酸盐细菌，分类属于胶质芽孢杆菌。此外，用原子吸收光谱分析和高效液相色谱，对培养液中的产物进行了测定。结果表明，这种硅酸盐细菌具有分解玻璃中钾的能力。在摇瓶培养72小时后，水溶性钾的含量比对照物提高了77％。这就证明了硅酸盐细菌的确具有解钾的性能，可用于促进土壤中矿物性钾分解的微生物肥料的研制和生产。