Microgravity and the human exploration of space technology challenges

If humans are to explore space beyond low-earth orbit, their health and welfare must be ensured, not only for survival in harsh environments but also so that they can work productively. The requisite technologies, and human physiology itself, are subject to reduced levels of gravity that are indigenous to space travel. Numerous studies have shown that it will require many years of intensive research to develop reliable, efficient, and self-sustaining technologies and to understand the effects of gravity on humans. The research community that was developed to provide crucial specific information has essentially been deactivated because of budget constraints. Thus, the great engineering challenge—to develop advanced and novel technologies that will enable further space exploration—will remain for future generations.     

A massive bolometer on the international space station to measure energy deposition by the space radiation environment

We describe a novel space-based low-temperature radiation detector, the “Particle Heating Detector” (PhD), which was recently selected to be part of the first mission of the Low-Temperature Microgravity Physics Facility, scheduled to fly on the International Space Station in 2008. This massive bolometer will measure total heating induced in an aluminum absorber by the space radiation environment. The use of paramagnetic alloy thermometers with SQUID readout, giving resolution, combined with a large-area absorber, will enable the detector to perform high-resolution, real-time measurement of the low energy deposition levels caused by galactic cosmic rays in low-Earth orbit.     

Assessment of electronics for cryogenic space exploration missions

Space exploration missions require electronics capable of efficient and reliable operation at low temperatures. Presently, spacecraft on-board electronics are maintained at approximately 20 °C through the use of radioisotopes. Cryogenic electronics would enhance efficiency of space systems, improve reliability, and simplify their design. A Low Temperature Electronics Program at the NASA Glenn Research Center focuses on research and development of electronics suitable for space exploration missions. The effects of cryogenic temperature and thermal cycling are being investigated for commercial-off-the-shelf components as well as for components specially developed for low temperature operation. An overview of this program along with selected experimental data is presented in this paper.     

深空光通信中导航星表的构造

提出一种导航星表的构建方法，该方法以星跟踪器视场内最亮恒星作为信标，把信标锁定在视场中心，测量视场内其他恒星到信标的角间隔，把测量的所有恒星角间隔和信标的赤经、赤纬存储到导航星表中。基于该方法，利用史密森天文观测台恒星星表（SAO），选择星等小于6等的恒星，建立起导航星表，该星表仅包括5103颗星，其容量仅为1.2兆。相对三角形算法，该星表容量更小，可节省星载系统的存储空间，减少识别时间，提高跟踪速率。蒙特-卡诺仿真结果表明，利用该导航星表识别信标具有较好的抗干扰性，且当星跟踪器测角误差（30σ）在1μrad以内时，信标正确识别概率几乎为100％。     

Potential new solidification experiments in space environment

The paper discusses the potential effects of space environment on solidification; reviews the previous solidification experiments in space and suggests new-experiments. The proposed experiments in space include (a) breakdown of planar interfaces in transparent systems, (b) thermal perturbations ahead of interfaces, (c) dendrite spacings, (d) fragmentation of dendrites and their transport, (e) solute concentration profiles in castings, (f) maximum undercoolings in alloy melts under containerless conditions; ultrafine structures produced on freezing of highly under-cooled melts, (g) preparation of wires and ribbons from alloys; solidification in ultrathin films and (h) dendritic shrinkage.     

Thermal convection induced byg-jitter in space environment

The article discusses thermal convection in an enclosure induced by spacecraft vibrations (g-jitter). Two theoretical investigations are described. The conclusions are that if theg-jitter is decomposed into a time-mean part and an oscillatory part, the mean part is more important than the oscillatory part, in determining the flow field and heat transfer rate. Under normal circumstances (no manoeuvres, no intentional spinning of the spacecraft) theg-jitter generates predominantly oscillatory velocity and temperature fields with zero time-mean values. Theg-jitter can also generate secondary flows with non-zero mean but they are of much smaller order. Some implications of theg-jitter on materials processing in space are also discussed.     

深空光通信中恒星信标的捕获跟踪技术研究

提出一种深空光通信系统的信标捕获、跟踪方案,该方案是以恒星作为信标,根据恒星在惯性坐标系中的绝对位置信息,基于航天器和地球星历表、航天器的姿态信息来进行下行光束瞄准方向的精确控制。理论分析和计算机仿真都表明,星敏感器的测量精度和焦距,下行信号光的束散角将影响激光链路成功建立概率。下行信号光束散角为30μrad,星敏感器视场为8°×8°,焦距为143mm,恒星的中心位置测量精度达到0.10个像素时,链路成功建立的概率达到96.4%,表明该方案是可行的。     

An exploration of link-based knowledge map in academic web space

The World Wide Web has become an important source of academic information. The linking feature of the Web has been used to study the structure of academic web, as well as the presence of academic and research institutes on the Web. In this paper, we propose an integrated model for exploring the subject macrostructure of a specific academic topic on the Web and automatically depicting the knowledge map that is closer to what a domain expert would expect. The model integrates a hyperlink-induced topic search (HITS)-based link network extending strategy and a semantic based clustering algorithm with the aid of co-link analysis and social network analysis (SNA) to discover subject-based communities in the academic web space. We selected to use websites as analytical units rather than web pages because of the subject stability of a website. Compared with traditional techniques in Webometrics and SNA that have been used for such analyses, our model has the advantages of working on open web space (capability to explore unknown web resources and identify important ones) and of automatically building an extendable and hierarchical web knowledge map. The experiment in the area of Information Retrieval shows the effectiveness of the integrated model in analyzing and portraying of subject clustering phenomenon in academic web space.     

Characterisation of bubble detectors for aircrew and space radiation exposure

The Earth's atmosphere acts as a natural radiation shield which protects terrestrial dwellers from the radiation environment encountered in space. In general, the intensity of this radiation field increases with distance from the ground owing to a decrease in the amount of atmospheric shielding. Neutrons form an important component of the radiation field to which the aircrew and spacecrew are exposed. In light of this, the neutron-sensitive bubble detector may be ideal as a portable personal dosemeter at jet altitudes and in space. This paper describes the ground-based characterisation of the bubble detector and the application of the bubble detector for the measurement of aircrew and spacecrew radiation exposure.     

高可靠处理器微体系结构设计空间的快速搜索

同一个程序运行在不同微体系结构配置的处理器上时,不同处理器的软错误率通常会有非常大的差别.所以,为了设计高可靠处理器,对处理器微体系结构设计空间进行搜索,选择出高可靠的配置,是至关重要的.然而,目前的处理器软错误率预测方法忽视了执行程序的影响,导致微体系结构设计空间搜索仍然需要大量周期精确的模拟.因此,本文提出了基于同时考虑程序固有特征(与微体系结构无关的程序特征)和处理器微体系结构配置而构建的统一的软错误率预测模型的设计空间快速搜索方案.该方案对新程序或新处理器配置都不需要额外的周期精确的模拟就可以准确预测软错误率,从而极大地缩短了高可靠处理器微体系结构设计空间的搜索时间.对SPEC CPU2000基准测试程序的实验结果表明,与基于反应构建软错误率预测模型的方案相比较,该方案搜索高可靠处理器微体系结构设计空间所需的模拟时间减少了99.8％.     

Characterization of the radiation environment by Liulin-type spectrometers

Liulin-type spectrometers can characterise the type of predominant particles and their energy in the radiation environment. The results from calibrations and space and aircraft experiments revealed that the most informative is by the shape of the deposited energy spectrum. Spectra generated by galactic cosmic rays (GCR) protons and their secondaries look like straight lines in the coordinates deposited energy/deposited per channel dose rate. The position of the maximum of the deposited energy spectra depends on the incident energy of the incoming protons. Spectra generated by relativistic electrons in the outer radiation belt have a maximum in the first channels. For higher energy depositions, these spectra are similar to the GCR spectra. All types of spectra have a knee close to 6.3 MeV of deposited energy, which corresponds to the stopping energy of protons in the detector.     

Passive coolers for pre-cooling of JT loops for deep space infrared imaging applications

Infrared instruments (IR) for deep space imaging missions, such as the James Webb Space Telescope (JWST) and Planck, require cryogenic cooling for proper operation of their focal plane arrays (FPA) in far infrared and sub-millimeter wavelength ranges. The FPA is sometimes located meters away from the spacecraft. To meet such remote cooling requirement, a Joule-Thomson (J-T) loop becomes a convenient choice for either direct cooling for the FPA or for serving as a heat sink for a cascade cooling system. The refrigerant lines of the JT loop inevitably suffer parasitic heat leak primarily due to IR backload as they traverse from the spacecraft to the FPA. An actively cooled JT loop using a mechanical pre-cooler located at the spacecraft will experience the highest parasitic heat leak since the lines are cold through the entire length whereas a passively cooled JT loop can utilize a number of radiators to cool the lines down gradually in stages and hence reduce the heat leak. In addition to savings in power and mass, a passive cooler offers consistent and predictable performance with practically no performance degradation in a thermally stable orbit, such as one around the Sun-Earth L2 point. Passive coolers are less popular in low temperature applications when their cooling capacity diminishes rapidly in proportion to T4 until the temperature reaches a point where either the parasitic heat leak becomes so significant or its size becomes so excessive that the passive cooling scheme becomes impractical. Despite the limited capacity, passive cooling may still prove to be a viable alternative to active cooling depending on the operating temperature and heat dissipation rate of the FPA. The current effort aims at evaluating the merit of using passive coolers as an alternative to using a mechanical cooler for pre-cooling of a JT loop for remote IR instrument cooling. A parametric study is conducted to explore the merits of passive cooling of a JT loop in a temperature range below 30 K. Correlations between cooling capacity, heat leak from supporting structure, and the operating temperature are investigated to provide design guidelines. Radiator staging options will also be presented and discussed.     

Usage scenarios for design space exploration with a dynamic multiobjective optimization formulation

In a recent publication, we presented a new strategy for engineering design and optimization, which we termed formulation space exploration. The formulation space for an optimization problem is the union of all variable and design objective spaces identified by the designer as being valid and pragmatic problem formulations. By extending a computational search into this new space, the solution to any optimization problem is no longer predefined by the optimization problem formulation. This method allows a designer to both diverge the design space during conceptual design and converge onto a solution as more information about the design objectives and constraints becomes available. Additionally, we introduced a new way to formulate multiobjective optimization problems, allowing the designer to change and update design objectives, constraints, and variables in a simple, fluid manner that promotes exploration. In this paper, we investigate three usage scenarios where formulation space exploration can be utilized in the early stages of design when it is possible to make the greatest contributions to development projects. Specifically, we look at formulation space boundary exploration, Pareto frontier generation for multiple concepts in the formulation space, and a new way to perform targeted boundary expansion. The benefits of these methods are illustrated with the conceptual design of an impact driver.     

HETC radiation transport code development for cosmic ray shielding applications in space

In order to facilitate three-dimensional analyses of space radiation shielding scenarios for future space missions, the Monte Carlo radiation transport code HETC is being extended to include transport of energetic heavy ions, such as are found in the galactic cosmic ray spectrum in space. Recently, an event generator capable of providing nuclear interaction data for use in HETC was developed and incorporated into the code. The event generator predicts the interaction product yields and production angles and energies using nuclear models and Monte Carlo techniques. Testing and validation of the extended transport code has begun. In this work, the current status of code modifications, which enable energetic heavy ions and their nuclear reaction products to be transported through thick shielding, are described. Also, initial results of code testing against available laboratory beam data for energetic heavy ions interacting in thick targets are presented.     

Predicting the radiation environment at high-luminosity hadron-collider experiments

The physics requirements of future hadron-collider experiments require very high collision rates, leading to harsh radiation environments never before confronted in large-scale high-energy physics experiments. The high levels of radiation backgrounds becomes a major design criterion for such experiments. Considering the enormous cost and effort involved in building modern high-energy physics experiments, it is vital that particle fluences and energy depositions can be predicted reliably. This is done using Monte-Carlo simulation programs. Given in this paper are the results of comparisons in which the predictions of different simulation programs, all used in the evaluation of radiation backgrounds in the ATLAS and CMS experiments at the CERN Large Hadron Collider, are analysed. Such comparisons give confidence when the predictions agree, and possible cause for further investigation when they disagree.     

Few-field radiation therapy optimization in the phase space of complication-free tumor control

The phase space of P₊, describing the probability of achieving tumor control without causing severe complications in normal tissues, has been investigated for three different clinically relevant treatment geometries. These include tumors in the head and neck region, thorax, and pelvis. Some general conclusions about the shape and properties of the P₊ phase space are given for the selected target volumes. The use of three different radiation beam types-strictly homogeneous, wedged, and generally nonuniform beams-has been investigated and the considerable differences in the P₊ phase space are shown. One conclusion is that the exact selection of beam entry direction becomes gradually less important as the number of beam portals becomes larger. One of the most important results is that use of appropriately selected nonuniform beam profiles reduces the number of necessary beam portals to such a low level that the treatment technique becomes simple and reliable at the same time as the probability of achieving tumor control without severe complications is almost as high as with an unlimited number of beams This means that most ordinary treatment units equipped with beam compensating filters can be used for closely optimal radiation therapy.     

Solid modeling of space stations in a concurrent processing environment

This article presents solid modeling of space station structures in a multiprocessing environment such as the Cray YMP 8/864. A space station is modeled as a collection of space trusses. Elements of trusses are created concurrently using constructive solid geometry. Concurrent solid modeling of large structures can be integrated with parallel algorithms for optimization of such structures in order to fully automate their computer-aided design in a multiprocessing environment.     

Dosimetry of densely ionising radiation with three LiF phosphors for space applications

A new method of thermoluminescence dosimetry of densely ionising radiation based on the ratio of different efficiency-LET functions of three thermoluminescent detectors (TLDs) has been developed. The applied TLD types are: MTS-7 ((7)LiF:Mg,Ti), MCP-7 ((7)LiF:Mg,Cu,P) and MTT-7 (a newly developed (7)LiF:Mg,Ti with modified activator composition and increased response to high-LET radiation). The tests of this method, performed with high-energy ion beams at the HIMAC accelerator within the ICCHIBAN project, proved that good agreement with the true dose values may be achieved even in very complicated mixed fields. The proposed method will be applied for analysis of several thousand TLDs used for the determination of organ doses in an anthropomorphic phantom orbiting outside the International Space Station within the MATROSHKA experiment.     

西门子帮助美国国家航空航天局开创太空探索新纪元

在近日召开的联合记者会上,美国国家航空航天局(NASA)火星探测计划项目主管Doug McCuistion与西门子股份公司工业业务领域首席执行官鲁思沃博士(Siegfried Russwurm)共同探讨了即将到来的太空探索新时代以及NASA工程师和西门子软件技术在实现未来太空探索中发挥的重要作用。双方谈及了计划于