The Japan Aerospace Exploration Agency recently teamed up with a number of universities to successfully complete a ground-breaking ground combustion test of the ramjet engine of a Mach 5 hypersonic aircraft. This marks that the vision of a two-hour flight between the two sides of the Pacific is one step closer to reality.
The test, jointly conducted by a team of engineers from the Japan Aerospace Exploration Agency, Waseda University, the University of Tokyo and Keio University, was conducted at the agency's Space Center in Tsunoda. It simulated a flight environment at 5 times the speed of sound and focused on verifying the performance of the aircraft's thermal protection system, control surfaces and engines under extreme conditions.
The technology at the heart of the test is the ramjet, an air-breathing jet engine with no moving parts. Its working principle relies on the ram effect generated by high-speed advancement to compress the incoming air, which is then mixed with fuel and ignited to generate thrust. This design eliminates the need for a heavy rotating compressor, allowing it to run at speeds far beyond that of a traditional turbofan engine, but the ramjet cannot start from a standstill and must first be accelerated to supersonic speeds before it can work.
In this test in Japan, the experimental aircraft was installed in a wind tunnel to simulate environmental conditions at an altitude of about 25 kilometers. The density of the atmosphere at this altitude is only one percent of that at sea level. At this altitude at Mach 5, the air temperature around the nose and leading edge can reach over 1,000 degrees Celsius. In response to such high temperatures, engineers built an advanced thermal protection system to successfully maintain the aircraft's internal temperature close to normal operating temperature, ensuring that the onboard avionics and control electronic systems can operate normally. At the same time, sensors map surface temperature profiles to validate thermal structure calculations, which will be critical for scaling to full-size passenger aircraft.
What needs to be made clear is that this preliminary test is still quite far away from the actual test flight, and only the ground verification of the reduced-scale model has been completed. The Japan Aerospace Exploration Agency plans to install the experimental aircraft on a sounding rocket in the next step and attempt to conduct an actual flight test at Mach 5. If progress goes well and regulatory and technical hurdles can be overcome, the goal is to enable commercial hypersonic passenger service by the 2040s.
If this progress continues, an aircraft flying at Mach 5 speed at an altitude of 25 kilometers, which can fly at almost twice the altitude of existing commercial airliners, can theoretically shorten the flight time from Tokyo to Los Angeles from the current approximately 10 hours to approximately two hours, without the need for complex operations to enter a full orbit. This means that flights from the United States to Japan will be revolutionized, transforming a trip that originally took a week into a same-day round trip in just a few hours in the air.