The future of Hypersonic Travel

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Imagine traveling from New Delhi to London in just a couple of hours or waking up in L.A. and flying to Beijing in time for lunch. The hypersonic flight could change the way we travel and in ways, we haven’t seen since the invention of flight itself. But flying at hypersonic speed isn’t easy. It presents incredible engineering and logistical challenges. So, what’s the future of Hypersonic Travel?

Concorde Aircraft

Before we get the hypersonic speed, we should probably talk about supersonic speed. Basically, supersonic speed is when we are traveling faster than the speed of sound. Which is something we can and frequently do? Certain military airplanes will fly above Mach 1 and the Concorde commercial plane famously flew at supersonic speeds from 1976 to 2003. Supersonic speed is really fast but hypersonic speed is in a league of its own. so hypersonic means typically velocities above Mach 5 or equivalently velocities above 3,800 miles per hour.

The Achievement:

X-15 Jet

Now going at least five times faster than the speed of sound may seem crazy but it’s actually a milestone we have reached multiple times in the past. From the general public’s perspective probably the most visible example of hypersonic flight is watching a space shuttle re-entering the atmosphere. The space shuttle reaches hypersonic speed just by falling back to earth. But in the 1960s NASA did achieve manned hypersonic travel through actual propulsion with an X-15 jet setting a speed record (7,274 km/h) that has yet to be broken and there’s pretty good reason for that. The effects of flying hypersonically in the atmosphere are catastrophic. This is where the problem with long-duration hypersonic travel starts.

When we are traveling below the speed of sound the temperature around the aircraft stay as close to the ambient temperature. But once you break the sound barrier a shock wave is created and the gas molecules behind the shock wave become compressed. This makes the air around the plane really hot. Near hypersonic speeds, it’s so hot that it can damage the materials that make up the body of the airplane.

Shielding for Hypersonic:

Now traditional airplanes are made of aluminum alloys that have a melting temperature of about 600 degrees Celsius. An advanced aircraft has titanium bodies with even higher melting points. But the air around an aircraft flying at Mach 10 can reach 3,000 degrees Celsius. So how did vehicles like the Space Shuttle not burn up completely when they re-enter the atmosphere at hypersonic speeds. Because we have just put on the heat shield that’s ten times heavier and thicker than it needs to be. But those heat shields typically burn off completely during re-entry and reapplying a heat shield for every single flight wouldn’t exactly be practical or possible for hypersonic commercial travel. Different materials are needed to withstand these extreme temperatures and researchers are exploring all kinds of options from Tantalum Carbide to Boron Nitride Nanotubes.

Effects on People:

If hypersonic speed does this kind of damage to planes what about the people inside. Traveling at hypersonic speeds isn’t harmful as long as it’s constant. Rapid acceleration or a sudden change in direction is another story. If we were to do the turn at Mach 10, the accelerations that we will be generating with the cabin for the passengers will be about 40 G’s. Right 40 times the gravitational acceleration which will basically kill everybody on board. Another potential concern could be increased radiation from flying at higher altitudes which a hypersonic jet would need to do. There’s also the issue of losing cabin pressure while traveling that high up in the stratosphere. But flying commercially already comes with similar risks that airlines prepare for.

Of course, none of these problems really matter if we aren’t able to reach speeds of Mach 5 and above. In the first place just because we have done it before doesn’t mean it’s easy to replicate. Historically we have just strapped people to a rocket and fired him into space but if we wanted to fly from New York to Los Angeles on a hypothetical hypersonic airliner, a rocket is not a very efficient way to do things. One idea is to use something called a supersonic combustion Scramjet. A rocket has to carry the liquid oxygen it needs for combustion making it incredibly heavy and not efficient for commercial travel. A scramjet on the other hand is able to use oxygen from the atmosphere to create combustion even at hypersonic speeds, but the scramjet is still a work in progress.

In 2015 Boeing’s scramjet equipped X-51 flew at Mach 5.1 but only for about three and a half minutes. It was also unmanned and was launched from an aircraft already in flight which isn’t exactly what we have in mind for a long duration hypersonic flight. Despite this there is real progress being made in hypersonic engineering just in a different kind of setting. Both China and Russia have claimed to have tested hypersonic weapon systems and the U.S. is currently trying to catch up. And this wouldn’t be the first-time hypersonic research started in military applications.

Boeing X-51

During the development of ICBM (Intercontinental Ballistic Missiles), a lot of research was done in hypersonic. Most of the fundamental concepts that we know today are derived from those things. Boeing is one company that’s hoping to make the jump from military applications to commercial flight. It’s concept for a hypersonic airliner comes after working with DARPA on a hypersonic space plane and working on the scramjet-powered X-51 with the air-force. Boeing plans for this potential airliner to be able to travel at Mach 5 reducing your transpacific commute to a measly two hours. And that’s the potential of hypersonic speed. The ability to connect to anywhere in the world in that amount of time would be an incredible achievement.

It’s also critical to study as we plan to explore places like Mars because entering that planet’s atmosphere would be done at hypersonic speed. The public imagination or perspective and the desire to have successful space missions, we need to do a good job of, and working through these technologies and research problems. I see hypersonic travel similar to what prehistoric fish did 300 million years ago when they left water and they began the life on land. So, the conquest of air and space is also fundamental step in the evolution of mankind.

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