Walker: Hypersonic HAWC and TBG Neck-And-Neck to Fly by End of Year


An Air Force Magazine illustration of a Hypersonic Conventional Strike Weapon (HCSW) or “Hacksaw” after launch from an airborne platform. Staff illustration by Mike Tsukamoto.

Two hypersonic missile development projects jointly underway between the Air Force and the Defense Advanced Research Projects Agency are in a “race” to see which will fly first, but DARPA’s director said he expects it will happen by the end of this year, or early next.

Steven Walker, at a press roundtable in Washington, said he’s “hopeful” the Tactical Boost Glide or Hypersonic Air-breathing Weapon Concept projects will fly by December, though he said making that timetable will be “sporty.”

“As you get into the building of these things [and] qualify flight hardware, things tend to slip,” Walker allowed. “So, I’m hopeful that we can fly both of those by the end of ’19 [but] it may slip into the early ’20 timeframe.”

He said, “It’s really a race between HAWC and TBG to see which one goes first. They’re actually both scheduled around the same time … I can’t really see right now which one’s going to win out.”

Both approaches are accelerated to hypersonic speed atop a booster stage, but the TBG is a maneuvering coast vehicle that gradually bleeds off its velocity, while the HAWC takes in air to mix with fuel for a powered trajectory. They are both “focused on tactical and theater-level operations,” Walker noted.

Taking two different approaches to a hypersonic weapon is sensible, Walker asserted. “It’s good to have what I consider intended redundancy, because it’s a harder technology. Materials and propulsion systems that last in 3,000 degrees Fahrenheit temperatures is not easy.” He added, “These are going to be important tests for DARPA and the Air Force.”

The Advanced Rapid Response Weapon, or ARRW, will be an outgrowth of the TBG, Walker noted, suggesting it’s considered the most likely to be in service first. Prototyping activities on the concept with the Air Force are designed “so that the service could accept these concepts if they were successful in flight.” Under ARRW, USAF would be “taking that TBG concept and flying it several more times through the prototyping level, building some number for the Air Force.” This was “a very important thing we were able to do last year in the budget.”

Walker noted that Pentagon research and engineering czar Mike Griffin “has been able to get a lot more money into the service budgets for hypersonics for ’20,” and “you will see in the next several years the US aggressively pursuing these technologies; and not just pursuing, … but really thinking about how to turn it into a capability.”

Both projects are entering the “assembly, integration, and test phase,” Walker noted, a period when it’s not uncommon to have to “requalify things … [You] put all that together and you test the whole system, you hope it all works and has been done correctly. We’re still very much in the early stages of AIT for both programs.” He also cautioned that scheduling range tests and ensuring they’re done “by the book” can complicate or cause delays to testing. “Once you get into test hardware, there are all sorts of things you have to face down every day and beat back,” he added.

Technologically, tough challenges include managing temperatures and materials to withstand them, Walker said.

DARPA is also working with the Army on a variant of TBG that would be lofted to altitude and speed by an all-new booster. The project, called “Op Fires,” is a 50-50 cost sharing program with the Army. The booster is being eyed “to give some controllability to where that front end can be put. Re-entry conditions for a glider are very important for how far it can go, and what the environment it sees is.” Three “small companies” are working on the booster, he said.

For the Air Force versions, Walker said the B-52 will be the test launch vehicle.

The Navy, meanwhile, is considering whether the HAWC approach could be a solution to its needs, though it hasn’t finished studying the issue and has made no decision, Walker reported.

“I do know the Navy is working on the larger OSD program, but that’s not really a DARPA thing,” he added.

Hypersonics is an urgent technology push, Walker insisted, because although the US has “led the way” in research previously, “some of our peer competitors have taken that technology and turned it into a capability faster than we have.” It’s “an area that I believe the US really needs to make progress in and be a leader in.”