Hypersonic vehicles for Europe’s fast future into space

The momentum is growing for a new generation of aircraft flying faster than the speed of sound and passengers dashing from Brussels to Sydney in just three hours. However, we are still years away from civilians traveling routinely again at the speed of sound. An incipient air travel revolution aims to reduce both time travel and fuel consumption.

Faster travel would bring space closer. ESA is looking at the challenges and opportunities in the air and space industries to build vehicles flying at hypersonic speeds in Earth’s atmosphere and beyond.

The fast future

Hypersonic speed refers to speeds over five times the speed of sound. Scientists measure it with a Mach number, named after Austrian physicist Ernst Mach.

Sound has a speed of Mach 1, or roughly 1235 kilometres per hour. While there is not a clear-cut physical definition for hypersonic speeds, vehicles travelling at Mach 5 or above – at around 6000 km/h – are considered hypersonic.

Europe’s efforts

ESA continues to identify synergies tics and space sectors.and pinpoint technological locks for hypersonic vehicles on Earth and in space. A two-day workshop in Germany earlier this spring brought together industry, academic and agencies experts from the aeronautics and space sectors.

“We did not aim at providing concrete solutions but rather to first identify challenges and technical dependencies between fields. This is a starting point to enable future reusable hypersonic vehicles for an Earth-to-orbit hub,” says Didier Schmitt, ESA’s Future Preparation Group leader.

Bringing experts together served as a technical kick-off to leapfrog technologies for a vehicle taking astronauts to low Earth orbit. As many as 70 experts raised key questions and challenges to overcome.

“We called for both industries to learn about each other’s showstoppers. To deliver a transformational change, reusable is the key word. Concepts for hypersonic reusable vehicles include lifting bodies designs for European crew access to space and landing on a runaway or landing pad,” explains Didier.

Hot topics

Participants in the workshop listed several topics to make a crew vehicle for low Earth orbit a reality. The experts identified eight areas of synergy:

–  Airbreathing propulsion as a key to reach hypersonic speeds.

–  Wing body designs and morphing structures. Adaptable geometries in combination with high-temperature and lightweight materials for aerodynamic efficiency.

–  Insulation and thermal management. Thermal protection systems, novel materials, and cryogenic propellant.

–  Guidance, Navigation and Control (GNC).  Specific challenges associated with high-speed flight, including precision.

–  Reuse of lightweight high-temperature materials. Evaluation of fatigue and reflight capabilities for two distinct cases: controlled reentry and long-duration flights.

–  Safety considerations specific to crew vehicles. There is a need to regulate human roles and responsibilities. This includes the distinction between passengers, crew members, ground operators and considerations for the environment.

–  Crew survival systems.  Crew safety and survival systems for anomalies as major drivers in the design of the vehicle.

–  Cryogenics storage and distribution systems. Cryogenic fuel and oxidiser storage technologies, and their management.

For the past 25 years, ESA has invested efforts in EU-funded studies for hypersonic materials, aerothermodynamics and propulsion concepts. Some of these studies are HEXAFLY, ATLLAS, LAPCAT, FAST 20XX, HIKARI and STRATOFLY.

HEXAFLY, for example, has built a quite extensive knowledge on hypersonic capabilities since the 2000’s. The Space Rider project, Europe’s first reusable space transportation system, adds to the research towards reusable launchers.

ESA has also successfully tested critical reentry technologies. In 1998, the Advanced Reentry Demonstrator (ARD) performed a guided reentry back to Earth.

In 2015, the Intermediate eXperimental Vehicle (IXV) reached an orbit of 25 000 km and completed a searing atmospheric descent and safe splashdown at the targeted spot in the Pacific Ocean.

“It’s time for Europe to mature and test these new concepts with breakthrough technologies on a high-speed vehicle,” urges Didier.