A team of engineers from the University of Glasgow and Oles Honchar Dnipro National University in Ukraine has built and test-fired a new style of "autophage" rocket engine that eats its own structure from the bottom up during flight. They believe it could lead to cheaper, more efficient and less wasteful small satellite launches.

Rather than using a heavy tank to store its fuel, the autophage rocket's main structure is a cylindrical propellant rod consisting of solid, strong plastic fuel on the outside with a core of powdered oxidizer.

As the rod is pushed into the hot engine, it gets vaporized, producing thrust via exhaust gases as well as more heat to burn the next bit of the propellant rod. So the rocket gets shorter as it eats itself from the bottom up.

Many solid fuel motors, the researchers say, don't have the capability of being throttled. With the autophage engine, that's not a problem. You simply increase the speed at which you're feeding the propellant rod in if you want more thrust.

"Launch vehicles tend to be large," says Dr. Patrick Harkness, senior lecturer at the University of Glasgow's School of Engineering, who's heading up the team. "You need a large amount of propellant to reach space. If you try to scale down, the volume of propellant falls more quickly than the mass of the structure, so there is a limit to how small you can go. You will be left with a vehicle that is smaller but, proportionately, too heavy to reach an orbital speed.

"A rocket powered by an autophage engine would be different. The propellant rod itself would make up the body of the rocket, and as the vehicle climbed the engine would work its way up, consuming the body from base to tip.

"That would mean that the rocket structure would actually be consumed as fuel, so we wouldn't face the same problems of excessive structural mass. We could size the launch vehicles to match our small satellites, and offer more rapid and more targeted access to space."

Dropping a large fuel tank from the design helps remove one of the heaviest components of a rocket engine, making for a much more efficient launch vehicle. But as the entire fuel unit is consumed in the launch, it also helps put less space debris into orbit along with the payload.

The team has successfully fired a small-scale test version for 60 seconds at this point, and is working to further improve the design.

Source: University of Glasgow

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