Current commercial airliners typically cruise at around Mach 0.8, just shy of the speed of sound. While air travel is undeniably fast, journeys between continents like Japan and Europe or the United States can still take upwards of 12 hours. Imagine halving that flight time. Supersonic Transport Planes, aircraft capable of exceeding the speed of sound, promise to do just that, potentially shrinking transcontinental travel to approximately six hours.
Shorter travel times could revolutionize society. Increased business and tourism activities would boost economies, and rapid response to emergencies, such as natural disasters, would become more feasible. Furthermore, reducing flight durations to under six hours could lessen the risk of economy class syndrome, making long-distance travel healthier and more accessible for a wider population.
Despite these compelling advantages of supersonic transport, the era of civilian supersonic flight seemed to stall after the retirement of the Concorde in 2003. The Concorde, while iconic, was plagued by high fuel consumption and exorbitant operating costs. Moreover, the loud sonic boom it generated restricted supersonic flight to overwater routes, severely limiting its operational flexibility and commercial viability.
However, research and development efforts have been ongoing to overcome the technical hurdles faced by the Concorde. Since the 2010s, a renewed global interest in supersonic transport has emerged. The International Civil Aviation Organization (ICAO) is actively engaged in formulating international standards for sonic boom levels, specifically for supersonic flights over land, signaling a potential shift towards more widespread supersonic operations. International collaboration is now seen as crucial for the successful development of next-generation supersonic transport. The Japan Aerospace Exploration Agency (JAXA) is at the forefront of this research, aiming to contribute significantly to global aircraft technology advancements through its innovative concepts and technological demonstrations.
The Concept of Small Supersonic Civil Transport
JAXA’s “S4 (R&D for System integration of Silent SuperSonic airplane technologies)” program, active from FY2016 to FY2020, focused on designing a conceptual small supersonic civil transport aircraft. This design 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). This ambitious project identified key technical objectives necessary to realize this aircraft concept and make supersonic travel commercially viable and environmentally sustainable.
Tackling the Sonic Boom Challenge
A major obstacle to the widespread adoption of supersonic transport is the sonic boom. When an aircraft flies at supersonic speeds, it generates shock waves from various parts of its structure. These shock waves coalesce as they travel through the atmosphere, forming an N-shaped pressure wave. Upon reaching the ground, this wave manifests as two sudden pressure changes, which we perceive as a loud, impulsive sonic boom. Mitigating this sonic boom is critical to enabling supersonic flight over populated areas.
JAXA has been deeply involved in projects aimed at minimizing sonic boom impact.
Re-BooT Project: Demonstrating Low-Boom Technology
Launched in FY2024, the Re-BooT (Robust en-route sonic-Boom mitigation Technology demonstration) project is focused on demonstrating “robust low-boom design technology.” The goal is to create sonic booms that are significantly quieter on the ground. Flight tests are planned to validate this technology, which will then be used to design a concept aircraft for quiet supersonic civil transport. This project represents a significant step towards making supersonic flight more acceptable for overland routes.
D-SEND Project: Validating Sonic Boom Reduction Concepts
The earlier D-SEND (Drop test for Simplified Evaluation of Non-symmetrically Distributed sonic boom) project, conducted from FY2010 to FY2015, achieved a major milestone. JAXA successfully demonstrated the effectiveness of its design concepts and methodologies for reducing sonic booms through flight tests. The project proved the feasibility of the “low sonic-boom design concept” and developed crucial sonic boom measurement techniques. The valuable data and results from D-SEND have been instrumental in informing international discussions on setting regulations for sonic booms for next-generation supersonic aircraft.
NEXST-1 Project: Enhancing Fuel Efficiency
From FY1997 to FY2005, JAXA’s NEXST-1 project focused on another critical aspect of supersonic flight: fuel efficiency. Flight experiments with the NEXST-1, a small supersonic experimental aircraft, were conducted in Australia. These experiments successfully demonstrated that the low-drag design implemented in NEXST-1 could reduce air resistance by approximately 13% compared to the Concorde. Improving fuel efficiency is paramount for making supersonic transport economically viable and environmentally responsible in the long term.
The Future is Supersonic
The journey to bring back supersonic transport planes for civilian use is complex and challenging. However, the potential benefits are substantial, and ongoing research and development efforts, such as those by JAXA, are making significant strides. As technology advances and international collaborations strengthen, the prospect of a future where supersonic flight is commonplace and accessible appears increasingly within reach. The dream of faster global travel, shrinking distances and connecting the world more efficiently, may soon become a reality with the next generation of supersonic transport planes.
