Living Universe Documentary

Back in early September, PSS and PPPL were visited by a film crew from Australia. The project? Living Universe: An Interstellar Voyage, which will include a feature documentary, a 4 episode TV miniseries, and a podcast. The documentary touches all aspects of an interstellar mission, from exoplanets to astrobiology, including transportation – which is where our fusion engine work comes in. The film is in production now and the producers expect to launch in late 2018.

The PFRC experiment at PPPL is the only hardware the documentary team could find with a path to fusion propulsion! Dr. Cohen was able to run the machine for the film crew, and both Mike and Stephanie were interviewed extensively. We discussed the rocket equation and the fundamental speed of fusion products, and how DFD moderates that speed with additional propellant to produce higher thrust. For an interstellar voyage, DFD would have to be much, much lighter than we know how to make it today – but who knows what innovations in magnets are possible in the future!

How will you be able to watch the film and TV series? The film should do the rounds of museums and IMAX theaters. The TV series will be available for streaming from Curiosity Stream, a service which specializes in science, history, tech & nature documentaries. We will post an update when we have a firm release date!


Fusion Power Associates Meeting

I attended the 2017 Fusion Power Associates meeting in Washington, D.C. on December 6 and 7. Fusion Power Associates is a non-profit, tax-exempt research and educational foundation, providing timely information on the status of fusion development and other applications of plasma science and fusion research.

The annual meeting brought together experts in all areas of nuclear fusion research including scientists and engineers from ITER, the Princeton Plasma Physics LaboratoryTAE TechnologiesGeneral Atomic and many others! The meeting gave a great overview of the state of nuclear fusion power generation. We learned that ITER is 50% complete and on its way to first plasma in 2025. Planning has begun on Demo, the follow-on to ITER.

The Joint European Torus plans a D-T campaign in 2019 and hopes to set new fusion benchmarks. We learned about Korea Superconducting Tokamak Advanced Research  (KStar). It has achieved longer than 70 second pulses in H-mode and has suppressed ELM for more than 34 seconds. KStar has in-vessel control coils.

There were several speakers from the University of Rochester along with colleagues from the national laboratories talking about advances in laser compression of fuel pellets. This work is for nuclear weapons research but could be applied to inertial confinement fusion.

I gave the last talk of the meeting on Princeton Satellite Systems and PPPL’s work on DFD, nuclear fusion propulsion for spacecraft.

Second DFD Patent Awarded

We are pleased to report that an additional patent has been awarded for DFD! US Patent 9,822,769, “Method and Apparatus to Produce High Specific Impulse and Moderate Thrust from a Fusion-Powered Rocket Engine”, was published on Nov. 21, 2017. It’s now available from the US patent office website!

Here is a link to the patent from the Department of Energy’s Energy Innovation Portal! The inventor on the patent are Dr. Cohen, of PPPL, and three PSS engineers: Gary Pajer, Michael Paluszek, and Yosef Razin.

Fusion Rocket Engine

Rendezvous with 1I/’Oumuamua

An interstellar asteroid, 1I/’Oumuamua, was discovered on a highly hyperbolic orbit by Robert Weryk on October 19, 2017 moving with a speed of  26.32 km/s. It appears to come from the direction of the star Vega in the constellation Lyra. It would be really great to send a mission to rendezvous and fly in formation with 1I/’Oumuamua to study the asteroid. The high velocity makes it hard to do with current technology.

Direct Fusion Drive (DFD) might provide a answer. We designed a spacecraft with a 1 MW DFD power plant and assumed a launch on March 16, 2030. The following plots show the trajectory and the force, mass and power of the spacecraft during the 23 year mission. As you can see we don’t have to use the full 1 MW for propulsion so we have plenty of power for data transmission and the science payload.


The code for this analysis will be available in Release 2018.1 of the Princeton Satellite Systems  Spacecraft Control Toolbox for MATLAB.

PRISMS Secondary School Student Builds a Sun Sensor

The Princeton International School of Mathematics and Science is a private secondary school in Princeton New Jersey.

One of their students, Savva Morozov, undertook a project to build a miniature 2-axis sun sensor for a CubeSat. Here is his blog post!

My name is Savva, I’m a senior at Princeton Int’l School of Math & Science. This summer I designed, built and tested a 2-axis solar tracking sensor for Princeton Satellite Systems.

The sensor can determine the relative position of the sun using a set of photodiodes. Bearing in mind that the solar sensor would be used in vacuum environment, I decided to make the sensor out of printed circuit boards (PCBs) and solder them to each other. Originally, I wanted to 3D print the sensor, but shifted to the PCB solution to eliminate the risk of outgassing.

Picture 1: solar tracking sensor, 2nd prototype.

My solar sensor design resembles the shape of a square-based pyramid that is approximately the size of a quarter. It consists of 5 PCBs: 4 sides and a base to which the sides are attached. Each side contains a photodiode, and by measuring the voltage outputs from at least 2 of the diodes, the device can determine the sunlight’s direction.

One of the initial problems I encountered was the handling and attachment of the photocells to the side PCBs. Each cell came with an anode and cathode wires already soldered to its front and back. I desoldered the cathode wire from every cell and affixed them to the PCB using a space grade silver conductive epoxy. This way I attached the cell to the device and grounded its cathode at the same time. I thought I killed two birds with one stone, but instead I killed two photodiodes: they were damaged in the soldering process. I resolved the issue in the second prototype: I threaded the cathode wire into a hole in a side PCB and then glued the diode to that same board. This way I didn’t have to use soldering iron at all, preventing possible risks. I then connected the cathode of every photodiode to a common ground and outputted the voltage readings from each cell in a single data bus.

Picture 2: Solar sensor, 2nd prototype, quarter for scale.

The diode, being attached to the outer side of the satellite, might be exposed to light that is reflected off the Earth or satellite surfaces. To partially prevent this, I soldered a shield to the edge of the sensor. Each surface of the shield would be covered with non-reflective material to further decrease the amount of ambient light.

To protect the diodes from the impacts of micrometeoroids and other space debris, I plan to cover the diodes with a thin shield of hard glass crystalline window (tempered glass or sapphire).

Testing the first prototype indicated a number of drawbacks that were solved in the second. Such problems are attaching the shield and the cells to the device, decreasing sensor’s size while increasing its aperture, and making the assembly process simpler.

I also calibrated photocell’s voltage outputs and their exact positions to account for manufacturing imperfections and for those created during the manual assembly of the device. I wrote a program to calculate the vector of sunlight direction and using Processing IDE created a visual representation of my sensor as well as its output result:

Picture 3: Visual illustration of a working solar sensor.

In order for my sensor to survive the vacuum environment, I attempted to use only space qualified materials in the device’s assembly: PCBs, solder, epoxy, and sheets of copper. I have finished working on the development stage of designing the solar sensor. Testing procedures on my last prototype showed that such device would be ready for further usage and launch.

A Great Quote!

For everyone doing cutting edge work, here is a great quote from a pioneer in rotary wing aircraft:

Every very radical research needs an eccentric person who, by a certain amount of freedom from convention is not too afraid to go far afield for solutions.


Gerard Herrick

Richard Whittle, “The Dream Machine: The Untold History of the Notorious V-22 Osprey,” Simon & Schuster Paperbacks, 2010, p. 20

AIAA Space Forum paper on Pluto mission is live

Sadly, the AIAA Space Forum in Orlando, FL was canceled due to hurricane Irma. So, we didn’t get to present our paper on our DFD mission to Pluto. AIAA has, however, published all the forum papers and is providing free access for a few months in lieu of the actual conference. This means anyone can download it!

Fusion-Enabled Pluto Orbiter and Lander paper:

Open access to the AIAA Space Forum technical program:


Sun Sensor Design Project


My name is Anna Cruz and I am Mechanical Engineering major and rising sophomore at The College of New Jersey (TCNJ). This summer I was given the opportunity to work at Princeton Satellite Systems (PSS) as their engineering intern. The most recent project I have been working on is the mechanical design and 3D model of the sun sensor that will be made using a 3D printer. All the models I have created were done using SolidWorks. I have been working alongside my coworker Gary, and manager of the project Mike that have done a wonderful job in giving me helpful tips when I needed it the most.

Figure 1.1

This sun sensor will fly on a CubeSat or small spacecraft in low earth orbit. The main body of the sensor has a pyramid shape with a solar cell on each side. I had already been given a drawing and STEP file of the circuit board that will be attached to the sun sensor so the dimensions for the sensor I am making were based on that single part. To start, I did some research on different sun sensor models to get a sense of how they work. I first needed to figure out how these parts would be assembled. To make it simple, I decided to use 4 screws on each corner to attach the sensor to the circuit board. The base is rectangular with dimensions a bit larger than the circuit board to allow space for the screw clearance holes and room for the screw head as shown in figure 1.1.

Then it was time to design the pyramid itself. I created a pyramid with a flat top and placed it at the center leaving space from each edge of the pyramid to the edge of the rectangular base adjusting the dimensions as needed. The pyramid holds one solar cell on each side. To make sure that the cells fit nice and snug, I added a placeholder feature deep enough to hold the chip. However, after discovering that the solar cell did not have a flat surface and that there was a wire attached to the back and front of the chip, my original design had to change completely! After a few days of trying out new designs and working with Gary to find the best solution, we liked the idea of creating a trench like feature in the middle of the placeholder extruding a bit further into the pyramid. This will accommodate the wire from the back of the solar cell as well as increase the tolerance regarding the location of the wire for each chip. As for the wire coming out the front of the chip, I added a rectangular slot feature next to the placeholder which channels all the way down the pyramid shown in figure 1.2. This will help gather and guide both wires all the way down one channel to the circuit board. There is one channel on each side of the pyramid, a total of 4. Aside from these hollow channels, the entire pyramid is a solid piece.

Figure 1.2

The placeholder for the solar cell is deep enough so that nothing sticks out of the pyramidal faces. This will aid in the application of the glass window on top of each solar cell using a space qualified adhesive. The same adhesive will be used to attach the solar cells to their placeholders.

Because the sun sensor is attached to a spacecraft, there is a high change of reflective light bouncing off the spacecraft and onto the sensors. To prevent this, a lip feature around the pyramid needed to be added. I went along and added an extruded frame like feature surrounding the pyramid leaving a gap between the end of the frame and the end of the pyramid. The outside edge of this feature is perpendicular to the base surface. The inside edge is at about a 50 degree angle from the base surface as shown in the section view in figure 1.3.

Figure 1.3

Since this sun sensor will be used in space, the plan is to do a vacuum test of this part. As of right now, I am currently waiting on the entire part to be printed so that it could be tested. I am very excited to see the final product!

WHYY Radio Story Featuring DFD

WHYY reporter Alan Yu has done a radio show featuring our work for The Pulse, which presents stories of health, science, and innovation. You can read the article and listen to a podcast of the show segment, which features Stephanie, Mike, Sam, and members of the NASA NIAC program including director Jason Derleth, external council member Ariel Waldman, and NIAC fellow Phil Lubin.

The headline for the show is, aptly, “Inside the NASA program that makes science fiction technology real.” Reporter Alan Yu visited the lab to see the PFRC in action during development of the show. The show played on the radio today, July 21, at 9 am and will repeat on Sunday at noon. Enjoy!