The hypersonics community is accustomed to failure, but that has done nothing to temper the deep disappointment after the X-51A Waverider demonstrator's third flight ended before its supersonic-combustion ramjet engine could be fired. The Aug. 14 test fizzled seconds after it began due to a control fin malfunction. It followed a largely successful first test in May 2010, and is the latest in a string of failures.
But there have also been successes, and it is those that continue to keep the hopes for hypersonics alive. The first U.S. Air Force X-51A achieved 143 sec of scramjet-powered flight—11 times the duration set by's X-43A in 2004. The rocket-boosted Army Hypersonic Weapon flew from Hawaii to Kwajalein Atoll in less than 30 min. in November 2011, and in May of this year, under a U.S.-Australian cooperative program, the HIFire 2 scramjet was launched successfully from Hawaii.
Now there is a debate about whether the Air Force should fund the flight of a fourth X-51A demonstrator already built byand scramjet developer Pratt & Whitney Rocketdyne as part of the original program. The answer is an emphatic yes!
After more than 10 years of irregular warfare in Iraq and Afghanistan, where the aerospace and defense industry's ingenuity has been directed toward fighting insurgents and terrorists, the U.S. is looking again at what it will take to fight an adversary with the ability to deny the U.S. freedom to operate with impunity in enemy airspace. The development of stealth bought the U.S. a huge technology advantage, but that will erode over time.
One direction to follow could be to achieve substantially higher speeds and greater range, dramatically reducing a defender's reaction time while keeping U.S. forces safely out of range. As a technological game-changer in a future near-peer conflict, the idea of a hypersonic strike weapon is very appealing. That is why the Air Force Research Laboratory andcontinue to pursue technology demonstrations.
And therein lies the problem. There is just enough data to suggest such a weapon is feasible but not enough to establish its practicality. Still, whenever the military comes looking for technological superiority, hypersonics gets another lease on life.
In the current budget environment, and with today's demands for program performance, it takes a leap-ahead concept to get customers' attention. High-speed and global-range strike weapons are such ideas. We are talking revolutionary science here, not your garden variety technology innovations. In such endeavors, failure is an integral part of the learning process, and the knowledge base required to achieve success is still being built. The result is that industry ends up conducting system design, technology development and basic research all in parallel, with predictable results.
Despite decades of research, industry is still compiling new information about aerodynamics, propulsion, flight control and thermal protection in the hypersonic regime. Unlike stealth, which was developed in a focused, albeit secretive effort, there has been no sustained research program in hypersonics with a sufficient number of flights to master both the art and the science.
In an interview for a special report on small, innovative companies to be published in the next issue, the CEO of a fledgling space-technology developer tells Aviation Week & Space Technology that his company's culture includes “making mistakes as fast as possible.” By making them early, when they are inexpensive, and openly discussing the reasons, the CEO believes costly, fundamental failures can be avoided later. That has not happened with hypersonics.
There have been relatively few flight tests conducted over the decades to bring down the costs and risks that hypersonics entails. Managers of each new program try to justify its existence by reaching further than the one before, increasing the risk and cost of failure. Sadly, neither the nation nor the aerospace industry seem willing any longer to countenance failure. And that in itself is a failure of the engineering community, the culture we have created for ourselves and ultimately leadership.
Hypersonics is just the tip of the iceberg. Throughout aerospace, potentially valuable technologies are being held back because of a fear of failure, even at an early stage of R&D. Somehow this industry—essential as it is—has reached a point where there is little or no tolerance for risk. If we are to make progress in hypersonics, then it is time to come to terms with the fact that setbacks will occur. Four X-51s were built for a reason: More flights mean more lessons learned. The last flight failed. So what!
Now it is time to pick ourselves up, resume flight testing and solve the tough problems associated with the development of hypersonics. Fly the remaining X-51, and use it for the purpose for which it was intended: a flying testbed.