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Self-eating rocket engine burns itself for extra fuel

New developments on a nearly century-old concept for a "self-eating" rocket engine capable of flight beyond the Earth's atmosphere could help the UK take a bigger bite of the space industry.

University of Glasgow engineers in Scotland have built and fired the first unsupported "autophage" rocket engine that consumes parts of its own body for fuel.

The design of the autophage engine (the name comes from the Latin word for "self-eating") has several potential advantages over conventional rocket designs.

Test firing of slef-eating rocket. [Credit: University of Glasgow]

 

 

The engine works by using waste heat from combustion to sequentially melt its own plastic fuselage as it fires. The molten plastic is fed into the engine's combustion chamber as additional fuel to burn alongside its regular liquid propellants.

This means that an autophage vehicle would require less propellant in onboard tanks, and the mass freed up could be allocated to payload instead. The consumption of the fuselage could also help avoid adding to the problem of space debris -- discarded waste that orbits the Earth and could hamper future missions.

Overall, the greater efficiency could help autophage rockets take more payload into space compared to a conventional rocket of the same mass. They could, for example, take tiny nanosatellites into space directly without having to share space on more expensive, conventionally fueled rockets.

The concept of a self-eating rocket engine was first proposed and patented in 1938. However, no autophage engine designs were fired in a controlled manner until a research partnership between the University of Glasgow and Dnipro National University in Ukraine achieved this milestone in 2018.

Now, with support from Kingston University in London, the Glasgow engineers have demonstrated that more energetic liquid propellants can be used, and that the plastic fuselage can withstand the forces required to feed it into the engine without buckling. These are essential steps in developing a viable flight concept.

The team's design developments were showcased recently as a paper presented at the international AIAA SciTech Forum in Orlando, FL.

In the paper, the team describes how they successfully test fired their Ouroborous-3 autophage engine, producing 100 newtons of thrust in a series of controlled experiments. The test fires were conducted at the MachLab facility at Machrihanish Airbase in Scotland.

The Ouroborous-3 uses high-density polyethylene plastic tubing as its autophagic fuel source, burning it alongside the rocket's main propellants -- a mix of gaseous oxygen and liquid propane.

The tests showed that the Ourobourous-3 is capable of stable burn -- a key requirement for any rocket engine -- throughout the autophage stage, with the plastic fuselage supplying up to one-fifth of the total propellant used.

The tests also showed the rocket's burn could be successfully controlled, with the team demonstrating its ability to be throttled, restarted, and pulsed in an on/off pattern. All of these abilities could help future autophage rockets control their ascent from the launchpad into orbit.

Self-eating rocket researchers from the University of Glasgow are shown with their rocket on the test stand (l. to r.): Krzysztof Bzdyk, postgraduate researcher; Professor Patrick Harkness; and Jack Tufft, postgraduate researcher. [Credit: University of Glasgow]

 

 

 

 

Professor Patrick Harkness of the University of Glasgow's James Watt School of Engineering led the development of the Ourouboros-3 autophage engine. "These results are a foundational step on the way to developing a fully functional autophage rocket engine," he said. "Those future rockets could have a wide range of applications which would help advance the UK's ambitions to develop as a key player in the space industry.

"A conventional rocket's structure makes up between five and 12 percent of its total mass. Our tests show that the Ouroborous-3 can burn a very similar amount of its own structural mass as propellant. If we could make at least some of that mass available for payload instead, it would be a compelling prospect for future rocket designs."

"Getting to this stage involved overcoming a lot of technical challenges, but we're delighted by the performance of the Ourouboros-3 in the lab," said Krzysztof Bzdyk, a postgraduate researcher at the James Watt School of Engineering and the paper's corresponding author. "From here, we'll begin to look at how we can scale up autophage propulsion systems to support the additional thrust required to make the design function as a rocket."

Source: University of Glasgow

Published January 2024

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