Libration Points in Schwarzschild's Circular Restricted Three-Body Problem

The restricted three-body problem in Schwarzschild's gravitational field is analyzed. The existen- ce of the equilibrium points in the orbital plane is discussed and the corresponding positions are established. There are three collinear libration points, and, if they exist, two triangular libration points (situated in the orbital plane of the primaries). If triangular points exist, they may not form equilateral triangles; the triangles are isosceles for equal masses of the primaries, and scalene else.     

A Validation of MODIS Snowcover Products in Romania: Challenges and Future Directions

The MODIS snowcover product is one of many geophysical products derived from MODIS data. A cross‐validation of the MODIS snowcover daily products with data obtained from the meteorological network stations was conducted for the entire territory of Romania. The validation time interval covered the period between 29 October, 2004 and 1 May, 2005. The overall accuracy for the whole set of cloud‐free useful data proved to be 95%. The validation time interval included the three common snow situations: (1) late autumn months where 37.1% of the initial set of the data was used, and the overall accuracy was 98.6%; (2) the “winter” months where the clouds reduced the set of useful data – 31.75%– and the overall accuracy was 93.7%; and (3) the months of February and March which returned the highest accuracy (> 95%). Additionally, a cross‐validation using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) high‐resolution imagery was carried out. Furthermore, the MODIS, meteorological data and ASTER data were integrated into a Geographic Information System (GIS) environment to perform flexible and comprehensive cross‐checking followed by a thematic analysis based on additional sets of data such as digital elevation models (DEMs) and land‐cover datasets.     

The Difference between the Nodal and Keplerian Periods of Artificial Satellites as an Effect of Atmospheric Drag

On donne une expression analytique de la différence causée par le frottement atmosphérique entre les périodes nodale et képlérienne des satellites artificiels aux orbites quasi-circulaires, évoluant dans une atmosphère à symétrie sphéque. Quelques équations correspondantes trouvées par divers auteurs sont obtenues en tant que cas particuliers de l'équation donnée.     

Poynting–Robertson effect in non-singular gravitational potential

We use a non-singular potential that appears in the literature under the influence of which the Poynting-Robertson effect is studied. For that, dust particles originating within the asteroid belt are used, in circular and elliptic orbits, and expressions for the semimajor axis as a function of time are obtained. The derived expressions are written in terms of the two basic dust particle parameters, namely the density and the diameter. In both cases, we obtain expressions for the time that the dust particles take to reach the orbit of Earth under the action of the non-singular potential and solar radiation. For the non-singular potential, dust particles of diameter 10⁻³ m in circular and elliptical orbits require times of the order of 4.058×10⁷ and 2.823×10⁷ y to reach the orbit of the Earth respectively. Finally, the derived expressions and numerical results are compared with those of the Newtonian potential.     

(137)Cs baseline levels in the Mediterranean and Black Sea: a cross-basin survey of the CIESM Mediterranean Mussel Watch programme

The common mussel Mytilus galloprovincialis was selected as unique biomonitor species to implement a regional monitoring programme, the CIESM Mediterranean Mussel Watch (MMW), in the Mediterranean and Black Seas. As of today, and upon standardization of the methodological approach, the MMW Network has been able to quantify (137)Cs levels in mussels from 60 coastal stations and to produce the first distribution map of this artificial radionuclide at the scale of the entire Mediterranean and Black Seas. While measured (137)Cs levels were found to be very low (usually < 1 Bq kg(-1) wet wt) (137)Cs activity concentrations in the Black Sea and North Aegean Sea were up to two orders of magnitude higher than those in the western Mediterranean Basin. Such effects, far from representing a threat to human populations or the environment, reflect a persistent signature of the Chernobyl fallout in this area.     

A look at global seismicity during 1999 in the longer-term time frame

An analysis and discussion of the main features and effects of the 1999global seismicity based especially on the inferred patterns of strong(M_w 7) earthquakes using NEIC/USGS data is presented.Based on the above data and their statistical features (see also Table 1)one may state that from the point of view of occurrence rate (number/yr)the 1999 global seismicity was fairly regular, but from the moment (orenergy) release standpoint it is well under the long-term average. The spacepartition was again rather typical and time distribution was quasi-Poissonian,noteworthy, the 1999 worldwide seismicity had an anomalously high deathtoll, to be discussed later. Two main new insights are brought by ouranalysis: (i) a (mega)quiescence along the whole south American segmentof circum-Pacific earthquake belt, which was inferred and rated asanomalous while it was underway and which, in retrospect, ended with thegreat (M_w = 8.4 HRV) 2001 Arequipa (Peru) event; (ii) an intriguingmonotonous rate decrease within only magnitude class 5.0 to 5.9 duringthe analyzed period (i.e., 1990–1999).     

Photoelectric lightcurves of asteroid 433 Eros

Photoelectric observations of the asteroid 433 Eros were carried out with the 50-cm reflector of the Astronomical Observatory of the University of Cluj-Napoca on January 21 and February 4 and 5, 1975.     

Infinitesimal librations with variable primary masses

The motion around the libration points is studied with Charlier's first order theory assuming the isotropic mass variation of the primaries does not exceed the order of the small primary and the derivatives of the masses with respect to time are negligible second order quantities. The results are analogous to those obtained with constant primary masses.     

Navigating to the Moon along low-energy transfers

This paper presents a navigation strategy to fly to the Moon along a Weak Stability Boundary transfer trajectory. A particular strategy is devised to ensure capture into an uncontrolled relatively stable orbit at the Moon. Both uncertainty in the orbit determination process and in the control of the thrust vector are included in the navigation analysis. The orbit determination process is based on the definition of an optimal filtering technique that is able to meet accuracy requirements at an acceptable computational cost. Three sequential filtering techniques are analysed: an extended Kalman filter, an unscented Kalman filter and a Kalman filter based on high order expansions. The analysis shows that only the unscented Kalman filter meets the accuracy requirements at an acceptable computational cost. This paper demonstrates lunar weak capture for all trajectories within a capture corridor defined by all the trajectories in the neighbourhood of the nominal one, in state space. A minimum Δv strategy is presented to extend the lifetime of the spacecraft around the Moon. The orbit determination and navigation strategies are applied to the case of the European Student Moon Orbiter.