A bistatic SAR mission for earth observation based on a small satellite

The authors present a new scientific space mission consisting of a satellite carrying a receiving- only SAR which receives the signal transmitted by the ENVISAT-1 SAR. The integration of ENVISAT-1 SAR and bistatic radar data offers an improved potentiality of surface classification, three-dimensional observation, and the opportunity of advanced scientific experiments in the field of bistatic scattering. The small satellite nominal orbit and the attitude manoeuvres are designed in order to maintain an adequate overlap between the two radar swaths along the whole orbit, taking into account the ENVISAT-1 attitude and pointing. A preliminary satellite design (2-year lifetime) is then performed to evaluate the orbit decay and to determine the appropriate orbit manoeuvres (every 4 days) to control the satellites relative phase. The numerical simulation shows that a spacecraft of about 584kg is able to meet the mission requirements.     

GPS based onboard and onground orbit operations for small satellites

In extension to common applications such as groundtrack displays and antenna steering, the SGP4 orbit model is proposed for operational orbit determination in small satellite missions. SGP4 is an analytical orbit model for Low-Earth orbiting satellites that is widely used for the propagation of NORAD twoline elements. Twoline elements may hence be generated completely independent of NORAD. Their use as exclusive source of orbital information simplifies the operations concept and reduces mission costs through the extensive use of existing low-cost mission support software. Due to small computer resource requirements of 8–10kByte, the SGP4 model may also be applied for onboard orbit computations making use of e.g. a 80186 processor, thus ensuring full compatibility of ground-based and onboard operations. The proposed approach is particularly suited in combination with a space-borne GPS receiver, were the C/A-code navigation solutions are treated as measurements that are adjusted in a least-squares sense using the SGP4 model. As consequence, inherent drawbacks of the pure navigation solutions such as data gaps and scatter as well as limited velocity accuracy are avoided, while the operational navigation activities are kept at a minimum. The feasibility of the concept is illustrated based on real GPS navigation data from the TOPEX/Poseidon and the MIR space station with an inherent data quality of 50–100 m. It is shown that 3 hours of data within a 4 day period are sufficient to keep the position error within 4 km, that is considered sufficient for most applications.     

k-ε-g紊流燃烧模型数值研究

本文对k-ε-g紊流燃烧模型中模型系数C_R,C_(g1),C_(g2)的选定和计算浓度脉动均方值g的不同方法进行数值研究。计算结果表明模型系数值的选定直接与化学反应速率有关,而其中C_R影响最大。g的计算虽然可有不同方法,而其中微分方程求解最佳。并用实验数据来验证计算结果。     

减少机床噪声污染的方法

噪声污染已成为世界三大污染之一.在工业企业中机床噪声是重要的噪声污染源之一.本文主要从机床的齿轮传动、轴承的选用和齿轮箱的结构等方面对机床噪声产生的影响以及提出相应的降噪措施进行了探讨.从而降低机床噪声,保障工人身心健康,改善车间工作环境.     

打造广州现代产业体系的思路与建议

对广州市产业发展现状进行评价,认为其主要问题表现为产业发展方式整体粗放、资源供给紧张、产业发展调节能力差、成熟完备的产业系统尚未形成,等等.进而借用循环经济有关理念,提出广州产业升级的四大思路:资源型向资本型转变、实体经济向真空经济转变、断裂经济向循环经济转变和产业分割向产业整合转变.最后,对广州发展新型现代产业体系提出若干建议:建立常设性机构、完善现行法规体系、进行制度建设、鼓励技术创新、树立循环经济发展理念.     

广播内存实时网节点卡的LabVIEW驱动开发

广播内存实时网技术是一种高效的网络数据传输技术。本文向读者介绍了LabVIEW环境下利用CIN技术的网络内存节点卡驱动模块的设计方法。     

8mm衰减标准装置

对8mm衰减标准装置的工作原理、系统设计、主要技术特点、误差分析等进行了详细介绍,并附有测试和分析数据。该装置达到了80dB的量程、全频段和±0.003dB/10dB的准确度。     

测定钡含量的快速方法

本文研究了测定钡盐中钡含量的快速方法。该法是基于被测的钡离子与过量的铬酸钠标准溶液反应形成铬酸钡沉淀，剩余的铬酸根离子以溴甲酚绿-甲基红为混合指示剂，用盐酸标准溶液滴定，而间接测定钡的量。该法操作简便、快速，可应用于多种钡盐中钡的测定。     

煤粉粒径分布在气固两相流场中的测试技术研究

针对输送管道内煤粉颗粒的粒径分布宽的特点，用侧向接收散射光的Mie散射方法和Fraunhofer衍射方法作了理论分析和实际测试。利用分子筛和显微镜对被测粒子进行了静态测量，其结果可以作为相对准确的测量标准。研究结果表明，针对细粉分离器内煤粉颗粒的形状、浓度和粒径的分布规律，用衍射测试方法可以达到较高的测试精度，取得较好的测试效果。     

共析钢的相变超塑性扩散连接

根据高温扩散和空洞蠕变闭合理论，在恒温超塑性扩散连接基础上建立相变超塑性扩散连接数学模型，可确定各工艺参数，诸如循环上限温度、压力、循环次数以及升、降温速率等对连接的影响，作为选择合适工艺参数的依据。经过对T8共析钢相变超塑性扩散连接试验研究，证明该理论模型与试验结果吻合较好。