Propulsion and Energy

Accelerating toward hypersonic civilian flight

The High-Speed Air-Breathing Propulsion Technical Committee works to advance the science and technology of systems that enable supersonic and hypersonic air vehicle propulsion.

This year was exciting for high-speed air-breathing propulsion, HSABP. In May, the hydrogen/oxygen air vitiator facility at test bench M11.1 at the German Aerospace Center, or DLR, in Lampoldshausen was readied for upcoming hydrocarbon-based liquid fuel tests for the MORE&LESS, or Multidisciplinary Design Optimization and Regulations for Low-Boom and Environmentally Sustainable Supersonic Aviation project. The tests use biofuels and kerosene to test their pollutant generation, atmospheric impact and combustion processes. DRL’s Institute of Space Propulsion operates the test bench, which is capable of simulating combustion chamber inlet conditions at Mach 5.5 to Mach 8.

The facility also continued an injector reference test campaign for MORE&LESS, funded by the European Union, to address the technical challenges and legal framework for sustainable supersonic flight. Within the project, an extensive test campaign validated computational fluid dynamics simulations for various partners, including Lund University in Sweden, the von Karman Institute for Fluid Dynamics in Belgium and Reaction Engines of the U.K. Initial comparisons show good agreement between experimental and computational data. Additionally, throughout 2023, DLR carried out several internal test campaigns to address material testing for HSABP and injector development.

In June, the European Space Agency held a three-day innovative propulsion workshop to centralize academic and industrial efforts on advanced propulsion technologies, including hypersonic propulsion.

Also in June, Ohio-based Velontra announced the testing of  Bronco, a1.5-meter-long, 28-centimeter-diameter engine suited for smaller hypersonic drones and air vehicles. The Bronco design utilizes a Velontra-developed afterburner and a ramjet to accelerate to hypersonic speeds. Velontra tested the combination engine early in the year at the Filtered Rayleigh Scattering for ThrustHigh-Pressure Combustion Laboratory in Indiana. Velontra CEO Robert Keane III said that Bronco was tested “at speeds over Mach 4.5 and altitude simulated over 100,000 feet, and it successfully screamed through vigorous testing with flying colors.” The company last year signed a contract to provide four Broncos to Venus Aerospace of Texas for testing Venus’ planned Stargazer hypersonic passenger aircraft.

In Alberta, Canada, Space Engine Systems ground tested its DASS GNX engine in turbojet and ramjet modes in preparation for installation into the Hello-1X demonstrator. Currently under construction, the Hello-1X is being designed for point-to-point, suborbital and low-Earth orbit missions with payloads up to 550 kilograms. The campaign was conducted in the company’s first mobile turbo-ramjet test cell, which can withstand  up to 111 kilonewtons of force. Space Engine Systems used multiple fuels, including Jet A and hydrogen, with a 3D-printed gyroid hydrogen precooler. Precooler materials mainly consisted of Inconel 718 and titanium, with various internal coatings to mitigate hydrogen embrittlement at high temperatures. Assessment included heat exchanger expansion and stress at simulated altitudes from sea level to 30 kilometers and speeds up to Mach 5.

In August, Boom Supersonic announced the receipt of an FAA Special Airworthiness Certificate for its XB-1 subscale demonstrator. The aircraft was moved from Boom’s Colorado facilities to the Mojave Air and Space Port in California in preparation for its inaugural flight. Boom Supersonic has agreements with airspace authorities to facilitate flights over the Mojave Desert, the iconic airspace where Chuck Yeager broke the sound barrier in the Bell X-1 and the SR-71 Blackbird made its first flight in 1964. The XB-1 has a 20-meter carbon composite and titanium fuselage and is propelled by three General Electric J85 engines, producing a combined thrust of 55 kilonewtons.

Also this year, the Japan Aerospace Exploration Agency, JAXA, performed post-flight analysis on a Mach 8-plus integrated scramjet vehicle model it tested in its High Enthalpy Shock Tunnel, and continued post-flight analysis of the RD1 supersonic combustion flight test conducted in July 2022.

Contributors: Joel Malo de Molina, Khaled Sallam and Hideyuki Tanno

Accelerating toward hypersonic civilian flight