Hypersonic refers to aircraft, missiles, rockets, and spacecraft that can reach atmospheric speeds in excess of Mach 5, which is almost 4,000 miles per hour or 6,125 kilometers per hour or more. Hypersonic flight is flight through the atmosphere below about 90 km at speeds greater than Mach 5, a speed where dissociation of air begins to become significant and high heat loads exist. Speeds of Mach 25+ have been achieved below the thermosphere as of 2020.
In order to maneuver in the atmosphere at faster speeds than supersonic, the forms of propulsion can still be airbreathing systems, but a ramjet does not suffice for a system to attain Mach 5, as a ramjet slows down the airflow to subsonic. Some systems (waveriders) use a first stage rocket to boost a body into the hypersonic regime. Other systems (boost-glide vehicles) use scramjets after their initial boost, in which the speed of the air passing through the scramjet remains supersonic.
What sets hypersonic aircraft apart from other rocket-powered aircraft is that they are powered by a scramjet engine. The disadvantage of a conventional rocket engine is that it requires a lot of onboard oxygen. For example, the space shuttle needs 143,000 gallons of liquid oxygen, which weighs 1,359,000 pounds (616,432 kg). Without the liquid oxygen, the shuttle weighs a mere 165,000 pounds (74,842 kg).
Instead of using onboard oxygen to combust the hydrogen fuel, the scramjet scoops up oxygen as it travels through the atmosphere. By eliminating the need for onboard oxygen, cutting the weight of the spacecraft, hypersonic aircraft could lead to cheaper Earth-to-orbit space travel.
Hypersonic Aircraft Race
US, Russia and China are engaged in Hypersonic Weapons Race that shall revolutionize warfare by providing prompt global strike capability and defeat all missile defences.
The fastest any aircraft with an engine has ever flown is Mach 9.6 (about 6,800 mph), a record set in 2004 by the NASA X-43A — an unmanned aircraft measuring about 12 feet in length. This flight broke the previous speed record of Mach 7, set in March 2004 by the X-43A in a previous test flight.
Mach 5 passenger plane
Hermeus, an Atlanta-based startup whose goal is to develop hypersonic aircraft, believes so. It’s already testing a new type of engine it says will eventually be capable of reaching Mach 5 (over 3,000 mph). The engine is designed for a small, unmanned hypersonic aircraft Hermeus is currently creating for the US Air Force, but scaled to a bigger size, it will be able to power a passenger plane.
That passenger plane is a long way away — Hermeus hopes to get it in the air for the first test flight before the decade is out, in 2029 — but because its technology has to be built almost entirely from the ground up, the company is already planning it out. For a start, it will be much smaller than current airliners and even Concorde, which had a capacity of around 100 passengers.
“To help us size the aircraft, we basically built a business model for an airline,” says AJ Piplica, CEO of Hermeus. “We focused on the business class and first class travelers, and then played around with some parameters such as speed and operating costs. What came out of that was an aircraft with a 20-passenger cabin,” he adds.
That’s not far from the capacity of a large business jet, which means there will be just one class.
“We expect it to be profitable at today’s business class prices,” says Piplica, with the caveat that it’s hard to gauge how much people will be prepared to pay to fly five times faster, because “you can’t really answer that question until there’s a product out there and you have the real data.”
The range of the plane will be about 4,000 nautical miles, enough for transatlantic routes such as New York to Paris, but not for transpacific routes like LA to Tokyo, which would require a stopover. Routes over land, such as New York to LA, are out of the question due to noise regulations: breaking the sound barrier comes with a loud boom, which usually must happen over water.
Tests started in February 2020 for a new type of engine design, based on an existing model used in fighter aircraft and manufactured by General Electric. It will be a hybrid of two traditional technologies: a turbojet, which is similar to what airliners use, and a ramjet, a type of engine that only works at supersonic speeds and above. Initially, the engine will power Quarterhorse, the sleek hypersonic drone that Hermeus is developing through a $60 million partnership with the US Air Force.
Hermeus will use its hybrid engine in turbojet mode when taking off and landing, as well as at subsonic speeds. Then, the engine will gradually reconfigure itself into a ramjet mode as it reaches Mach 3 and until Mach 5. “The turbojet portion and the ramjet portion by themselves are mature technologies that we’ve been using for 50 years. The trick is to put them together, so we designed our own architecture around an off-the-shelf turbojet engine and then built out from there,” says Piplica.
China ‘successfully tests first hypersonic aircraft
In July 2022, China completed the testing of a small hypersonic prototype aircraft for civilian use, paving the way for developing a full-sized hypersonic aircraft that can travel six times the speed of sound. The first phase of testing for the Nanqiang No. 1, a model that will probably serve as a technology demonstrator for a hypersonic airliner, is now complete. The model, referred to as a prototype, has undergone testing in a lab in the Chinese province of Fujian.
According to the report, the crewless aircraft weighs just 500 kilograms (1,100 pounds). Scientists working on the project hope to complete the test program and move on to building a flyable prototype by 2025.
According to U.S. defense officials, China also successfully tested Starry Sky-2 (or Xing Kong-2), a nuclear-capable hypersonic vehicle prototype, in August 2018. It was released in the air after about 10 minutes in Northwest China, reaching 30 kilometers in altitude at a top speed of Mach 6 — six times the speed of sound, according to the China Academy of Aerospace Aerodynamics (CAAA). The aircraft flew independently while performing several turns and other movements, and finally landed in a designated area.The contractor said the test was a “complete success.” “The Starry Sky-2 flight test project was strongly innovative and technically difficult, confronting a number of cutting-edge international technical challenges,” CAAA said.
China claims the vehicle reached top speeds of Mach 6 and executed a series of in-flight maneuvers before landing. Unlike the DF-ZF, Starry Sky-2 is a “waverider” that uses powered flight after launch and derives lift from its own shockwaves. Some reports indicate that the Starry Sky-2 could be operational by 2025.
Beijing-based missile expert said that although China had made great strides in hypersonic technology, it was mainly used in “strategic weapons”.“Among the hypersonic weapons, the land-based hypersonic missile is the most powerful one,” the expert said. “But the missiles are huge and even China’s biggest military transport aircraft, the Y-20, cannot carry them.” Tests on the ground have fared better.
The expert added that because of the high cost of hypersonic technology, China would only produce a small stockpile of such missiles for deployment in key economic centres such as Zhejiang, Fujian and Guangdong provinces. According to Song, China was not likely to use hypersonic technology in antisatellite weapons because laser-directed weapons, high-powered microwave beams and other more sophisticated weapons would be better alternatives.
Russia’s Hypersonic Strategic Bomber
The Russian Strategic Missile Forces Academy is developing a hypersonic strategic bomber capable of striking with nuclear warheads from outer space, Lt. Col. Aleksei Solodovnikov told RIA Novosti. The jet will be very capable and will need only one-two hours to reach any place on Earth through outer space. Russian commander of the Strategic Missile Forces (SMF), Colonel General Sergei Karakayev, had earlier reported that the Russian Strategic Missile Forces Academy has already developed and tested an engine for the experimental aircraft.
“The idea is that the bomber will take off from a normal home airfield to patrol Russian airspace. Upon command it will ascend into outer space, strike a target with nuclear warheads and then return to its home base,” Solodovnikov told RIA Novosti. Called the PAK-DA strategic bomber, the hypersonic aircraft – which will be invisible to radar – will be armed with a special hybrid Turbofan engine, making it capable of low-level space flight. The bomber will burn traditional kerosene fuel when flying inside the earth’s atmosphere. However, once in space, the engine switches to methane and oxygen which allows the PAK-DA to fly without air.
“We are cooperating with Russia’s Central Aerohydrodynamic Institute on the design of an airframe and the aircraft’s characteristics. I think that its lift-off mass must be 20-25 metric tons for it to be a strike aircraft. It will [be able to accelerate to] hypersonic speed in rocket mode,” he added.
US Hypersonic Strike Aircraft
The U.S. Air Force has revealed new details about its secretive Mayhem hypersonic air vehicle program. The service has now disclosed that it is seeking a modular experimental design that could be configured to carry one of two different kinds of payloads for strike missions, or a sensor package to enable it to conduct “responsive” intelligence, surveillance, and reconnaissance, or ISR, sorties.
The new information about Mayhem was contained in a contracting document that the Air Force Research Laboratory (AFRL) posted online on Dec. 14, 2021. That same document also indicates that the full formal name of the program has changed from “Expendable Hypersonic Multi-Mission Air-Breathing Demonstrator” to “Hypersonic Multi-mission ISR and Strike.” Mayhem is also part of a larger AFRL effort known as Enabling Technologies for High-Speed Operable Systems (ETHOS).
“The Mayhem Program is focused on delivering a larger class air-breathing hypersonic system capable of executing multiple missions with a standardized payload interface, providing a significant technological advancement and future capability,” the contracting document says. “The system goal is to carry payloads five-times the mass and double the range of current technology capability systems. The standardized payload interface would create multiple opportunities for various payload integration within the same hypersonic system.”