Thrust Stand micro-Mass Balance Diagnostic Techniques for the Direct Measurement of Specific Impulse

Abstract

Abstract : A technique has been developed to directly measure the specific impulse from pulsed thruster systems. The technique is especially useful for propulsion devices that utilize solid propellants where a direct measurement of the propellant mass flow is extremely difficult. A torsion balance is used with a horizontal axis of rotation. A thruster is placed on the balance such that the impulse of the thruster firing and the change in mass due to the expending of propellant act in the same direction. The coupled force measurements can then be decoupled to assess the ratio of the impulse to the weight of propellant expended, also known as the specific impulse. A model has been developed to show the utility of the technique for pulsed systems with a firing time less than the natural period of the balance. In this study, a laser ablation thruster using Buna, Viton and Teflon propellants was investigated. Specific impulse measurements on the order of 200 sec have been demonstrated with the laser ablation thruster.