A survey of current developments in surface tension devices for propellant acquisition

T task of a propellant expulsion system is to supply gas-free propellant on demand to spacecraft thrusters for the duration of the mission. For orbital spacecraft, which may experience periods of adverse or near zero-gf accelerations, the expulsion system must assure that all or portions of the propellants are in contact with the tank outlet; that gas is prevented from entering the tank outlet during thruster startup; that pressurization gas entrained in the settling propellant bulk does not enter the tank outlet; and that propellant vortexing, gas pull-through, and propellant slosh do not significantly reduce the system expulsion efficiency. Many types of positive propellant expulsion systems have been developed for orbital spacecraft, each with advantages and problems, as summarized in Table 1. Development of these devices usually centers on. mechanical testing in simulated prototype environments. Although performance of these devices has been good, the reliability concern of the mission planner increases when very long missions are considered because there are no established accelerated life testing techniques. Recent experience with capillary systems has shown that they satisfy expulsion system requirements as well as the desire for passive simplicity. Indeed, the question of long-