Dual Mode Feasibility Testing

Advances in in-space transportation is tantamount to the successful attainment of NASA’s goals which include “Go” domain of the recent Space Technology Mission Directorates (STMDs) Strategic Framework language. Specific call outs include green and ‘dual mode’ propulsion capability. As the Agency seeks cost effective and high impact technology development, new ideas must be developed, demonstrated, matured, and tested both in laboratory scale and in-flight opportunities.

Rocket propulsion technology is rather broad but no one type of propulsion is optimal for all space applications. Rockets which rely on chemical reactions (either monopropellant or bi-propellant) are beneficial in high thrust applications but are limited by the efficiency of the chemical reaction. As such, they produce relatively low specific impulse (the thrust per unit mass flow of propellant). Rockets which rely on ionized gases accelerated through electric fields or electrospray thrusters are higher in specific impulse and can achieve much higher exhaust velocities than chemical thrusters but they do not produce nearly the high thrust performance of chemical rockets. Typically, propellants are useful for either chemical or electric propulsion. Thus, if a mission wanted to use chemical and electric propulsion, system weight might be a driver as there would be a need for two internal propulsion systems. The green dual mode propulsion uses an ionic liquid (AF-315E) or ASCENT, developed by AFRL as both a chemical monopropellant for a chemical thruster and also as an electric propellant using the same propellant and feed system, allowing an operator to do both high thrust and high efficiency propulsion when operating in one or the other mode. This can improve the range of possible propulsion mission use cases vs. “all chemical” or “all electric propulsion.”

The green dual mode work at MSFC has relied heavily on CIF funds, CANs, university grants, the NSTGRO program, and the SBIR/STTR programs. Green dual mode research has engaged university, industry, as well as the NASA workforce. Having fresh and diverse perspectives has overall strengthened the technical products created from the green dual mode activities over the years.

Dual mode propulsion has the potential to expand the envelope on the capabilities of using green propellant on future space missions. ASCENT has both a 50% higher specific impulse density and a lower vapor pressure lending it favorable for both severely reducing cost and risk to ground handling and propellant loading operators as well as improved performance during in-space translation operations. Currently, the technology is applicable to small spacecraft but as the technology matures, there’s a strong possibility for larger dual mode systems which can fly more complex missions to a variety of destinations in deep space.

Much work remains in maturing dual mode propulsion technology, future potential investments should include the development of lower cost catalyst materials and electric micropumps to reduce propellant pressure for operating in electrospray mode. Overall, a technical audience has much to be excited about in terms of the potential for dual mode technology development. Thus far, several missions have flown ASCENT- including the Green Propulsion Infusion Mission (GPIM) and the recent Lunar Flashlight mission. The Green Propulsion Dual Mode (GPDM) mission is seeking to expand the capability of ASCENT with the hopes that data collected and lessons learned can be applied to future dual mode green missions.

This is early/mid-stage (TRL 3) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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