Nobody is planning to put a hypersonic glide vehicle on the next silo-based, intercontinental ballistic missile, but that doesn’t mean it could never happen, according to careful statements Wednesday by the Air Force general who advises the service’s leadership about nuclear-weapons.

The Ground Based Strategic Deterrent (GBSD) silo-based missile slated to replace the Minuteman III in 2030 or so has an “open architecture” that would let the Air Force “roll different technologies … into GBSD,” Lt. Gen Richard Clark, deputy chief of staff for strategic deterrence and nuclear integration, said in a webcast question and answer session with reporters on Wednesday. The Washington-based Mitchell Institute hosted the event.

Clark said GBSD isn’t required to have any hypersonic capability before it’s deployed, and declined to say whether GBSD eventually should have such a capability. This year, the Congressional Research Service said,

without citing a source, that the U.S. was not developing nuclear options for such hypersonic glide vehicles. However, the outgoing Air Force nuclear evangelist left the possibility on the table, for those listening.

On Aug. 6, the Senate confirmed Clark as superintendent of the Air Force Academy near Colorado Springs, Colo. He is slated to leave for his new assignment later this year. 

Hypersonic glide vehicles, so far a unicorn, would allow for extremely high-speed delivery of payloads at lower altitudes and along different flight paths than those achievable by current ballistic and cruise missiles. Militaries globally covet the technology as a means of evading any deployed air defense. 

Lockheed Martin [LMT], which has taken a forward role in U.S. defense-hypersonics development, is part of the Northrop Grumman [NOC]-led team expected to win a roughly $20 billion Air Force contract this month to build GBSD.

The Air Force plans to buy more than 650 GBSD missiles, including spares and test articles, and will use them to replace the 400-strong Minuteman III fleet on a one-for-one basis. The missiles could initially use W87-0 warheads provided by the Department of Energy’s National Nuclear Security Administration (NNSA). These warheads now tip some Minuteman III missiles and would need flight tests aboard GBSD — using dummy warheads — to be certified for the next-gen missiles.

Eventually, the Air Force will mix in the NNSA’s planned W87-1 warhead into the GBSD fleet. U.S. nuclear forces always deploy at least two versions of a warhead, in case there is an unforeseen, design-specific problem with one of them.

Meanwhile, Clark said Wednesday that he was not aware of discussion within the Air Force to transfer responsibility for intercontinental ballistic missiles to the newly created Space Force: a service that is to the Air Force what the Marine Corps is to the Navy.