Determination of the Equivalence Principle Violation Signal for the MICROSCOPE Space Mission: Optimization of the Signal Processing

The MICROSCOPE space mission aims at testing the Equivalence Principle (EP) with an accuracy of 10^?15. The test is based on the precise measurement delivered by a differential electrostatic accelerometer on-board a drag-free microsatellite which includes two cylindrical test masses submitted to the same gravitational field and made of different materials. The experiment consists in testing the equality of the electrostatic acceleration applied to the masses to maintain them relatively motionless at a well-known frequency. This high precision experiment is compatible with only very little perturbations. However, aliasing arises from the finite time span of the measurement, and is amplified by measurement losses. These effects perturb the measurement analysis. Numerical simulations have been run to estimate the contribution of a perturbation at any frequency on the EP violation frequency and to test its compatibility with the mission specifications. Moreover, different data analysis procedures have been considered to select the one minimizing these effects taking into account the uncertainty about the frequencies of the implicated signals.     

Classification of Geostationary Objects

This paper lists all geostationary and near-geostationary objects contained in ESA's DISCOS database.     

Qualitative Spatial Reasoning for Topological Map Learning

Abstract

In this paper we investigate the application of qualitative spatial reasoning methods for learning the topological map of an unknown environment. We develop a topological mapping framework that achieves robustness against ambiguity in the available information by tracking all possible graph hypotheses simultaneously. We then exploit spatial reasoning to reduce the space of possible hypotheses. The considered constraints are qualitative direction information and the assumption that the map is planar. We investigate the effects of absolute and relative direction information using two different spatial calculi and combine the approach with a real mapping system based on Voronoi graphs.     

Book reviews

The general significance of streamers of the solar corona is discussed in the frame of our knowledge of the solar wind phenomenon and the large-scale solar magnetic structure. Thermodynamical and geometric parameters of streamers observed and measured at total solar eclipses are reviewed. Both the low part (in the form of a helmet with a cusp) and the external part (in the form of a stalk extended at many solar radii) are considered. The modelling of streamers starts with the analysis of effects produced by the solar wind flow on a magnetic structure. Facts and arguments are presented in favor of a model with a current sheet and reconnection processes going on along the axis of the streamer, especially in the non-collisional part of the radially extended streamer. Further development of the Pneuman and Kopp (1971) model is discussed, including difficulties occurring in the interpretation of a stationary solution. An empirical model satisfying observations is presented. Future researchs on streamers were discussed with emphasis on observations to be done with the space-borne coronagraphs on the SOHO spacecraft.     

NeQuick 2 and IRI Plas VTEC predictions for low latitude and South American sector

Using vertical total electron content (VTEC) measurements obtained from GPS satellite signals the capability of the NeQuick 2 and IRI Plas models to predict VTEC over the low latitude and South American sector is analyzed. In the present work both models were used to calculate VTEC up to the height of GPS satellites. Also, comparisons between the performance of IRI Plas and IRI 2007 have been done. The data correspond to June solstice and September equinox 1999 (high solar activity) and they were obtained at nine stations. The considered latitude range extends from 18.4°N to ?64.7°N and the longitude ranges from 281.3°E to 295.9°E in the South American sector. The greatest discrepancies among model predictions and the measured VTEC are obtained at low latitudes stations placed in the equatorial anomaly region. Underestimations as strong as 40?TECU [1?TECU?=?10¹⁶?m^?2] can be observed at BOGT station for September equinox, when NeQuick2 model is used. The obtained results also show that: (a) for June solstice, in general the performance of IRI Plas for low latitude stations is better than that of NeQuick2 and, vice versa, for highest latitudes the performance of NeQuick2 is better than that of IRI Plas. For the stations TUCU and SANT both models have good performance; (b) for September equinox the performances of the models do not follow a clearly defined pattern as in the other season. However, it can be seen that for the region placed between the Northern peak and the valley of the equatorial anomaly, in general, the performance of IRI Plas is better than that of NeQuick2 for hours of maximum ionization. From TUCU to the South, the best TEC predictions are given by NeQuick2.The source of the observed deviations of the models has been explored in terms of CCIR foF2 determination in the available ionosonde stations in the region. Discrepancies can be also related to an unrealistic shape of the vertical electron density profile and or an erroneous prediction of the plasmaspheric contribution to the vertical total electron content. Moreover, the results of this study could be suggesting that in the case of NeQuick, the underestimation trend could be due to the lack of a proper plasmaspheric model in its topside representation. In contrast, the plasmaspheric model included in IRI, leads to clear overestimations of GPS derived TEC.     

Partially Ionized Plasmas in Astrophysics

Partially ionized plasmas are found across the Universe in many different astrophysical environments. They constitute an essential ingredient of the solar atmosphere, molecular clouds, planetary ionospheres and protoplanetary disks, among other environments, and display a richness of physical effects which are not present in fully ionized plasmas. This review provides an overview of the physics of partially ionized plasmas, including recent advances in different astrophysical areas in which partial ionization plays a fundamental role. We outline outstanding observational and theoretical questions and discuss possible directions for future progress.     

Magnetospheric and Plasma Science with Cassini-Huygens

Magnetospheric and plasma science studies at Saturn offer a unique opportunity to explore in-depth two types of magnetospheres. These are an ‘induced’ magnetosphere generated by the interaction of Titan with the surrounding plasma flow and Saturn's ‘intrinsic’ magnetosphere, the magnetic cavity Saturn's planetary magnetic field creates inside the solar wind flow. These two objects will be explored using the most advanced and diverse package of instruments for the analysis of plasmas, energetic particles and fields ever flown to a planet. These instruments will make it possible to address and solve a series of key scientific questions concerning the interaction of these two magnetospheres with their environment. The flow of magnetospheric plasma around the obstacle, caused by Titan's atmosphere/ionosphere, produces an elongated cavity and wake, which we call an ‘induced magnetosphere’. The Mach number characteristics of this interaction make it unique in the solar system. We first describe Titan's ionosphere, which is the obstacle to the external plasma flow. We then study Titan's induced magnetosphere, its structure, dynamics and variability, and discuss the possible existence of a small intrinsic magnetic field of Titan. Saturn's magnetosphere, which is dynamically and chemically coupled to all other components of Saturn's environment in addition to Titan, is then described. We start with a summary of the morphology of magnetospheric plasma and fields. Then we discuss what we know of the magnetospheric interactions in each region. Beginning with the innermost regions and moving outwards, we first describe the region of the main rings and their connection to the low-latitude ionosphere. Next the icy satellites, which develop specific magnetospheric interactions, are imbedded in a relatively dense neutral gas cloud which also overlaps the spatial extent of the diffuse E ring. This region constitutes a very interesting case of direct and mutual coupling between dust, neutral gas and plasma populations. Beyond about twelve Saturn radii is the outer magnetosphere, where the dynamics is dominated by its coupling with the solar wind and a large hydrogen torus. It is a region of intense coupling between the magnetosphere and Saturn's upper atmosphere, and the source of Saturn's auroral emissions, including the kilometric radiation. For each of these regions we identify the key scientific questions and propose an investigation strategy to address them. Finally, we show how the unique characteristics of the CASSINI spacecraft, instruments and mission profile make it possible to address, and hopefully solve, many of these questions. While the CASSINI orbital tour gives access to most, if not all, of the regions that need to be explored, the unique capabilities of the MAPS instrument suite make it possible to define an efficient strategy in which in situ measurements and remote sensing observations complement each other. Saturn's magnetosphere will be extensively studied from the microphysical to the global scale over the four years of the mission. All phases present in this unique environment — extended solid surfaces, dust and gas clouds, plasma and energetic particles — are coupled in an intricate way, very much as they are in planetary formation environments. This is one of the most interesting aspects of Magnetospheric and Plasma Science studies at Saturn. It provides us with a unique opportunity to conduct an in situ investigation of a dynamical system that is in some ways analogous to the dusty plasma environments in which planetary systems form. This revised version was published online in August 2006 with corrections to the Cover Date.     

Geoscience for Understanding Habitability in the Solar System and Beyond

Space Science Reviews - This paper reviews habitability conditions for a terrestrial planet from the point of view of geosciences. It addresses how interactions between the interior of a planet or...