In this article, we design an end-to-end free-space optical (FSO) communication coding scheme for deep space exploration. Take the Mars exploration as an example, we first establish the synodic ...period FSO channel model by taking into account the solar scintillation, and derive the corresponding upper bound of bit error rate (BER) for L-ary pulse position modulation (LPPM). Then, we propose a staircase code-ordered statistics decoder (SC-OSD) algorithm for staircase low density parity check (LDPC) codes under synodic period FSO channel, and derive the probability density function (PDF) and Gaussian approximation of the ordered statistics of the SC-OSD algorithm, which provide a guideline to derive a lower bound of block error rate (BLER) and reduce the decoding complexity of SC-OSD. Furthermore, we propose a soft OSD-sliding window decoding (SOSD-SWD) algorithm for staircase LDPC codes under scintillation states to address the error floor problem in conventional SWD decoder. Simulation results validate that the proposed SOSD-SWD algorithm can achieve much lower BER than the related algorithms in all scintillation conditions, and shed light to tradeoff the achievable BER and complexities under different scintillation conditions.
CCDLAB was originally developed as a FITS image data reducer and viewer, and development was then continued to provide ground support for the development of the UVIT detector system provided by the ...Canadian Space Agency to the Indian Space Research Organization's ASTROSAT satellite and UVIT telescopes. After the launch of ASTROSAT and during UVIT's first-light and PV phase starting in 2015 December, necessity required the development of a data pipeline to produce scientific images out of the Level 1 format data produced for UVIT by ISRO. Given the previous development of CCDLAB for UVIT ground support, the author provided a pipeline for the new Level 1 format data to be run through CCDLAB with the additional satellite-dependent reduction operations required to produce scientific data. Features of the pipeline are discussed with focus on the relevant data-reduction challenges intrinsic to UVIT data.
We completely characterize the validity of the inequality $\| u \|_{Y(\mathbb R)} \leq C \| \nabla^{m} u \|_{X(\mathbb R)}$, where X and Y are rearrangement-invariant spaces, by reducing it to a ...considerably simpler one-dimensional inequality. Furthermore, we fully describe the optimal rearrangement-invariant space on either side of the inequality when the space on the other side is fixed. We also solve the same problem within the environment in which the competing spaces are Orlicz spaces. A variety of examples involving customary function spaces suitable for applications is also provided.
An increasing direct participation of private companies in the space sector started in the early 2000s and became known as the New Space movement. Despite the media buzz from this movement and the ...corresponding increased interest in space, most analyses focus on a specific industry such as launch systems or satellites, producing limited insights. History shows that disruptive innovation usually comes from adjacent industries that threaten incumbent companies and change several industries at once (microelectronics, the internet, and streaming services are some of the examples). Industry leaders of the past have become irrelevant not by their direct competitors but because of new products and services coming from other industries that enveloped the old ones. Can the same phenomenon happen in the space sector? To answer that, this research offers a multi-industry analysis of the space sector's contemporary business environment by studying it through an ecosystem approach, producing a first draft of the space ecosystem based on a comprehensive literature review. It opens discussion on upcoming trends and uncertainties regarding potential transformations in the space sector, comprehending space launch vehicles, satellites, commercial space applications, and multi-industry reconfigurations. From those, a scenario planning process is conducted producing four possible futures for the space ecosystem in a 5- to 10-year timeframe. Those scenarios are described and discussed, contributing to the strategic perspective of both academics and practitioners and also of policy makers and executives.
The He ii transverse proximity effect-enhanced He ii transmission in a background sightline caused by the ionizing radiation of a foreground quasar-offers a unique opportunity to probe the morphology ...of quasar-driven He ii reionization. We conduct a comprehensive spectroscopic survey to find quasars in the foreground of 22 background quasar sightlines with Hubble Space Telescope/COS He ii transmission spectra. With our two-tiered survey strategy, consisting of a deep pencil-beam survey and a shallow wide-field survey, we discover 131 new quasars, which we complement with known SDSS/BOSS quasars in our fields. Using a restricted sample of 66 foreground quasars with inferred He ii photoionization rates greater than the expected UV background at these redshifts ( ) we perform the first statistical analysis of the He ii transverse proximity effect. Our results show qualitative evidence for a large object-to-object variance: among the four foreground quasars with the highest only one (previously known) quasar is associated with a significant He ii transmission spike. We perform a stacking analysis to average down these fluctuations, and detect an excess in the average He ii transmission near the foreground quasars at significance. This statistical evidence for the transverse proximity effect is corroborated by a clear dependence of the signal strength on . Our detection places a purely geometrical lower limit on the quasar lifetime of . Improved modeling would additionally constrain quasar obscuration and the mean free path of He ii-ionizing photons.
The central nervous system is lined by meninges, classically known as dura, arachnoid, and pia mater. We show the existence of a fourth meningeal layer that compartmentalizes the subarachnoid space ...in the mouse and human brain, designated the subarachnoid lymphatic-like membrane (SLYM). SLYM is morpho- and immunophenotypically similar to the mesothelial membrane lining of peripheral organs and body cavities, and it encases blood vessels and harbors immune cells. Functionally, the close apposition of SLYM with the endothelial lining of the meningeal venous sinus permits direct exchange of small solutes between cerebrospinal fluid and venous blood, thus representing the mouse equivalent of the arachnoid granulations. The functional characterization of SLYM provides fundamental insights into brain immune barriers and fluid transport.
The purpose of this paper is to study the development of space-age aesthetics culture and arts in seven decades since 1950s. The first known use of “space-age” was in 1946, and was defined as “of, ...relating to, or befitting the age of space exploration.” A more popular definition for the “space age” is “The space age is the time period in human history related to the space race, space exploration, and space technology. Most people say this started when Sputnik 1 was launched in 1957, and continues to today. This has influenced culture such as in movies, television, music, art, and architecture.” Culture, in the anthropology, is the patterns of behaviour and thinking that people living in social groups learn, create, and share. Culture distinguishes one human group from others. It also distinguishes humans from other animals. A people's culture includes their beliefs, rules of behaviour, language, rituals, art, technology, styles of dress, ways of producing and cooking food, religion, and political and economic systems. Therefore, the space-age art is one of the major elements of the space-age culture of human beings. On the other hand, the space exploration has significant inspiration and influence on the aesthetics art. In particular, the following aspects shall be studied in this paper: architecture and exhibition craftworks.
•The space-age architecture and exhibition craftworks were investigated.•Five space-age architecture shapes investigated are disc, rocket, tower, spherical and combined.•Three space-age installation craftworks studied are sky waves, embroidery, planet models, etc.•Many space-age architectures are destroyed due to many reasons.•Hopefully the young generations can be inspired to carry forward these precious heritages.
This paper proposes a simplified space vector modulation (SVM) scheme for multilevel converters. Compared with earlier SVM methods, the proposed scheme simplifies the detection of the nearest three ...vectors and the generation of switching sequences, and therefore is computationally more efficient. Particularly, for the first time, the proposed scheme achieves the same easy implementation as phase-voltage modulation techniques. Another superior characteristic of the proposed scheme over earlier methods is its potential for multiphase multilevel applications. The proposed scheme also offers the following significant advantages: 1) independence of the level number of the converter; 2) more degrees of freedom, i.e., redundant switching sequences and adjustable duty cycles, to optimize the switching patterns; and 3) no need for lookup tables or coordinate transformations. These advantages make the proposed scheme well suited to large level-number applications, such as modular multilevel converters and high voltage direct current systems. Simulation and experimental results verify this new concept.
In tenuous plasma the floating potential of sunlit spacecraft reaches tens of volts, positive. The corresponding field disturbs measurements of the ambient plasma by electron and ion sensors and can ...reduce micro-channel plate lifetime in electron detectors owing to large fluxes of attracted photoelectrons. Also the accuracy of electric field measurements may suffer from a high spacecraft potential. The Active Spacecraft Potential Control (ASPOC) neutralizes the spacecraft potential by releasing positive charge produced by indium ion emitters. The method has been successfully applied on other spacecraft such as Cluster and Double Star. Two ASPOC units are present on each spacecraft. Each unit contains four ion emitters, whereby one emitter per instrument is operated at a time. ASPOC for the Magnetospheric Multiscale (MMS) mission includes new developments in the design of the emitters and the electronics. New features include the use of capillaries instead of needles, new materials for the emitters and their internal thermal insulators, an extended voltage and current range of the electronics, both for ion emission and heating purposes, and a more capable control software. This enables lower spacecraft potentials, higher reliability, and a more uniform potential structure in the spacecraft’s sheath compared to previous missions. Results from on-ground testing demonstrate compliance with requirements. Model calculations confirm the findings from previous applications that the plasma measurements will not be affected by the beam’s space charge. Finally, the various operating modes to adapt to changing boundary conditions are described along with the main data products.
The Energetic Particle Detector (EPD) Investigation is one of 5 fields-and-particles investigations on the Magnetospheric Multiscale (MMS) mission. MMS comprises 4 spacecraft flying in close ...formation in highly elliptical, near-Earth-equatorial orbits targeting understanding of the fundamental physics of the important physical process called magnetic reconnection using Earth’s magnetosphere as a plasma laboratory. EPD comprises two sensor types, the Energetic Ion Spectrometer (EIS) with one instrument on each of the 4 spacecraft, and the Fly’s Eye Energetic Particle Spectrometer (FEEPS) with 2 instruments on each of the 4 spacecraft. EIS measures energetic ion energy, angle and elemental compositional distributions from a required low energy limit of 20 keV for protons and 45 keV for oxygen ions, up to >0.5 MeV (with capabilities to measure up to >1 MeV). FEEPS measures instantaneous all sky images of energetic electrons from 25 keV to >0.5 MeV, and also measures total ion energy distributions from 45 keV to >0.5 MeV to be used in conjunction with EIS to measure all sky ion distributions. In this report we describe the EPD investigation and the details of the EIS sensor. Specifically we describe EPD-level science objectives, the science and measurement requirements, and the challenges that the EPD team had in meeting these requirements. Here we also describe the design and operation of the EIS instruments, their calibrated performances, and the EIS in-flight and ground operations. Blake et al. (The Flys Eye Energetic Particle Spectrometer (FEEPS) contribution to the Energetic Particle Detector (EPD) investigation of the Magnetospheric Magnetoscale (MMS) Mission,
this issue
) describe the design and operation of the FEEPS instruments, their calibrated performances, and the FEEPS in-flight and ground operations. The MMS spacecraft will launch in early 2015, and over its 2-year mission will provide comprehensive measurements of magnetic reconnection at Earth’s magnetopause during the 18 months that comprise orbital phase 1, and magnetic reconnection within Earth’s magnetotail during the about 6 months that comprise orbital phase 2.
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