Rationalized speed/altitude thresholds for ABM testing

The Antiballistic Missile (ABM) Treaty sharply restricts the development, testing, and deployment of defenses against strategic ballistic missiles. But it places no limitations on military systems for air defense, defense against tactical ballistic missiles, or the destruction of satellites. Without a clear definitional line between ABM defenses and other military systems, a nation that developed, tested, and deployed these other systems might be able to acquire a significant ABM capability despite the ABM treaty. Specific quantitative criteria that differentiate between permitted and prohibited activities could help to define such a line. This note proposes that any test involving a target with an altitude in excess of about 70 kilometers or a speed in excess of about 3 kilometers per second at the moment of closest approach between a weapon and a target should be considered either a “test in an ABM mode” or a test involving a target equivalent to a strategic ballistic missile or its elements in flight t...