The boost phase is the portion of the flight of a ballistic missile or space vehicle during which the booster and sustainer engines operate until it reaches peak velocity. This phase can take 3 to 4 minutes (for a solid rocket shorter than for a liquid-propellant rocket), the altitude at the end of this phase is 150–200 km, and the typical burn-out speed is 7 km/s. Boost-phase intercept is a type of missile defense technology that would be designed to disable enemy missiles while they are still in the boost phase.
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