During their bilateral meeting on the sidelines of the NATO summit in Ankara, US President Donald Trump and Ukrainian President Volodymyr Zelensky reached a major agreement regarding Patriot Advanced Capability-3 (PAC-3) missile interceptors.

The PAC-3 is the premier hit-to-kill air defense missile used by the US and many of its allies. The weapon has played a major role in the Iran conflict.

The proposed arrangement for Ukraine has two parts: a political agreement to give Ukraine a license to manufacture PAC-3 interceptors; and a short-term supply of PAC-3 interceptors from US inventory, "to bridge the gap." Ukraine is confident it can manufacture PAC-3 missiles under license.

Today, the only production of PAC-3 missiles outside the US is in Japan, where Mitsubishi Heavy Industries produces them under license.

The designation "PAC-3 Interceptor" is important. The US is focusing on expanding production of the PAC-3 MSE interceptor missiles, which offer significantly greater range and other improvements over the PAC-3. While it needs clarification, it appears President Trump offered PAC-3 but not PAC-3 MSE to Ukraine.

The US and Ukraine will soon start "technical talks" where many of the major issues, still undecided, can be addressed.

The MSE variant represents a comprehensive redesign optimized to defeat more complex, faster tactical ballistic missiles and hypersonic threats. There are many changes to the MSE. One of them is to go from a single pulse to a dual pulse rocket motor. 

The MSE's motor can ignite its first pulse to clear the launcher and accelerate toward the target area, then coast before igniting a second pulse later in flight. This provides a critical burst of kinetic energy right during the terminal phase, allowing the missile to pull high-G maneuvers against actively evading or high-velocity incoming threats.

It is not clear if the MSE version can defeat Russia's hypersonic missiles such as the Kinzhal, Zircon or Oreshnik. The PAC-3 version would face problems against the Kinzhal and Zircon and probably not be able to stop the Oreshnik.