Current commercial aircraft typically cruise at around Mach 0.8, a speed just shy of the sound barrier. While air travel is already a rapid mode of transportation, journeys between continents, such as from Japan to Europe or the United States, can still take upwards of 12 hours. Imagine halving that travel time by flying at twice the speed of today’s planes – this is the promise of Supersonic Transportation. Cutting flight durations to approximately six hours for long-haul routes could revolutionize global connectivity.
Shorter travel times offer a multitude of societal benefits, fostering a more interconnected and dynamic world. Business operations and tourism would experience a significant boost, and critical responses to emergencies, like natural disasters, could be expedited. Furthermore, reducing flight times to under six hours can mitigate health risks associated with prolonged air travel, such as economy class syndrome, making air travel more accessible and comfortable for a wider range of people.
Aircraft designed to achieve these high speeds are known as supersonic transports, aptly named for their ability to travel faster than the speed of sound. Despite the clear advantages of supersonic transportation, the skies have remained without a commercially viable successor to the Concorde since its retirement in 2003. The Concorde, while iconic, was plagued by issues like high fuel consumption and exorbitant operating costs. A significant hurdle was also the intense sonic boom it generated, prohibiting supersonic flight over land and severely limiting its potential routes. These factors ultimately contributed to its commercial unsustainability.
However, dedicated research and development efforts have been underway to address the technical shortcomings of the Concorde era. Since the 2010s, a renewed global interest in supersonic transportation has been building momentum. In response to this resurgence, the International Civil Aviation Organization (ICAO) is actively engaged in discussions to establish international standards for acceptable sonic boom levels during supersonic overland flights. This collaborative effort signals a potential pathway for the future of supersonic transportation.
International cooperation is anticipated to be the driving force behind the development of the next generation of supersonic transport. The Japan Aerospace Exploration Agency (JAXA) is positioned to play a vital role in advancing aircraft technology both in Japan and globally. JAXA is contributing by developing its own innovative aircraft concepts and pioneering essential technologies in this field.
Conceptualizing a Small Supersonic Civil Transport
From fiscal year 2016 to 2020, JAXA’s S4 (R&D for System integration of Silent SuperSonic airplane technologies) program focused on designing a conceptual aircraft for small-scale supersonic civil transportation. This concept was based on a target speed of Mach 1.6, a capacity of 50 passengers, an approximate takeoff weight of 70 tons, and a cruising range exceeding 3,500 nautical miles (around 6,300 km). Achieving this ambitious aircraft concept necessitated the identification of critical technical objectives.
Understanding Sonic Booms in Supersonic Transportation
When an aircraft surpasses the speed of sound and enters the supersonic regime, shock waves emanate from various parts of its structure. As these shock waves propagate through the atmosphere over considerable distances, they coalesce into an N-shaped pressure waveform. Upon reaching the ground, this waveform manifests as two rapid pressure fluctuations, creating the distinct phenomenon known as a sonic boom. Characterized by an abrupt and loud impulsive sound, sonic booms are a key challenge in supersonic transportation development.
JAXA’s Supersonic Project Initiatives
JAXA is actively engaged in research and development of core technologies crucial for realizing a quieter and environmentally responsible next-generation supersonic aircraft. To validate these advancements, JAXA has implemented several supersonic flight projects aimed at demonstrating the effectiveness of these developed technologies.
Re-BooT Project: Pioneering Robust Low-Boom Technology (FY2024-)
The Re-BooT (Robust en-route sonic-Boom mitigation Technology demonstration) project, initiated in FY2024, is focused on demonstrating robust low-boom design technology. The goal is to significantly reduce the sonic boom impact heard on the ground. Through flight tests, the project aims to validate this technology and utilize it in the design of a conceptual quiet supersonic civil transport aircraft.
D-SEND Project: Validating Sonic Boom Reduction (FY2010-FY2015)
JAXA’s D-SEND (Drop test for Simplified Evaluation of Non-symmetrically Distributed sonic boom) project, conducted from FY2010 to FY2015, successfully demonstrated the effectiveness of JAXA’s design concepts and methodologies for supersonic airframe configurations in mitigating sonic booms. A primary objective was to prove the feasibility of the “low sonic-boom design concept” through flight experiments and to refine techniques for measuring sonic booms in flight. The findings from the D-SEND project have contributed significantly to ongoing international discussions regarding sonic boom regulations for next-generation supersonic aircraft.
NEXST-1 Project: Enhancing Fuel Efficiency in Supersonic Flight (FY1997-FY2005)
From FY1997 to FY2005, JAXA conducted flight experiments with NEXST-1, a small supersonic experimental aircraft designed to improve fuel efficiency for supersonic flight. These experiments, carried out at the Woomera Test Range in Australia in 2002 and 2005, successfully demonstrated that the low-drag design principles applied to the NEXST-1 could reduce air resistance by approximately 13% compared to the Concorde. This project marked a significant step towards more sustainable supersonic transportation.
