The Aerospace Corporation has been advancing a concept for a restartable solid rocket motor (RSRM), a propulsion configuration that has long posed engineering difficulties because conventional solid motors burn continuously once ignited and cannot be throttled or shut down mid-flight.

To solve the problem, the Aerospace Corporation is collaborating with the University of Southern California (USC) and the Naval Postgraduate School (NPS). They are researching the use of the Nanosecond Pulsed Plasma Discharge (NPPD) mechanism to overcome the single-use limitation of traditional solid rocket motors.

NPPD is a type of low-temperature plasma created by very short (typically less than 100 nanoseconds), high-voltage electrical pulses. It has demonstrated utility in combustion enhancement. The research efforts are investigating whether NPPD can augment the traditional chemical spacecraft thrusters relying on combustion for thrust generation.

Why restartability matters for solid propulsion

Solid rocket motors are favored for their simplicity, long shelf life, and high thrust-to-weight ratio. Unlike liquid-propellant engines, they have no turbopumps, propellant lines, or complex valve assemblies, which makes them mechanically robust.

The trade-off has always been control: once the propellant grain ignites, combustion proceeds until the fuel is exhausted. For missions requiring multiple burn periods, such as orbit insertion followed by a later apogee kick, this limitation has historically pushed designers toward liquid or hybrid systems.

A restartable solid motor would retain the mechanical simplicity of a conventional solid while recovering some of the operational flexibility associated with liquid engines. That combination is particularly attractive for small satellite operators, who generally cannot afford the complexity of a liquid bipropellant upper stage but still need more than a single impulse from their propulsion system.

Alejandro L. Briseno, project lead and senior scientist in the Microelectronics Technology Department at Aerospace, said: “This advancement will greatly increase the maneuverability and capabilities of our satellites to support our government and commercial partners”.

He further says, “By leveraging ionic liquid polymers, we have created a fuel-efficient system that taps into unprecedented potential, impacting mission longevity, adaptability, and sustainability. The ionic liquid polymer combines the thermal stability of ionic liquids with the mechanical resilience of polymers, allowing the propellant to remain stable and electrochemically active across a broad temperature range”.

Present status

Currently, the research team has designed a proof-of-concept propulsion device incorporating NPPD technology. The device uses electronically controlled short plasma pulses, which require minimal energy.

The design is fuel-versatile, which allows tailoring of propellants to specific mission requirements. It also does not make use of pressure vessels, facilitating simple device construction. Additionally, its compact form will facilitate integration into a wide range of space platforms, ranging from CubeSats to large spacecraft.

According to the Aerospace Corporation, early research results are encouraging and are pointing toward meaningful advancements in solid rocket propulsion control. The work is currently in the experimental phase in a lab environment.

With technological maturity, the NPPD can enable spacecraft to more effectively engage in multi-phase missions, orbital maneuvers, and deep-space course corrections.

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