The autophage engine uses waste heat from combustion to sequentially melt its own plastic fuselage as it fires. It then feeds the molten plastic into the engine’s combustion chamber as additional fuel to burn alongside its regular liquid propellants.
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 Glasgow University and Dnipro National University, Ukraine achieved this milestone in 2018.
Now, with support from Kingston University, 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.
In the paper, the team describe how they test-fired their Ouroborous-3 autophage engine, producing 100 newtons of thrust in a series of controlled experiments.
The Ouroborous-3 uses high-density polyethylene plastic tubing as its autophagic fuel source, burning it alongside the rocket’s mix of gaseous oxygen and liquid propane.
The tests showed that the Ourobourous-3 is capable of stable burn throughout the autophage stage, with the plastic fuselage supplying up to one-fifth of the total propellant used.
The tests also showed that the rocket’s burn could be controlled, with the team demonstrating its ability to be throttled, restarted and pulsed in an on/off pattern.
In a statement, project lead Professor Patrick Harkness from Glasgow University’s James Watt School of Engineering said: “These results are a foundational step on the way to developing a fully-functional autophage rocket engine. 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 per cent 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.”
Development of the team’s autophage engine will continue with the support of new funding from the UK Space Agency and the Sciences and Technology Facilities Council.