Space Propulsion Group’s New Motor Roars to Life

The flame generated during the Space Propulsion Group's 22-inch hybrid liquid oxygen and paraffin motor test on June 29, 2012. Photo Credit: Space Propulsion Group

Last Friday June 29, the California-based Space Propulsion Group tested a new motor that promises to be a game changer. It’s for a hybrid propulsion system – half liquid fuel and half solid fuel – that’s safer, more environmentally benign, and more economically viable than other rocket propellants. It’s an alternative the motor’s builders think could significantly reduce the price of space accessibility.

Developing the technologies to reduce cost, lower environmental impact, and increase safety of propulsion and power generation systems has been SPG’s mission since its inception in 1999. Their method is to replace toxic and expensive materials with safer and abundant green alternatives.

This latest test was of a paraffin/liquid oxygen hybrid rocket stage. The 22-inch diameter fired for about 20 seconds at the company’s testing facility in Butte, Montana. The roar accompanied by a blindingly bright flame was the fifth test of this particular motor and it demonstrated a flight-weight version of the design. It also gave its designers a wealth on information about the design, useful since it will eventually be scaled up.

Proponents of hybrid rockets praise the designs for bringing together the best of both solid and liquid propellants. Hybrids are simple like solids that burn through once they’re lit but add the safety associated with liquid fuel; combining paraffin and liquid oxygen won’t cause an explosion without a spark. Hybrids are also cheaper. Not only is paraffin much more readily available than traditional rocket fuels, SPG says future propulsion systems using the motor’s hybrid technology have the potential to be five to 10 times cheaper than existing rockets.

Those aren’t the only benefits. SPG’s hybrid is a powerful one that’s on track to compete with more traditional solid and liquid propulsion systems in terms of performance. It could be a match for ATK’s Orion 38 upper stage, for example.

An earlier test of a 10-inch hybrid rocket motor. Photo Credit: Space Propulsion Group

“We believe propulsion drives the cost of access to space and that complexity generally drives propulsion system cost,” said Arif Karabeyoglu, president and chief technical officer of SPG. “By using a commercially available paraffin-based fuel, we have created an economically viable alternative that could significantly reduce the price of space accessibility, as well as help preserve the environment.”

This isn’t the first time engineers have explored the benefits of hybrid propellants. Sergei Korolev, the famed Chief Designer behind the Soviet Union’s early success in space, experimented with hybrid rockets in the 1930s. He used jellied gasoline suspended on a metal mesh and liquid oxygen under its own pressure to launch hybrid rockets of varying size and sophistication. Herman Oberth, Wernher von Braun’s mentor who eventually joined NASA after the Second World War, use tar-wood-saltpeter and liquid oxygen as rocket fuel around the same time.

As for modern hybrids, SPG isn’t the only game in town. Virgin Galactic’s suborbital SpaceShipTwo uses hybrid motors, as does Sierra Nevada’s Dream Chaser.

Later this month, SPG is planning an extended test fire of the same motor. Eventually on a mission, this hybrid will burn between 80 and 100 seconds in a vacuum to propel payload with 5,000 pounds of thrust. In its finished form, SPG’s hybrids will have orbital and suborbital applications. Hopefully the “fraction of the cost of traditional rocketry” factor pans out.


  1. Thanks Amy. I assume that since one of the fuels is LOX the engine can be throttled or even cutoff before burnout?

  2. They have a 25 second video of the test showing how they have stabilized the engine. You can check it out at here.

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