Beating the hypersonic heat barrier: all weapons, no quick flights

New ways of beating the heat barrier to sustained hypersonic flight are being researched at the University of Queensland.

They involve composite materials that could replenish the critical heat abraded surfaces of a vehicle flying at eight times the speed of sound and allow it to reach European cities from Australia in as little as two hours.

The UQ has been at the leading edge of hypersonic flight for two decades. After pioneering the shock tubes that allowed hypersonic model testing in the 90s it took on the challenge of generating positive thrust by a hypersonic engine in flight. On July 30, 2002, one of its tiny Hyshot test vehicles piggybacked a rocket ride at Woomera to demonstrate hypersonic combustion for the first time, for all of around five seconds at more than mach 7.6

Operating on a shoe string budget, that breakthrough upstaged a massively funded US program attempting to achieve a similar result.

But this next stage in the UQ program, while still funded at a tiny fraction of the cost of overseas programs, is attracting strong interest, and money, from home and abroad.

To really grasp what it is doing it necessary to watch this video (below) as well as read the press release that follows it.

[youtube]https://www.youtube.com/watch?v=m0OG_NnL61k[/youtube]

University of Queensland researchers are testing new materials to withstand the extreme heat experienced by hypersonic vehicles in flight so they can fly for substantially longer.

Previous Australian experimental flight tests of scramjets, a type of very fast jet engine, have not lasted longer than five seconds.

The tests, conducted at Woomera in South Australia over the past eight years, have used scramjet engines made of conventional materials which have problems with extreme heat including melting, and are not designed for re-use.

However, further experimental tests are planned in 2011 through to 2013 in the HiFIRE series at Woomera using free-flying engines and eventually, a whole free-flying vehicle which will generate enough thrust to fly for a minute.

The leader of UQ’s Hyshot scramjet experiment program and UQ Professor in Hypersonic Propulsion, Professor Michael Smart said the project was testing new composite materials for the longer flights at Mach 8 (eight times the speed of sound).

“If they can fly for a minute, they can fly for an hour,” he said.

“A scramjet-powered vehicle could fly between London and Australia in two hours so we’re looking at materials that can survive hypersonic speeds for longer periods.”

[Hypersonics is the study of flight speeds faster than mach 5 (five times the speed of sound or more than twice as fast as the Concorde). Supersonic speed is greater than mach 1, while modern commercial airliners fly below the speed of sound. ]

Professor Smart said the research was particularly looking at new materials for leading edges, the parts of the wings that first contact the air.

In high speed aircraft air friction can cause extreme heating of the leading edge — temperatures on the surface of an object travelling at mach 5 can reach 1000 degrees C . These high temperatures can not be sustained by most materials.

Another challenging problem area is inside the scramjet engine, which must handle a corrosive mix of hot oxygen and combustion products, as well as high thermal, mechanical and acoustic loadings.

At higher speeds the temperatures can be even more extreme — for example at mach 8 the temperatures can reach 2700 C at the leading edge and 3000 C in the engine combustion chamber.

Professor Smart said hypersonic propulsion heating problems could be overcome through the selection of materials, as well as design and cooling arrangements.

He is working with ceramic composite materials pioneer Professor John Drennan, Director of UQ’s Centre for Microscopy and Microanalysis, and postdoctoral researchers Dr James Turner and Dr Anna Lashtabeg on the current project. Student David Yu (School of ITEE,eResearch Centre) has prepared animations showing processes occurring at extreme temperatures.

Professor Drennan is looking at a number of concepts to enable hypersonic vehicles to handle extreme heat for prolonged periods.

One of the concepts that is looking promising is to design materials which ablate at high temperature.

However, unlike the usual systems where material is lost to the surroundings, this new material is able to replenish the lost material through microstructural design.

“The technologies we are developing will have application anywhere where performance is needed from materials in high temperature environments for long periods,” he said.

“Some potential uses for the new materials might include in power plants and for exhaust nozzles of jet engines.”

Professor Drennan said the technologies developed would benefit Australian industry by providing further capabilities in materials science.

“Australian industries will be able to build components of aircraft, rather than having to import these materials from the U.S. and Europe,” he said.

The $1.5 million project is led by UQ and also involves The University of Melbourne, Swinburne University of Technology, BAE Systems, DSTO and ANSTO. It has received $700,000 funding from the newly formed Defence Materials Technology Centre as well as in-kind funding from UQ.

The UQ achievements in hypersonics began with the inventions and research projects of Professor Ray Stalker, who became Australia’s first professor of space engineering and is recognised world wide as the father of hypersonic flight.

In an interview with Stalker at the time of the original Hyshot program, he surmised that one solution to the problem of the heat barrier in sustained hypersonic flight might involve venting what would turn into a thin sheet of ultra cold hydrogen fuel over critical parts of the outer skin of such a vehicle to prevent it burning up from atmospheric friction.

Or, circulating the fuel just under the outer layer of the most heat sensitive surfaces.

Now, instead of fuel as the refrigerant, advances in materials technology offer a radically new process using the skin of the hypersonic craft itself.

While the UQ program is often marketed to the media in terms of sustained hypersonic flight and trips between Australian cities and London in less than two hours, the reality is that it is of far more immediate interest as a means of lowering the cost of lifting payloads into orbit, or designing better thermonuclear warheads for the targeted incineration of cities.

For orbital lift, hypersonic technology offers the promise of replacing at least some of the oxidants used in conventional rockets with air scooped up by scramjets. This would greatly improve overall payload efficiency.

And it is not unreasonable to surmise that the protective warhead shields used by the nuclear powers have already moved toward more efficient ablative materials like those being explored in the UQ program. We already known that multiple warheads can be targeted to within a few hundred metres if a ground burst is intended, such as one that will break open and destroy the reinforced missile silos of enemy rocket bases before they can be launched. Or what was termed the first strike strategy in the 1960s, before the consequences of a subsequent global nuclear winter sank in.

Putting aside such horrific thoughts, the notion of a two hour hypersonic flight to Paris or New York is attractive. Especially if the ground connection at either end can also be shrunk to well below the two hours it can take in some cities.