Vol 61, No 2 (2023)

In this paper, a method for estimating the spectra of wave processes based on a special type of measuring lattices, which are a set of rotating and static sensors, called “circular,” is developed. A method for correcting spectra estimated on the basis of discrete digital series obtained from circular lattice sensors is described. Spectra estimates are based on the multidimensional maximum entropy method. The data of test calculations for several types of circular lattices are presented as applied to wave processes in the form of harmonics distorted by white noise. The effectiveness of the proposed method for correcting spectra is shown. The general principles of using circular lattices for estimating the spectra of wave processes with the help of sensors located on rotating satellites are outlined. The possibility of using this approach for estimating the spectra of wave processes using sensors installed on micro- and nanosatellites is discussed.

The results of studies of the coronal emission line λ = 5303 Å (Fe XIV) for the period of solar cycle 24 are presented. The spectral data were obtained with an out-of-eclipse Lyot coronagraph at the Mountain Astronomical Station of the Pulkovo Observatory, Russian Academy of Sciences (near Kislovodsk). As a result of processing of out-of-eclipse observations, a database of three types of daily coronal maps of green line intensity I5303 was created with a height distribution h from 1R☉ to 1.38R☉ (R☉ is the radius of the Sun). Irregularities along the λ = 5303 Å line were found and identified, which were associated with the configuration of magnetic fields in the solar corona above active regions. The length of the green line from the position angle of the Sun was calculated. We have shown that the time distribution of the line length in the polar regions has two maxima, which coincide with the times of the reversal of the polar magnetic field on the Sun. The maximum values of the average length of the coronal line along the entire limb occur in 2012–2014. For different phases (the rise, the period of maximum, the decline, and the minimum solar activity) of this solar cycle and for different regions of solar activity, dependences of the height variations of the I5303 values were plotted and studied. The regression equations for these fitting curves are presented. The variation in I5303 with height for the polar regions is most likely determined by a logarithmic function, and the approximating trend curves for the remaining latitudinal zones are determined by a third-order power function.

The mode of maintaining a solar orientation of spacecraft–gyrostat in low Earth orbit for a long time has been studied. The spacecraft is close to a cylinder in shape with two fixed solar arrays. The arrays are located along the longitudinal axis of the cylinder, symmetrically with respect to it. In the solar-orientation mode, the normal to the plane of the spacecraft solar arrays is invariably directed to the Sun, and the longitudinal axis oscillates relative to the plane of the orbit. To implement the specified mode of the spacecraft motion, a system of four reaction wheels is used, the rotation axes of which are directed parallel to the lateral edges of the quadrangular pyramid. The position of the lateral edges of the pyramid relative to the coordinate system rigidly connected to the spacecraft is given by two angles, which are the parameters of the reaction-wheel system. The law of control of the gyrostatic moment is considered, which ensures the attenuation of the perturbed motion of the spacecraft in the vicinity of the position of its solar orientation and limits the accumulation of the own kinetic moment of the reaction wheels by controlling the angle of rotation of the spacecraft around the normal to the light-sensitive side of the solar arrays. The study shows that with the help of a certain choice of parameters of the reaction-wheel system, it is possible to implement the solar-orientation mode without unloading the gyrostatic moment during the entire flight time. The results of numerical simulation of the complete system of equations of the spacecraft motion in the mode of its solar orientation, taking into account the influence of gravitational and aerodynamic moments, are presented, confirming the correctness of the chosen values of the parameters.

The problem of changing the apogee altitude of orbits with ultralow perigee (altitude 120–250 km) is considered. To compensate for the aerodynamic drag of the spacecraft, an air-breathing electric propulsion (ABEP) is used, the fuel for which is the gases of the outboard atmosphere. The decrease in the efficiency of an ABEP with an increase in the angle of attack and the possibility of ABEP operation only at a sufficient gas concentration in the ionization chamber are taken into account. The problem is solved on the basis of the Pontryagin maximum principle under the assumption that the aerodynamic drag and thrust are small compared to the gravitational forces. The results of studies of optimal programs for controlling the thrust vector of an ABEP depending on the parameters of the orbit, the layout of the spacecraft, the engine, and the power of the energy source are presented.