Throw weight

Throw-weight is a measure of the effective weight of ballistic missile payloads. It is measured in kilograms or tonnes. Throw-weight equals the total weight of a missile's warheads, reentry vehicles, self-contained dispensing mechanisms, penetration aids, and missile guidance systems--generally all components except for the launch rocket booster and launch fuel. While throw-weight may refer to any type of warhead, in normal modern usage it almost exclusively refers to nuclear or thermonuclear payloads. It was once also a consideration in the design of naval ships and the number/size of guns they carried.

Throw-weight was used as a criterion in classifying different types of missiles during Strategic Arms Limitation Talks between the Soviet Union and the United States. The term became politically controversial during debates over the arms-control accord, as critics of the treaty alleged that Soviet missiles were able to carry larger payloads and therefore enabled the Soviets to maintain higher throw-weight than an American force with a roughly comparable number of lower-payload missiles.

Culturally, being able to discuss throw-weight was often used as shorthand to suggest that a politician was capable of understanding a serious and high-profile but arcane and supposedly mathematically complex public policy issue.

Throw-weight is normally calculated using an optimal ballistic trajectory from one point on the surface of the Earth to another. An optimal trajectory maximizes the total payload (throw-weight) using the available impulse of the missile. By reducing the payload weight, different trajectories can be selected which either extends the nominal range, or decreases the total time in flight. A depressed trajectory is a non-optimal, lower and flatter trajectory which takes less time between launch and impact, but with a lower throw-weight. The primary reasons to choose a depressed trajectory are either to evade anti-ballistic missile systems by reducing the time available to shoot down the attacking vehicle (especially during the vulnerable burn-phase against space-based ABM systems), or in a nuclear first-strike scenario. An alternate, non-military, purpose for a depressed trajectory is in conjunction with the space plane concept with use of air-breathing engines, which requires the ballistic missile to remain sufficiently low inside the atmosphere for air-breathing engines to function.

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