Faster. Further. Higher. A lot is riding on the back of a revolutionary Australian scramjet engine. Including the future of the US military’s hypersonic warfare capability.
The United States defence establishment watched in despair last year when China launched a hypersonic aircraft that flew south over Australia, turned left twice and then eventually flew over the US from the south.
The US has nothing like it and has to catch up fast.
The US Defense Innovation Unit wants a testbed drone to skip through the upper atmosphere at extreme speeds. Ultimately it is expected it will use hypersonic aeroplanes and drones for reconnaissance, weapons delivery; satellite launch and maybe far into the future, manned flight.
Surprisingly the first contract the Innovation Unit let was to an Australian company with a unique hydrogen-powered, printable engine – Hypersonix.
“This is where you can think of Top Gun 2,” says Hypersonix Launch System’s managing director David Waterhouse. “But we’re not letting Tom Cruise anywhere near our plane.”
Hypersonic is defined as any speed greater than Mach 5 (6200km/h). The famous SR-71 Blackbird spy plane of the Cold War flew at up to Mach 3.3 (4100km/h).
The Dart AE testbeds, to be delivered next year, will be single-use vehicles only.
But the Brisbane-based deep tech company’s goal is to develop a reusable commercial low-orbit delivery system and it’s recently received a new version of its engine from Europe.
It’s just like the old one, with one crucial difference – it’s made of High-Temperature Ceramic Matrix Composites (HTCMCs).
“The scramjet engine itself has been designed to work between Mach 5 all the way up to Mach 12 (14,800km/h). So it’s really the ability to manage the thermals for the engine that determines what speed we get out of it,” says Waterhouse.
The scramjet engine, called Spartan (Scramjet Powered Accelerator for Reusable Technology Advancement) is printed from a composite material known as Inconel 718, and is limited to Mach 7 (8600km/h).
They’re combining materials in a way that you couldn’t do just five or 10 years ago.”David Waterhouse
“Inconel 718 has been around since the days of the Saturn V (Moon launch rocket),” says Waterhouse.
“But now I can 3D print it and do things you could never imagine. And there’s the whole additive engineering thing. They’re combining materials in a way that you couldn’t do just five or 10 years ago.”
This high-strength, corrosion-resistant nickel chromium material has a long history of use in the space industry because of its ability to cope with temperatures up to 700C. Coatings are added for specific hotspots.
“But the ceramic matrix composite is good for temperatures above 1800C for sustainable operations,” Waterhouse explains. “So that would be the engine we would use for our reconnaissance drone design”.
It burns hydrogen.
“Hydrogen is great,” says Washington. “It burns clean – it doesn’t leave coking or anything behind. And that enables reusability. But the great thing about the hydrogen economy is you can buy fuel tanks off the shelf now. A few years ago, building them in-house would have cost heaps. And I’d have to blow a bunch of them up before I was certified to use them.”
At the heart of Hypersonix’s SPARTAN scramjet technology is the way its shape contains – and exploits – different shockwaves generated by high-speed flight. When combined with hydrogen, the explosive interaction generates thrust.
All it takes to turn the engine off and on again are the valves of a fuel injection system.
“Basically, this injects fuel at the right spot for the right speed,” explains Waterhouse. “A lot of other scramjets are designed for a fixed speed. But we’ve got an accelerating scramjet. And the same design works over that whole range from Mach 5 to theoretically Mach 12, with no moving pieces”.
And hydrogen brings another set of advantages.
“Hydrogen has the most energy per kilo, and I’m worried about weight,” Waterhouse says. “And a kilo of hydrogen can give me 1000km of range. So I don’t need a lot.”
Other hypersonic engines use kerosene which is more complex.
“You get coking, and you can’t turn it on and off when in flight,” he explains. “And when you fail to relight, you fall out of the sky. That’s been a big problem with some of the US tests. Whereas with hydrogen, we can simply turn it on and turn it off.”
The patented SPARTAN scramjet has other unique features that put it ahead of a pack of more than 60 contenders for the US Pentagon hypersonic contract.
“Because of its fixed geometry with no moving parts, it’s very reliable,” says Waterhouse. “It’s very inexpensive to build. And literally, you can fly it back, use a toothbrush to scrape off any unwanted grit, and then fly it again”.
Scramjets are not a new concept, but they have proven to be an especially difficult one.
Their predecessor, ramjets, were experimented with before World War 2. Scramjets evolved out of them in the 1950s. And the University of Queensland began its hypersonic engine research in 1981.
But the idea only recently became viable.
“We’ve had the convergence of three distinct sets of technology,” says Waterhouse.
Modern materials, hydrogen and the third: supercomputers.
“It’s cheap and cheerful. What would have taken me a week to run just a decade or two ago I can now do in 15 minutes. And it’s affordable to even small companies.”
Waterhouse is confident in his product, although it is still undergoing testing.
What would have taken me a week to run just a decade or two ago I can now do in 15 minutes.David Waterhouse
The 1.8m long scramjet engine is being printed in Australia by Amiga Engineering in its Inconel 718 form. It’s assembled from three parts as the printer can only handle segments up to 60cm.
The ceramic composite version was supplied by a European manufacturer as Australia doesn’t yet have the capability to print carbon matrix composites.
“What we have here is a pilot manufacturing testbed,” says Waterhouse. “We’re trying to make sure we can measure its performance, build it to the tolerances we need out of the materials we have and do thermal testing on it. And we also have to push hydrogen through it to make sure it doesn’t leak through the composite matrix”.
The tests are expected to be undertaken Wallops Island Research Range in Virginia in the US in 2024.