Destinus, the European start-up developing a hydrogen-powered hypersonic aircraft, is preparing to start flight tests with a subscale propulsion system prototype on its Jungfrau technology demonstrator in February. The next phase of work will build on recently completed tests using an afterburner it has integrated with an off-the-shelf turbojet engine as part of a long-term goal to produce an aircraft that would operate on intercontinental flights at speeds exceeding Mach 5.

In a strategic shift, Destinus has now resolved to use its afterburner technology with a turbofan produced by an existing aircraft engine maker for early cargo-carrying examples of its planned aircraft. Senior development manager Martina Löfqvist explained to FutureFlight that these early production aircraft will require four as-yet-unspecified turbofans and that “for bigger passenger-carrying vehicles, we may still have to consider developing an engine ourselves.”

This longer-term plan to introduce its own design for what it refers to as a hydrogen-fed air turborocket is still being worked on by Destinus engineers. In fact, they recently produced a prototype compressor for the engine, which would burn air. At the same time, the company says, it has already begun conversations with potential turbofan manufacturing partners or suppliers.

The test flights starting in February will continue to be run on gaseous hydrogen and will be carried out only at subsonic speeds of now more than around 300 km/h (163 knots). The Destinus team is already working on a larger prototype of the propulsion system that it expects to be able to support supersonic test flights by early 2024. The company started test flights with the Jungfrau aircraft in 2021, and has also flown a larger model called the Eiger.

Destinus recently tested a new afterburner that it intends to integrate with a turbofan engine. (Image: Destinus)

The company intends for its production aircraft to eventually run on liquid hydrogen fuel but it acknowledges that the aviation sector is some way from having an assured supply of green hydrogen. Nonetheless, Destinus is adapting its ground test infrastructure in Switzerland to be ready to start working with liquid hydrogen from around mid-2023.

Still to be defined are the key performance details for the proposed family of hypersonic aircraft and how operating costs might compare with those for both existing equipment and Boom’s proposed Overture supersonic airliner, which is expected to carry up to 85 passengers. According to Destinus, its initial passenger-carrying aircraft will likely have fewer than 100 seats.

“We believe we can bring down the price of using hydrogen because it has a very high energy density and will match the cost of kerosene within this decade,” said Löfqvist.

As a new company, Destinus is conscious that it needs to set itself apart from existing players like Airbus, which is working to introduce a hydrogen-powered airliner carrying up to 200 passengers on trips of up to around 2,300 miles by the mid-2030s. In its case, the differentiator will be the ability to shrink the globe by flying at five times the speed of sound to make it possible to fly from Europe to Australia, for example, in just four hours.

Over the past 12 months or so, Destinus has shifted its medium-term product focus to prioritize bringing a passenger-carrying aircraft to market by the end of the 2020s. At the same time, it sees scope for other versions of the design that could be used for applications like freight deliveries, and perhaps enter service at an earlier date. It also aims to attract further funding for its work from public grants, having previously closed a $29 million seed funding round in February 2022.

The Destinus avionics team is developing a guidance, navigation, and control system that it says will support highly automated flight following predetermined mission plans. “The future passenger airplanes will be a combination of autopilot systems and human pilots, where the autopilot will be primarily used during hypersonic acceleration and cruise,” Löfqvist explained.

By taking a flexible approach to automating flight controls, rather than sticking with its earlier focus on full autonomy, Destinus believes, it has opened up more options for developing spin-off products that could operate without humans on board. This approach has also accelerated prototype testing by avoiding the need to involve highly trained test pilots.

What remains to be fully understood is how much of a premium the traveling public will pay for a combination of unprecedented speed and range. Destinus says that it has been doing some market forecasting, in part based on comparisons with other new transportation services, but for now it is hard to accurately project direct operating costs for a hypersonic aircraft.

“We’ve done some cost calculations and the aircraft will be cheaper than flights in Concorde [the supersonic airliner that went out of service in 2003], but it will be more expensive [than current airliners] at first,” Löfqvist acknowledged. She indicated that initially, airfares will likely be around current levels for business-class flights, but that as production is scaled up they could edge closer to economy-class levels.

As with supersonic aircraft, current regulations—driven by noise concerns—would require a hypersonic aircraft to operate at subsonic speeds when flying over land. Unless permission is granted for these aircraft to fly over unpopulated desert regions, Destinus’s envisaged operating model could see aircraft from Europe flying all the way around Africa to get to destinations in Asia and Australasia. Current political restriction on access to Russian airspace is a further complicating factor for now.

Destinus has started plotting possible long-haul routes for its hypersonic airliner, factoring in current regulations that prohibit supersonic flights over populated areas. (Destinus)

The company has commissioned a white paper on hypersonic noise levels and how these might impact humans. This is part of a series of publications intended to demystify hypersonic travel and includes explanations as to how the sonic boom can be mitigated at exceptionally high speeds and by adjusting the shape of the airframe.

To generate income progressively, Destinus envisages some early-use cases for smaller versions of its aircraft in roles such as scientific research and disaster relief. The earliest cargo-carrying version is expected to have a payload of around one metric ton (2,204 pounds). In September 2022, Brazilian on-demand charter flight broker Flapper signed a letter of intent under which it will work with Destinus to explore possible use cases for hypersonic cargo delivery flights in Latin America and Europe.

Destinus has been testing hydrogen propulsion systems at its facility in Switzerland. (Image: Destinus)

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