Thermal resistance in satellite mounting plates due to conductive heat transfer

The thermal resistance due to conductive heat transfer between two heat generating boxes mounted symmetrically on a thin mounting plate, one side of which is subjected to a constant heat flux and the opposite side is convectively cooled, is considered. The other two sides are maintained at constant temperature. A numerical solution for the temperature field is obtained and the heat transfer between the boxes is found by integrating between the critical heat flow lines. Various nondimensional parameters are identified and their influence on the thermal resistance is studied.     

线性四元树表示图象的距离变换

二元数组表示的图象使用的距离概念运用于线性四元树表示。指出棋盘距离特别适合于线性四元树。定义线性四元树的棋盘距离变换为树中各个黑四分形中心到最近边界四分形黑一白边界的距离。这里提出的距离变换算法主要特点是(1)它是一种代数方法,(2)各个四分形只计算一次距离,和(3)距离信息非常快地传递到区域内部。该算法可以推广到线性八元树表示的三维客体。     

Using computer graphics to enhance astronaut and systems safety.

Computer graphics is being employed at the NASA Johnson Space Center as a tool to perform rapid, efficient and economical analyses for man-machine integration, flight operations development and systems engineering. The Operator Station Design System (OSDS), a computer-based facility featuring a highly flexible and versatile interactive software package, PLAID, is described. This unique evaluation tool, with its expanding data base of Space Shuttle elements, various payloads, experiments, crew equipment and man models, supports a multitude of technical evaluations, including spacecraft and workstation layout, definition of astronaut visual access, flight techniques development, cargo integration and crew training. As OSDS is being applied to the Space Shuttle, Orbiter payloads (including the European Space Agency's Spacelab) and future space vehicles and stations, astronaut and systems safety are being enhanced. Typical OSDS examples are presented. By performing physical and operational evaluations during early conceptual phases. supporting systems verification for flight readiness, and applying its capabilities to real-time mission support, the OSDS provides the wherewithal to satisfy a growing need of the current and future space programs for efficient, economical analyses.     

Orbital and relative motion of a tethered satellite system

A simplified model for the orbital and relative motion of a tethered satellite system is presented. The tether acts as a light elastic string with small structural damping but without bending stiffness. Its mass is taken into account in the calculation of the total kinetic and potential energies of the tethered system. This formulation allows the inclusion of the complete gravity gradient influence on the dynamics of the system. The resulting three-dimensional motion is separated in the centre of mass orbital motion on the one hand and the relative motion of the end-bodies on the other. No restrictions on length of the tether or on mass ratio of the end-masses are imposed. It is found that the frequencies and amplitudes of the longitudinal tether oscillations are realistic as long as the tether mass is less than that of the subsatellite.     

微型FM/FM副载波解调器的设计与实现

介绍一种应用于FM/FM遥测系统的微型副载波解调器,相时于传统副载波解调器单独使用硬件进行解调处理的模式,系统在硬件上直接对多路副载波信号进行高速采样,然后将数据通过USB2．0总线实时上传到计算机,利用计算机强大的数字运算能力对副载波信号进行解调。这种方式极大地减小了硬件系统的尺寸和成本,并且便于实现对FM/FM遥测信号的存储和进一步分析处理。     

Aeroshell design techniques for aerocapture entry vehicles

A major goal of NASA's In-Space Propulsion Program is to shorten trip times for scientific planetary missions. To meet this challenge arrival speeds will increase, requiring significant braking for orbit insertion, and thus increased deceleration propellant mass that may exceed launch lift capabilities. A technology called aerocapture has been developed to expand the mission potential of exploratory probes destined for planets with suitable atmospheres. Aerocapture inserts a probe into planetary orbit via a single pass through the atmosphere using the probe's aeroshell drag to reduce velocity. The benefit of an aerocapture maneuver is a large reduction in propellant mass that may result in smaller, less costly missions and reduced mission cruise times. The methodology used to design rigid aerocapture aeroshells will be presented with an emphasis on a new systems tool under development. Current methods for fast, efficient evaluations of structural systems for exploratory vehicles to planets and moons within our solar system have been under development within NASA having limited success. Many systems tools that have been attempted applied structural mass estimation techniques based on historical data and curve fitting techniques that are difficult and cumbersome to apply to new vehicle concepts and missions. The resulting vehicle aeroshell mass may be incorrectly estimated or have high margins included to account for uncertainty. This new tool will reduce the guesswork previously found in conceptual aeroshell mass estimations.     

电火花仿真加工技术在航天发动机氧泵壳体返修中的应用

分析了某航天发动机的氧泵壳体零件的返修难题,提出了在线测量与计算机仿真相结合的解决方法并确定了具体的返修方案,介绍了计算机仿真技术在电火花加工中的具体应用。经实际应用,说明了在电火花加工中采用计算机仿真技术可大大提高产品加工的准确性。     

Advantages and disadvantages of prizes in a portfolio of financial incentives for space activities

The National Aeronautics and Space Administration (NASA) has proposed to use financial prizes to encourage innovation in space technology. Public debate about the use of prizes questions their effectiveness, the role of government compared with the private sector in administering prizes—for example, the Ansari X-Prize for human suborbital flight was privately funded and administered—and other issues that are likely to influence the success of this approach.     

n-Body problem: Selective effects of triple close approaches

In Celestial Mechanics the triple close approach is a highly unstable phenomenon that leads very often to the formation of a very small binary escaping with a large velocity in the direction opposite to the escape of the third body.That third escaping body is generally either the smallest mass or the second smallest and it implies a very selective effect in star clusters: the lightest stars are statistically the first to be ejected.     

Benefits to world agriculture through remote sensing

Remote sensing of agricultural land permits crop classification and mensuration which can lead to improved forecasts of production. This technique is particularly important for nations which do not already have an accurate agricultural reporting system. Better forecasts have important economic effects. International grain traders can make better decisions about when to store, buy and sell. Farmers can make better planting decisions by taking advantage of production estimates for areas out of phase with their own agricultural calendar. World economic benefits will accrue to both buyers and sellers because of increased food supply and price stabilization.

This paper reviews the econometric models used to establish this scenario and estimates the dollar value of benefits for world wheat as 200 million dollars annually for the United States and 300–400 million dollars anually for the rest of the world.