With Help from Markforged, MIT Rocket Team Successfully Built and Fired a 3D Printed Plastic Rocket Motor

A Sciaky EBAM 3D Printed metal part for the JSF.

We say it all the time, and if that’s not enough, the evidence surely speaks for itself: metal 3D printing is a pretty big deal these days, and growing bigger all the time. There are stories of new developments in metal 3D printing all the time, and the need is so great, Thrinno even introduced a worldwide sourcing platform for the metal 3D printing market. One industry that frequently uses metal 3D printing technology is the aerospace sector, whether it’s individual parts for commercial airplanes, military planes, or aircraft up in space. We’ve seen a metal 3D printed satellite bracket, a huge airliner door hinge manufactured on a powder bed 3D printer, 3D printed flexible metal space fabric, and 3D printed South Korean metal military jet parts.

So naturally, you’d assume that anyone working in the aerospace field would want to 3D print using metal, right? Wrong! One week ago, the MIT Rocket Team at the Massachusetts Institute of Technology (MIT) successfully fired a 100% 3D printed rocket motor, but instead of using metal, the team used plastic. In an MIT Rocket Team post, Charlie Garcia, the team’s Co-Outreach and Publicity Chair, wrote that the team believes this is “the first time anyone has done so.”

Plastic rocket cannon during burn

The Rocket Team has been around for 14 years at MIT, and is an independent student group focused on (you guessed it!) rocket-related projects, from developing lighter, stronger composite airframes and designing and building a custom centrifugal liquid engine. In 2015, the team’s Project Odyssey won first place in the basic category at the Intercollegiate Rocket Engineering Competition. The team’s personal lab was recently renovated, and now features dedicated work stations for a multitude of activities, from an avionics workstation with stocked components perfect for prototyping to flammables storage lockers, which hold ejection charge powder, flammable solvents, and of course, rocket motors.

The team tested its rocket motor case twice, and team members Garcia, Kelly Mathesius, and Matt Vernacchia used a less energetic propellant at first, as the lower heat and pressure would be easier on the motor case. The rocket motor successfully achieved supersonic flow and produced thrust, and while a few millimeters of plastic eroded from the case’s throat, it was in pretty good shape. You can take a look at the first test in this short video below:

The team designed the motor case for single use only, but wanted to experiment with what would happen if it was fired a second time. A more energetic propellant was used for the second test, and the rocket motor case didn’t hold up quite as well. Since the throat was already a little worn from the first test, it eroded fast and was unable to maintain supersonic flow a second time. Little thrust was produced, and the rocket’s combustion quickly became unstable.

Garcia wrote, “While this unstable combustion is not useful for propulsion, it looks really cool in 240 fps slow motion!”

Only the first test of the rocket motor case yielded clean pressure data, and the falling pressure is indicative of the case’s throat erosion. The team has already started some follow-up work to explore more resilient, larger motors, and maybe even flight hardware, and will keep this data in mind for future designs, by “varying the propellant regression rate to match the nozzle erosion.”

Garcia, Mathesius, and Vernacchia spent two weeks working on the project together with Markforged, which supported the team’s efforts and helped them design and print the necessary parts for the two-piece 3D printed rocket motor, using a Mark Two 3D printer and the company’s high-performance Onyx material. The team said that the project would not have been possible without the company’s generous support.

“Printing rocket motors from plastic is a unique accomplishment. Several groups, including SpaceX and NASA, print rocket engines from metal,” said Garcia. “But metal printers are expensive, costing north of six figures. Our plastic motor is produced on an innovative, lower-cost plastic printer, which has a price accessible to hobbyists and small teams. We also designed our case to work with modern composite propellants.”

So while metal 3D printing is definitely a continuously developing and necessary technology, with many possible applications, the MIT Rocket Team shows us that sometimes, you need to go back to the basics for a project to really lift off. Discuss in the MIT forum at 3DPB.com.