Racemic Grieco lactone was hydrolyzed to 2-[(1RS,5SR)-5-hydroxycyclopent-2-en-1-yl]acetic acid. The reaction of the latter with N-bromosuccinimide afforded (3aSR,4SR,6SR,6aSR)-6-bromo-4-hydroxyhexahydro-2H-cyclopenta[b]furan-2-one as a kinetic product, which can be further converted into the thermodynamic (3aRS,4SR,5SR,6aSR)-5-bromo-4-hydroxy-substituted isomer. The reaction with N-chlorosuccinimide gave 4-chloro-5-hydroxy- and 5-chloro-4-hydroxyhexahydro-2H-cyclopenta[b]furan-2-ones with the exo-position of the hydroxy groups and the endo-position of the chlorine atoms. Typical transformations of the obtained compounds were carried out, the results of which were analyzed considering literature data on the reactions of Grieco lactone and its derivatives with electrophilic agents.

A numerical simulation of satellite dynamics in a near-circular orbit at an altitude of 250 km is performed. The satellite is equipped with a magnetic attitude control system that complements its aerodynamic stabilization properties. A continuous-thrust engine is utilized to mitigate the effects of atmospheric drag. A brief description of the models used is provided. The magnitudes of microaccelerations are simulated and analyzed with respect to various satellite parameters, the models employed, and the algorithms implemented.

A bias momentum satellite motion in the stabilization phase is considered. The satellite is equipped with a pitch momentum wheel that maintains a constant rotation rate, and three-axis magnetorquers set. The wheel axis should point along the orbital normal which is the stable position, thus enabling roll/yaw passive stability, without active pitch stabilization. To achieve convergence to this attitude, active attitude damping with Bdot control is employed, which ensures asymptotic stability. An explicit form of approximate solution of the equations of motion is obtained for a polar satellite. Through a comparison between Bdot and asymptotic damping algorithms, the superior performance of Bdot control in this specific scenario is demonstrated.

The kinetics of the cyclization of (E)-1,5-diphenylpent-1-en-4-yn-3-one phenylhydrazone in ethylene glycol in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene at temperatures ranging from 373.15 to 407.15 K was studied. The reaction product is (E)-1,2-diphenyl-4-styryl-1H-pyrazole in a yield of 99

Dissociation energies (DC—H) of labile C—H bonds in radical adducts formed by coordination of thiyl radicals across the cyclohexadiene rings of 1,4-benzoquinone, N-phenyl-1,4-benzoquinone monoimine, and N,N′-diphenyl-1,4-benzoquinone diimine have been determined using composite methods of the Gaussian family and data on the enthalpies of formal homodesmotic reactions involving the adducts and simpler reference compounds. The DC—H values were found to be in the range of 140–170 kJ mol−1. These values are typical of the strength of bonds between atomic hydrogen and olefins. The weakness of the C—H bonds in both types of compounds is due to the compensation of bond breaking by the stabilization of the reaction products, viz., an olefin molecule or the cyclohexadiene ring of a quinoid. The proximity of the DC—H values in these adducts and the significant difference (∼50 kJ mol−1) between these values and the strength of the C—H bond in the adduct of atomic hydrogen with a benzene molecule confirms the fact that quinones and quinone imines are not aromatic compounds. The obtained DC—H values are required for the quantitative interpretation of the kinetic regularities found for the chain reactions of thiols with quinoids, as well as the catalysis of these reactions at the stage of chain propagation under the action of compounds with X—H groups (X = O, S, etc.).

The termination kinetics of the adduct of molecular oxygen (3Σg- ) and 4-(N,N-dimethylamino)-phenylnitrene generated by pulse photolysis from the corresponding azide in hexane has been studied using UV spectroscopy in a wide temperature range. The adduct is represented by cis- and trans-isomers of 4-(N,N-dimethylamino)- phenylnitroso oxide (4-Me2NC 6 H4 NOO). It was experimentally established that an abnormal increase in the ter- mination rate of aryl nitroso oxide is observed with decreasing temperature of the reaction mixture. A two-center five-step mechanism of nitroso oxide transformation is proposed. A satisfactory description of the kinetic curves of the change in the optical density of the reaction mixture can be achieved according to the mechanism: along with ortho-cyclization of the cis-isomer of aromatic nitroso oxide, accompanied by the formation of the corre- sponding nitrile oxide, the interaction of trans- and cis-isomers of the nitroso oxide fragments, leading to a prereaction complex, is possible. The structural features of the complex allow its decomposition either (channel I) into nitro- and nitroso compounds or (channel II) trans-isomers of aryl nitroso oxide. With a decrease in the temperature of the reaction mixture the stability of the complex increases. The latter ensures a more probable decomposition through one of the aforementioned channels.

This research studies the potential of frozen low lunar orbits to be used in the design of constellations for global and regional communication or navigation. We introduce a robust two-stage approach to the frozen low lunar orbit design based on the successive application of non-gradient techniques, the Bayesian optimization and the Nelder–Mead method. The developed methodology has a number of advantages over existing numerical design techniques and allows revealing orbits with the periodic behavior of the eccentricity vector over long propagation intervals in the full dynamical model. By leveraging a convenient nomogram with constellation visibility parameters and lower bound coverage curves, we have identified most suitable low-altitude orbital configurations of Walker type and then adjust them to be frozen. The frozenness condition can be achieved without changing the orientation of orbital planes. Visibility and coverage metrics (multiplicity of continuous coverage for specified sites, polar regions, or the whole lunar surface; position dilution of precision) of candidate constellations are analyzed. Several promising designs of frozen constellations in near-circular low lunar orbits are singled out. The frozen orbit stability and the station-keeping cost are discussed.

Results are given for a kinetic study of the synthesis of a new fullerene derivative containing a diterpene fragment obtained using HPLC and subsequent mathematical modelling. Kinetic and activation parameters were found for the cyclopropanation of fullerene using the Bingel procedure and a reaction mechanism was proposed. The optimal synthesis conditions were found to entail a slight excess of a chlorine‑containing cyclopropanation agent and carrying out the reaction at room temperature.

The paper proposes algorithm for angular motion control of a dynamically elongated spacecraft. The algorithm is based on the direct Lyapunov method using matrix control coefficients. The calculated mechanical torque is implemented using magnetorquers. Control parameters are selected using Floquet theory to ensure convergence to the required motion.

A servicing spacecraft motion control approach for the problem of on-orbit truss structure assembly is developed in this paper. It is considered that a cargo container with a rod set and servicing spacecraft are in orbit initially. The assembly procedure is based on spacecraft free-flight motion between the structure’s specified points. The spacecraft is equipped with two robotic manipulators capable of attaching to the structure and holding rods. In addition, the spacecraft can repulse from the structure with a given relative velocity using a manipulator, so the spacecraft and the structure receive impulses. The repulsion velocity vector is calculated in order to reach the structure target point to deliver and install the rod into the truss structure, or to reach the cargo container and take a rod. The problem of searching the repulsion velocity is formulated as an optimization problem with constraints, taking into account the limited value of the repulsion velocity, collision avoidance with structure, restrictions on the angular velocity and translational motion of the structure in the orbital reference frame. This problem is solved numerically with an initial guess vector obtained analytically for simplified motion cases. The application of the proposed control scheme to the assembly of a truss-based antenna is demonstrated. It is shown that the servicing spacecraft is successfully transferred between the structure points by means of manipulator repulsion. Main features and limitations of the assembly problem using a spacecraft with two manipulators are discussed.

The problem of small tetrahedral satellite formation maintenance in a Low Earth Orbit is being considered. The main purpose is to develop a simple algorithm for tetrahedron control via atmospheric drag. To design a controller, the direct Lyapunov method is used. The control obtained is suitable for tetrahedral formation maintenance, with an average distance of about 1 km. During the controlled motion, the geometric characteristics of the tetrahedron are preserved.

A spin stabilized satellite reorientation maneuver in the inertial space is investigated. Spin axis pointing and nutation damping magnetic attitude control algorithms are utilized. Evolutionary equations for the oscillations of a symmetrical satellite near the required position are derived. The exact solution for the wobble amplitude is obtained for the averaged equations of motion. Spin axis attitude angles relative to the required direction are analyzed. Optimal control gain is found for the reorientation maneuver. Theoretical results are verified with numerical simulation.

Asymmetrical spin stabilized satellite dynamics in the vicinity of the required motion is considered. The principal axis of the maximum moment of inertia slightly deviates from its assumed direction in the satellite reference frame. This is formalized in the cross products of inertia. This inertial uncertainty results in a wobble, that is undesired angular velocity components perpendicular to the rotation axis, and oscillations of this axis near the required direction. The torque-free motion is investigated first. Expressions that explicitly relate satellite inertia parameters to wobble are provided. Wobble evolution under the action of magnetic damping control is analyzed next. Its ampli-tude approximate exponential decay behavior and residual unavoidable wobble level are derived. These expressions are compared with numerical simulation results of nonlinear equations of motion including various disturbance sources.(c) 2022 COSPAR. Published by Elsevier B.V. All rights reserved.

The problem of relative drift elimination between the satellites in the swarm is considered in the paper. The proposed decentralized control takes into account a communication constraint such as limited size of communication area. Only the satellites within the communication area can be identified by relative motion determination system. The control aim is to eliminate the mean relative drift between all the satellites inside the communication area. The purpose of the work is to study the performance of the proposed decentralized control algorithm. It is shown that the system matrix of differential equations for the vector of relative drifts is related to the Laplacian matrix of the communication graph. In the case of the connected swarm, all but one eigenvalues of the system are negative, and the remaining one is equal to zero. It means that all the relative drifts converge to the same value under the proposed control. The speed of convergence is defined by the minimum absolute eigenvalue that depends on the graph topology. The initial drift and the convergence speed make it possible to estimate the communication distance that provides the connectivity of the graph. Considering normally distributed errors of the initial velocity after the launch, it is possible to estimate the distance between any two satellites after the convergence. It allows us to estimate the communication distance that ensures the relative drift elimination between all the satellites in the swarm. The obtained estimations are validated using Monte Carlo simulations. In numerical simulations the swarm of 3U CubeSats in low-Earth orbit is considered. The decentralized control is implemented by differential aerodynamic drag via the change of cross-sectional area using onboard reaction wheels.

The kinetics of sulfoxide formation during oxidation of tert -amylethyl sulfide by cyclohexylidene hydroperoxide in methanol and toluene was studied using mass spectrometry. The data obtained were considered within the framework of a model involving the formation of an intermediate 1-hydroxy-1-peroxy derivative and hydrogen peroxide. A mechanism for the oxidation process was proposed, which makes it possible to describe the observed kinetic regularities. The rate constants of individual stages of the process were estimated.

A formation flying control algorithm using the Lorentz force for Low Earth Orbits to achieve a trajectory with required shape and size is proposed in the paper. The Lorentz force is produced as a result of interaction between the Earth’s magnetic field and an electrically charged spacecraft. Achievement of the required trajectories represents a challenge since the control in three-dimensional space is a scalar value of the satellite’s charge. A Lyapunov-based control algorithm is developed for elimination of the initial relative drift after the launch. It also aims at reaching a required amplitudes for close relative trajectories for in-plane and out-of-plane motion. Due to the absence of full controllability, the algorithm is incapable of correcting all the parameters of the relative trajectory such as in-plane and out-of-plane phase angles. The proposed control allows to converge to the trajectory with required shape and size, though with some oscillating errors in the vicinity of the required trajectory parameters. Numerical simulation of the relative motion is used to study performance of the control algorithm for one case of one controlled satellite and two cases of five controlled satellites forming a nested ellipses and train formations. The convergence time and final trajectory accuracy are evaluated for different control parameters and orbits using Monte Carlo approach.

In this article, five feedback magnetic attitude control algorithms are compared in terms of stabilization accuracy and implementation problems. The control strategies are classic Lyapunov control with scalar gain; the same control strategy with matrix gain and a specific gain-tuning procedure; sliding control with a variable surface; a linear quadratic regulator constructed for a special time-invariant system of a higher degree than the initial time-varying system; and a special controllable trajectory developed using particle swarm optimization. A new sliding surface construction method is proposed in this paper. Surface parameters were changed in every control iteration to ensure that the required control torque component along the geomagnetic induction vector was small. The advantages and drawbacks of the considered methods and their applicability for different target attitudes are discussed.

Purely magnetic satellite attitude control is considered. Special reference motion is constructed which provides local controllability. The angular trajectory is found in the neighborhood of unstable gravity gradient torque equilibrium. Direct solution for the minimization of the quadratic cost function representing the deviation from the equilibrium is derived. Linear equality type constraint on the torque direction is imposed. This solution is compared to the one found by the particle swarm optimization.

This research presents a geometric analysis of Sun-assisted low-energy lunar transfers and several convenient tools that enable the systematic trajectory design in the framework of the planar bicircular restricted four-body problem. By analogy with the patched conic approximation approach for high-energy transfers, a Sun-assisted low-energy trajectory is divided into three legs. Two interior legs, departing and arriving, are located inside the Earth–Moon region of prevalence and designed in the Earth–Moon circular restricted three-body problem, whereas the exterior leg lies outside the region of prevalence and is calculated in the Earth–Moon–Sun bicircular restricted four-body model. The whole trajectory is obtained by smoothly patching the three legs on the boundary of the region of prevalence. The arrival conditions are met by targeting a specific point in the L2 lunar gateway. The interior legs are easily adjustable to the four-body dynamics. The database of planar lunar transfer trajectories can be used to select an initial guess for the multiple-shooting procedure of designing a three-dimensional Sun-assisted lunar transfer in high-fidelity dynamical models.