The possibility of controlling the motion of a solar sail in a vicinity of a collinear libration point of the Sun–Earth system is investigated. An approach is proposed to constructing laws for controlling the orbital motion of a solar sail in the vicinity of a collinear libration point using nonlinear links of “output signal limitation” type. The approach is based on the use of a stable invariant manifold and elements of the theory of automatic regulation. It allows controllers to be constructed for the task of solar-sail keeping near the libration point. The control is implemented in two cases: changing the orientation of the sail or changing its reflectivity. Numerical examples with the solar sail model from the IKAROS project (2010) are considered.
The isotopic composition of water is an important indicator of its quality and determines its suitability for human use in space missions. The features of the infrared (IR) spectra in the middle region of various isotopic forms of water (–OH, –OD, H2O, HDO, and D2O) included in the crystal structure and adsorbed on the surface of the main rock-forming mineral of the lunar crust, anorthite, are considered. The results of numerical simulation of the main molecule’ vibrations using the ALT/CUSTEP module (Biovea Materials Studio) and experimental studies using an FT-801 IR Fourier spectrometer (Simex, Novosibirsk), as well as an inVia Reflex Raman spectrometer (Renishaw, United Kingdom), are presented. Numerical calculations of the lattice stability have shown that anorthite can contain both hydroxyl groups –OH(D) and molecular water H(D)2O in its crystal structure. The possibility of retaining various isotopic forms of molecular water by anorthite has been experimentally verified, and the corresponding mid-IR spectra of mineral grains with an aqueous film have been obtained. The presence of “light” isotopic forms of water on the lunar surface is confirmed by data from the SOFIA Stratospheric Infrared Observatory (NASA/GAS), but additional research will be required to detect “heavy” water.
The paper presents the results of experiments on board the Avion 6U CubeSat satellite to observe the effects of space weather, hard X-rays and gamma radiation from solar flares and cosmic gamma-ray bursts. The structure and main parameters of the Avion spacecraft, its onboard systems and payload are considered. New data on the dynamics of subrelativistic electron fluxes in the areas of precipitation from the inner and outer belts, as well as the results of observations of processes leading to a significant change in radiation conditions in the near-Earth space are analyzed. In particular, such phenomena include changes in the spatial structure of the distribution of subrelativistic electron fluxes in the outer belt due to magnetic storms and the penetration of solar cosmic rays into the polar cap regions, leading to a significant restructuring of radiation fields in the inner magnetosphere. Examples of detecting bursts of hard X-ray and gamma radiation from solar flares and cosmic gamma-ray bursts are given.
Dynamics of two passively gravitating small bodies of equal mass (planets or asteroids) in the gravitational field of two main bodies (stars) is studied. Stars of equal mass move in a circular orbit with the center at the origin, small bodies are mutually attracted and move in the plane of stars. Relative equilibria of small bodies have been found, and it is shown that all of them are unstable. Internal motions of the system are considered. They are determined by the fact that the center of mass of small bodies always coincides with the origin, and small bodies are so close to each other that gravitational forces between them exceed the gravitational forces from the stars. Equations in Keplerian osculating elements describing the perturbed motion of small bodies are written down. They are reduced to a dimensionless form and then averaged. An explicit formula for the averaged perturbation function is obtained. Bifurcations of phase portrait of the averaged system are investigated.
A lunar eclipse occurs on the Earth orbiting satellite when the Sun, Moon and the satellite are aligned in such a way that shadow of the Moon falls on the satellite. In 2015, Srivastava et al. (2015) extended the well-known Earth shadow models: projection map and line of intersection models for predicting the lunar shadow eclipses of the Earth orbiting satellites. In this paper, we extend other existing available Earth conical shadow models such as algorithm 34 of Vallado (2013), Wertz (2002), and Hubaux (2012) for the lunar shadow eclipses of the Earth orbiting satellites. The extended lunar shadow models are simulated on Indian LEO and GEO satellites: Oceansat-2 and INSAT-4CR. Further, an assessment of the extended models is studied with the lunar shadow model given by Escobal and Robertson (1967) and commercial software package, Systems Tool Kit (STK) of Ansys Inc.
