VII: CLOSING SESSION: GOCE: ESA's First Earth Explorer Core Mission

This paper introduces the first ESA Core Earth Explorer mission, GOCE, in the context of ESA's Living Planet programme. GOCE will measure highly accurate, high spatial resolution differential accelerations in three dimensions along a well characterised orbit: the mission is planned for launch in early 2006. The mission objectives are to obtain gravity gradient data such that new global and regional models of the static Earth's gravity field and of the geoid can be deduced at length scales down to 100 km. These products will have broad application in the fields of geodesy, oceanography, solid-earth physics and glaciology. This revised version was published online in August 2006 with corrections to the Cover Date.     

Galileo: the way forward: implementing the strategy

In line with the conclusions of the previous articles in this dossier, the following scheme to develop a European GNSS-2 constellation (Galileo) is recommended. It is envisaged that the EU Council of Ministers, and perhaps the European Council, will take decisions on the main issues by the end of June 1999. The European Parliament also has a crucial role to play. Within this framework, the meeting of the ESA Council in May should provide clarification of the role ESA can play in the technical, financial and organisational development of Galileo.     

VI: FUTURE CONCEPTS: Attitude and Drag Control: An Application to the GOCE Satellite

The Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite, currently planned to he launched in the course of 2006, will require a precise drag compensation and a fine attitude control along the Local Orbiting Reference Frame (LORF) of a polar Sun-synchronous low orbit, allowing the Earth gravity field to be recovered with unprecedented accuracy by post-processing the scientific telemetry. To this aim, the spectral density of the spacecraft linear and angular accelerations must be limited below 0.025 respectively, in the frequency range from 5 mHz to 0.1 Hz, the gradiometer measurement bandwidth. In the same range, the orientation errors of the spacecraft in the LORF and of the LORF in the inertial frame must be kept below 10 . The Drag-Free Mode, encharged of drag-free and attitude control (DFAC) during measurement phases, determines the spacecraft state vector using a very precise gradiometer, one large Field-of-View Star Tracker and a Satellite-to-Satellite Tracking Instrument. Force and torque commands are actuated by two assemblies of thrusters: a single ion-thruster acting along the orbital direction, a set of eight micro-thrusters acting along the other five degrees of freedom. To cover every mission scenario, other control modes have been studied and designed: the Coarse Pointing Mode dedicated to rate damping and Sun acquisition, the Fine Pointing Mode handling the transition to Drag-Free Mode and the Ultimate Safe Mode, a survival operative mode to improve mission reliability. Results presented in this paper give a positive perspective on the solidity of the current DFAC design. This revised version was published online in August 2006 with corrections to the Cover Date.     

Wave dynamics in the thermosphere: I: Tidal motion

The atmospheric tides, their transmission and excitation in the thermosphere, are discussed in reviewing various investigations in this field. We are still fairly ignorant on the subjects and facing various unsolved problems although there is an established link between the theory and the observation in the dynamo region, the lower boundary of the thermosphere. As to the middle and upper thermosphere the observed data are scanty and only those obtained by satellite drag are available; the theoretical approach is very complicated because of viscosity, thermal conduction, hydromagnetic forces and non-linearity, all of which are effective above certain heights. Moreover, the thermosphere couples mainly with the lower atmosphere, this coupling having been considered only in a very simplified way. Another coupling is between thermal excitation and the resultant motion, the coupling of which has never been considered; thermal excitation has been discussed on a given input. International cooperation in the observations is of vital importance for future studies. New developments of observation techniques are desirable.     

POWOW: power without wires: a SEP concept for space exploration

Electric propulsion has emerged as a cost-effective solution to a wide range of satellite applications. Deep Space 1 successfully demonstrated electric propulsion as the primary propulsion source for a satellite. The POWOW concept is a solar-electric propelled spacecraft capable of significant cargo and short trip times for traveling to Mars. It would enter aerosynchronous orbit and from there, beam power to surface installations via lasers. The concept has been developed with industrial partner expertise in high efficiency solar cells, advanced concentrator modules, innovative arrays, and high power electric propulsion systems. The latest version of the spacecraft, the technologies used, and trip times to Mars are presented. The POWOW spacecraft is a general purpose solar electric propulsion system that uses new technologies that are directly applicable to commercial and government spacecraft with power levels ranging from a LEO power level of 4 kW up to GEO spacecraft about 1 MW. The system is modular, expandable, and amenable to learning curve cost projection methods     

Galileo: financial aspects

Given the present policy of the US to provide the basic GPS signal free of charge, it would be illusory to imagine that Galileo could be developed and provided exclusively by the private sector.     

Galileo: organisational framework

The Commission's Communication of January 1998 summarised the roles and responsibilities which should be included in a GNSS organisational framework. The GNSS-2 Forum has further refined the work on these questions.     

明星:美的搭配

<正>5月26日,为期12天的第66届戛纳电影节完美落幕,各项牵动人心的大奖一一揭晓。本届戛纳电影节司仪"天使爱美丽"奥黛丽·塔图(Audrey Tautou)佩戴CHAUMET尚美巴黎白金镶嵌摩根石耳环主持颁奖典礼。奥黛丽·塔图当天选择一袭红色搭配粉色肩带礼服,搭配晶莹剔透的摩根石耳环,将甜美与精灵气质显露无疑。凭借在电影《过往(Le Passe)》中的出色表演     

奥地利哈尔斯塔特小记

时光倒流约两个世纪,德国著名科学家和探险家亚历山夫.冯.洪堡,来到这个峰峦环抱的湖区,面对旖旎的湖光山色,留下也这是"世界上最美丽的湖泊"的赞叹,引发了后人飞越的神思和向往。     

III: OCEAN CIRCULATION: Global Ocean Data Assimilation and Geoid Measurements

Parts of geodesy and physical oceanography are about to mature into a single modeling problem involving the simultaneous estimation of the marine geoid and the general circulation. Both fields will benefit. To this end, we present an ocean state estimation (data assimilation) framework which is designed to obtain a dynamically consistent picture of the changing ocean circulation by combining global ocean data sets of arbitrary type with a general circulation model (GCM). The impact of geoid measurements on such estimates of the ocean circulation are numerous. For the mean circulation, a precise geoid describes the reference frame for dynamical signals in altimetric sea surface height observations. For the time-varying ocean signal, changing geoid information might be a valuable new information about correcting the changing flow field on time scales from a few month to a year, but the quantitative utility of such information has not yet been demonstrated. For a consistent estimate, some knowledge of the prior error covariances of all data fields is required. The final result must be consistent with prior error estimates for the data. State estimation is thus one of the few quantitative consistency checks for new geoid measurements anticipated from forthcoming space missions. Practical quantitative methods will yield a best possible estimate of the dynamical sea surface which, when combined with satellite altimetric surfaces, will produce a best-estimate marine geoid. The anticipated accuracy and precision of such estimates raises some novel modeling error issues which have not conventionally been of concern (the Boussinesq approximation, self-attraction and loading). Model skill at very high frequencies is a major concern because of the need to de-alias the data obtained by the inevitable oceanic temporal undersampling dictated by realistic satellite orbit configurations. This revised version was published online in August 2006 with corrections to the Cover Date.     

World airport traffic growth continues: : Asia/Pacific leads again

October 2000 results from 650 airports worldwide show passenger traffic rising 4% and cargo 2% with movements down 1% compared with October 1999. From January to October 2000, passenger traffic was up to 6%, cargo 7% and movements 1%.     

FIP Fractionation: Theory

In this review, the main models of ion-neutral frationation leading to an enhancement of the low FIP to high FIP abundance ratio in the corona or in the solar wind, are presented. Models based on diffusion parallel to the magnetic field are discussed; they are highly dependent on the boundary conditions. The magnetic field, that naturally separates ions from neutrals moving perpendicular to the field lines direction, when the ion-neutral frequency becomes lower than the ion gyrofrequency, is expected to play an active role in the ion-neutral separation. It is then suggested that ion-neutral fractionation is linked to the formation of the solar chromosphere, i.e. in magnetic flux-tubes at a temperature between 4000 and 6000 K. This revised version was published online in June 2006 with corrections to the Cover Date.     

Correction to: Mission to Planet Earth: The First Two Billion Years

Space Science Reviews - The Ionospheric Connection Explorer (ICON) mission makes measurements in near-Earth space that provide knowledge of the state of the ionosphere. From the vantage of...     

Correction to: Water in the Earth’s Interior: Distribution and Origin

Space Science Reviews - Correction to: Space Sci Rev DOI This article has been corrected. Figure 3 was initially published with erroneous axis titles in Fig. 3B and 3D where the $x$ axis should be...