A Numerical Model of the SEIS Leveling System Transfer Matrix and Resonances: Application to SEIS Rotational Seismology and Dynamic Ground Interaction

Both sensors of the SEIS instrument (VBBs and SPs) are mounted on the mechanical leveling system (LVL), which has to ensure a level placement on the Martian ground under currently unknown local conditions, and provide the mechanical coupling of the seismometers to the ground. We developed a simplified analytical model of the LVL structure in order to reproduce its mechanical behavior by predicting its resonances and transfer function. This model is implemented numerically and allows to estimate the effects of the LVL on the data recorded by the VBBs and SPs on Mars. The model is validated through comparison with the horizontal resonances (between 35 and 50 Hz) observed in laboratory measurements. These modes prove to be highly dependent of the ground horizontal stiffness and torque. For this reason, an inversion study is performed and the results are compared with some experimental measurements of the LVL feet’s penetration in a martian regolith analog. This comparison shows that the analytical model can be used to estimate the elastic ground properties of the InSight landing site. Another application consists in modeling the 6 sensors on the LVL at their real positions, also considering their sensitivity axes, to study the performances of the global SEIS instrument in translation and rotation. It is found that the high frequency ground rotation can be measured by SEIS and, when compared to the ground acceleration, can provide ways to estimate the phase velocity of the seismic surface waves at shallow depths. Finally, synthetic data from the active seismic experiment made during the HP³ penetration and SEIS rotation noise are compared and used for an inversion of the Rayleigh phase velocity. This confirms the perspectives for rotational seismology with SEIS which will be developed with the SEIS data acquired during the commissioning phase after landing.     

Geomagnetic activity indicators for geomagnetically induced current studies in South Africa

Intense geomagnetic activity is known to give rise to large geomagnetically induced currents (GICs) in power transmission grids. Recordings of geomagnetic activity provide an efficient and economical way for power transmission system operators to assess GIC risks in retrospective studies. This study investigates local geomagnetic indicators (i.e., hourly peak value, hourly range indicator and hourly standard deviation) in order to determine their usefulness for understanding the drivers of GICs in the South African power network. Results show that the GICs have a higher correlation with the geomagnetic indicators derived from the East–West component of the horizontal geomagnetic field, than the indicators derived from the North–South component of the horizontal field. This directional dependence corresponds very well with the North–South orientation of the power lines feeding the power transformers at the South African Grassridge electrical substation GIC site. It therefore follows that, the geoelectric field driving the GICs at Grassridge is North–South oriented. Further, it is shown that the hourly range indicator has a higher correlation with the GICs than the hourly standard deviation for this particular network configuration.     

Space solar arrays and concentrators

This paper presents some research activities conducted at the Centre Spatial de Liege (CSL) in the field of space solar arrays and concentration.With the new generation of high efficiency solar cells, solar concentration brings new insights for future high power spacecrafts. A trade-off study is presented in this paper. Two different trough concentrators, and a linear Fresnel lens concentrator are compared to rigid arrays. Thermal and optical behaviors are included in the analysis.Several technical aspects are discussed:

• Off-pointing with concentrators induces collection loss and illumination non uniformity, reducing the PV efficiency.

• Concentrator deployment increases the mission risk.

• Reflective trough concentrators are attractive and already proven. Coating is made of VDA (Aluminum). A comprehensive analysis of PV conversion increase with protected silver is presented.

• Solar concentration increases the heat load on solar cells, while the conversion efficiency is significantly decreasing at warm temperatures.

To conclude, this paper will point out the new trends and the key factors to be addressed for the next generation of solar generators.     

Molecular Hydrogen

Observations of H₂ line emission in galactic and extragalactic environments obtained with the Infrared Space Observatory (ISO) are reviewed. The diagnostic capability of H₂ observations is illustrated. We discuss what one has learned about such diverse astrophysical sources as photon-dominated regions, shocks, young stellar objects, planetary nebulae and starburst galaxies from ISO observations of H₂ emission. In this context, we emphasise use of measured H₂ line intensities to infer important physical quantities such as the gas temperature, gas density and radiation field and we discuss the different possible excitation mechanisms of H₂. We also briefly consider future prospects for observation of H₂ from space and from the ground. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands, and the United Kingdom), and with the participation of ISAS and NASA.     

Microscope Instrument Development,Lessons for GOCE

Two space missions are presently under development with payload based on ultra-sensitive electrostatic accelerometers. The GOCE mission takes advantage of a three axis gradiometer accommodated in a very stable thermal case on board a drag-free satellite orbiting at a very low altitude of 250 km. This ESA mission will perform the very highly accurate mapping of the Earth gravity field with a geographical resolution of 100 km. The MICROSCOPE mission is devoted to the test of the “Universality of free fall” in view of the verification of the Einstein Equivalence Principle (EP) and of the search of a new interaction. The MICROSCOPE instrument is composed of two pairs of differential electrostatic accelerometers and the accelerometer proof-masses are the bodies of the EP test. The satellite is also a drag-free satellite exhibiting a fine attitude control and in a certain way, each differential accelerometer is a one axis gradiometer with an arm of quite null length. The development of this instrument much interests the definition and the evaluation of the sensor cores of the gradiometer. The in flight calibration process of both instruments is also very similar. Lessons form these parallel developments are presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

Paleomagnetic Records of Meteorites and Early Planetesimal Differentiation

The large-scale compositional structures of planets are primarily established during early global differentiation. Advances in analytical geochemistry, the increasing diversity of extraterrestrial samples, and new paleomagnetic data are driving major changes in our understanding of the nature and timing of these early melting processes. In particular, paleomagnetic studies of chondritic and small-body achondritic meteorites have revealed a diversity of magnetic field records. New, more sensitive and highly automated paleomagnetic instrumentation and an improved understanding of meteorite magnetic properties and the effects of shock, weathering, and other secondary processes are permitting primary and secondary magnetization components to be distinguished with increasing confidence. New constraints on the post-accretional histories of meteorite parent bodies now suggest that, contrary to early expectations, few if any meteorites have been definitively shown to retain records of early solar and protoplanetary nebula magnetic fields. However, recent studies of pristine samples coupled with new theoretical insights into the possibility of dynamo generation on small bodies indicate that some meteorites retain records of internally generated fields. These results indicate that some planetesimals formed metallic cores and early dynamos within just a few million years of solar system formation.     

Advancing Earth observation from space: A global challenge

Global Earth observation goes well beyond taking pictures of the Earth from space. Earth observation aims to identify and characterize planetary-scale processes that occur in the Earth interior or the world's oceans, at the Earth's surface or within the global atmosphere, on the basis of weak signals that may be detected in space. This is a truly challenging task that requires the dedicated efforts of professionals and firm public support commitments. The article reveals the scope of global Earth observation, highlights the technical and managerial challenges involved in undertaking it and discusses ways of making it more effective. Competent international cooperation and cost-sharing arrangements are essential for the ultimate success of existing and future activities in this field.     

Multi-station observation of ionospheric irregularities over South Africa during strong geomagnetic storms

This paper presents results pertaining to the response of the mid-latitude ionosphere to strong geomagnetic storms that occurred from 31 March to 02 April 2001 and 07–09 September 2002. The results are based on (i) Global Positioning Systems (GPSs) derived total electron content (TEC) variations accompanying the storm, (ii) ionosonde measurements of the ionospheric electrodynamic response towards the storms and (iii) effect of storm induced travelling ionospheric disturbances (TIDs) on GPS derived TEC. Ionospheric data comprising of ionospheric TEC obtained from GPS measurements, ionograms, solar wind data obtained from Advanced Composition Explorer (ACE) and magnetic data from ground based magnetometers were used in this study. Storm induced features in vertical TEC (VTEC) have been obtained and compared with the mean VTEC of quiet days. The response of the mid-latitude ionosphere during the two storm periods examined may be characterised in terms of increased or decreased level of VTEC, wave-like structures in VTEC perturbation and sudden enhancement in hmF2 and h′F. The study reveals both positive and negative ionospheric storm effects on the ionosphere over South Africa during the two strong storm conditions. These ionospheric features have been mainly attributed to the travelling ionospheric disturbances (TIDs) as the driving mechanism for the irregularities causing the perturbations observed. TEC perturbations due to the irregularities encountered by the satellites were observed on satellites with pseudo random numbers (PRNs) 15, 17, 18 and 23 between 17:00 and 23:00 UT on 07 September 2002.     

普惠加拿大公司为A400M提供发动机

空客军用飞机公司即将启动A400M计划,可供选择的发动机有两种,一是欧洲国际涡桨发动机公司将要研制的TP400—D6涡桨发动机,另一种是普惠加拿大公司将要研制的PW180发动机。PW180将以PW800涡扇发动机为基础研制,究竟选用哪种发动机,近期将做出决定     

Automatic Carbon Tape Laying for Structural Composite Parts

The technology of automatic carbon tape laying for structural composite parts is introduced. The most effective form of automatic carbon tape laying technology is presented with emphasis.