Artificial satellites orbits in 2:1 resonance: GPS constellation

In this work, the resonance problem in the artificial satellites motion is studied. The development of the geopotential includes the zonal harmonics J₂₀ and J₄₀ and the tesseral harmonics J₂₂ and J₄₂. Through an averaging procedure and successive Mathieu transformations, the order of dynamical system is reduced and the final system is solved by numerical integration. In the simplified dynamical model, three critical angles are studied. The half-width of the separatrix is calculated through a linearized model which describes the behavior of the dynamical system in a neighborhood of each critical angle. Through the resonance overlap criterion the possible regular and irregular motions are investigated by the time behavior of the semi-major axis, argument of perigee and eccentricity. The largest Lyapunov exponent is used as tool to verify the chaotic motion.     

Interplanetary Origin of Intense,Superintense and Extreme Geomagnetic Storms

We present a review on the interplanetary causes of intense geomagnetic storms (Dst≤−100 nT), that occurred during solar cycle 23 (1997–2005). It was reported that the most common interplanetary structures leading to the development of intense storms were: magnetic clouds, sheath fields, sheath fields followed by a magnetic cloud and corotating interaction regions at the leading fronts of high speed streams. However, the relative importance of each of those driving structures has been shown to vary with the solar cycle phase. Superintense storms (Dst≤−250 nT) have been also studied in more detail for solar cycle 23, confirming initial studies done about their main interplanetary causes. The storms are associated with magnetic clouds and sheath fields following interplanetary shocks, although they frequently involve consecutive and complex ICME structures. Concerning extreme storms (Dst≤−400 nT), due to the poor statistics of their occurrence during the space era, only some indications about their main interplanetary causes are known. For the most extreme events, we review the Carrington event and also discuss the distribution of historical and space era extreme events in the context of the sunspot and Gleissberg solar activity cycles, highlighting a discussion about the eventual occurrence of more Carrington-type storms.     

M. Livio, S. M. Fall and P. Madau (eds.), The Hubble Deep Field, Space Telescope Conference Series 11

The proceedings of a conference dealing with only one piece of observational activity: the deepest optical image obtained by the HST during a 150 orbit observational program. The main result, presented in several papers, is that we are now able to witness the period of galaxy formation. Very readable too is Allan Sandage's historical review, being the introductory paper to the meeting. This revised version was published online in August 2006 with corrections to the Cover Date.     

Global behavior of the equatorial anomaly since 1999 and effects on GPS signals

Tools to generate VTEC maps were developed. These maps have been used to study the global behavior of the equatorial anomaly since 1999 up to now, and its effects on GPS signal. The VTEC data for any place around the world is based on IONEX data. In this way, a quick annual behavior of the VTEC may be analyzed, and also compared to the VTEC behavior for different places and different years. Based on these data an electron density model taking into account radial as well latitudinal and longitudinal gradients were developed. This model was incorporated in a 3D ray-tracing program. Using this program it was possible to compare the STEC conversion to the VTEC. As expected the results show that the lower the elevation angles of the Satellite Vehicle, the greater the error in the VTEC estimation.     

Monitoring of biologically effective UV irradiance at El Arenosillo (INTA), Andalucia, in Spain.

Biological UV (ultraviolet) dosimetry was applied using the biofilm-technique (DLR patent) to determine the UV levels weighted of biologically weighted UV radiation at the INTA Sounding Station of El Arenosillo at Huelva, Spain (37 degrees 06'N, 6 degrees 44'W, 50 m a s 1=above sea level) on 2 days in 1997 [correction of 1977] (April 1, and May 5). Exposure periods were calculated for clear sky days using a radiative transfer model for erythemal doses to reach 1.3 to 1.5 MED (minimal erythemal dose). Reliability of the radiative transfer model was demonstrated by the doses registered by a Yankee-UV biometer for the same exposure periods as used for the biosensor. This work presents the methodology employed (biofilm-technique utilized [correction of utiliced], calculation of exposing periods with radiative transfer model, etc) and the results obtained with the Yankee biometer and the biofilm. At noon, the ratio of biofilm measurements (Ieff, W/m2=biological effective irradiance, in W/m2) to the UV Biometer data (in MED/h) was 3-4.     

The new international political and strategic context for space policies

For several years there has been substantial growth in the ‘nationalist’ nature of space programmes around the world, traditionally focused on unaligned useful space applications. It seems that China, India, in the future South Korea, Malaysia and others will set themselves objectives of a more political colouring symbolising national pride in their programmes. At the same time, some countries, like Iran, make no attempt to hide their plans to have their own space defence capabilities. The absolute pre-eminence of the USA, Russia and Europe is starting to fade. For emerging countries space resources are becoming an integral component of their strategic position or an asymmetrical capability aimed at weakening the credibility of advantages held by potential rivals. This article examines the new context and the role that various countries are playing in it. It is how space policies should be determined in order to understand their politico-strategic determinants and to highlight their characteristics. Nevertheless, the competitive spirit is not the only possible way. Permanent space infrastructures could also be organised globally, as ‘global public goods’, to contribute to answering questions related to major issues facing humanity.