Heliosphere-Geosphere Interactions Using Low Energy Neutral Atom Imaging

Development of the low energy neutral atom (LENA) imager was originally motivated by a need to remotely sense plasma heating in the topside ionosphere, with the goal of greatly enhanced temporal resolution of an otherwise familiar phenomenon. During ground test and calibration, the LENA imager was found to respond to neutral atoms with energies well above its nominal energy range of 10–750 eV, up to at least 3–4 keV, owing to sputtering interactions with its conversion surface. On orbit, LENA has been found to respond to a ubiquitous neutral atom component of the solar wind, to the neutral atoms formed by magnetosheath interactions with the geocorona during periods of high solar wind pressure, and to the interstellar neutral atoms flowing through the heliosphere during the season of maximal relative wind velocity between spacecraft and interstellar medium. LENA imaging has thus emerged as a promising new tool for studying the interplanetary medium and its interaction with the magnetosphere, in addition to the ionospheric heating and outflow that result from this interaction. LENA emissions from the ionosphere consist of a fast component that can be observed at high altitudes, and slower components that evidently create a quasi-trapped extended superthermal exosphere. The more energetic emissions are responsive to solar wind energy inputs on time scales of a few minutes.     

PMA件的过去、现在与未来

<正>通过对PMA件市场的起步、发展和现状的简述,以及对市场背后本质因素的分析,预测了PMA件市场的未来发展趋势。在竞争激烈的飞机部件制造市场中,PMA件正在逐渐打破以往由OEM件垄断的局面,并占有一定的市场份额。在欧洲、亚洲、拉丁美洲和中东地区,PMA     

The Columbus programme : European steps towards the considered development of near-Earth space

The European Space Agency's Columbus Programme is nearing the end of its study phase and European ministers now need to take decisions on proceeding with the development phase. Columbus is directed towards the creation of an autonomous European space capability, and at the same time towards furthering genuine partnership with the USA on the international Space Station. This article reviews the elements which make up the Columbus Programme, and examines their probable developments over the next few years. The need for ESA to ensure coherence among the major European space initiatives is stressed.     

Ring Currents and Internal Plasma Sources

The discovery of terrestrial O⁺ and other heavy ions in magnetospheric hot plasmas, combined with the association of energetic ionospheric outflows with geomagnetic activity, led to the conclusion that increasing geomagnetic activity is responsible for filling the magnetosphere with ionospheric plasma. Recently it has been discovered that a major source of ionospheric heavy ion plasma outflow is responsive to the earliest impact of coronal mass ejecta upon the dayside ionosphere. Thus a large increase in ionospheric outflows begins promptly during the initial phase of geomagnetic storms, and is already present during the main phase development of such storms. We hypothesize that enhancement of the internal source of plasma actually supports the transition from substorm enhancements of aurora to storm-time ring current development in the inner magnetosphere. Other planets known to have ring current-like plasmas also have substantial internal sources of plasma, notably Jupiter and Saturn. One planet having a small magnetosphere, but very little internal source of plasma, is Mercury. Observations suggest that Mercury has substorms, but are ambiguous with regard to the possibility of magnetic storms of the planet. The Messenger mission to Mercury should provide an interesting test of our hypothesis. Mercury should support at most a modest ring current if its internal plasma source is as small as is currently believed. If substantiated, this hypothesis would support a general conclusion that the magnetospheric inflationary response is a characteristic of magnetospheres with substantial internal plasma sources. We quantitatively define this hypothesis and pose it as a problem in comparative magnetospheres.     

Lagrangian analysis of satellite-derived currents: Application to the North Western Mediterranean coastal dynamics

Optimal interpolation methods for improving the reconstruction of coastal dynamics from along-track satellite altimetry measurements have been recently developed over the North Western Mediterranean Sea. Maps of satellite-derived geostrophic current anomalies are generated using these methods, and added to different mean circulation fields in order to obtained absolute geostrophic currents. The resulting fields are then compared to standard AVISO products, and their accuracies are assessed with Lagrangian diagnostics. The trajectories of virtual particle clusters are simulated with a Lagrangian code either with new current fields or with the AVISO ones. The simulated trajectories are then compared to 16 in situ drifter trajectories to evaluate the performance of the different velocity fields. The comparisons show that the new current fields lead to better results than the AVISO one, especially over the shallow continental shelf of the Gulf of Lion. However, despite the use of innovative strategies, some altimetry limitations still persist in the coastal domain, where small scale processes remain sub-sampled by conventional altimetry coverage but will benefit from technological development in the near future. Some of the limitations of the Lagrangian diagnostics presently used are also analyzed, but dedicated studies will be required for future further investigations.     

关于复合材料修理标准化

随着波音787飞机和空客A350XWB等复合材料飞机的投入运营,许多运营商呼吁要实现复合材料培训认证的标准化。由OEM、运营商和管理当局组成的美国汽车工程师学会(SAE)民用飞机复合材料修理委员会(CACRC)自1991年以来     

Optimal Cooperative Sensing using a Team of UAVs

The authors investigates the joint optimal estimation of both the position and velocity of a ground moving target (GMT) using pulse Doppler radars on-board unmanned aerial vehicles (UAVs). The problem of cooperative estimation using a UAV team and the optimization of the team's configuration to achieve optimal GMT position and velocity estimates are addressed. Based on the Cramer-Rao bound, the minimum achievable error variance of the GMT position and velocity estimates is derived. The expression of the minimum achievable estimation error variance for unbiased estimation provided by the Cramer-Rao bound is minimized yielding the optimal configuration of the UAV team. Our solution is complete in that it addresses various GMT tracking scenarios and an arbitrary number of UAVs. Optimal sensor geometries for typical applications are illustrated     

European response to the NASA space station initiative

This article contrasts the political motivations behind the US space station initiative with those underlying the European Space Agency's Long Term Plan. Philip Chandler concludes that European cooperation in NASA's space station programme (SSP) will serve three needs: to buy time; to allow European users to undertake longer, manned experiments; and, to keep the Spacelab teams intact. However, in itself the SSP holds little value for Europe.     

合作与竞争

随着发动机可靠性的提高,发动机制造商(OEM)、航空公司和维修企业(MRO)之间的合作协议越来越多. 先进的技术使得制造商和维修企业的发动机变得更为可靠,与早期的发动机相比,返厂维修的次数明显地减少,而OEM与MRO之间的合作却越来越多.     

Confidence Limits for the Pointing Error of Gimbaled Sensors

The confidence limits for the pointing error of a gimbaled sensor relative to an off-gimbal reference are derived in this paper. The various misalignment angles and errors that lead to discrepancies between the indicated and the actual pointing direction are discussed in detail. A mathematical model is developed from which the statistics of the pointing error are derived. The confidence limits are obtained for a variety of cases.