The United States cannot sustain the high cost of the Ballistic Missile Defense System (BMDS) to take out adversaries’ relatively inexpensive missiles, US Northern Command (NORTHCOM) Commander Adm. William Gortney said in congressional testimony on Thursday

WASHINGTON (Defense News) — US adversaries are developing "relatively inexpensive technologies," such as long-range cruise missiles and road-mobile intercontinental ballistic missiles that can reach the US homeland, Gortney explained. "By contrast, our interceptors are vastly more expensive.""Today, our BMDS is in an unsustainable cost model, which has us postured to shoot down inexpensive rockets with very expensive ones," Gortney told to the Senate Armed Services Committee.
The United States is currently working to reduce the costs of missile defense, including improving sensors used to detect incoming missiles, the development of the multiple-object kill vehicle, a single interceptor missile capable of engaging and destroying multiple targets, and directed energy weapons.
By the end of 2017, US homeland missile defense will be comprised of 44 interceptor missiles, when the final 14 are installed in Alaska.