PlasmaWorks

At Phase Four we are constantly pushing the envelope of RF plasma propulsion. We have active R&D in plasma physics of RF thrusters, advanced propellants, and new applications of plasma propulsion in space.

ADVANCED DEVELOPMENT SPOTLIGHT: IODINE BASED RF PLASMA PROPULSION

AN IODINE PLASMA THRUSTER
Iodine propellant has been on the roadmap of plasma propulsion around the world for a number of years. Studies by NASA Glenn Research Center affirmed that iodine has promise, but its incompatibility with cathodes found in traditional plasma thrusters limits their use with this advanced propellant. Phase Four’s RF thruster contains no cathode or anode, and in 2021 Phase Four won a Phase 2 Small Business Innovation Research grant funded by AFWERX to develop the first electrodeless iodine plasma thruster in the United States.

WHY BUILD IT?
Iodine propellant  brings a number of critical advancements to the market:

  • it is 5% the cost of xenon, and 25% the cost of krypton, the two standard plasma propellants used in electric propulsion systems
  • its supply chain is more robust and less prone to dramatic price and lead-time swings, compared to xenon and krypton
  • it it similar in atomic mass to xenon, promising similar performance to the standard bearing plasma propellant
  • it is stored as a solid, meaning it can sit fueled on the shelf ready for rapid deployment
  • it is stored at roughly 3.5x the density of xenon, meaning you can pack more total impulse in a smaller volume storage vessel.

Phase Four is partnering with the Air Force Research lab and working closely with NASA to help advance the state of the art in iodine electric propulsion. “There is a growing need for more options for advanced electric in-space propulsion, to provide satellites with better maneuverability and operability in space at an affordable cost, and propellant flexibility could provide new options for in-space propulsion,” said Dr. Eckhardt, Electric Propulsion Lead at AFRL.

The successful development of an advanced propellant like iodine will enable lower cost, higher reliability deployment of infrastructure in space. Stay tuned here for more updates on the iodine development program!

OTHER DEVELOPMENT PROGRAMS

SBIR FOR POWER ELECTRONICS DEVELOPMENT

A PHASE 1 SBIR TO EXPLORE SCALING OF RF POWER ELECTRONICS

One of the key advantages of the Phase Four RF thruster is that it has a simple “PPU” or power processing unit, compared to traditional plasma thrusters. This is because the thruster is a single frequency RF plasma source that operates in the low MHz frequency range. Unlike traditional plasma thrusters there is no heater circuit, no igniter circuit, no high voltage circuit, no anode, no cathode, and no electromagnet. Fewer circuits means smaller electronics packaging, and fewer components that can fail. Unlike “microwave” plasma thrusters, operating in the low MHz range means Phase Four’s PPU are much more power efficient.

Because of these reasons there is interest to develop MHz range RF power electronics for propulsion applications that scale to above 1 kW. This can unlock development of RF thrusters for higher power satellites, allowing them to take advantage of electrodeless plasma thrusters in smaller packages, and using advanced propellants.

The Phase 1 SBIR will identify key users in the US Government that will benefit from advancement of RF power electronics. Stay tuned for more developments!

RF THRUSTER PHYSICS & PERFORMANCE IMPROVEMENTS

EXPLORING A NEW KIND OF RF PLASMA SOURCE

Phase Four’s RF plasma thruster is comprised of an inductive plasma source that operates at 10-100x greater volumetric power density compared to typical RF plasmas seen in the plasma processing industry. At Phase Four we have observed significant populations of very energetic non-thermal electron populations in the plasma plume. Furthermore we have evidence for very high ion temperatures in our system, both of which play a large role in generating thrust. State of art plasma models do not accurately convey these driving factors in our RF source.

To understand these phenomena better, with an eye to improving performance, we map plasma parameters and thrust as a function of every tunable parameter in the system. To optimize this process, we are building an automated thruster mapping system where we will take a new thruster design and automatically vary every tunable parameter while simultaneously measuring performance and plume characteristics. This will accelerate the optimization and performance improvements and generate very large sets of data to lead the development of advanced RF plasma thruster models.

UPCOMING PERFORMANCE IMPROVEMENTS IN THE RF THRUSTER

Phase Four has already performance tested the next RF plasma thruster to enter into the next Maxwell Block. This new thruster doubles the peak specific impulse compared to Block 1 and Block 2 to above 900 seconds, doubling total impulse for a fixed propellant tank size or reducing the wet mass and volume of the total propulsion system.

ADVANCED DEVELOPMENT SPOTLIGHT: AIR BREATHING RF PLASMA PROPULSION

AN AIR-BREATHING ENGINE
Encouraged by initial test results using atmospheric air as propellant in Phase Four’s RF thruster (RFT), and inspired by very low Earth orbit (VLEO) test missions like ESA’s GOCE and JAXA’s TSUBAME (SLATS), Phase Four VP of advanced development Jason Wallace and propulsion engineer Chris Cretel teamed up to conceptualize a US-based air-breathing engine for VLEO and deep space missions.  The core idea is to build a harvester to collect air at ~200 km as propellant and to use an electrodeless RF thruster to accelerate the propellant to compensate for the drag on a spacecraft flying at these very low orbital altitudes. This may unlock a persistent orbital platform at altitudes inaccessible to traditional spacecraft for extended periods of time. Because Phase Four’s RF thruster does not use a cathode it eliminates the critical component of traditional plasma thrusters that are incompatible with the oxygen-rich environment in VLEO.

TECHNICAL CHALLENGES & NEXT STEPS 

Phase Four is actively proposing development in three key areas to help unlock the promise of air-breathing spacecraft propulsion. First, Phase Four must develop and demonstrate a laboratory analog of the VLEO environment. This environment consists of atomic and molecular oxygen, and some nitrogen, flowing at orbital velocities. The second challenge is to map and optimize the Phase Four RF thruster on oxygen-dominant plasmas. If the thruster can generate enough thrust and Isp using oxygen-nitrogen plasmas to compensate for a spacecraft’s drag in this environment, then the third challenge is to model and develop an atmosphere harvester with sufficient efficiency to supply the thruster with the appropriate propellant flow rate. Phase Four is working with funding agencies and academic partners to help attack these challenges and bring this technology closer to reality.