Published: May 14, 2024

Members of the team at the Pawnee National Grasslands.The team at the Pawnee National Grasslands launch site.

Blastoff! The rocket soared over the prairie, its unique engine screaming in unison with cheers from more than two dozen students. The months of work, late nights, calculations, and validations had all been worth it.

Three University of Colorado Boulder aerospace senior design teams had come together and successfully designed, built, and launched a 10’ tall, 50 lb. hybrid liquid/solid fuel rocket at Pawnee National Grasslands in rural Weld County.

“This was a really hard design challenge, a very difficult technical dance,” said Matt Rhode, teaching assistant professor in the Ann and H.J. Smead Department of Aerospace Engineering Sciences and the lead faculty advisor on the project. “A hybrid motor is very difficult technically, requiring analysis in structures, fluids, propulsion, aerodynamics, remote sensing and control. This is a true triumph.”

All CU Boulder aerospace seniors spend two semesters tackling a capstone project that brings together their education with real-world engineering challenges. There are myriad project options for students, from space mission prototypes to reconnaissance drone concepts.

The 36 students of the rocket teams signed up for a project that had bedeviled years of previous seniors.

“I liked the challenge,” said senior Matt Bechtel, who served on the ground system team. “It was something completely different than any other project and had a practical endpoint. We would be able to test it in the exact environment it was designed for, which had a bigger appeal to me than any other project.”

The project saw its genesis more than 20 years ago, when a student approached Rhode about hybrid rockets, which are safer than solid fuel propulsion and not subject to the same U.S. government export restrictions that the turbo pumps necessary for liquid rockets are.

The complexity of the project presented a unique challenge for senior design, and proved to be more than could be accomplished by a single team in just two semesters. This academic year, Rhode split the project into three separate parts: ground systems, airframe, and engine. With dedicated teams for each, they made it to the finish line.

“This project was bigger than any of us,” said senior Gavin Morales, who was project manager for the engine team. “We had highs and lows. Our lowest point was when our second static fire test had an actuation failure with the main valve and just burned out. But we came back, and everybody had the attitude that we’re going to do whatever it takes.”

The rocket mid-flight.The rocket mid-flight.

The students designed and built everything themselves. Even the rocket fuel and oxidizer was manufactured on campus.

“All the mixes went well. The solid propellant was aluminum powder with HTPB, which is a rubbery binder. It’s a non-standard fuel but has high thrust initially, and we were really concerned about getting off the pad, so it made sense,” Morales said.

Each team worked separately toward their portion of the project goals while interfacing regularly to stay aligned. As students like Morales tackled engine design, others were perfecting the embedded systems and dual-deploy parachute systems necessary for the ground station and airframe.

Hybrid solid/liquid rockets are unusual in industry, with Sierra Nevada’s Dream Chaser and Virgin Galactic as the primary users in the United States. Team members, however, discovered commercial interest is high, as the project helped numerous students get post-graduation jobs.

“I’ve been hired by a defense contractor and during the interview process I got to give specific examples from this project that were relevant to their work,” Morales said. “Another team member got a job at SpaceX doing exactly what he did on this project and a member of the ground team posted on LinkedIn about the launch and someone else from SpaceX tagged their boss about hiring him.”

Watching the students progress over two semesters, Rhode was impressed with their commitment to the project.

“These were a bunch of good students,” Rhode said. “They were motivated and dedicated and spent a lot of extra hours and got it done. Students don’t build this kind of rocket because it’s so hard, but this department has outstanding faculty and a world-class program, and these students got the job done.”

Preparing for the final launch, team members spent 36 hours setting up the rocket and ground equipment. Although there were some final hiccups with a load cell and morning fog that took far longer to clear than hoped, when the final countdown came the rocket went up without a hitch.

“I don’t think I’ve ever been so stressed and I don’t think I’ve ever had such instant relief,” Bechtel said.

Additional Photos

Installing avionics in the rocket body.

Erecting the launchpad and rocket.

Mach diamonds visible during liftoff.