One major object of study is a boost-phase defense, meaning a system to intercept missiles while they are in their boost phase.

The Russians say they are developing technology that could down missile-bearing rockets in the boost phase.

And the Soviets have demonstrated a capability of destroying our missiles in the boost phase.

Therefore, the radar was incapable of seeing a missile in the boost phase.

Other theater defenses have been specifically intended to work in the boost phase.

But Russia has not objected to theater systems that work in the boost phase.

Six separate Soviet radars detected the missiles' boost phase, then lost them as they went low.

We have to catch them all, and our best chance for that is while they're still in boost phase.

During the boost phase, missiles move relatively slowly.

That boost phase must also serve those initial requirements of the astronomers.