Enhanced resolution in simple radars

Many simple radars use fact-risetime pulses, but wide bandwidth does not translate into corresponding high resolution since the spectrum is far from flat. A scheme for enhancing down- and cross-range resolution of multiple targets through a two-step partial equalization of the spectrum is illustrated by detailed computer simulation, with emphasis on the tradeoffs between resolution and signal-to-noise ratios. Three examples are treated: two equal scattering centers, two unequal scattering centers, and compound target     

轨道测量差分精确定轨方法

航天器轨道精确测定重要环节之一是有效地消除观测系统误差,在轨道测量数据处理时,一类是利用轨道约束自校准技术来估算和校准系统误差,另一类可以应用测元差分方法来消除系统误差(例如导航卫星测定目标)。本文提出一种新的差分技术,即利用观测数据时序差分消除系统误差技术,并推导相应确定航天器轨道的公式。     

Ion beam produced plasma waves observed by the δn/n plasma wave receiver during the porcupine experiment

The Porcupine sounding rocket consisted of a central instrumented payload with 4 smaller payloads ejected in the radial direction. One of the smaller payloads contained a xenon ion gun which directed a 200eV Xe+ ion beam roughly perpendicular to the magnetic field. During the ion gun exercises a variety of plasma waves were observed by the δn/n experiment on the central spacecraft. For small separations betwen the ion gun and the plasma wave receivers, intense and very narrow band emissions were observed just above harmonics of the hydrogen gyrofrequency extending from n=1 to at least n=11 and perhaps to much higher harmonics. Additional structure at the helium gyrofrequency was also observed and the width of each spectral line was the order of the oxygen gyrofrequency. The fastest growing modes were at n=5 or 6. For larger separations between the ion gun and plasma wave receiver, band limited emissions were observed between the NO+ and O+ lower hybrid frequencies. The intense ion cyclotron harmonic waves observed for short separations are very similar to plasma waves observed at high altitudes in ion conics by the S3-3 satellite. In those examples, natural ion beams, which were nearly perpendicular to the magnetic field, produced plasma waves between harmonics of the hydrogen gyrofrequency and the most intense waves occurred between n=3 and n=7. Hence the ion beam experiment is directly applicable to understanding ion beams within the magnetosphere.     

JTIDS Relative Navigation with Measurement Sharing: Design and Performance

Alternative approaches for conducting relative navigation (relnav) using the joint tactical information distribution system (JTIDS) communication network are presented. The design and performance of the current JTIDS relnav with estimate sharing are discussed, including its shortcomings. We offer first a conceptually simpler alternate design that provides more accurate relnav between any pair of members, provided they have time to maneuver. A second alternative design includes the features of the first plus measurement sharing by designated primary members. It has even better performance including faster more accurate relnav fixes and relaxed maneuvering requirements. Simulation results are presented showing the superior performance of the new designs. The advantages and disadvantages of relnav with measurement sharing compared with relnav with estimate sharing are summarized.     

Artificial particle and wave stimulation in the trigger experiment

The Trigger experiment was designed to test the response of the auroral ionosphere to an impulsive release of a hot, dense plasma. It consisted of a sounding rocket payload divided into two parts, an instrumented diagnostic section and a cesium doped high explosive canister. When the two sections were separated by about 1 km, but close to the same magnetic field line, the cesium high explosive was ignited and the plasma around the payload was observed to increase briefly by a factor of 4 in density and a factor of 2 in temperature.A variety of particle and field phenomena occurred in rapid succession after the cesium release. A drastic increase in the field aligned charged particle flux was observed over the approximate energy range 10 eV to more than 300 keV, starting about 150 ms after the release and lasting about 1 second. There is also evidence of a second particle burst, starting one second after the release and lasting for tens of seconds. A transient electric field pulse of 200 mV/m appeared just before the particle flux increase began. Additional effects include electrostatic waves associated with the cesium cloud boundary. The field aligned currents associated with the electric field pulse and cloud conductivity gradient may be responsible for the observed electron acceleration in a manner similar to the electrodynamic origin of auroral arcs.     

Analysis of electromagnetic and electrostatic effects of particle impacts on spacecraft

Particle impacts on spacecraft can cause considerable damage, even leading to complete failure. A theory for the resulting vehicle potential changes and the electromagnetic radiation from impact-induced plasma has been published by Close et al. (2010). Here we compare this theory to impacts registered by the Radio and Plasma Wave Science instrumentation on the Cassini spacecraft. We study both low-velocity (16 km/s) large particles (2.6 μm radius) detected in Saturn’s rings and high-velocity (450 km/s) small particles (1 nm radius) in the solar wind. The agreement with the theory is quite good. We also apply these results to earth orbit and conclude that both Electrostatic Discharge and Electromagnetic Pulse radiation are likely and could lead to spacecraft failure.     

ATLAS2K--以信号描述为核心的可扩展的可移植的自动测试语言

详细介绍了以信号描述为核心的新一代测试语言ATLAS2K的特点及层模型，并提出了ATLAS2K在自动测试设备ATE中的应用。     

直升机主最低设备清单的确定

为提高民用直升机的利用率和经济性,可编制主最低设备清单(MMEL).根据AC313型机MMEL项目的经验,总结出民用直升机MMEL的确定逻辑决断程序,并探讨MMEL在军用直升机上的应用前景.     

Substrate limitation for methanogenesis in hypersaline environments

Motivated by the increasingly abundant evidence for hypersaline environments on Mars and reports of methane in its atmosphere, we examined methanogenesis in hypersaline ponds in Baja California Sur, Mexico, and in northern California, USA. Methane-rich bubbles trapped within or below gypsum/halite crusts have δ13C values near -40‰. Methane with these relatively high isotopic values would typically be considered thermogenic; however, incubations of crust samples resulted in the biological production of methane with similar isotopic composition. A series of measurements aimed at understanding the isotopic composition of methane in hypersaline systems was therefore undertaken. Methane production rates, as well as the concentrations and isotopic composition of the particulate organic carbon (POC), were measured. Methane production was highest from microbial communities living within gypsum crusts, whereas POC content at gypsum/halite sites was low, generally less than 1% of the total mass. The isotopic composition of the POC ranged from -26‰ to -10‰. To determine the substrates used by the methanogens, 13C-labeled methylamines, methanol, acetate, and bicarbonate were added to individual incubation vials, and the methane produced was monitored for 13C content. The main substrates used by the methanogens were the noncompetitive substrates, the methylamines, and methanol. When unlabeled trimethylamine (TMA) was added to incubating gypsum/halite crusts in increasing concentrations, the isotopic composition of the methane produced became progressively lower; the lowest methane δ13C values occurred when the most TMA was added (1000 μM final concentration). This decrease in the isotopic composition of the methane produced with increasing TMA concentrations, along with the high in situ methane δ13C values, suggests that the methanogens within the crusts are operating at low substrate concentrations. It appears that substrate limitation is decreasing isotopic fractionation during methanogenesis, which results in these abnormally high biogenic methane δ13C values.