The purpose of this work was to create a safe, green, controllable solid rocket motor that can be pulsed a number of times with electricity to control the ignition and extinguishment times to produce a required thrust or impulse bit. The innovation features an Electric Solid Propellant (ESP). The key problem is that the geometry of the ESP grain changes because of the evolution of the propellant to exhaust gases, but a closed electrical circuit is required to keep the electrical power applied to the grain and continue burning. The chamber pressure is utilized in the multi-pulse motor (MPM) design to ensure electrical contact is retained during the pulsing event.

The MPM is a solid propellant rocket motor that is able to produce a number of pulses for various thrust levels (5-30 pulses and thrusts between 0.25-1.5 N, depending on the electric power delivery system) that can be turned on and off through the application of electrical power.

The functional operation of the MPM is that as the propellant burns, the burning face of the grain retreats from the point of ignition and generates a chamber pressure. This innovation utilizes the chamber pressure to keep the propellant grain in contact with the point of ignition to ensure consistent gas generation from the ESP while electricity is applied to the system. Non-conductive inserts ensure that the propellant and the two electrodes are the only parts of the thruster assembly to be part of the electric firing circuit. By understanding the current density and electric field acting on the ESP in the thruster, the point of ignition can be determined, and utilizing the mechanical features of the thruster, the pulsing thrusts can be turned on and off electrically.

Peripheral equipment includes the electrical power delivery system. By applying electrical power at various frequencies, voltages, and currents for various lengths of time, a chosen level of thrust or impulse bit can be achieved. Because the MPM is intended to be disposed of once the pro-pellant is entirely utilized, there is no maintenance other than replacement.

This work was done by Jason Thrasher, Phillip Takahashi, and Shae Williams of Digital Solid State Propulsion for Marshall Space Flight Center. NASA is seeking partners to further develop this technology through joint cooperative research and development. For more information about this technology and to explore opportunities, please contact Ronald C. Darty at This email address is being protected from spambots. You need JavaScript enabled to view it.. MFS-33329-1

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This article first appeared in the September, 2017 issue of Tech Briefs Magazine.

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