6 mins read 26 Feb 2021

Experimental Rocket Engine Being Tested by Australian Collaboration

An Australian-led collaboration has been researching and testing an experimental rocket propulsion system design, which could revolutionise sovereign access to space for the local Australian space industry.

Successful rocket engine test at the DefendTex/RMIT test facility. Credit: DefendTex/RMIT.

In an Australian first, researchers from RMIT, the University of Sydney, and Universität der Bundeswehr in Germany have collaborated to test an experimental rocket propulsion system that could potentially help expand Australia’s space sovereign launch capabilities.

The team, which also includes Australian defence innovation company DefendTex, have released details on last week’s successful test of a non-conventional propulsion system known as a Rotating Detonation Engine (RDE) at their Australian facility after it was designed and developed as part of the Cooperative Research Centre Project for Responsive Access to Space.

To date, RDE technology is currently being researched and tested around the world, with supporters of the experimental design confirming that whilst the technology is still in its infancy, future developments could be utilised to launch Australian rockets, carrying Australian payloads into orbit – thus helping us achieve commercial and sovereign launch capabilities – a goal that several Australian launch companies, as well as the Australian Space Agency, are working towards.

Project technical lead and RMIT University aerospace engineer, Dr Adrian Pudsey, said successful ground demonstrations at the engine test cell, which was custom designed and operated by RMIT with support from DefendTex, had triggered enormous excitement.

“To succeed in such an exceptionally challenging project means a lot to everyone involved,” he said. “Through strong collaboration over the past two years, we now have a truly unique capability and have demonstrated the know-how and science required to push the boundaries of this technology even further.”

What is a Rotational Detonation Engine (RDE)?

To achieve propulsion, conventional rockets burn or combust fuel and oxidizers inside chambers to create thrust. To picture a simplified version of the model, consider a fuel (e.g. liquid kerosene) being injected into a combustion chamber, along with an oxidizer (e.g. liquid oxygen), where it is ignited.

This ignition creates a controlled detonation, that causes the exhaust gases produced in this detonation to press outwards on the combustion chambers walls in all directions. However, at the bottom of the chamber, a nozzle is placed, which allows these exhaust gases to escape.

As defined by Newton’s third law, for every action there is an opposite and equal reaction, the escaping exhaust gases pushing down towards the ground – also press up towards the top of the chamber – thus causing the rocket to propel upwards with thrust.

Schematic of a liquid rocket engine. Credit: Glenn Research Centre, NASA.

RDEs operate a little differently. Instead of burning their fuel at constant pressure, they create thrust by detonating their propellant in a ring-shaped combustor – which once started, can create a self-sustaining wave that travels around the chamber at supersonic speeds, before it leaves the in the axial direction.

At a basic level, it can be described as a cylindrical ring combustion chamber with the head end closed, excluding tiny micro nozzles which are drilled into it, allowing fuel and oxidants to be injected into the system. Once injected, the detonation sequence commences which generates a pressure wave that propagates in the circumferential direction.

As this wave propagates around the cylindrical ring, burnt exhaust products behind the wave (which are at high pressures and temperatures) flow out of the downstream exit and provide the required thrust to propel the vehicle forward.

Schematic diagram of an RDE. Credit: Aerospace America - AIAA.

Some of the theoretical advantages that are being tested include one-time initiation – that is, once detonation is commenced it will continue as the wave rotates around the chamber. There’s also a suggested 25% increase in efficiency due to the self-sustaining and self-compression of detonation waves, which in turn produce a larger thrust for a lower pressure ratio.

The technology is still in its early days but is starting to gain momentum as theory turns to application, and several countries and institutions now are working towards building RDEs for multiple types of applications, including space propulsion and aviation requirements.

DefendTex Chief Executive Travis Reddy said he was proud of the researchers for achieving an ‘Australian first’, while joining an elite list of countries who’d successfully demonstrated this technology.

“A few years ago, little funding and support was available for early-stage research in space technology, and through the Cooperative Research Centre Program the opportunity for collaborative engagement between academia, industry and defence has been made possible,” Reddy said.

“This is allowing Australia to rapidly strengthen capability and expertise in this field to achieve game-changing breakthroughs, future-proofing our economy and capturing a greater share of the space launch market.”

It's still early days ...

Credit: Oak Ridge National Library.

Dr. Pudsey also stated that this technology is in its early stages, and there would be some future challenges that would need resolving before commercial applications could be achieved on a large scale such as resolving how to ensure the engine would not overheat, and even start to consider fully 3D-printed components that could remain actively cooled as part of the next prototypes.

There’s still also longer-term problems that need to also be considered, such as advance modelling of the engine's behaviour, and integrating the engine into a functioning launch vehicle, even before test flights can begin.

The University of Sydney’s Deputy Head of School of Aerospace, Mechanical and Mechatronic Engineering, Associate Professor Matthew Cleary, said computational fluid dynamics simulations, a mathematical method that models the movement of liquids and gases, will be an important element to the improved design of the engine and its testing.

“The rotating detonation engine combustor is an extreme environment that cannot easily be tested. Experimental measurements cannot provide all the information we need to optimise these engines,” Cleary said.

“Not only did the simulations complement the experiments, but at the same time, the new models that we are developing will be validated from the experimental data and then used for future design work.”

The research into RDEs continues, with further scrutinizing and testing of results to be presented in the future.


Video credit: Argonne Lab/ConvergeCFD YouTube