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Spaceborne synthetic aperture radar (SAR) is an advanced microwave imaging technology that provides all-weather and all-day target information. However, as spaceborne SAR resolution improves, traditional echo signal models based on airborne SAR design become inadequate due to the curved orbit, Earth rotation, and increased propagation distance. In this study, we propose an accurate range model for high-resolution spaceborne SAR by analyzing motion trajectory and Doppler parameters from the perspective of the space geometry of spaceborne SAR. We evaluate the accuracy of existing range models and propose an advanced equivalent squint range model (AESRM) that accurately fits the actual range history and compensates for high-order term errors by introducing third-order and fourth-order error terms while maintaining the simplicity of the traditional model. The proposed AESRM's concise two-dimensional frequency spectrum form facilitates the design of imaging algorithms. Point target simulations confirm the effectiveness of the proposed AESRM, demonstrating significant improvements in fitting accuracy for range histories characterized by nonlinear trajectories. The developed AESRM provides a robust foundation for designing imaging algorithms and enables higher resolution and more accurate radar imaging. [ABSTRACT FROM AUTHOR]

With the advancement of spaceborne synthetic aperture radar (SAR) resolution, the conventional stop-and-go approximation-based motion model is no longer suitable for high-resolution imaging algorithms. This paper conducts a comprehensive analysis of the approximation errors resulting from the stop-and-go approximation and proposes corresponding compensation methods. Firstly, an accurate echo model based on continuous platform motion is derived from the SAR geometry configuration. The impact of these errors on range and azimuth imaging is analysed from a spectral perspective, and the applicable boundary conditions are examined. Subsequently, compensation methods are proposed to eliminate the introduced approximation errors, addressing both"fast time" and"slow time" effects, thus enabling high-resolution imaging through improvements in traditional imaging algorithms. Experimental simulations validate the effectiveness of the error analysis and compensation methods, using X-band low Earth orbit SAR as an illustrative example. The proposed methods are not only compatible with existing mature imaging algorithms, but the analytical approach and compensation methods are also applicable to SAR systems operating on different carrier frequencies, orbits, and platforms. [ABSTRACT FROM AUTHOR]

Simulated raw data have become an essential tool for testing and assessing system parameters and imaging performance due to the high cost and limited availability of real raw data from spaceborne synthetic aperture radar (SAR). However, with increasing resolution and higher orbit altitudes, existing simulation methods fail to generate SAR simulated raw data that closely resemble real raw data. This is due to approximations such as curved orbits, "stop-and-go" assumption, and Earth's rotation, among other factors. To overcome these challenges, this paper presents an accurate range model with a "nonstop-and-go" configuration for raw data simulation based on existing time-domain simulation methods. We model the SAR echo signal and establish a precise space geometry for spaceborne SAR. Additionally, we precisely identify the target illumination area based on elliptical beams through space coordinate transformation. Finally, the SAR raw data were accurately simulated using high-precision time-domain simulation methods. The accuracy of the proposed model was validated by comparing it with the traditional hyperbolic model and the curved orbit model with "stop-and-go" assumption through image processing of the generated raw data. Through the analysis of point target quality parameters, the errors of various parameters in our distance model compared with the other two models are within 1%. Furthermore, this simulation method can be adapted to simulate raw data of other modes and satellite orbits by adjusting beam control and satellite orbit parameters, respectively. The proposed simulation method demonstrated high accuracy and versatility, thereby providing a valuable contribution to the development of remote sensing technology. [ABSTRACT FROM AUTHOR]

Abstract: More and more plastic encapsulated microcircuits (PEMs) are used in space missions to achieve high performance. Since PEMs are designed for use in terrestrial operating conditions, the successful usage of PEMs in space harsh environment is closely related to reliability issues, which should be considered firstly. However, there is no ready-made methodology for PEMs in space applications. This paper discusses the reliability for the usage of PEMs in space. This reliability analysis can be divided into five categories: radiation test, radiation hardness, screening test, reliability calculation and reliability assessment. One case study is also presented to illuminate the details of the process, in which a PEM part is used in a joint space program Double-Star Project between the European Space Agency (ESA) and China. The influence of environmental constrains including radiation, humidity, temperature and mechanics on the PEM part has been considered. Both Double-Star Project satellites are still running well in space now. [Copyright &y& Elsevier]

Abstract: This paper presents a new electric control system (ECS) with small size, light weight and low-power consumption for the microgravity fluid experiment of drop Marangoni migration on SZ-4 spaceship, a test module of the manned space mission of China. The ECS is designed as a key part to set up and maintain a suitable temperature gradient field for microgravity fluid experiment. It acquires, stores and transmits the experiment data, and acts as an interface keeping contact between the experiment device and a remote-terminal in the return capsule. In addition, the ECS is an executing unit to control the whole space experiment and to change the working modes of the experiment through commands from the ground, or by prestored program in EEPROM. The ECS, presented in this work, has run in-orbit successfully to operate the microgravity fluid experiment on SZ-4 and its performance is shown in the experiment results in space. [Copyright &y& Elsevier]

• Different acidic polysaccharides affect the properties of collagen fibrillar gels distinctly. • Gel with SA exhibited denser network while those with CS and HA depicted larger ordered structures. • Gelling time and enzymatic resistance are maintained with HA addition but compromised in gels with CS and SA. • Acidic polysaccharides can increase mechanical strength and d -periodicity of the gels. Fibrillar gel of pepsin-solubilized collagen from tilapia skin was prepared by self-assembly in neutral phosphate buffer at 28 °C. Then effects of acidic polysaccharides, such as sodium alginate (SA), chondroitin sulfate (CS), and hyaluronic acid (HA), on the formation and properties of self-assembled fibrillar gel were investigated. SA and CS prolonged gelling time, whereas HA had no obvious effect. SA made fibril network denser, while CS and HA induced the presence of larger ordered structures. All the acidic polysaccharides broadened the D-periodicity of fibrils. SA and HA increased the maximum mechanical strength of gel to 39.64 and 34.49 kN/m2, respectively, significantly higher than that of pure collagen gel (14.53 kN/m2), while that only 17.20 kN/m2 after CS introduced. HA had no evident effect on enzymatic resistance, while SA and CS decreased. Therefore, tilapia skin collagen with HA has a higher potential as a biomaterial than that with CS or SA. [ABSTRACT FROM AUTHOR]

A sounding rocket experiment undertaken by the Chinese Meridian Project from a low latitude station on Hainan Island (19.5°N, 109.1°E), China, measured the DC electric field during 05:45-05:52 LT on April 5, 2013. The data observed using a set of electric field double probes, as part of the rocket's scientific payload, revealed the special profile of how the vectors of the DC electric field vary with altitude between 130 and 190 km. During the experiment, the vertical electric field was downward, and the maximum vertical electric field was nearly 5.1 mV/m near the altitude of 176 km. The zonal electric field was eastward and slightly less than 0.6 mV/m. The plasma drift velocity was estimated from the E×B motion, and the zonal drift velocity was eastward and of the order of 100 m/s. The zonal wind velocity was also estimated using the drift velocity near the maximum density height in the F1-region, and it was found to be nearly 120 m/s. This work constituted the first in situ measurement of the DC electric field conducted within the F1-region (between 130 and 190 km) in the East Asian Sector. [ABSTRACT FROM AUTHOR]

Though clarifying the relationship between packing and emission is very important and highly desirable for understanding the mechanism behind responsive luminescent materials, it is not an easy case for piezochromic luminescent materials, due to the difficulties of in situ tracking the interactions change during pressurization. Herein, a smart supramolecular assembly strategy based on two macrocyclic hosts with tailored guests' packing has been proposed for illustrating the mechanism of piezochromic luminescence. The elusive changes of molecular packing associated with variable luminescence behavior under mechanical forces, such as grinding and high pressure, can be expressed intuitively by cryptand (CP) or cucurbit [7]urils (CB [ 7 ])-based host-guest complex in a visualized way. Specifically, the enhanced π-π stacking interactions induced by CP corresponds well to the dim and red-shifted emission under isotropic compression, while the isolated chromophore in non-aromatic CB [ 7 ] with reduced intermolecular π-π interactions perfectly explains the brightened and blue-shifted emission after grinding. This controllable self-assembly strategy provides a reliable and smart strategy for visualizing the mechanism of piezochromic luminescence. [Display omitted] • Developing a novel supramolecular strategy to reveal the mechanism of piezochromic luminescence. • The fluorescence of the assemblies are highly consistent with that of guest under different mechanical stimulation. • This strategy provides a prototype to visualize untraceable intermolecular interactions during pressuring. • This work opens a new world for supramolecular macrocycles. [ABSTRACT FROM AUTHOR]