The flight of a spacecraft is characterized by the alternation of active sections of the trajectory, when the propulsion system is operating, and passive sections, in which the liquid components of the fuel in the tanks are under the influence of microgravity and, as a result, various disturbing factors (actions: aerodynamic forces, solar wind, internal gravitational forces, disturbances from the engines of the orientation and stabilization system, etc.) can occupy any position in them. At the same time, the situation is not ruled out when the gas phase can get into the flow line, which in the future can lead to a failure to restart the propulsion system and an emergency end of the mission. Therefore, an almost obligatory element of the systems for storing and supplying liquid rocket fuel components of the propulsion system of a spacecraft is the means of ensuring fuel continuity, the main criterion for the perfection of which is the amount of residual fuel components that cannot be produced due to a violation of the fluid continuity at the inlet to the propulsion system. The design of the fuel continuity means is directly determined by the internal geometry of the tank and the characteristics of the pneumohydraulic system of the spacecraft. A significant complication of the design of the fuel continuity means occurs in the presence of several factors that are present when a spacecraft performs a flight task: multiple launch and stop of the propulsion system, performing complex maneuvers under conditions of multidirectional external force impulses, which is just inherent in spacecraft. The position uncertainty and heterogeneity of the boundaries between the boost gas and fuel components at the time of launching the propulsion system require additional measures to prevent premature gas breakthrough into the flow line with its subsequent entry into the propulsion system. Therefore, over more than five decades, fuel continuity tools have been developed, the operation of which is based on various principles. At the same time, capillary-type fuel continuity means are most widely used. During this time, the basic physical principles of the behavior of a liquid under the action of capillary forces under weightless conditions were studied, the main types of designs of means for ensuring fuel continuity were determined, and the range of tasks they solved was described.
