DFD for Europa Exploration


The Galileo moons of the Jovian system are of great interest for future space exploration due to the belief that three of the four of the largest moons (Europa, Ganymede, and Callisto) contain water (in liquid and/or ice form). So far the eight spacecraft that have visited the vicinity of Jupiter are Pioneer 10 and 11, Voyager 1 and 2, Ulysses, Galileo, Cassini, and most recently New Horizons. NASA has ambitions to send another probe to further study Europa.

At Princeton Satellite Systems, in collaboration with Dr. Samuel Cohen at the Princeton Plasma Physics Laboratory, we’ve been working on the Direct Fusion Drive (DFD) engine, an advanced technology for space propulsion and power generation. Using the DFD, we have simulated two potential missions to Europa, an orbiter mission and a lander mission. The simulations were completed in MATLAB using functions contained within our Spacecraft Control Toolbox.

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DFD at the IEPC

Explosions. Orbits. Stuff hurtling through space at high speed. At the George Washington University campus last week, eyes young and old were trained on the screen, witnessing an amazing story of what can happen in space.

And no, it was not “Gravity”. Nothing against Ms. Bullock or Mr. Clooney, but the 33rd International Electric Propulsion Conference was the place to be last week. The IEPC showcased some fascinating new developments in electric propulsion, including some very promising work on plasma and fusion engines. MSNW gave a great overview of their Fusion Driven Rocket, Ad Astra showed off impressive experimental results of their VASIMR engine, and the University of Surrey presented a novel quad confinement thruster, to name a few.

We were happy to present our paper on the Direct Fusion Drive Rocket for Asteroid Deflection.

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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 Time.com

Only two days after a visit by journalist Michael Lemonick, our DFD fusion drive was featured in his post on Time.com’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

Direct Fusion Drive to Mars – A FISO Talk

The Future In-Space Operations (FISO) working group invited us to give a talk in their weekly seminar track. On Wednesday, July 24, 2013, we gave a presentation entitled “Direct Fusion Drive for Fast Mars Missions with the Orion Spacecraft”. You can find the slides we presented in their online archive here.

We first discussed the need to get to Mars and back home fast (see our recent blog post on the risks of extended durations in space). We then presented some preliminary studies on the double rendezvous problem of Earth -to- Mars -to- Earth, and introduced the Direct Fusion Drive (DFD) as a future propulsion technology that can make this mission happen.

Dozens of people dialed in from around the country. Dr. Dan Lester (U Texas) and Dr. Harley Thronson (NASA Goddard) gave us a warm introduction, and there were a number of insightful questions throughout the talk that sparked interesting dialog. We were also joined by colleagues at MSNW who are developing another form of fusion propulsion, called the “The Fusion Driven Rocket“.

It was an honor to be part of the FISO working group. The questions and feedback we received from this group have been extremely valuable, and it is another sign of the growing interest in fusion propulsion!


Direct Fusion Drive Mars Mission – Deep Space Habitat

Check out our new banner! We modified our spacecraft to use NASA’s Deep Space Habitat:







Image Source: NASASpaceFlight

The habitat has a 500 day configuration, with more than enough room for all of the astronauts and their supplies!


We will use the Orion spacecraft for transfer from Earth’s surface to Earth orbit, where it will dock with the DFD powered spacecraft.  That is what the banner image is portraying! Once the astronauts are aboard the DFD powered spacecraft, they will travel to Mars and back in roughly 10 months, including a 1 month stay at Mars.  After they have returned to Earth orbit, the spacecraft will dock with the Orion capsule. The crew can then safely return to Earth’s surface aboard the Orion!

Twenty-Four People

That is the number of people in the entire history of human civilization who have left Low Earth Orbit (LEO).  You heard me right, only 24 people (all Apollo astronauts) have left the protection of Earth’s magnetic field.  The prospects of journeying past LEO is a daunting one.  There is dangerous radiation in deep space that the magnetic field protects us from.

There are two types of radiation that pose a risk to astronauts: those that originate outside the solar system, the Galactic Cosmic Rays (GCR), and those that come from the sun, called Solar Proton Events (SPE).  The GCR consist mainly of heavy atomic nuclei, while the SPE, as the name suggests, consists mostly of protons.  Both of these types of radiation are high energy, so if they hit an unshielded astronaut they could cause damage to DNA, cell replication, and even lead to cell death.

The SPE, released during solar flares and coronal mass ejections, are especially dangerous as they emit so much radiation that it could be fatal to an unprotected astronaut.  Luckily SPEs are rare and none occurred during the Apollo missions.  Most of the damage from radiation is from prolonged exposure to it, which increases an astronaut’s risk of developing problems such as cancer and cataracts.

Radiation is not the only danger to astronauts on a deep space mission, though.  On a long mission, such as our proposed 308 day DFD powered mission to Mars, the extended period in weightlessness can cause issues as well.  Bones and muscles that normally have to deal with gravity suddenly do not have any load on them.  For this reason astronaut’s bones and muscles (including the heart!) begin to atrophy and lose mass.  The ones most affected are those that fight with gravity: the bones and muscles in the lower back and legs.

Astronaut Ken Bowersox runs on a treadmill using a loading harness.

Image Source: NASA

Astronauts will need to exercise daily to minimize these losses, but even that will not be 100% effective.  Similarly there will be radiation shielding on the spacecraft and a storm shelter for the SPE, but nothing is perfect.  These are just some of the risks associated with a voyage to Mars.  Despite the risks, I do not think we will have any problems finding volunteers to be number 25!

Human Missions To Mars

You may have noticed that we have a new banner image of our Direct Fusion Drive (DFD) transfer vehicle with the Orion spacecraft.


This is because we have been able to shrink the spacecraft so that it fits on top of a single NASA Space Launch System (SLS)


Evolved Configuration launcher which can launch up to 130 metric tons into low earth orbit! The first mission would be to orbit Mars for a few days and then return to Earth. The vehicle would remain in orbit around the Earth. The next SLS launch would bring up a second transfer stage with the lander. A third launch would bring up another Orion and the crew for the landing mission.

The DFD transfer vehicles stay in low-earth orbit where they can be used for a variety of missions, such as deflecting asteroids or lunar missions.

We are currently working on the mission design along with conceptual designs of the transfer vehicle and Mars lander. A key consideration in the mission plan is keeping the astronauts healthy so astronaut physiology is a key part of our research.

Our colleagues at the Princeton Plasma Physics Laboratory


are running two experiments that support DFD. One is PFRC-2, Princeton Field Reversed Configuration 2, which is testing the reactor core. Here you see the experiment in action!


and MNX which is studying magnetic nozzles. We have two more test reactors planned, PFRC-3 and PFRC-4. The last will burn deuterium and helium-3 to produce fusion power. After that we will be ready to build a space version of the fusion propulsion system.

Of course, this reactor could be used for terrestrial power generation. In future posts we’ll talk about sources of helium-3 and alternative fuels that could power this reactor.