Engineers at NASA have created a prototype of an electromagnetic propulsion system that would use a linear motor and ramjet engine boost system–instead of an all rocket propulsion system–to fling a vehicle into space. It is the first system that would operate beyond the sound barrier using the combination of an air-breathing ramjet engine and an electromagnetic catapult. The work was presented this week at the Space 2009 Conference in Pasadena, CA.

The system is an alternative to traditionally-used chemical propulsion, which requires large amounts of fuel that limits cargo capacity. It is also a zero-emission, reusable system. The idea of electromagnetic launch using linear motors has been around since 1946, but it was not until the late 1990s that NASA started seriously investigating the idea.

The electromagnetic system works by tethering a spacecraft to a rail or track and using a linear motor to accelerate it to supersonic speeds.

“Linear motors are basically electric motors unwound,” says Kurt Kloesel, an engineer in aeronautics and propulsion and lead researcher of the system at Dryden Flight Research Center, in Edwards, CA. “There are two groups of coils and an aluminum plate goes inside the gap [between the coils], when you hit the juice you are energizing the coils and the inductive reaction of that throws the aluminum plate out of this motor. ”

“You are essentially propelling this vehicle along a track up to the point is disengages from the track and takes off,” says Michael Wright, flight systems integration and test manager of exploration systems and co-principal investigator of the system at Goddard Space Flight Center, in Greenbelt, MD.

Kloesel explains that, as a vehicle starts to pick up speed, it incurs drag: “As you go faster and faster, getting towards the speed of sound, the drag goes up significantly, creating this shock wave structure on the vehicle. And once you pass the supersonic barrier the drag goes down again.”

So what the researchers are proposing, says Kloesel, is using the electromagnetic system to get past the supersonic barrier. Then, the air-breathing ramjet engine–which feeds on incoming air at very high speed–would take the vehicle out of Earth’s atmosphere. The ramjet engine would not be on the rail, but part of the vehicle itself.

The researchers have tested the concept in lab experiments with “bench top models”, which have reached approximately 156 miles per hour. Wright says the technology might even be used someday on highway vehicles and airplanes.