The sleek aircraft, really more rocket than plane, dropped from the wing of a B-52 before shooting through the sky above Point Mugu Sea Range off the California coast, leaving a long, white contrail in its wake.
The unmanned X-51A hit Mach 4.8, almost five times the speed of sound, with help from a solid rocket booster. Then the Boeing Co. aircraft jettisoned the booster and its experimental scramjet engine took over, sucking in highly-compressed air to propel the vehicle even faster — to a hypersonic speed of about 3,400 mph, or Mach 5.1.
The aircraft relied on that scramjet for only 3½ minutes during the 2013 test flight, but researchers say reliable technology that propels aircraft to hypersonic speeds of Mach 5 or higher could be functional within 10 years, initially for use in missiles.
The stakes are high.
The Pentagon sees hypersonic weaponry as a potential game changer that could give it — or an opponent — the kind of edge that stealth aircraft or smart bombs did in decades past. Hypersonic missiles would be extremely difficult to shoot down, arriving with little to no warning and maneuvering to avoid defenses.
Russia and China are also developing hypersonic missiles, and in November, there were reports China had started building the world’s fastest wind tunnel to test hypersonic aircraft and weapons.
“I am also deeply concerned about China’s heavy investments into the next wave of military technologies, including hypersonic missiles,” Adm. Harry Harris Jr., head of the Navy’s U.S. Pacific Command, said last week before a House Armed Services Committee. “If the U.S. does not keep pace, (U.S. Pacific Command) will struggle to compete with the People’s Liberation Army on future battlefields.”
As with past programs, including stealth technology and ballistic-missile research, Southern California could be poised to take a leading role in its development.
The Defense Advanced Research Projects Agency, or DARPA, the same agency that helped develop the Internet, and the Air Force are spearheading a program called the Hypersonic Air-breathing Weapon Concept. It has awarded defense firms, including Raytheon Co. and Lockheed Martin Corp., contracts to work on technologies that would enable an “effective and affordable” air-launched hypersonic cruise missile.
Aerospace firm Orbital ATK Inc. also was recently selected to take part in a hypersonic aircraft engine project with DARPA, while military aircraft manufacturers have discussed their own concepts for hypersonic planes.
Nearer term, the Defense Department is prepared to start testing a hypervelocity projectile for gun systems that could reach speeds close to Mach 6, according to reports. The projectile could have implications for future missile defense.
Reliable hypersonics not only could propel a missile to incredible speeds that make them harder to shoot down but also could allow for greater maneuverability at unusual altitudes — both nearer to the ground and far higher than the range of current missile defense systems, according to a Rand Corp. report released last year.
“There was this old saying that hypersonics was the future and always would be,” said Kevin Bowcutt, senior technical fellow and chief scientist for hypersonics at Boeing, who came up with the original concept design for the X-51A in 1995. “Now people believe it. It’s real.”
The U.S.’ current technological emphasis on hypersonics is multifold. Historically, the U.S. has been a leader in this field, and the technology is promising. But development is not being driven by a specific mission need, said James Acton, co-director of the Nuclear Policy Program at the Carnegie Endowment for International Peace think tank.
Other analysts have said the current push for hypersonics could be an attempt to discourage other countries from considering hypersonic missile attacks.
But to develop functional hypersonics technology, the U.S. will need to develop engine systems and materials that can operate at high speeds and temperatures for extended periods of time. That research and development cost alone would be significant, and wouldn’t even include the billions of dollars needed to develop operational vehicles, experts say.
Tens of billions of dollars could be spent on hypersonics contracts between 2020 and 2035 if the research “comes to fruition in real weapons programs,” said Loren Thompson, an aerospace analyst with the Lexington Institute think tank, which receives funding from Lockheed Martin and Boeing.
U.S. development of hypersonics dates to the 1940s, when JPL attached a WAC Corporal rocket in the nose of a German V-2 rocket to create a two-stage rocket as part of the Army’s Bumper program. Launched from New Mexico’s White Sands Missile Range in 1949, the rocket reached 5,150 mph, or about Mach 6.7.
Another major breakthrough came in the 1950s and 1960s with the X-15 program, experimental rocket-propelled aircraft that reached a top speed of Mach 6.7 and were designed to advance understanding of hypersonic flight.
Data from the test flights helped influence the spacecraft design of the Apollo capsule and the Saturn V rocket that took astronauts to the moon.
The Space Shuttle, which flew from 1981 to 2011, also reached hypersonic speeds as it reentered the Earth’s atmosphere, leading to developments in heat-absorbing ceramic tiles and large, rounded edges to lower reentry temperatures.
But despite these incremental developments, hypersonics researchers say there are still big technical hurdles to solve, especially in materials science.
When reentering the Earth’s atmosphere, the outer surface of the space shuttle orbiter encountered temperatures of nearly 3,000 degrees Fahrenheit. Aircraft-grade aluminum melts at a temperature about three times less than that, and the structure of a plane would fail at even lower temperatures.
One possible solution are materials such as titanium or nickel-based alloys, which can be used at speeds slightly beyond Mach 5. Past that, ceramic-matrix composites, a more exotic blend of strong, lightweight fibers, may be an answer.
“The better you can predict a heat load, the better you can come up with materials or structure to handle that heat load,” said Stuart A. Craig, an assistant professor in the aerospace and mechanical engineering department at the University of Arizona who researches hypersonic aerodynamics.