My name is Matthew Daigger and I’m a mechanical and aerospace engineering major at Princeton University going into my senior year. I was given the opportunity to intern and learn at Princeton Satellite Systems this summer. Through this internship, I got a lot of valuable experience in 3-D modelling, research and design. I was able to work with the fantastic engineers at Princeton Satellite Systems as well as Princeton Plasma Physics Lab, who helped whenever questions in their areas of expertise arose.
The Direct Fusion Drive (DFD) is an innovative and exciting new technology being designed by Princeton Satellite Systems. This Rocket engine utilizes the Princeton Reverse Field Cycle fusion reactor setup in order to create both thrust and power for a satellite. The vehicle it is currently being designed for is an exploratory satellite being sent to Pluto. What makes the DFD unique is that it can potentially halve the flight time to Pluto, from ten years to five, as well as have enough fuel left to put the satellite into orbit. Along with this, the craft should have enough extra power to deploy a rover to the surface of Pluto and power a drill. This technology could also open other exciting doors, such as manned missions to Mars, given its capability to cut travel times so drastically.
The first task I worked on this summer was looking into how to incorporate a Brayton cooling cycle into the design of the DFD. This Brayton cycle had a dual purpose. The first is to help cool the reactor and prevent too much heat and radiation from escaping and potentially damaging other parts of the satellite. The second function is to re-use this waste heat and convert it back into usable energy. Two simple brayton cycles running in parallel were chosen in order to maximize heat absorption from the reactor and power developed. The working fluid, its flow rate and the diameter of piping, as well as approximate dimensions of the turbine and compressor were also determined. Another important design factor is the ability for the satellite to withstand launch loads. Preliminary launch load calculations were also done in order to get a better idea for the stresses involved with launch using a Delta IV Heavy launch vehicle.
All of this information helped to conceptualize the physical design, which was drawn up in Inventor. The shielding and incorporation of the Brayton cycle flowing through the shielding were ideas which were confirmed by members at PSS and PPPL. The length of the reactor is a key factor in determining how high energy it will be. The length was chosen so to produce a 1 MW engine. The superconducting coils were also a main topic of research. These are active superconductors which are used to shape the plasma. This is still an ongoing process, as using active coils hasn’t been done before, and our engine has unique weight and size limitations which other similar lab reactors don’t. The debate as to whether to use high temperature or low temperature superconducting coils comes down to total size and weight, including that of a cryo-cooling system in the case of the low temperature coils. High temperature superconducting coils are the more massive option, which generally makes them less desirable for space application. The support structure was designed to keep the size compact while being able to handle the stresses calculated earlier. All information about the RMF heating coils, which are used to actually excite and drive the plasma, was received and confirmed by colleagues at Princeton Plasma Physics Lab. The separation coils at the tail-end of the thruster are power variable, and allow the expelled products to be manipulated, giving the engine high precision control in space travel.
Overall, this was an incredibly interesting and educational experience. The work that the Engineers are doing at PSS is innovative and exciting. The big ideas that are being developed here today are what lead to the next big step in space travel tomorrow. I am very thankful for the opportunity to spend my summer here and learn from some of the best engineers in the industry.