Improving Airgun Signal Detection with Small-Aperture Seismic Array in Yunnan

Repeating airgun sources are eco-friendly sources for monitoring the changes in the physical properties of subsurface mediums,but their signals decay quickly and are buried in the noises soon after traveling short distances.Stacking waveforms from different airgun shots recorded by a single seismic station(shot stacking)is the most popular technique to detect weak signals from noisy backgrounds,and has been widely used to process the data of Fixed Airgun Signal Transmission Stations(FASTS)in China.However,shot stacking sacrifices the time resolution in monitoring to recover a qualified airgun signal by stacking many shots at distance stations,and also suffers from persistent local noises.In this paper,we carried out several small-aperture seismic array experiments around the Binchuan FAST Station(BCFASTS)in Yunnan Province,China,and applied the array technique to improve airgun signal detection.The results show that seismic array processing combining with shot stacking can suppress seismic noises more efficiently,and provide better signal-to-noise ratio(SNR)and coherent airgun signals with less airgun shots.This work suggests that the array technique is a feasible and promising tool in FAST to increase the time resolution and reduce noise interference on routine monitoring.

Surface Charging Controlling of the Chinese Space Station with Hollow Cathode Plasma Contactor

A highly charged manned spacecraft threatens the life of an astronaut and extravehicular activity, which can be effectively reduced by controlling the spacecraft surface charging. In this article, the controlling of surface charging on Chinese Space Station （CSS） is investigated, and a method to reduce the negative potential to the CSS is the emission electron with a hollow cathode plasma eontactor. The analysis is obtained that the high voltage （HV） solar array of the CSS collecting electron current can reach 4.5 A, which can be eliminated by emitting an adequate electron current on the CSS. The theoretical analysis and experimental results are addressed, when the minimum xenon flow rate of the hollow cathode is 4.0 sccm, the emission electron current can neutralize the collected electron current, which ensures that the potential of the CSS can be controlled in a range of less than 21 V, satisfied with safety voltage. The results can provide a significant reference value to define a flow rate to the potential controlling programme for CSS.

Interference Management for DS-CDMA Systems through Closed-Loop Power Control, Base Station Assignment, and Beamforming

In this paper, we propose a smart step closed-loop power control (SSPC) algorithm and a base station assignment method based on minimizing the transmitter power (BSA-MTP) technique in a direct sequence-code division multiple access (DS-CDMA) receiver with frequency-selective Rayleigh fading. This receiver consists of three stages. In the first stage, with constrained least mean squared (CLMS) algorithm, the desired users’ signal in an arbitrary path is passed and the inter-path interference (IPI) is reduced in other paths in each RAKE finger. Also in this stage, the multiple access interference (MAI) from other users is reduced. Thus, the matched filter (MF) can use for more reduction of the IPI and MAI in each RAKE finger in the second stage. Also in the third stage, the output signals from the matched filters are combined according to the conventional maximal ratio combining (MRC) principle and then are fed into the decision circuit of the desired user. The simulation results indicate that the SSPC algorithm and the BSA-MTP technique can significantly reduce the network bit error rate (BER) compared to the other methods. Also, we observe that significant savings in total transmit power (TTP) are possible with our methods.

Technical challenges of space solar power stations:Ultra-large-scale space solar array systems and space environmental effects

Space solar power station(SSPS)are important space infrastructure for humans to efficiently utilize solar energy and can effectively reduce the pollution of fossil fuels to the earth’s natural environment.As the energy conversion system of SSPS,solar array is an important unit for the successful service of SSPS.Today,solar arrays represent the standard technology for providing energy for spacecraft,thanks to their high conversion efficiency and reliability/stability in orbit.With the development of solar arrays,many new materials,new photovoltaic devices and new control systems have emerged.Solar arrays are directly exposed to the space environment,and harsh environmental factors can degrade the performance.To ensure the long-term safe inorbit service of SSPS as well as its ultra-large solar array,these new materials,devices,and control systems must operate certification and evaluation that can be used in space applications.In this review,the development history and research progress of SSPS and the corresponding space solar arrays are summarized and discussed,and the space environmental effects of solar arrays are analyzed at multiple levels(materials,devices,and systems).Finally,in response to the current space environmental effects of the ultra-large solar array used in the SSPS,future development trends and challenges are proposed.

Research on PV array reconstruction and Full-cycle maximum power point tracking technology of space solar power station

Space solar power station is an energy system that converts solar energy into electrical energy in the space environment and then transmits it to the space platform or ground using wireless power transmission technology.To improve the power generation and system efficiency of the space solar power station,an adaptive and reconfigurable photovoltaic array with multi-configuration is proposed,which can avoid large attenuation of the output power and efficiency of the photovoltaic array when the photovoltaic modules have a fault occurs or the receive different irradiation intensity.Then,according to the orbit area and light condition of the space solar power station,the operation mode are divided in detail.Furthermore,a novel full-cycle and multi-mode GMPPT(maximum power point tracking)strategy is proposed.Compared to the single mode MPPT,the control strategy has shorter response time,faster convergence and higher tracking accuracy.Through the above research,the output power and photoelectric conversion efficiency of space solar power station can be significantly improved.

Impact of solar cell failure on the performance of solar arrays in space

Space solar power station adopts large-area solar arrays for efficient photovoltaic conversion,making it one of the best solutions to future energy problems.In-orbit failure of solar arrays can affect the service life of spacecraft,thereby it is crucial to comprehend the impact of solar cell failure on the electrical performance of solar arrays and propose appropriate circuit design criteria.The root cause of solar array failure is the degeneration of solar cells.In this paper,power loss caused by an open circuit or short circuit failure of solar cells in pure parallel and series–parallel circuits is described,and it reveals that an open circuit of the cell is more harmful in the pure parallel circuit,while a short circuit in the series–parallel circuit is more detrimental,which causes loss of electrical performance in series and parallel units,respectively.All conclusions have been validated through model calculations and corresponding experiments.The electrical loss is also influenced by the control mode.For the Maximum Power Point Tracking control mode favored by space solar power station,which can significantly increase generated power,application suggestions have been proposed based on the results of cell failure analysis.The research will provide a reference for circuit selection and boundary design for solar arrays,reducing the probability of solar array failure and saving the manufacturing and redeployment costs of space solar power station.