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How Hypersonic Flight is the Fastest?

The civil aviation industry is going through a revolution across the world. It seems that travelling fast is no longer a territory of science-fiction movies. Aerospace companies are increasingly picking up the pace to develop commercial planes that transport humans at hypersonic speed. Currently, the modern aircrafts fly at 550 mph, and hypersonic flight will move above 3,840mph. This speed is equal to Mach 5 or 5 times the speed of sound. Even though aircrafts had been achieved a speed of Mach 25 in the past, it never became the norm due to risk, complexity, and several other challenges. Till now, hypersonic objects have only been used either as spacecraft or long-range weapons. However, this technology will soon be able to allow faster ways of travelling across the world and out of it.

The Aircrafts Reaching Hypersonic Flight Briefly

Generally, anything that breaks the sound barrier by surpassing Mach 1 is called supersonic. There is no clear indication of the boundary that separates hypersonic from supersonic, but aerospace engineers take Mach 5 as the point where hypersonic speed begins.

The first-ever human-made object that achieved hypersonic flight was the Bumper WAC rocket. It consisted of a small liquid-propellant sounding rocket known as the WAC Corporal set on top of the nose of V-2. According to archives, it once travelled at 5,150 mph or Mach 6.7 for nearly one minute before crashing and burning upon reentering the atmosphere. The first-ever human to reach hypersonic speed was also the first human to reach space and orbit around earth safely. Russian Major Yuri Gagarin reached Mach 25 in his Vostok 1 capsule when he re-entered the atmosphere after his historic mission in 1961. Similarly, NASA X-43, Boeing X-51, and HTV-2 also went hypersonic.

Many have been extensively studying the field ever since. The US, China, and Russia are major players testing this technology. However, many technical challenges hinder the development of hypersonic vehicles.

Technical Challenges

Hypersonic flight is difficult to predict because several physical factors come into play at extreme speeds. The aircraft first has to go into space where the atmospheric air pressure can exceed 1000 degrees Celsius. All modern aircrafts made of titanium and aluminium will melt at this temperature.

The oncoming air gets stuck on the craft’s surface and forms a thin layer around it called the boundary layer. It heats up and gets dragged along the vehicle, making it significantly slower. It grows along the length of the craft and shifts from “laminar flow” (fluid particles following a smooth path) near the leading edge (vehicle’s point that faces the airflow) to “turbulent flow” (fluid particles go through chaotic changes) towards the end. Turbulent flow can drastically increase heat and drag force. NASA cancelled its plans to launch NASP hypersonic space plane in the 1990s due to this very problem. The challenge is to predict where this boundary layer transition happens before successfully designing a hypersonic vehicle that works.

In 2021, Esrange Space Center in Sweden ran a 6 million USD BOLT test to study boundary layer transition. The mission failed due to problems with the launch mechanism. Then NASA launched BOLT II on March 21, 2022, to gain valuable flight data to understand boundary layer transition and turbulence properly. It ascended at the speed of Mach 6, turned over in space and re-entered the atmosphere at Mach 5.5, as planned. Unfortunately, one cannot gain the number regarding hypersonic measures and low-disturbance air and high Reynolds numbers in flight from ground testing facilities.

Design

Besides technical issues, several more factors make the reality of hypersonic flight seem far away. The materials required to properly equip the craft for hypersonic speed, such as air-breathing engines, are in early stages and need more tests. Moreover, a shield that will protect the aircraft from outer heat costs a fortune. And, a better design is required that is more efficient than the rocket boosters.

In 2004, NASA’s X-43A reached a speed of Mach 10 in a crewless test flight and broke all previous records of the agency. The X-43A was different because it used a scramjet (supersonic combustion ramjet) air-breathing engine instead of traditional rocket-powered ones. There is no need for onboard oxygen as it will take in oxygen as it moves along the atmosphere. Another advantage of having a scramjet engine in a hypersonic vehicle is lesser weight. A space shuttle requires 143,000 gallons of liquid oxygen that weighs more than 600,000kg. If one removes the liquid oxygen, the shuttle will weigh only about 73,000kg, making it possible to travel fast.

The scramjet-powered aircraft has no onboard oxygen, so it will not take off like a typical rocket. As per the case of X-43A, it requires a booster rocket to get the aircraft at hypersonic speed and then release it into space at about 20,000 feet for flying on its own. NASA’s test revealed that the scramjet engine could be a safer, flexible, and less expensive method for travelling at hypersonic speed.

Who Is Leading the Race?

China, Russia, and the US have been ahead of the game, among the plethora of countries trying to acquire supersonic and hypersonic flight abilities. Well, mainly it’s China because its aerospace firm Space Transportation claimed to conduct its first suborbital hypersonic flight by 2023. If it goes according to plan, it will test the first-ever manned hypersonic flight by 2025. Both of these flights will use a smaller aircraft than the one being developed for commercial use. The Chinese company is confident that its hypersonic vehicle will be ready to take off before 2030. This aircraft is proposed to travel from Shanghai to New York in only 2 hours. In a conventional flight, this journey approximately takes 15 hours.

On the other hand, an American startup Hermeus has received 60 million USD funds from the United States Air Force (USAF) and other venture capitalists to develop the world’s first reusable hypersonic aircraft. According to reports, Hermeus has already built and tested a sub-scale prototype and was now working on a full-scale one.

Russia is mostly obsessed with hypersonic missiles, but a businessman named Mikhail Korkorich is reportedly developing a hypersonic cargo drone capable of reaching Mach 15. His company Destinus said that the drone would transport cargo between Europe and Australia in a couple of hours using clean liquid hydrogen fuel. It will travel at altitudes over 160,000 feet, where air resistance is comparatively lower.

From the current looks, the hypersonic flight is indeed nearer, but initially, only the ultra-elite class will be able to access the service.

Also Read

All You Need to Know About World’s Longest Flight

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