ARPA-E Energy Innovation Summit 2022

We will be at the 2022 ARPA-E Summit in Denver, CO next week – May 23 to 25 – representing our two ARPA-E programs, WIDE BAND GAP SEMICONDUCTOR AMPLIFIERS FOR PLASMA HEATING AND CONTROL and Next-Generation PFRC. The post on our Princeton Fusion Systems website has links to our marketing and technical documents:

We will have booths for each program at the Technology Showcase.

Our ARPA-E funding has allowed us to increase the magnetic field and RF power in the PFRC-2 experiment in pursuit of hotter plasma, a key precursor to demonstrating the conditions needed for Direct Fusion Drive!

Writing about Fusion

Hi! I’m Paige, and I’m an undergraduate at Princeton interested in physics and science communications. This January, I got to work as an intern here at Princeton Satellite Systems. These past few weeks, I’ve been writing about the fusion-related projects PSS is working on, such as their Princeton Field-Reversed Configuration (PFRC) fusion reactor concept and plans for a space propulsion engine.

My first task was to write a four-page report on the PFRC, including its design, market demand, and development timeline. I knew very little about fusion coming into this internship, so first I had to learn all I could about the process that powers the sun and has the potential to supply the earth with clean, practically limitless energy.

Various types of fusion reactors are under development by companies and coalitions all over the world; they differ in the reactors they use and their methods of confining and heating plasma. ITER, for instance, is an example of a tokamak under construction in France; it uses superconducting magnets to confine plasma so that the reaction of tritium and deuterium can occur. 

The PFRC, currently in the second stage of experiments at the Princeton Plasma Physics Laboratory, uses radio frequency waves to create a rotating magnetic field that spins and heats the plasma inside, which is contained by closed magnetic field lines in a field-reversed configuration resulting from the opposition of a background solenoidal magnetic field to the field created by the rotating plasma current. The fusion reaction within the PFRC is that of helium-3 and deuterium, which offers multiple advantages over reactions involving tritium. Compared with other fusion reactors, the PFRC is incredibly compact.  It will be about the size of a minivan, 1/1000th the size of ITER; this compactness makes it ideal for portable or remote applications.

After learning about the design and market applications of the PFRC, I created a four page brochure about PFRC, writing for a general audience. I included the basics of the reactor design and its advantages over other reactors, as well as market estimates and the research and development timeline. I went on to write four page brochures about PSS’s Direct Fusion Drive engine, which will use PFRC technology for space propulsion purposes, and GAMOW, the program under which PSS is collaborating on developing various power electronics for fusion reactors.

These past few weeks have been quite informative to me, and I realized how much I loved writing about science and technology! I learned all about fusion, and I especially loved learning the details of the PFRC reactor design. To summarize the design, research, and development of the PFRC and other technologies within four page flyers, I had to learn how to write about technology and research comprehensively and engagingly for a general audience, which improved my science communication skills.

The Space Show appearance

It was my pleasure to appear on David Livingston’s “The Space Show” radio program last night, now available as a podcast:

People from all over the country called and emailed in their questions about fusion and fusion-propelled spaceflight, and we had a great discussion! David has been running this educational program for 20 years and there are almost 4000 archived episodes covering a wide range of space topics. Author David Brin, whom I met during my NASA NIAC fellowship, is going to be on next week!

So have listen and add to the conversation on The Space Show website!

Direct Fusion Drive Mission to Titan

Titan, a moon of Saturn, is of great interest to space scientists. Titan is the only moon with a dense atmosphere and clouds and with liquids on its surface. Universe Today reports on a masters thesis that proposes a mission using Direct Fusion Drive to put an orbiter around the moon. The thesis, “Trajectory design for a Titan mission using the Direct Fusion Drive,” is by Marco Gajeri under the direction of Professor Sabrina Corpino of the Politecnio di Torino and Professor Roman Kezerashvili of the City University of New York.

The thesis gives an excellent overview of nuclear fusion technology and space propulsion. The author then goes on to do trajectory analysis for the Titan mission using STK. He presents three different mission strategies using Direct Fusion Drive. He includes all of the orbital maneuvering needed to get into a Titan orbit. His mission designs would get a spacecraft to Titan in two years.

Mr. Fusion (8 Wheeler)

A famous scene in “Back to the Future” is when Doc returns from the future and refuels his “Mr. Fusion” generator mounted on his DeLorean:

PFRC is a little too big for a DeLorean but not for a U.S. Army Heavy Expanded Mobility Tactical Truck (HEMTT).

There is a version of the HEMTT that uses Oskhosh’s ProPulse diesel-electric hybrid system with ultra capacitors for energy storage. Electric motors drive the wheels.

A PFRC mounted on an HEMTT would provide electric power directly to the ProPulse system. The diesel might only by used to start up the fusion reactor. In effect we would have a 8 wheeler Mr. Fusion!

MIT Externs at Princeton Satellite Systems

Every year during MIT’s Independent Activities Period in January MIT students can apply for externships at alumni’s places of business. Externships last from one to four weeks. Over 300 undergraduate and graduate students participate each year. As part of the program, MIT also helps students find housing with alumni who live near the businesses sponsoring the externship. Externships are a great opportunity to learn about different types of career opportunities. Students apply in September and go through a competitive selection process run by the MIT Externship office.

This year Princeton Satellite Systems had two externs, Tingxao (Charlotte) Sun, a sophomore in Aeronautics and Astronautics and Eric Hinterman, a first year graduate student in Aeronautics and Astronautics. Eric started January 9th and Charlotte on the 16th after spending time on the west coast visiting aerospace companies as part of an MIT Aeronautics and Astronautics trip. Eric took a break during the externship to attend a meeting at JPL on an MIT project.

Both externs worked on our Direct Fusion Drive research program to develop a space nuclear fusion propulsion system. An artist’s conception is shown below.

Second Unit-render-1d

This project is currently funded by NASA under a NIAC grant. Eric worked primarily on the Brayton cycle heat recovery system that turns waste energy from bremsstrahlung radiation, synchrotron radiation and heat from the plasma into power that drives the rotating magnetic field (RMF) heating system. He produced a complete design and sized the system. He also wrote several MATLAB functions to analyze the system. Charlotte worked on the design of the superconducting coil support structure making good use of her Unified Engineering course skills! Here is a picture of Charlotte and Eric in front of the Princeton Field Reversed Configuration Model 2 test machine (PFRC-2) at the Princeton Plasma Physics Laboratory. Dr. Samuel Cohen, inventor of PFRC, is showing them the machine.


Both Charlotte and Eric made important contributions to our project! We enjoyed having them at Princeton Satellite Systems and wish them the best of luck in their future endeavors!

Pluto Orbiter – the Next Step after New Horizons

The spectacular success of the NASA New Horizons mission has led to many new discoveries about Pluto. The next step would be to send an orbiter. That isn’t easy to do with chemical propulsion but could be done with Direct Fusion Drive.

We’ve done a preliminary mission analysis for a Pluto orbital mission. We are baselining a Delta IV Heavy that can put up to 9,306 kg into interplanetary orbits. These plots show various parameters versus mission duration. The maximum duration is the same as the New Horizons mission, 10 years.


Let’s use the 4 year mission as a baseline. It would use a 2 MW DFD engine to reach Pluto in about 4 years and go into orbit. The engine would thrust for 270 days out of the 4 year mission producing 110 km/s delta-V. The trajectory is shown below


Once there, almost 2 MW of power would be available for the science mission, over 10000 times as much power as is available to New Horizons! The New Horizons bit rate is no more than 3000 bits per second. The high power would allow for a bit rate of over 135 Mbps for data transmission back to Earth using the JPL Deep Space Optical Communications System and a 30 kW laser transmitter. The time in transit is much shorter than New Horizons and would produce significant savings on operations costs. Launch times would be more flexible since gravity assists would not be needed.

DFD would use deuterium and helium-3 as fuels. Only 1700 L of helium-3 would be needed for this project. Current U.S. production of helium-3 is about 8,000 L per year.

Since we would be going all the way to Pluto it would make sense to include a lander. One way to power the lander is using laser power beamed from the orbiter. Here are results for a possible system, beaming over 30 Wh per pass from a 200 km orbital altitude.


Currently, experiments are taking place in the Princeton Field Reversed Configuration laboratory. Here is the machine in operation at the Princeton Plasma Physics Laboratory:


The next step is to build a slightly larger machine to demonstrate fusion. Fusion power generation has been demonstrated in the Princeton Plasma Physics Laboratory Tokamak Fusion Test Reactor and the Joint European Torus but never in a machine using helium-3. A flight engine would follow. Its small size would keep the development and production costs down.

DFD would enable many challenging missions include human exploration of Mars, Europa landers and interstellar probes.

Nuclear Fusion Power

Nuclear fusion power research started in earnest in the 1950’s. Initially, researchers thought that the work needed to produce a fusion power plant would be comparable to that needed to produce the first fission plants. That turned out to be unrealistic as the physics was not well understood and plasma confinement was much more difficult than expected. Many of the first machines were Stellarators. One of the first was Lyman Spitzer’s Stellarator at the Princeton Plasma Physics Laboratory (PPPL).

Many machine geometries were tried such as mirrors and pinches. In the 1960’s the Soviets disclosed success with the Tokamak (тороидальная камера с аксиальным магнитным полем). Unlike the Stellarators, Tokamaks have a circulating current that helps confine the plasma. Since then Tokamaks have been the focus of fusion power research. The Princeton Plasma Physics Laboratory produced 10.7 MW of fusion power in 1994 in the Tokamak Fusion Test Reactor (TFTR). The Joint European Torus (JET) produced 22 MW of fusion power in 1997. In 1998 the Japanese JT-60 produced an equivalent power gain of 1.25, that is 1.25 MW of fusion power for 1 MW of input power. The next step in Tokamaks is the International Thermonuclear Experimental Reactor (ITER).

ITER is a large-scale scientific experiment to demonstrate that it is possible to produce commercial energy from fusion. Its goal is to produce a fusion power gain of 10 at a power level of 500 MW and to generate this power for 500 seconds. Operation with tritium is scheduled to begin in 2027. The next step after ITER is DEMO which will be a prototype of a practical fusion power plant. Demo will produce between 2 and 4 GW of thermal power and have a power gain of 25. After DEMO the next machine will be PROTO which will be a fully commercial power plant. PROTO is expected to built after 2050.

In parallel with ITER many other magnetic confinement devices are under test. These include the U.S. National Spherical Tokamak (NSTX) and the Princeton Field Reversed Configuration (on which DFD is based) both at PPPL. Many new Stellarators are under test including the Wendelstein 7-X in Germany, the Helically Symmetric eXperiment (HSX) in the U.S. and the Large Helical Device in Japan. These devices may result in more economical fusion machines than Tokamaks. The field of fusion researchis very vibrant and work around the world is serving to improve our knowledge of plasma physics and the help solve the engineering problems. For example, recently a new method for reducing instabilities was developed at JET.

The first commercial reactors will likely use deuterium and lithium as fuels. The reaction (used in TFTR, JET and ITER) is deuterium and tritium but in a commercial plant the tritium would be produced from the neutron bombardment of lithium as the D-T reaction produces most of its energy in energetic neutrons. Advanced fuels like deuterium helium 3 and boron proton that produce fewer neutrons are also under investigation. Deuterium and helium 3 would power the DFD. The boron-proton reaction would power TriAlpha’s reactor.

PSS featured on

Only two days after a visit by journalist Michael Lemonick, our DFD fusion drive was featured in his post on’s science section!

Going to Mars via Fusion Power

The article does misstate that Sam Cohen is a PSS engineer, when in fact he is the lead researcher on the PFRC at Princeton Plasma Physics Lab (PPPL). The proposed NASA mission to the Jupiter Icy Moons was JIMO – Jupiter Icy Moon Orbiter Mission. JUICE JUpiter ICy moon Explorer is a European Space Agency mission.

For more information on DFD, go to our fusion propulsion page.

Direct Fusion Drive