硬回收穿地弹高速撞地的缩比模型试验及穿地弹设计中的几个问题

引言为了获取导弹被动段的飞行数据,可以采用遥测、软式、半硬式或硬式回收。由于硬回收不仅能获取直至撞地时的全部数据,并且简单、经济,所以一直是设计者所希望的回收方案。但因导弹落地速度的不断增加,沿用过去设计的穿地弹方案很少成功,因此人们提出在高马赫数落地情况下,硬回收方案是否可行的问题。由于弹丸高速撞靶时所产生的现象是极其复杂的。它不仅和弹、靶材料的物理性质有     

Energy utilization rates during shuttle extravehicular activities

The work rates or energy utilization rates during EVA are major factors in sizing of life support systems. These rates also provide a measure of ease of EVA and its cost in crew fatigue. From the first Shuttle EVA on the STS-6 mission in 1983, we have conducted 59 man-EVA and 341 man-hours of EVA. Energy utilization rates have been measured on each of these EVA. Metabolic rate was measured during each EVA using oxygen utilization corrected for suit leakage. From 1981–1987, these data were available for average data over the EVA or over large segments of the EVA. Since 1987, EVA oxygen utilization data were available at 2-minute intervals. The average metabolic rate on Shuttle EVA (194 kcal/hr.) has been significantly lower than metabolic rates during Apollo and Skylab missions. Peak rates have been below design levels, infrequent, and of short duration. The data suggest that the energy cost of tasks may be inversely related to the degree of training for the task. The data provide insight on the safety margins provided by life support designs and on the energy cost of Station construction EVA.     

Effect on the cardiac function of repeated LBNP during a 1-month head down tilt

Cardiovascular assessment by ultrasound methods was performed during two long duration (1 month) Head Down Tilt (HDT) on 6 healthy volunteers. On a first 1 month HDT session, 3 of the 6 subjects (A, B, C) had daily several lower body negative pressure tests (LBNP), whereas the 3 subjects remaining (D, E, F) rested without LBNP. On a second 1 month HDT session subjects D, E, and F had daily LBNP tests and the A, B and C subjects did not. The cardiac function was assessed by Echocardiography, (B mode, TM mode). On all the "6 non LBNP" subjects the left ventricule diastolic volume (LVDV), the stroke volume (SV) and the cardiac output (CO) increase (+10%, -15%) after HDT then decrease and remain inferior (-5%, -5%) or equal to the basal value during the HDT. Immediately after the end of the HDT the heart rate (HR) increase (+10%, +30%) whereas the cardiac parameters decrease weakly (-5%, -10%) and normalize after 3 days of recovery. On the "6 LBNP" subjects the LVDV, SV and CO increase (+10%, 15%) after 1 h HDT as in the previous group then decrease but remain superior (+5%, +15%) or equal to the basal value. After the HDT session, the HR is markedly increased (+20%, +40%) the LVDV and SV decrease (-15%, -20%) whereas the CO increases or decreases depending on the amplitude of the HR variations. These parameters do not completely normalize after 3 day's recovery. Repeated LBNP sessions have a significant effect on the cardiovascular function as it maintains all cardiac parameters above the basal value. The LBNP manoeuvre can be considered as an efficient countermeasure to prevent cardiac disadaptation induced by HDT position and probably microgravity.     

STARDUST: finessing expensive cometary sample returns

The STARDUST Discovery mission will collect samples of cometary coma and interstellar dust and return them to Earth. Five years after launch in February 1999, coma dust in the 1- to 100-micrometers size range will be captured by impact into ultra-low-density silica aerogel during a 6 kms-1 flyby of Comet Wild 2. The returned samples will be investigated at laboratories where the most critical information on these primitive materials is retained. The Jet Propulsion Laboratory will provide project management with Lockheed Martin Astronauts as the spacecraft industrial partner. STARDUST management will aggressively and innovatively achieve cost control through the use of Total Quality Management principles, the chief of which will be organization in a Project Engineering and Integration Team that "flattens" the traditional hierarchical structure by including all project elements from the beginning, in a concurrent engineering framework focusing on evolving Integrated Mission Capability.     

超声自动检测系统的应用

介绍了基于无损探伤技术的C扫描自动检测系统的工作原理和软硬件设计思路,并提供了测试方法.     

经纬仪测点工艺技术研究

经纬仪定标测点是通过两台经纬仪进行互瞄,并对一根标尺标定组成测量系统,再由该系统进行点坐标测量.该技术是目前卫星部件制造和总装中的一项关键工序.文章阐述了经纬仪定标测点的原理,对测量过程中的定标和测点两个环节进行了精度分析,对标尺的不同摆放方案进行了比较,给出了最佳布局方法和被测点在不同位置时的误差分布曲线.     

异构数据库集成的研究与实现

对异构数据库集成做了详细的研究并提出了具体的实现方法。通过分析比较了目前已有的集成方案,本文提出集成异构数据库可以有四个步骤,分别是用控制表变化法提取有效数据、用XML定义传输数据格式、用JMS传输数据、用全局数据模式集成数据来实现。     

位移约束下火箭橇结构拓扑优化方法研究

兼顾安全性与经济性的高性能结构优化设计是结构设计领域的重要需求,面向火箭橇结构的拓扑优化设计对火箭橇试验具有重要意义.本文在火箭橇结构动力学仿真分析的基础上,基于变密度法建立了火箭橇结构的拓扑优化模型,利用伴随矢量求解了目标函数与约束函数关于设计变量的灵敏度,通过移动渐近线算法驱动了设计变量的更新迭代,最后对拓扑优化设...