U.S. Should Strive For Hypersonic Flight Technology, UF Professor Says

November 13, 1998

GAINESVILLE — Whether or not it provides information about aging and space travel, John Glenn’s triumphant return to space seems to indicate continued U.S. superiority in space.

But the United States could fall behind if it doesn’t get serious in a worldwide race to create air-breathing hypersonic vehicles that can deliver satellites to orbit more frequently and cheaply than the space shuttle or current rockets, says a University of Florida professor.

Corin Segal, a professor of aerospace engineering, mechanics and engineering sciences, says Japan, France and Germany all have well-funded programs for development of next-generation hypersonic vehicles, which travel more than five times the speed of sound. The United States is renewing its research in this field, but it needs to avoid repeating a history of funding programs for a few years and then dropping them, he said.

“In previous cycles, there was no competition, but now there is,” Segal said. “The bottom line is, there is a danger now that we’ll lose the technology edge in this field, and with it our dominance in space.”

The shuttle and other vehicles that reach hypersonic speeds today require heavy tanks to store oxygen used in the combustion process, said Mike Owens, an aerospace engineering, mechanics and engineering science master’s student. Air-breathing hypersonic vehicles will not require oxygen for at least part of their flight into orbit, making them far cheaper to operate and easier to re-use over short time periods, he said. Ideally, the vehicles would take off and land from ground-based runways like airplanes.

Segal, who specializes in fluid mechanics, combustion and aircraft design, said the challenges of hypersonic flight are huge because scientists and engineers understand very little about how to build hypersonic vehicles.

“We don’t yet have a demonstrated propulsion system, we don’t have a good understanding of hypersonic aerodynamics, we don’t have the materials and we don’t know how to do the dynamics and controls,” he said. “Ground facilities that simulate the extreme conditions of hypersonic flight are nonexistent, and the cost of building such facilities is prohibitive. Thus, the technology is likely to be developed largely based on flight testing.”

Commercial jets travel just below the speed of sound, while military fighters reach speeds of Mach 1.5 or greater. The U.S. Air Force’s SR-71 Blackbird spy plane, likely the fastest plane in the world, reaches in excess of Mach 3, though its precise top speed is classified, Segal said.

Vehicles moving at Mach 5 travel about 1 mile per second, or 3,600 mph. To allow them to reach and maintain such speeds while burning atmospheric oxygen, engineers have to figure out how to redesign engine combustion chambers to burn a fuel-air mixture efficiently at supersonic speeds in excess of Mach 1.5, Segal said.

They also must learn how to ensure the engines never “flame out” because losing engine power at such high speeds would be catastrophic.

“If the engine goes off, you lose thrust and you’re left with immense drag,” Segal said. “It’s like hitting a wall. The airplane would smash to pieces.”

For his research, Segal uses a model of a section of a generic hypersonic engine. A compressor supplies air to the small model at speeds of about Mach 2. It then is mixed with fuel and burned, with the flame visible through a small glass window. Segal measures pressure, temperature and other variables during the process, which produces a deafening roar that reaches 120 decibels and temperatures of at least 4,000 degrees Fahrenheit.

The Air Force and NASA each have current projects to build hypersonic vehicles, Segal said. The Air Force is shooting for a hydrocarbon fuel-powered vehicle that will travel speeds ranging from Mach 4 to Mach 8, while NASA will test in the near future a series of small, hydrogen-powered experimental vehicles aimed at flying up to Mach 10, or more than 7,000 mph, Segal said.

He said his research, sponsored by Boeing North American, involves hydrocarbon-burning propulsion systems. His results could play a role in the development of the propulsion system for the Air Force project, called Hi TECH.

“The idea of hypersonic flight is not new, but our research is very current,” Owens said.