Dual mode operation of a hydromagnetic plasma thruster to achieve tunable thrust and specific impulse

Abstract

We report here on initial studies of a pulsed hydromagnetic plasma gun that can operate in either a pre-filled or a gas-puff mode on demand. These modes enable agile and responsive performance through tunable thrust and specific impulse. Operation with a molecular nitrogen propellant is demonstrated to show that the hydromagnetic thruster is a candidate technology for air-harvesting and drag compensation in the very low Earth orbit. A dual mode operation is achieved by leveraging propellant gasdynamics to change the fill fraction and flow collisionality within the thruster. This results in the formation of distinct modes that are characterized by the current-driven hydromagnetic waves that they allow, namely, magneto-deflagration and magneto-detonation, respectively. These modes form the basis of using gasdynamics to enable responsive thruster performance. Using time-of-flight emission diagnostics to characterize near-field flow velocities, we find that a relatively dramatic transition occurs between modes as gas is allowed to expand in the thruster, with exhaust velocities ranging from 10 to 55 km/s in the deflagration and detonation regimes, respectively. Simulations of the processed mass bit offer the first glimpse into possible thruster performance and trade-offs between specific impulse and thrust. An impulse bit tunability of ∼22% is predicted, with differing propellant fill fractions when operating in a burst mode.