Parametric excitation of gyroscopic waves in Thomson-Delaney cells of the ocean of Jovian moon Europa

A possible mechanism (of parametric resonance type) of excitation of planetary gyroscopic waves in Thomson-Delaney cells of the ocean of Jovian moon Europa is considered. It is assumed that the basis of this mechanism is a variation of liquid depth in a cell caused by tidal oscillations under the action of gravitational perturbing influence of Galilean satellites of Jupiter. Such a model leads to a system of linear differential equations with periodic coefficients of the Hill’s type. Under some additional assumptions it changes over into a system of independent Mathieu equations. The regions of parametric resonance of this system are constructed.     

Planetary gyroscopic waves in Thomson-Delaney cells of the ocean of Jupiter’s moon Europa

Observational data of the Galileo mission testify that there is a possibility of existence of planetary waves in the ocean of Jupiter’s moon Europa. A model of rotating ocean is used for the analysis of dynamics of underlying wavy processes. The model uses geometrical stratification of the ocean’s icy surface into separate cells with a typical size of order of 100 km. These cells of hydrothermal nature contain liquid lenses, and the possibility of their origination was postulated and theoretically studied by P. Thomson and J. Delaney in 2001. Using the Bubnov-Galerkin method, the spectrum of natural vibrations of liquid (gyroscopic waves) in Thomson-Delaney cells was found taking into account the satellite’s rotation in a simple model of the icy crust. In order to study a possibility of resonance excitation of tidal oscillations of liquid in the cells, the dominant elements of this spectrum are compared to theoretical values of the frequencies of tide-generating forces associated with eccentricity of the orbit of the Jupiter’s moon Europa and with perturbations from other Galilean satellites of Jupiter. This allows one to discover a large number of resonances on dominant modes with periods of from 3.5 to 7 days in the Europa ocean regions, corresponding to latitudes from 30° to 70°.     

Stationary Motions of a Homogeneous Meteor Ring in the Gravitational Field of a Center

The problem of studying a ring in the gravitational field of a center arose after the discovery of Saturn's rings by Galileo and subsequent discovery of the rings of other planets of the Solar System. Modern theoretical investigations of the existence and stability of planetary rings are mostly related to studies of plane differentially rotating discs [1]. As opposed to this line of research, this paper follows the approach established in classical works [2–4].     

Doppler Detection of Gravitational Bursts Using the Earth's Satellites

We discuss the possibility of detection of low-frequency gravitational waves by means of Doppler tracking of a relatively close satellite of the Earth. A detailed analysis is performed of electromagnetic fluctuations in the space communication channel and of the instrumental noise of receiving–transmitting systems. It is shown that when certain compensating procedures are used, one can detect gravitational radiation generated in star collapses and coalescences of binaries in our Galaxy in the frequency range from 2 × 10^–3 to 5 × 10^–1 Hz and with a metric variation amplitude of 10^–15 and higher.     

A Search for Possible Mesolensing of Cosmic Gamma-Ray Bursts: II. Double and Triple Bursts in the BATSE Catalog

The paper is devoted to searching for a possible phenomenon of the gravitational lensing of cosmic gamma-ray bursts on celestial bodies of a globular cluster type (mesolensing). If this phenomenon takes place, gamma-ray bursts should have light curves with two or three similar components whose spectra are identical. These components are separated in time by a few seconds. Using a statistical method developed for comparing the components, we have found in the BATSE catalog 11 candidates of gamma-ray bursts with mesolensing for the entire time of operation of the Compton Gamma-Ray Observatory (1991–2000). Two of these 11 gamma-ray bursts have light curves with three components. The possibility of gravitational mesolensing of these gamma-ray bursts on the King's type bodies is investigated.     

Comparative Analysis of Models of the Earth's Gravity: 3. Accuracy of Predicting EAS Motion

This paper continues a comparative analysis of modern satellite models of the Earth's gravity which we started in [6, 7]. In the cited works, the uniform norms of spherical functions were compared with their gradients for individual harmonics of the geopotential expansion [6] and the potential differences were compared with the gravitational accelerations obtained in various models of the Earth's gravity [7]. In practice, it is important to know how consistently the EAS motion is represented by various geopotential models. Unless otherwise stated, a model version in which the equations of motion are written using the classical Encke scheme and integrated together with the variation equations by the implicit one-step Everhart's algorithm [1] was used. When calculating coordinates and velocities on the integration step (at given instants of time), the approximate Everhart formula was employed.     

A minicomputer finite elements program for microgravity hydroelastic analysis

A general hydroelastic analysis formulation is presented by using Green's function. Emphasis is placed on the case of an incompressible fluid model which is applicable to flexible tank hydroelastic analysis. Variational formulation of the sloshing problem is established in order to obtain a numerical treatment by a mixed finite element method. A minicomputer program is illustrated and the hydroelastic analysis technique is checked as an efficient and accurate approach with some numerical solutions.     

Orbit lifetime for microparticles in highly elliptical orbits with low perigee

On the basis of numerical experiments, we have shown the principal possibility of long (more than 1 month) and extremely long (more than 1 year) orbit lifetime of technogenic microparticles with radii from 1 to 100 μm injected into the near-Earth space in highly elliptical orbits with low perigee, including the case of an orbit with parameters corresponding to the orbital parameters of the Molniya satellite. Calculations are performed taking into account the perturbing effect on the orbital microparticle motion in the near-Earth space of gravitational perturbation caused by the Earth’s polar oblateness, the solar pressure force (calculated using methods of the Mie theory), and the drag force of neutral component of the background gas under conditions of low, medium, and high levels of solar and geomagnetic activities.     

Periodic motions of a nearly dynamically symmetric satellite in the neighborhood of hyperboloidal precession

The motion of a satellite close to a dynamically symmetric solid body in a Newtonian gravitational field over a circular orbit is studied. The system of differential equations describing the body’s motion is close to a system with cyclic coordinate. New classes of periodic motions are constructed in the neighborhood of a known partial solution to an unperturbed problem, hyperboloidal precession of a dynamically symmetric satellite. In the resonance case, when the ratio of one frequency of small oscillations of a reduced system with two degrees of freedom in the neighborhood of a stable equilibrium position to the frequency of cyclic coordinate variation is close to an integer number, there exist one or three families of periodic motions that are analytic in terms of fractional powers of a small parameter. A study of stability of these motions was performed with the help of KAM (Kolmogorov-Arnold-Moser) theoty. Faling the described resonance there exists a unique family of periodic motions that is analytic in terms of integer powers of a small parameter. The check-up of stability of these motrons was carried out. We distinguished the cases of parametric resonance, resonances of the third and fourth orders, and a non-resonant case. In the resonance cases our study relies on well-known results on stability of Hamiltonian systems during resonances [1]. In the non-resonant case we use the KAM theory [2].     

On the asteroid hazard

The concept of “space patrol” is considered, aimed at discovering and cataloging the majority of celestial bodies that constitute a menace for the Earth [1, 2]. The scheme of “optical barrier” formed by telescopes of the space patrol is analyzed, requirements to the observation system are formulated, and some schemes of sighting the optical barrier region are suggested (for reliable detection of the celestial bodies approaching the Earth and for determination of their orbits). A comparison is made of capabilities of electro-jet engines and traditional chemical engines for arrangement of patrol spacecraft constellation in the Earth’s orbit.     

Compensation of gravitational attraction disturbance to pure gravity orbit for Inner Formation Flying System

The Inner Formation Flying System (IFFS) consisting of an outer satellite and an inner satellite which is a solid sphere proof mass freely flying in the shield cavity can construct a pure gravity orbit to precisely measure the earth gravity field. The gravitational attraction on the inner satellite due to the outer satellite is a significant disturbance source to the pure gravity orbit and is required to be limited to 10⁻¹¹ m s⁻² order. However, the gravitational disturbance force was on 10⁻⁹ m s⁻² order actually and must be reduced by dedicated compensation mass blocks. The region of relative motion of the inner satellite about its nominal position is within 1 cm in dimension, which raises the complexity of the compensation blocks design. The iterative design strategy of the compensation blocks based on reducing the gravitational attraction at the nominal position of the inner satellite is presented, aiming to guarantee the gravitational force in the relative motion region within requirements after the compensation. The compensation blocks are designed according to the current status of IFFS, and the gravitational disturbance force in the region is reduced to 10⁻¹¹ ms⁻² order with minimized adding mass.     

Auroral kilometric radio emission in the period of quiet sun in 1996

The auroral kilometric radio emission (AKR) is the most powerful sporadic radio emission of the terrestrial magnetosphere. It was discovered in 1965 by Soviet scientists in the experiment onboard the Electron-2 satellite [1]. The AKR still continues to stay an object of a large interest and detailed study (see, for example, a review by Gurnett [2]). The mechanism of cyclotron maser instability proposed by Wu and Lee [3] is a commonly accepted mechanism of AKR generation. We have demonstrated the presence of powerful AKR simultaneously in both hemispheres of the Earth in the period from August 1995 to August 1997, including summer-winter periods, on particular examples of registration of this emission in [4] where the directivity and mechanism of the emission were studied. Since in that period AKR was observed in the vicinity of perigees of the satellite orbit in both hemispheres almost at every orbit (3.8 days), we have a possibility to trace in more detail the changes in the emission power from one orbit to another in 1996 during a deep minimum of solar activity.     

About one problem of trajectory optimization

The optimization problem for trajectories of spacecraft flight from the Earth to an asteroid is considered in this paper. The flight is realized in the central Newtonian gravitational field of the Sun with a possibility of gravitational maneuvers near planets. Perturbation maneuvers are taken into account using the method of point area of action with a limitation on the flyby altitude. The spacecraft is controlled by changing the value and direction of the engine thrust. The problem is solved taking into account constraints on the launch time, flight duration, and minimum distance to the Sun.     

Evolution of almost circular orbits of satellites under the action of noncentral gravitational field of the Earth and lunisolar perturbations

Based on the results of paper [1] by G.V. Mozhaev, joint perturbations produced by nonsphericity of the Earth and by attraction of the Moon and the Sun are investigated using the method of averaging. Arbitrary number of spherical harmonics was taken into account in the force function of the Earth’s gravitational filed, and only the principal term was retained in the perturbing function of the Sun. In the perturbing function of the Moon two parallactic terms were considered in addition to the dominant term. The flight altitude was chosen in such a way that perturbations produced by the Sun and Moon would have the second order of smallness relative to the polar oblateness of the Earth. As a result, the formulas for calculation of satellite coordinates are derived that give a high precision on long time intervals.     

Deep Structure of the Arctic and Antarctic according to Component Magnetic and Gravitational Anomalies

Cosmic Research - The results of a study of the deep structure of the Earth’s polar regions based on the interpretation of gravitational anomalies, geomagnetic-field anomalies, and...     

Time and energy characteristics of UV flashes in the atmosphere: Data of the <Emphasis Type="Italic">Universitetsky-Tatiana</Emphasis> satellite

Using a detector of near ultra-violet (UV) emission (wavelength range 300–400 nm) [1] onboard the Universitetsky-Tatiana satellite with an orbit height of 950 km and inclination of 81° we have detected and studied short UV flashes [2–5]. In this paper the observed UV flashes are classified according to the type of their time profiles, and the times of emission intensity rise and decay are investigated in every flash. Using the data on time profiles it turned out to be possible to estimate the flash energy in the atmosphere even in case of saturation of a signal measuring channel at the maximum of emission. The energy spectrum of observed flashes is estimated. Time and energy characteristics of the flashes are important for choosing a model of development of electric discharges in the upper atmosphere that are responsible for observed emission.     

A new universal equation for the time of transfer between two points of the central gravitational field

The paper presents the derivation of two new equations for calculating the time of transfer between two points of the central gravitational field: for hyperbolic orbits and the universal equation for elliptical and hyperbolic orbits. In the paper we have used as an independent variable, instead of the linear elements (semimajor axis, focal parameter of orbit or a chord connecting the ends of boundary radii of transfer), the angular parameter—the angle between the radius vector of an initial point of transfer and the vector of initial velocity of transfer. Paper’s material is a continuation of that presented in the “Space research“ Journal, vol. 2, March–April, 2009.     

Gravitational maneuvers as a way to direct small asteroids to trajectory of a rendezvous with dangerous near-Earth objects

A possibility to prevent collisions with the Earth of dangerous celestial bodies by directing at them small asteroids is considered. It is proposed to solve this problem using a gravitational maneuver near the Earth.     

A tether system for gravitational stabilization of satellites

The dynamics of a sufficiently complex system of gravitational stabilization is considered. The system includes a tether connection to increase restoring moment and an additional constructive element (adapter) to increase the efficiency of damping pendular oscillations of the system. A method of choosing the system’s desigh factors is suggested that ensures a minimum duration of transition processes.