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

Electric solid propellants (ESPs) are new energetic materials that combust when supplied with electrical power. ESPs combust with the same or higher Isp (242 to 270 s at sea level) as conventional solid propellants, but are inherently safer, cheaper, and easier to handle. Unlike other energetic materials, ESP materials are inherently storable and safe, with sustained ignition only possible via the sustained supply of electrical power, and not by spark or flame. When a non-metalized ESP grain is fitted with electrodes and sufficient electrical power is applied, it ignites and continues to burn energetically until the electrical power is removed.

A 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 design to ensure electrical contact is retained during the pulsing event.

By understanding the ambient 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.

The innovation features ESPs and utilizes its digital characteristics to pulse a solid motor several times, but ensures the ESP grain maintains contact with the electrodes during the pulse. As the propellant burns, the burning face of the grain retreats from the point of ignition and also 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.

The advantage of the innovation is a safe, green, and controllable solid rocket motor that can be electrically pulsed a number of times to control the ignition and extinguishment times to produce a required thrust or impulse bit.

This work was done by Jason Thrasher, Philip Takahashi, and Shae Williams of Digital Solid State Propulsion, Inc. for Marshall Space Flight Center. For more information, contact Ronald C. Darty, Licensing Executive in the MSFC Technology Transfer Office, at This email address is being protected from spambots. You need JavaScript enabled to view it.. Refer to MFS-33256-1.

NASA Tech Briefs Magazine

This article first appeared in the March, 2016 issue of NASA Tech Briefs Magazine.

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