Magnetic and Optical Properties of the TiO2-Co-TiO2 Composite Films Grown by Magnetron Sputtering

The TiO2-Co-TiO2 sandwich films were successfully grown on glass and silicon substrata making alternate use of radio frequency reactive magnetron sputtering and direct current magnetron sputtering. The structures and properties of these films were identified with X-ray diffraction (XRD), Raman spectra and X-ray photoemission spectra (XPS). It is shown that the sandwich film consists of two anatase TiO2 films with an embedded Co nano-film. The fact that, when the Co nano-film thickens, varied red shifts appear in optical absorption spectra may well be explained by the quantum confinement and tunnel effects. As for magnetic properties, the saturation magnetization, remnant magnetic induction and coercivity vary with the thickness of the Co nano-films. Moreover, the Co nano-film has a critical thickness of about 8.6 nm, which makes the coercivity of the composite film reach the maximum of about 1413 Oe.     

地基设备布站对空间碎片观测能力的影响分析

建立空间碎片地面观测站时,需要用数值仿真工具对其观测能力进行评估和分析.评估观测站能力的重要指标是测站设备对空间碎片的观测量和可观测频度.先进的设备指标和合适的测站位置能够大大提高观测能力.本文使用STK,PROOF等软件,对不同测站雷达和光学设备的观测能力(过境率和探测率)进行了数值仿真和比较分析,得到了一些初步结论,对于空间碎片监测网的设计有一定的参考作用.      

Comparative analysis of global optical observability of satellites in LEO

With a growing number of resident space objects (RSOs), the facilities for near-Earth space surveillance have to cope with increasing workload. It also applies to low-cost small optical surveillance facilities which may present regional, national and global networks. Improved methods of planning and scheduling optical telescopes are required to use these instruments efficiently. Today, optical observations are only feasible if the following quite stringent requirements are met: the object should be illuminated by sunlight, and it should be above while the Sun is below the observer’s horizon. For different orbits, these preconditions result in varying degrees of the space object observability at various ground-based sites. Certainly, satellites in low Earth orbit (LEO) are particularly difficult to observe. This study aims at developing a new technique for assessing observability of a satellite in different types of orbits – namely, low, medium and high Earth orbits, imaging of the opportunity for its visibility in respective diagrams and their analysing for the existing near-Earth population of RSOs. Unlike other researches, wherein one or several observational stations have been chosen as target sites for in-depth analyses of visibility of all the satellites or just the selected ones, the present study focuses on examining the probability of optical surveillance of satellites in a certain orbit from any locations worldwide. It offers considerable scope for automation of surveillance planning and scheduling optical surveillance networks.     

面向宇航应用光传输微系统集成技术

为了满足宇航系统对高速、宽带数据和图像传输产品小体积、轻质化的需求，研究光传输高速高密度集成技术。基板采用带状差分线设计和叠层组装工艺，提高集成密度、缩小体积提升了系统组装的空间，并通过建模仿真设计分析高速信号完整性；将光器件设计在外壳底板上，实现高效散热结构设计，同时提高了光器件使用可靠性；采用混合集成微组装工艺，硅转接基板实现芯片级三维立体集成，采用二次封装技术解决了光纤高效耦合与气密共实现的难题。微系统模块体积≤27 mm×24 mm×5 mm，气密封装漏率≤5×10–9Pa·m3/s(He)。     

DebrisWatch I: A survey of faint geosynchronous debris

Recent anomalies exhibited by satellites and rocket bodies have highlighted that a population of faint debris exists at geosynchronous (GEO) altitudes, where there are no natural removal mechanisms. Despite previous optical surveys probing to around 10–20 cm in size, regular monitoring of faint sources at GEO is challenging, thus our knowledge remains sparse. It is essential that we continue to explore the faint debris population using large telescopes to better understand the risk posed to active GEO satellites. To this end, we present photometric results from a survey of the GEO region carried out with the 2.54 m Isaac Newton Telescope in La Palma, Canary Islands. We probe to 21st visual magnitude (around 10 cm, assuming Lambertian spheres with an albedo of 0.1), uncovering 129 orbital tracks with GEO-like motion across the eight nights of dark-grey time comprising the survey. The faint end of our brightness distribution continues to rise until the sensitivity limit of the sensor is reached, suggesting that the modal brightness could be even fainter. We uncover a number of faint, uncatalogued objects that show photometric signatures of rapid tumbling, many of which straddle the limiting magnitude of our survey over the course of a single exposure, posing a complex issue when estimating object size. This work presents the first instalment of DebrisWatch, an ongoing collaboration between the University of Warwick and the Defence Science and Technology Laboratory (UK) investigating the faint population of GEO debris.     

飞行器半实物仿真装备研究进展与展望

根据制导体制不同，分别从光学制导仿真、射频制导仿真、光学/射频复合制导仿真等方面介绍了国内外半实物仿真装备研究进展。结合飞行器对半实物仿真技术提出新的发展需求，提出了全角度空间制导仿真、特殊环境/背景制导仿真、绕飞伴飞仿真、弹体气动伺服弹性仿真等特殊背景的半实物仿真方案。最后，结合飞行器技术和半实物仿真技术发展趋势，对飞行器半实物仿真装备的发展趋势进行了展望。     

Estimation of sediment settling velocity in estuarine and coastal waters using optical remote sensing data

A robust method has been developed for estimating sediment settling velocity (w_s) from high resolution optical remote sensing data in estuarine, coastal and harbor waters. This method estimates settling velocity as a function of the drag coefficient (C_d), Reynolds number (Re), grain size (D₅₀), specific gravity (Δ_SG) and grain shape (in terms of the Corey Shape Factor – CSF). These parameters were derived from the particulate inherent optical properties such as backscattering (b_bp), beam attenuation (c_p), suspended sediment concentration and turbidity using Landsat 8 OLI and HICO data. Preliminary results for the Gulf of Cambay in the eastern Arabian Sea and Yangtze river estuary in the East China Sea, showed that satellite-retrieved settling velocities (m?s^?1) varied from very low values in clear oceanic waters, intermediate values in coastal waters, to very high values in river plumes and sediment-laden coastal waters. The remote sensing retrievals of sediment properties and their settling velocities were generally consistent with the field and laboratory results, which indicate that the proposed methodology will have important implications in various coastal engineering, environmental and management studies.     

Space debris observations with the Slovak AGO70 telescope: Astrometry and light curves

The Faculty of Mathematics, Physics and Informatics of Comenius University in Bratislava, Slovakia (FMPI) operates its own 0.7-m Newtonian telescope (AGO70) dedicated to the space surveillance tracking and research, with an emphasis on space debris. The observation planning focuses on objects on geosynchronous (GEO), eccentric (GTO and Molniya) and global navigation satellite system (GNSS) orbits. To verify the system’s capabilities, we conducted an observation campaign in 2017, 2018 and 2019 focused on astrometric and photometric measurements. In last two years we have built up a light curve catalogue of space debris which is now freely available for the scientific community. We report periodic signals extracted from more than 285 light curves of 226 individual objects. We constructed phase diagrams for 153 light curves for which we obtained apparent amplitudes.