A flight from New York to Los Angeles takes six hours. But hypersonic travel could shrink this to 15 minutes. Hypersonic travel will not just reduce flight times in the U.S.
It could also shorten journeys across the globe, speed up supply chains, and improve emergency response times. However, developing hypersonic travel has proven difficult.
The famous Concorde planes that could undertake Trans-Atlantic flights in under 3.5 hours traveled at supersonic speeds. Concordes could travel at Mach 2 or twice the speed of sound, something that the present-day fighter jets can easily do. However, for a flight to be called hypersonic, it must travel at Mach 5 or higher, i.e., at least five times the speed of sound.
At these incredible speeds, air behaves the same way it does for other flights. When an object travels at hypersonic speeds, it not only encounters resistance from the air in front of it, but it also compresses it. The compression generates heat that can exceed 3,500 degrees Fahrenheit (~1,900 degrees Celsius).
At these high temperatures, the materials used to make the aircraft, its engine, its aerodynamics, and its propulsion systems all fail. Scientists need to rethink how to make them all work at hypersonic speeds.
Traditional engines slow down the air before combustion. However, in hypersonic speeds, this is not possible. Scientists have developed scramjet engines that allow air to remain supersonic inside the engine, but engines still need to contend with unstable airflow.
To maintain control, scientists are working on hypersonic detonation engines and aiming to develop sustained reactions that are stable and under control. The challenge in hypersonic systems is not generating energy but ensuring stability even at high speeds.
Higher hypersonic flight speeds also create additional stress on the materials used in the aircraft’s structure, which can accumulate and cascade throughout the entire system. Scientists working on materials for these flights must ensure they are both strong and light. This is because stronger materials are typically heavy, increasing the weight that needs to be carried and slowing the flight.
The toughest challenge for scientists, though, is testing these systems. While wind tunnels are effective for regular flight testing, conventional ones cannot simulate the temperatures, pressures, and velocities of hypersonic flight.
Although facilities like High-Hypersonic Enthalpy Facility (HiHYPER) at the University of Central Florida (UCF) exist, they can only provide snapshots of the impact of hypersonic travel on materials and airflow. Scientists have to rely on computer-based simulations to test scenarios that cannot be recreated in physical systems, and combining both can help advance hypersonic flight.
Hypersonic travel is not just about moving fast. It is about ensuring that the materials can survive the impact of travel. There is no sequential problem-solving. Scientists have to solve all problems at once, because only the overlap is where progress happens.
To solve the problem of hypersonic travel, scientists do not have to focus solely on speed but also on what can be achieved at a given speed. Once you start pushing the boundaries, new problems emerge, and only then can the holy grail of NY-to-LA flights that take 15 minutes or less be reached. Once we achieve that, the world won’t be the same again.
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Ameya is a science writer based in Hyderabad, India. A Molecular Biologist at heart, he traded the micropipette to write about science during the pandemic and does not want to go back. He likes to write about genetics, microbes, technology, and public policy.
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