Variations in statistical parameters of the NmF2 equinoctial asymmetry with latitude and solar activity near noon

Hourly values of the F2-layer peak density, NmF2, measured by 95 ionosondes near noon from 1957 to 2011 at low and middle geomagnetic latitudes of the northern and southern geographic hemispheres are used in a statistical study of the NmF2 equinoctial asymmetry. The ratios, R, of NmF2 measured during 61 days around the March equinox to NmF2 measured during 61 days around the September equinox at the same UT near noon during geomagnetically quiet daytime conditions for approximately the same solar activity conditions over the same ionosonde are analyzed. The conditional probability of the occurrence of R in an interval of R, the most probable value of R, and the mean expected value of R are calculated for the first time for the low, moderate, and high solar activity levels to study variations in these statistical parameters with latitude and solar activity. These statistical parameters are averaged over 5° geomagnetic latitude interval in the northern and southern geographic hemispheres to calculate and to study for the first time trends in latitude and solar activity of these averaged NmF2 equinoctial asymmetry statistical characteristics.     

Improved predictions of equatorial TEC for real time applications

It is important to use models developed specifically for the equatorial ionospheric estimation for real-time applications, particularly in Satellite Navigation. This work demonstrates a methodology for improved predictions of VTEC in real time using the model developed for the equatorial ionosphere by the authors. This work has been done using TEC data of the low solar activity period of 2005 obtained using dual frequency GPS receivers installed under the GAGAN project of ISRO. For the purpose, the model is first used in conjunction with Kriging technique. Improvement in accuracy is observed when compared with the estimations from the model alone using the measurements as true reference. Further improvement is obtained by Bayesian combination of these estimates with independent Neural Network based predictions. Statistical performance of improvement is provided. An improvement of ∼1 m in confidence level of estimation of VTEC is obtained.     

The concept of selecting the main parameters of a lightweight airplane with regard to the requirements of the contemporary Russian market

The basic principles of selecting some design parameters of a lightweight airplane for the contemporary Russian market are presented. Recommendations for selecting these parameters with the service requirements specified are given based on the study performed.     

Spectres auroraux

Summary The paper presents a review of the main spectroscopic studies of polar aurora accomplished during the past eight years.In a first part, the few new results concerning knowledge of the spectrum itself are examined. They concern detailed spectrum analysis, a few spectral features (sodium doublet, helium lines) and the extension of spectral observations to very low wavelengths (3000 to 1000 Å). The main features discovered in this region are the Vegard-Kaplan and Lyman-Birge-Hopfield systems as well as the 1304 oxygen line. A comparison of observed and theoretical intensities shows serious discrepancies, not all of which may be attributed to difficulties of observation. Next is given classification, from a spectral point of view, of the various kinds of auroral phenomena, with respect to altitude and latitude. Particular attention is given to high altitude and sunlit aurorae, and to low intensity, non discrete aurorae observed around the 70th degree (geomagnetic) and around the polar cap.A second part underlines the influence of two important parameters, time and location, mainly as a possible means of detection of different mechanisms.As far as the time parameter is concerned, a few pages are devoted to statistical analysis of the great wealth of observational data accumulated over twenty or thirty years.It is shown that important conclusions emerge from such studies. Very small scale time variations are mainly concerned with the study of metastable states, their lifetimes and de-excitation due to shocks between particles. Differences of spectra with the location of the observed emitting volume is a much more recent subject, which has, however, produced important results. These concern mainly observations made from rockets, although a few results have been obtained from the ground. All these indicate significant differences that may shed some light on the difficult problem of mechanisms. The latter has not been developed, since a recent review has been written on the subject. The same is true for the very important problem of hydrogen emissions.The last pages are concerned with the latest developments of experimental methods, with some stress on image tubes, which will probably be one of the main detecting devices for observing auroral spectra in the near future.     

Electron precipitation in the auroral zone

The present experimental knowledge of electron precipitation in the auroral zone is summarized, using observations primarily from riometer, balloon, rocket and satellite studies. This includes the association of electron precipitation events with aurora, magnetic disturbances as well as temporal and spatial aspects of the particle bombardment.     

Controlling spacecraft by means of solar radiation

The possibility of using solar sails in Earth orbit is investigated. The characteristic parameters of a solar sail consisting of six spheres attached by mutually orthogonal long rods are estimated.     

Toward Accurate On-Ground Attitude Determination for the Gaia Spacecraft

The work presented in this paper concerns the accurate On-Ground Attitude (OGA) reconstruction for the astrometry spacecraft Gaia in the presence of disturbance and of control torques acting on the spacecraft. The reconstruction of the expected environmental torques which influence the spacecraft dynamics will be also investigated. The telemetry data from the spacecraft will include the on-board real-time attitude, which is of order of several arcsec. This raw attitude is the starting point for the further attitude reconstruction. The OGA will use the inputs from the field coordinates of known stars (attitude stars) and also the field coordinate differences of objects on the Sky Mapper (SM) and Astrometric Field (AF) payload instruments to improve this raw attitude. The on-board attitude determination uses a Kalman Filter (KF) to minimize the attitude errors and produce a more accurate attitude estimation than the pure star tracker measurement. Therefore the first approach for the OGA will be an adapted version of KF. Furthermore, we will design a batch least squares algorithm to investigate how to obtain a more accurate OGA estimation. Finally, a comparison between these different attitude determination techniques in terms of accuracy, robustness, speed and memory required will be evaluated in order to choose the best attitude algorithm for the OGA. The expected resulting accuracy for the OGA determination will be on the order of milli-arcsec.