The US Air Force will be flying operational prototypes of hypersonic weapons by 2020. At least that’s according to Major General Thomas Masiello, commander of the Air Force Research Laboratory, who spoke last Friday at the Air Force Association Air Warfare Symposium in Orlando, Florida.

This may mean that hypersonics are just about through what engineers and program managers call the “Valley of Death,” which is a sort of Catch-22 where a lot of good ideas languish and die.

Taking any idea from the drawing board to operational deployment is expensive.

There’s one phase where that development starts getting really expensive, but it’s before anyone has enough confidence in the new idea that they’re will to lay out enough money to make that technology usable in practical terms.

Once a program makes it through the Valley of Death, it’s pretty much a given that it’ll go from being an exotic idea to an actual thing in the US arsenal.

That 2020 target is ambitious, and quite simply because going hypersonic is not easy at all. Hypersonic speeds begin at, roughly, Mach 5 — one mile per second or five times faster than the speed of sound.

That’s a sort of generic cutoff at the low end, while the top end runs all the way up to Mach 25, (depending on who you ask). However, the actual, not-completely-arbitrary, laws-of-physics cutoff is a bit harder to precisely define.

An object traveling at hypersonic speeds is going so fast that it generates enough heat, shock, and pressure to alter the basic chemistry (and therefore aerodynamic properties) of the air it’s plowing through. It just so happens that this kind of disruption is a pretty major factor by the time a vehicle has hit Mach 5. But the transition isn’t sharp. As you go faster, the whole engineering problem gets increasingly screwed up in new and extremely difficult ways.