Catching up with Superman

Mastering the art of hypersonic flight

Chuck Yeager once described breaking the sound barrier as a letdown: “The real barrier wasn't in the sky but in our knowledge and experience of supersonic flight.”

Today, Draper engineers are not only leading the nation in the direction of Yeager’s vision but are also pushing beyond to master guidance, navigation, and control (GNC) systems for hypersonic flight.

Since the Apollo space program, Draper has been a leader and innovator in GNC systems for rockets, missiles, and other high-speed vehicles and projectiles. But hypersonic flight presents new complexities.

“The concept of hypersonics is a huge topic,” said Ravi Gondhalekar, Ph.D., a Draper aerospace guidance and control research engineer. “The goal of achieving certain speeds, for a specific amount of time has not changed, but there is a technical question of finding out where the weak points are and how we can address them.”

In March, Draper successfully tested its GNC software in Stratolaunch’s first powered flight of its Talon-A (TA-1) hypersonic test vehicle, setting the course for continued advancement in hypersonics.

Go even faster

Supersonic flight is defined as traveling through the atmosphere at speeds greater than the speed of sound, or 767 mph. Yeager first broke the sound barrier in 1947, traveling at Mach 1.05, or 105% of the speed of sound. Since then, hundreds of planes and pilots have successfully traveled greater than Mach 1, including the Concorde passenger jet.

Hypersonic flight is the next leap in high-speed travel, with speeds greater than Mach 5, or five times the speed of sound. To date, the only US piloted aircraft to have flown hypersonic is the X-15, which achieved Mach 6 in 1961. Additionally, all US crewed spacecraft – Mercury, Gemini, Apollo, and the Space Shuttle – were hypersonic when re-entering the atmosphere. Though human-piloted hypersonic flight has proved challenging, the ultimate goal is to make hypersonic air travel routine and dependable, both for national security and commercial transport purposes.

The primary benefit of hypersonic travel is the ability to reduce travel times to reach anywhere on the planet. And because hypersonic flight is typically at high altitude, it could prove to be a more efficient form of air travel—though this has yet to be proved.

The sky really is the limit

Although engineers and aeronautics experts have mastered the art of supersonic flight, hypersonic flight is a fresh challenge.

The first issue is propulsion. As of now, nearly all vehicles that can travel at hypersonic speeds are powered by powerful rocket engines. Scramjet (short for supersonic combustion ramjet) engine technology is the next evolution in hypersonic travel, and Draper, along with several agencies, including NASA, the U.S. Air Force, and the Defense Advanced Research Projects Agency, are working to progress the technology.

Up next is aerodynamics. The thermodynamic and chemical nature of air particles changes when hitting vehicles traveling at hypersonic speeds. How they change and how much they change varies by the vehicle’s speed and shape, as well as how much it bends and flexes in flight. Those variables are hard to model.

“There’s little opportunity to know with precision what happens when you travel at those speeds without actually traveling at those speeds,” said Gondhalekar. “Wind tunnel tests and computer simulations are only going to take you so far in providing accurate models that represent what will happen.”

These complications mean that hypersonic aircraft must be designed and built as a single cohesive unit, with all parts, components, and systems designed to work together. This is why the recent Stratolaunch flight test marked a huge step forward in hypersonics.

Proving it can be done

Stratolaunch is an aerospace company focused on high-speed flight test services. Its Talon-A reusable, autonomous vehicle is designed to accelerate testing and development of high-speed and hypersonic technology. Powered by a liquid-fueled rocket, it can reach speeds as high as Mach 6, or six times the speed of sound.

The March test included air-launch release of the TA-1 vehicle, engine ignition, acceleration, sustained climb in altitude, and a controlled high-speed flight. The TA-1 approached Mach 5 during the test.

“Hypersonic flight testing requires robust, agile, and modular approaches,” said Dan Gallton, Ph.D., Draper director of space navigation and in-space servicing, assembly, and manufacturing (ISAM). “Draper’s GNC flight software had to be designed to successfully manage evolving requirements in vehicle equipment, flight scenarios, and mission parameters.”

To build the new GNC software, the team pulled from a variety of past programs, including the Space Shuttle and Dream Chaser. They also leveraged model-based engineering to develop and update other systems to address issues specific to the TA-1 and hypersonic travel.

“A positive surprise is that the way we modeled the systems was actually remarkably successful, and the actual TA1 flight could be recreated in simulation with high fidelity,” said Gondhalekar.

This was Draper’s second successful test with Stratolaunch, which used Draper’s GNC software in an unpowered TA-0 drop test last year. With a proven GNC system, Stratolaunch can continue its development of the TA-2 and TA-3 test vehicles – bringing the world closer to conquering Yeager’s “real barrier” and making hypersonic travel a reality.