For those outside the insular world of aerospace engineering, the term “hypersonics” seems to strike the perfect balance between evocativeness and inscrutability. Almost unfailingly, talking about flight at four or five times the speed of sound – and beyond – garners a mixture of disbelief and amazement from the average layperson. Certainly, the concept is a grand one – traveling through the upper atmosphere at speeds which make the rapidity of the legendary Concorde or Blackbird seem like a snail’s pace. And yet, within the aerospace industry, any mention of hypersonics is likely to receive a muted response – a jaded sense of deja vu and a dispiriting defeatism. Critics and doubters point to a littany of cancelled projects and technical challenges which have seemed insurmountable for half a century. Even the most optimistic of researchers will admit that the hypersonics business is a cyclical one, governed by a cruel boom-and-bust pattern with a twenty-year period. Hypersonics research, it seems, comes in waves – from the X-15 aircraft and lifting body research of the 1960s to the National Aerospace Plane of the 1980s, to today’s burgeoning interest in scramjet propulsion and hypersonic surveillance vehicles.
To put things simply, hypersonics is an intensely difficult problem – not only are the technical challenges eye-wateringly complex, but finding funding and support for the large-scale research projects it requires is a logistical nightmare. So, why study hypersonics at all? Why dedicate untold man-hours to a field where progress is measured in millimeters and the future is always 30 years away? Why struggle to chip away at overwhelmingly difficult problems that decades of researchers have failed to solve, when the rug could be pulled out from under you at any moment?
The answer is simple – because we must. Hypersonic flight – or at least, practical, usable applications thereof – is perhaps the last great frontier in aeronautics. We have long since crossed the oceans and the continents; smashed the sound barrier; and connected distant corners of the globe with an air transportation network of incredible safety and complexity, but the promises of manned hypersonic flight continue to elude us. The very inscrutability of hypersonics research – the poorly-understood flow physics, the mind-boggling constraints of material limitations, the heady systems-level logistics required – is perhaps what makes it so alluring. There is an appeal to the challenges themselves, and the battle of solving them – a certain certaminis gaudia, as Lord Kelvin might have said. And yet, there is something more to the hypersonic crusade than gluttony for punishment and a sense of academic abandon; beyond the huge challenges lies a beacon of hope that capabilities which will be unleashed by breakthroughs in fundamental hypersonics research – ultra-fast passenger transports, single-stage space access, fully-reusable spaceplanes – have the capability to fundamentally alter the landscape of aeronautics and of human society itself.
This, more than anything, is what I think drives hypersonics research – the faith that beyond the current limitations in the state of the art lies a vastly different world. And finally, as we start to ride the latest crest in a familiar cycle of boom-and-bust hypersonics research, it feels like the narrative is beginning to change. Massive increases in analytical capabilities enabled by supercomputers, coupled with rising geopolitical tensions and a rejuvenated public interest in space seem to be laying a foundation for meaningful hypersonics research, culminating in several planned flight projects. Players from across the public and private sectors around the world are spooling up programs, and media whispers suggest that in some locales, top-secret hypersonic test vehicles are already flying.
It may be rank optimism and naiveté, but it’s hard to avoid feeling like we are at long last turning a corner in the world of hypersonics. I certainly hope so – because our hypersonic future has been a dream deferred for far too long already.
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