Vol 53, No 4 (2019)

Venus, the closest planetary neighbor of the Earth in the Solar System, is eminently suitable for performing gravity assist maneuvers by a spacecraft for a low-cost change of its orbit inclination relative to the ecliptic. We calculate the resonance values of the spacecraft asymptotic velocity relative to the planet, such that each orbital period of the spacecraft after each gravity assist maneuver are commensurate with the few orbital period of Venus, providing a new encounter with it. This enables an increase in the orbital inclination of the spacecraft using gravity-assist maneuvers without transitions to adjacent resonances along the invariant line of the main resonance on \({{\operatorname{V} }_{\infty }}\)-sphere, reaching a maximum inclination. A Venusian invariant has been obtained that does not vary after performing gravity assist maneuvers near Venus. An adaptive semianalytic method and its geometric interpretation for creating a sequence of sequences of gravitational maneuvers near Venus for a low-cost changes in the orbital inclination of the spacecraft have been presented.

This paper presents the results that confirm the sublimation activity at the perihelion of the primitive main-belt asteroids 779 Nina, 704 Interamnia, and 145 Adeona; this activity was first discovered in September 2012 (Busarev et al., 2015; Busarev et al., 2016). The new spectrophotometric and/or UBVRI photometric observations of Nina, Interamnia, and Adeona were carried out in 2016–2018 during a regular perihelion passage of these asteroids. Additionally, probable spectral signs of weak sublimation activity were discovered on another two primitive main-belt asteroids, 51 Nemausa and 65 Cybele. In this study, we discuss the conditions for the occurrence of a periodic and/or continuous sublimation process on main-belt asteroids with low-temperature mineralogy; in particular, the conditions that are associated with their formation close to the “snow line” or beyond. We also consider general evolution processes that are able sustain a sufficiently high concentration of water ice close to the surface of the bodies in question and, therefore, their continuous sublimation activity, or lead to the recurrence of extinct activity.

This article presents a model of conjugated Gaussian random particles, which are convenient for simulation of irregular particles that constitute cometary dust. Computer simulation is conducted for the polarimetric properties of these particles; phase dependences are calculated for the linear polarization degree. The calculated results are used to interpret cometary polarimetric observations and determine possible physical and chemical characteristics of comets as well as the variation range within which the model adequately describes the observed data. The model calculations are used to refine the empirical formula that describes the phase dependence of the linear polarization degree for the cometary continuum.