This rocket will eat itself
Researchers are developing a rocket engine that uses waste heat to melt its own plastic fuselage to burn as fuel
A rocket that eats itself as it shoots for the stars sounds like a tragic metaphor for humanity's technological hubris; only it's the world we're eating in our efforts to escape our earthly limitations.
Oh, and the engine itself is very real.
That's probably not the first thing that's supposed to come to mind, when we consider the latest innovation in rocketry, put together by engineers at the University of Glasgow. The observation isn't about raining on anyone's parade; just recognising the sober realities we face as a species.
Anyway, this self eating rocket engine – or 'autophagic', to use the Latin word – carries some high hopes: that it might some day help the UK take a 'bigger bite' out of the growing space industry.
Curiously, the self-eating engine itself – or at least the concept of it – isn't what you'd call new; pretty vintage in fact. The notion is nearly a century old; apparently it's just been a long time coming off the drawing board.
Now the team at Glasgow have built and fired the first unsupported ‘autophagic’ rocket engine. The Ouroborous-3, as it's called, is claimed to have several potential advantages over conventional rocket designs.
Making it real
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 less propellant needs to be carried in onboard tanks, and the mass this frees up could be allocated to payload instead.
The consumption of the fuselage could also help avoid adding to the problem of space debris, say the engineers behind the project. Such discarded waste that orbits the Earth could hamper future missions, so it would help keep things tidy, as it were.
Overall, it's claimed that the greater efficiency of burning its own body could help autophage rockets take a bigger 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-fuelled rockets.
“A conventional rocket’s structure makes up between five and 12 percent of its total mass,” said Professor Patrick Harkness, of Glasgow University's James Watt School of Engineering, who led the development of the engine.
“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.”
He added: “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.”
Patent pending
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 the 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. These are essential steps in developing a viable flight concept, the team says.
The design developments were showcased in a paper presented at the international AIAA SciTech Forum in Orlando, Florida, back in January 2024.
In the paper, the team describe how they successfully test-fired their Ouroborous-3 autophage engine, and succeeded in producing 100 newtons of thrust in a series of controlled experiments. The test fires were conducted at the MachLab facility at Machrihanish Airbase, Scotland.
Plastic propellant
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 that 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.
“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 postgraduate researcher Krzysztof Bzdyk, of the James Watt School of Engineering, who is 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.”
Development of the team’s autophage engine is continuing with the support of new funding from the UK Space Agency (UKSA) and the Sciences & Technology Facilities Council (STFC), part of UK Research and Innovation (UKRI). The research was further supported by funding from the UK Ministry of Defence.
The autophage engine is one of 23 space technology projects recently selected to share in £4 million from the UK Space Agency, and the STFC. The Glasgow team received £290,000 to help establish further pilot testing of the prototype engine.
“One of the key ways we catalyse investment into the UK’s growing space sector is by backing innovations in emerging areas of space technology,” said Dr Paul Bate, chief executive of the UK Space Agency.
“The University of Glasgow’s impressive work towards an autophage engine is an example of one which has great potential to meet the growing global appetite for developments in the efficiency and sustainability of rocket propulsion.”
Even so, burning it's own plastic fuselage seems a little perturbing in an age where we're desperately trying to restrict the amount of carbon pumped into the atmosphere; easy to see why it might stir a little environmental unease in we lay-folk.
On the other hand, it's surely no worse than the incineration of plastic waste (or just dumping it in the environment). At least Ouroborous-3 might some day offer some bang for its buck.
MC