Topology of the high latitude magnetosphere during large magnetic storms and the main mechanisms of relativistic electron acceleration

One of the main endeavors of the “Space Weather” program is the prediction of the appearance of very large fluxes of relativistic electrons with energies larger than 1 MeV, because they represent a serious potential hazard for satellite missions. Large fluxes of relativistic electrons are formed in the outer radiation belt during the recovery phase of some storms. The formation of large fluxes is connected to a balance between the acceleration and loss processes. A two-step acceleration process is ordinarily analyzed. A “Seed” population with energies ∼hundreds of keV appeared during expansion phase of magnetospheric substorm. A “Seed” population is additionally accelerated obtaining relativistic energies by some other process. Several acceleration mechanisms have been proposed for the explanation of the electron acceleration, including radial diffusion and internal acceleration by wave-particle interactions. Nevertheless, none of them takes into account great changes of magnetospheric topology during a magnetic storm. Such changes are mainly connected with asymmetric and symmetric ring current development. We analyze the changes of magnetospheric topology during magnetic storms. We show that a change of the magnetospheric magnetic field can be the important factor determining the acceleration of relativistic electrons.     

Method of virtual trajectories for the design of gravity assisted missions

A novel method of virtual trajectories is proposed for the design of multiple gravity assist trajectories. The database of virtual trajectories can be tabulated for any planetary sequence and used in subsequent calculations. Requirements for the mission duration and the launch date are taken into account during the iterative procedure of database screening and refinement. The results of applying the virtual trajectories method to the design of a mission to Uranus are presented.     

A space observatory for astrophysical explorations in the REALM of gamma-ray astronomy

Conclusion The space observatory whose major systems are outlined in the present paper is being designed to ensure astrophysical explorations in the field of -ray astronomy during the course of one year. The observatory is supposed to travel along a circular orbit up to 400 km in altitude, inclined at 51.6°. Investigations to be accomplished in the observatory will enable us to make substantial progress in gaining a deeper insight into a wide variety of astrophysical phenomena.     

High-precision single-input control of relative motion in spacecraft formation

A Newton-type method is proposed to improve the accuracy of control for relative motion of two satellites in close formation. We assume that the deputy satellite is equipped with a passive attitude control system that provides one-axis stabilization, and one or two orbit control thrusters are installed along the stabilized axis. Previous studies show that it is possible to construct periodic relative trajectories both in case of passive magnetic and spin stabilization. However, the accuracy of the numerically obtained control is quite low due to modeling errors caused by linearization of the equations of relative motion. Therefore, a correction procedure is required to compensate for nonlinear effects. To this end we suggest a recently developed algorithm based on the Newton method for solving nonlinear systems with geometric constraints. Being implemented, this algorithm allows decreasing the modeling error by up to ten times. The previously found control and trajectory of the linearized system are used as initial approximations.     

Motion of a satellite equipped with a pitch flywheel and magnetic coils in gravitational field

A satellite equipped with a magnetic attitude control system and a pitch flywheel has been considered. The system performance in the transient mode has been investigated. The characteristic exponent of the system have been approximated for a satellite on a circumpolar orbit. In the steady-state mode of gravitational attitude, small motions are considered in the vicinity of equilibrium. The attitude accuracy has been analyzed. The algorithm of an arbitrary but given attitude of the satellite in the orbital plane has been investigated. A numerical simulation has been performed.     

Orbital corrections by a single-input impulsive control applied along the geomagnetic field

This paper examines the possibility of regular orbital corrections for a satellite controlled by an impulsive force applied along the induction vector of the local geomagnetic field. The main purpose of the correcting considered in the paper is to eliminate the drift in secular variation of the relative orbital parameters over the orbital period. The obtained results are applied to the formation flying problem. The developed method is tested using numerical simulation.     

Plasma sheet coefficient of diffusion: Predictions and observations

The theory of a plasma sheet with medium scale developed turbulence predicts a value for the plasma sheet diffusion coefficient in the Z direction. Its value becomes very near to the diffusion coefficient calculated from the assumption of isotropic turbulence on the basis of ISEE-2 velocity fluctuations in the X and Y directions. INTERBALL/Tail CORALL bulk velocity measurements make it possible to determine velocity fluctuations in the Z direction and calculate the diffusion coefficient in this Z direction. It is shown that INTERBALL/Tail observations are in very good agreement with theory predictions.     

Space dust high-velocity particle influence on electronic equipment

Determination of failure causes of the control systems and navigation electronic elements of space flying vehicles (SFV), observed in the process of long-time flights, is of current importance. Failures of the control systems in the process of long-time flights considerably reduce their reliability and, consequently, raise expenses in this field. In particular, this requires an additional backup of satellites-retransmitters, which results in an increase of the number of SFV launches. At present, experts are actively elaborating the hypothesis that one of the most probable causes of the SFV electronic system failures are the flows of the space dust particles, moving in the near-Earth and interplanetary space, and possessing velocities from 7.8 km/sec to 16 km/sec. The flows of the high energy (Galactic) ions, for a number of cases, are considered to be the basic cause of the destruction of electronic control systems. This, in particular, makes it possible to explain the failures in flights to Mars of the autonomous space modules performed by the European and American space agencies. The optimum flight route to Mars passes through agglomerations of dust clouds, which necessitates a high probability of collision for the flying vehicles with dust clots. Therefore, the success of the American research module is quite logical, which was done with the highest deviation from the optimum route.     

Nanosatellite <Emphasis Type="Italic">REFLECTOR</Emphasis>: Choice of parameters of the attitude control system

We consider methodological and applied problems of choosing parameters and developing a passive gravity-gradient attitude control system for the REFLECTOR nanosatellite. The attitude control system consists of appropriately distributed satellite mass and additional masses forming the required tensor of inertia, as well as of a set of hysteresis rods manufactured from a magnetically soft material. The combination of these elements allows one, independent of the satellite’s initial angular motion, to maintain its three-axial orientation in the orbital coordinate system with preset performance in precision and fast response. The satellite’s dynamics is investigated using asymptotic and numerical methods. The problems of arrangement of the additional masses and hysteresis rods are discussed, as well as their interaction with magnetizable elements.     

Determination of two Satellites’ relative motion using tracking measurements

A technique to determine the initial relative velocity of two satellites at the initial time instant, based on the results of NORAD system’s measurements, is presented. The determination of a relative initial position is shown to result in the unsatisfactory accuracy. This technique is applied to determining the initial velocity of separation of the first Russian nanosatellite TNS-0 from the International Space Station.