Synergies of Earth science and space exploration

A more flexible policy basis from which to manage our planet in the 21st century is desirable. As one contribution, we note that synergies between space exploration and the preservation of our habitat exist, and that protecting life on Earth requires similar concepts and information as investigations of life beyond the Earth, including the expansion of human presence in space. Instrumentation and data handling to observe both planetary objects and planet Earth are based on similar techniques. Moreover, while planetary surface operations are conducted under different conditions, the technology to probe the surface and subsurface of both the Earth and other planets requires similar tools, such as radar, seismometers, and drilling devices. The Earth observation community has developed some exemplary tools and has featured successful international cooperation in data handling and sharing that could be equally well applied to robotic planetary exploration. Here we propose a network involving both communities that will enable the interchange of scientific insights and the development of new policies and management strategies. Those tools can provide a vital forum through which the management of this planet can be assisted, and in which a new bridge between the Earth-centric and space-centric communities can be built.     

Characterizing bedrock lithologies using Small Crater Rims and Ejecta Probing (SCREP)

This paper describes the rationale, methodology, and importance of focusing on the rim and proximal ejecta of small (<5 km in diameter), immature impact craters to explore an underlying crustal lithology. Small Crater Rim and Ejecta Probing (SCREP) describes a methodology and application program that extracts bedrock spectral and compositional information from a remote sensing image. Extracted data can yield the pristine lithologies of a planetary crust that would otherwise be obscured by the products of space weathering processes. SCREP was developed with lunar data, specifically Clementine multispectral image mosaics, therefore the technique is discussed in this context. However, its application to other airless solar system bodies is apparent. Knowledge of the pristine bedrock compositions of a planetary crust provides insight into geological surface processes, which can be used to refine models of planetary interiors and their evolution.     

Space Debris Mitigation in France,Germany, Italy and United Kingdom

The Space systems today provide growing benefits to enhance the quality of humankind. However, as a by-product, the orbiting objects inevitably leaves some debris which after 50 years of space activities represent a concern for all space agencies and manufacturers and operators. Since last year no international agreement was in place to mitigate the growing population of space debris objects. The successful result obtained at UN-COPUOS in 2007 and available in the OOSA web site, now gives to the public, a set of voluntary international guidelines that could, if adopted by each space fairing Country, help in maintaining the present space environment. More further steps are necessary in the future to define a legal and normative framework. The paper will present the seven established UN Space Debris guidelines as well as examples of the minimum steps to be carried out at national level to enable the UN-COPUOS to start the discussion of the legal aspect associated with the space debris issue.     

自适应对角线加载的波束形成算法

采样协方差矩阵求逆(SMI)的波束形成方法在少快拍数、高信噪比情况下波束形成性能下降。对角线加载技术能减弱了小特征值对应的噪声波束的影响,改善了方向图畸变,但是加载量的确定一直以来是一个比较困难的问题。文中提出了一种自适应对角线加载波束形成算法,根据阵列接收信号协方差矩阵的特征结构,自适应地加载对角线,进而提高波束形成的鲁棒性。仿真结果表明:该算法在高、中、低的信噪比下都具有较好的波束形成性能,且在少快拍数情况下仍具有较好的波束形成性能,是一种鲁棒的且性能优越的波束形成算法,而且该算法容易实现。     

空间光通信系统比特差错率的计算及影响因素分析

文章以雪崩光电二极管(APD)作为光电探测器,针对两种常用的数据编码方式,在不同的传输带宽、背景光功率和探测器负载条件下,对空间光通信系统的比特差错率(BER)进行了计算,得到了BER和接收光功率之间的关系曲线。计算结果表明,传输带宽、背景光功率和探测器负载等参数均对BER有明显影响。传输带宽或背景光功率越大,BER越大;探测器负载电阻越小,BER越大。     

空间科学实验平台气液回路方案

空间科学实验平台是为突破单一化实验装置设计模式而研制的一种多用途空间科学实验平台. 根据空间科学实验平台内气液回路设计的相关问题, 给出了回路系统中主要设备的相关设计方法, 包括循环风机、气-液换热器、冷板, 并根据传热效率和系统安全性的考虑, 对流体工质的选择提出建议. 初步分析结果及国际类似研究证明, 气液回路技术结合其他主动及被动热控制措施, 可以很好地满足空间实验平台内部仪器设备及样本的不同温度控制要求.     

High-resolution, coupled thermosphere–ionosphere models for space weather applications

Current first-principles global models of the coupled thermosphere–ionosphere (T–I) system use grids that are too coarse to simulate the mesoscale and small-scale structures that occur in this complex system. These small-scale and mesoscale structures have a great effect on global-scale neutral and plasma distributions and have important consequences for daily space weather. In this paper, we present a new first-principles, high-resolution, T–I nested grid (TING) polar cap model that incorporates multiple nesting levels and two-way interaction. The TING model simulation of the electron densities and temperatures demonstrates the importance of high spatial resolution. It is found that both the mid-latitude electron density trough and its associated dawn electron temperature peak are more pronounced and structured in the nested grid than in the coarse grid. Using the TING model to simulate ionospheric F₂ region electron density variations with geomagnetic activity and universal time (UT) is also discussed.     

An experiment to study solar flare effects on radio-communication signals

The occurrence of radio signal fading events caused by ionospheric absorption plays an important role in the performance of radio-communication systems. It is necessary to know the magnitude and time-scale of such events in order to specify technical parameters of the communication system to be used. Generally, fading events are associated with solar flares, which are characterized by sudden increase in the solar X-ray flux that causes an increase in the ionization in the lower ionosphere. The abrupt increase of ionization causes the absorption of radio waves propagating in the Earth–ionosphere wave-guide and is reported as radio signal fading events. A simple experiment to monitor the behavior of lower ionosphere has been carried out at the Southern Space Observatory-SSO/INPE (29.43°S, 53.8°W), located in southern Brazil. The experiment is basically a computer controlled radio receiver that records the received signal strength of Amplitude Modulated (AM) radio signals in the HF (High Frequencies) range. We analyzed data of the 6 MHz beacon signal that has been transmitted by a broadcasting radio station located about 400 km from the observation site. In this work we present initial results of daily variation of the received signal strength and fading events associated with solar flares observed in the 6 MHz signal monitored by the experiment during 2001. X-ray solar flux data from the GOES-8 satellite were used to identify X-ray solar bursts associated with solar flares. Based on the one-year data collected by the experiment, a statistical summary of fading occurrences and their correlation with solar flares, as well as the distributions of time-scales and magnitudes of such events are presented.     

空间目标一维距离像畸变补偿的混合算法

高分辨距离像的畸变补偿是空间目标ISAR成像过程中的重要环节。由于空间目标基带回波的模糊函数峰值落在包含原点的平行直线族上,根据平行直线族的约束边界建立了一个多目标规划模型,并利用正则化原理提出了一种目标速度估计的直接算法,具有解析解。将其作为迭代初值,进一步利用一维迭代搜索算法搜索距离像波形熵的最小值,获得了更精确的速度估计量。仿真结果表明,文章提出的混合搜索算法综合了解析算法和迭代搜索算法在计算量和准确性方面的优点,能有效估计空间目标径向速度并补偿一维距离像畸变。