Launching a rocket from a high-altitude balloon

Sitting in their freshman dorm at Stanford, newfound friends Daniel Becerra and Charlie Cox – one from California, the other from Virginia – watched a video of students at the Massachusetts Institute of Technology launching a high-altitude balloon.

Go to the web site to view the video.

“We thought, ‘Well, that’s pretty cool, but that seems pretty easy,'” Cox recalled. “How could we go even higher? We were both studying aerospace. We figured why not launch a rocket off a balloon?”

As sophomores, they wrote a research proposal and won a $1,500 undergraduate research grant to carry out the project during the summer before their junior year. They are now seniors.

“Our project proposes to push the limits of amateur high-altitude exploration by utilizing the advantages of two distinct lift systems,” their proposal said.

“Our two-part launch vehicle will consist of an initial balloon-lift platform and a high-powered rocket. Once the balloon reaches its maximum altitude, the rocket will launch, carrying a suite of sensors and cameras. Using this combination, we will be able to achieve altitudes that would be rendered impractical or impossible by the cost and physics of using these systems independently.”

Neither Cox nor Becerra had launched a balloon or a rocket of that scale before, so they had a long “to do” list. In addition to doing research, they collected components and materials. They also:

• Developed a high-altitude flight computer and ignition system;
• Launched a test balloon with a complete payload, including a camera and active GPS tracking for the flight and for retrieving the balloon;
• Launched a prototype high-powered rocket;
• Developed a mechanical launch guide system; and
• Built a superlight rocket for the final rocket-balloon launch.

Undergraduates Daniel Becerra and Charlie Cox. (Image credit: L.A. Cicero)

If they needed outside expertise, they found it. They invited an aerospace student from the University of California, San Diego, who had been building rockets in the family garage for years, to join them. A NASA astronaut in Texas and an industry engineer in California provided technical assistance, and another friend at Stanford reviewed the flight code and pitched in on launch day.

Cox said one of the project’s key successes was the development and deployment of the mechanical launch system, which went through several iterations.

“The final solution, a pressured tube that utilized a centuries-old technique originally developed for cannons – the ‘sabot’ – allowed us to achieve a stable exit of the rocket from the balloon portion of the vehicle using a very small launcher,” he said.

Cox said the final launch – on Jan. 3, 2014, in Kern County, California – was a success. The rocket launched at 30,000 feet and soared to approximately 45,000 feet. All systems checked out perfectly.

“We were able to prove the feasibility of a number of extremely challenging feats, including real-time autonomous monitoring of the vehicle’s environment – constantly checking altitude and GPS position – so that our algorithm could determine when and where to launch without any input from us on the ground,” he said. “We also demonstrated that it was possible to achieve rocket motor ignition in the thin air and low temperatures at altitude without pressurizing the ignition system, which is critical to reducing cost and complexity in the launch system.”

Cox said the project’s greatest success was bringing together the diverse but necessary systems to demonstrate the feasibility of launching a high-powered rocket from a high-altitude balloon – and showing that it could be done at a much lower cost than traditional methods.

Cox and Becerra enrolled in Introduction to Aeronautics and Astronautics during their sophomore year in order to better understand the project’s technical challenges. Marco Pavone, an assistant professor of aeronautics and astronautics, taught the course, and later became their faculty adviser on the research project.

“The class gave us the tools and resources to undertake the project,” Cox said. “I can think of several instances in which I directly referenced lectures and homework assignments from Professor Pavone’s class to solve specific engineering problems in the project.”

Pavone said their work was “outstanding.”

“In general, aerospace projects tend to be very gratifying,” he said. “They also teach our engineering students how to tackle system engineering challenges, a very important skill for their future careers.”