That speed would also simply reduce the time available for any sensors , no matter how well placed or powerful, to identify the threat and then help cue the interceptors. This would only be more pronounced in a battlefield setting, where hostile forces might launch their weapons much closer to the actual target, further reducing the time available for U.S. forces to respond.

This has been described as trying to hit one bullet with another bullet . Engaging a hypersonic weapon would be akin to trying to hit a bullet that can erratically change course, is flying on a more level path through the atmosphere instead of space, and that is cruising at a consistent speed of five times the speed of sound or more throughout the majority of its flight.

Unfortunately, doing so will be easier said than done. Using hard-kill interceptors to knock down incoming ballistic missiles, which reach hypersonic speeds in the latter stages of their flight trajectory, is hard enough , even though they travel along relatively well-defined courses to get to their targets.

Glide Breaker’s core objective seems to be to find a way to challenge these inherent capabilities and make it clear to any potential opponent that a hypersonic weapon strike is in no way guaranteed to succeed against American forces. “A key figure of merit is deterrence: the ability to create large uncertainty for the adversary’s projected probability of mission success and effective raid size,” DARPA said in its Proposers Day notice .

Of course, existing ballistic missiles already travel at hypersonic speeds in their terminal phase of flight, so existing defense systems geared toward intercepting those weapons at the end of their trajectory might be adaptable to knocking down hypersonic weapons, as well. Adding a space-based missile defense weapon layer could be another option to help shoot down boost-glide vehicles, which typically briefly fly near or above the earth's atmosphere.

Undersecretary of Defense Griffin has already proposed deploying 1,000 anti-missile interceptors in space and has discussed concepts for destroying incoming ballistic missiles during their initial boost phase, when they most vulnerable, using satellites carrying directed energy weapons. He has said the interceptor constellation concept would cost $20 billion, but has not yet offered any concrete details about the interceptors, how they would operate in space, or where the U.S. would position them to provide a useful defense shield. In 1993, the U.S. government canceled a proposed plan to place 4,600 interceptors in space, which had a price tag of $55 billion – more than $95 billion in 2018 dollars.

The key in any one of these scenarios will be a robust sensor network to alert U.S. forces to incoming threats, monitor them as they head toward their targets, and help aim anti-missile weapons at them somewhere along the way. But despite these various potential difficulties, the growing danger of hypersonic weapons is already too great to ignore.

“In brief, we do not have systems today that give us globally, comprehensive, persistent, timely, multi-mode awareness of what is going on on earth, everywhere, all the time. We don't have that,” Undersecretary of Defense Griffin said at a conference earlier in September 2018. “The Chinese hypersonic threat is one that in today's world, we cannot see coming until it's too late.”

It will be very interesting to see what sorts of sensors, weapons, and other technologies come out of DARPA’s Glide Breaker program that might be able to counter hostile hypersonic weapons, or at least make an enemy think twice before employing them. We've reached out to DARPA for more information about the project and will let you know if and when we get any additional details.

Contact the author: jtrevithickpr@gmail.com