DARPA’s advancements in hypersonic time travel

The US Defense Advanced Research Projects Agency (DARPA) is investigating advances in materials that could allow hypersonic vehicles to travel through Earth’s atmosphere for longer periods of time.

DARPA released a Broad Agency Announcement for the Materials Architectures and Characterization for Hypersonics (MACH) programme in late January.

MACH aims to demonstrate new material solutions and thermal management designs for leading edges, the parts of an aircraft that first make contact with the air.

These are an essential design feature of hypersonic aircraft, according to the agency, and hypersonic vehicles’ range, velocity and manoeuvrability (among other factors) would be dramatically increased through developing leading edges that could handle high heat fluxes while retaining their shape.

The project is divided into two technical areas, said William Carter, MACH programme manager, in an interview with Shephard.

The first looks at ‘ways of teaching today’s materials how to take more heat’ through changing their internal architecture, allowing them to ‘cool’ during flight. This could be achieved through 3D printing/additive manufacturing, or through design approaches like ‘weaving and braiding’, manufacturing methods used to make advanced fibre composites that are used in a number of other areas, such as building turbine engines. Such approaches could enable the development of structures ‘that will allow us to add cooling’, Carter explained.

Cooling must take place during flight: as the vehicle travels through the air, a variety of processes cause the surface of the platform to heat up, eventually reaching a temperature where it begins to degrade.

The aim, then, is to pull that heat out and cool the structure. A good analogy is a turbine engine, Carter said: as the blades move at high velocity in a circle, they begin to heat, and are cooled through the use of gases, either through the engine blade itself or along its surface; this prevents the blade from degrading.

The second area will investigate different aspects of the materials, including considering the possibilities of new types of high-temperature alloys, ceramics and other materials that could better survive high temperatures.

This can involve the combination of five or more different elements to create materials known as ‘high entropy’. This is part of a ‘fundamentally new paradigm in material science’, Carter said, with major developments seen over the past two to three years. This area will also look at new coatings and other types of cooling strategies.

The second area is underpinned by high-performance computing, Carter said, developing sophisticated predictive models to explore challenging new design spaces. For example, putting various different elements together for high-entropy materials is extremely challenging, with the combinations only working in certain ratios.

‘Computation can help us start to access and hone in on combinations of materials that will be effective,’ he explained, adding that this can also be used to establish different types of coating combinations.

Hypersonic vehicles are not new, and have been used in a range of areas, such as re-entry capsules for spacecraft. However, the current set of use cases would see the vehicles travel in the atmosphere for longer periods of time, he said.

Materials and cooling were a focus for research at the very beginning of the field several decades ago, he said, though this dissipated with the development of materials that could withstand the heat and did not need to be cooled, such as carbon-carbon.

The idea with MACH is ‘to look at adding cooling to the equation and enabling such materials to have higher performance beyond simply taking the heat’.

There could be a wide range of use cases for such cooling technologies and advances in materials, Carter said, both in the military and commercial domains. The programme will take place over four years, he said, ‘a very aggressive schedule’ for what he said is a difficult challenge.

‘To ask the community to try to come up with something and mature it to the point where we can test this in a relevant environment in four years is extremely aggressive.’

Carter hopes to receive proposals from a wide range of companies and research organisations, he said, on both the materials and platform side.

‘I'm not just thinking materials people or thermal management people,’ he said. ‘I'm also pulling together folks who have use cases and platforms in mind and having them all work together to mature this as far as we can,’ he added.