WASHINGTON — The U.S. and Japan are exploring a partnership to develop a hypersonic missile defense capability as the Pentagon enters the early stages of a program to develop an interceptor capable of neutralizing hypersonic threats in the glide phase of flight.

Vice Adm. Jon Hill, who leads the U.S. Missile Defense Agency, confirmed last week that the organization is considering cooperation with Japan to work on the Glide Phase Interceptor, or GPI, one of the agency’s top priorities.

“Right now we’re exploring the opportunity to just identify what those cooperative development areas would be,” Hill said at the McAleese & Associates conference in Washington.

The effort could take on similar attributes to the successful U.S.-Japan development of the Raytheon Technologies-manufactured SM-3 block IIA program, which the company is now building and the countries will field, Hill said.

“The easy way to go with Japan is to offer up [development of] propulsion stacks because they build the second stage and the third stage on the SM-3 block IIA today,” Hill explained. But this time Japan would like to get “a little more into, say, the front end of the missile” — the portion of the interceptor containing the warhead — he added, “so we’re looking for common parts.”

But the effort is complicated because two companies are competing to design the GPI — Raytheon Technologies and Northrop Grumman. Each company won contracts to continue developing hypersonic weapons interceptors in an MDA-led competition in June 2022.

“The challenge is when you’ve got two [companies] in play, that means Japan has to sign up to do two different designs, knowing that one of them may be a throwaway,” Hill said. “They know one of them is going to go away downstream. I don’t know when that downselect will happen. It’s going to depend on how well they mature technically.”

Hill said during a press briefing at the March 15 conference that MDA has a team in Japan holding an executive steering council, which is essentially a technical interchange with the Japanese government that includes acquisition, technology and logistics officials.

Following the meeting, “we’ll come back, take a breather, then we’ll go back out [to Japan] and we’ll bring industry with us next time around so that we’re not speaking for industry.”

Ideally, Hill said, industry would willingly subcontract work to a Japanese company for agreed-upon components of the interceptor, but “if we can’t get to that, then we’ll do what we initially did in the SM-3 block IIA program, which is we directed the American company to go subcontract.”

Defeating a hypersonic weapon in its glide-phase of flight is a challenging technical problem, as the missiles can travel more than five times the speed of sound and can maneuver in flight, making it hard to predict a missile’s trajectory.

The MDA is still early in the development process — “the mission solution analysis phase,” as Hill put it during a fiscal 2024 budget request briefing on March 13 at the Pentagon. “What we’re doing during this phase is determining what technologies do we need and how we can bring that together as a weapons system.”

The budget, he added, supports “a deployment or getting to that first article out there in the early [20]30s.”

MDA is asking for $209 million in FY24 to fund the ongoing GPI competition.

The interceptors will be designed to fit into the U.S. Navy’s current Aegis ballistic missile defense-equipped destroyers. The weapon will fire from the standard vertical launching system and be integrated with the modified Baseline 9 Aegis Weapon System that detects, tracks, controls and engages hypersonic threats.

Jen Judson is an award-winning journalist covering land warfare for Defense News. She has also worked for Politico and Inside Defense. She holds a Master of Science degree in journalism from Boston University and a Bachelor of Arts degree from Kenyon College.

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