Sea Sparrow

Sea Sparrow was developed from the AIM-7 Sparrow air-to-air missile as a lightweight "point defense" weapon that could be retrofitted to existing ships, often in place of existing gun-based anti-aircraft weapons. The primary development issues were changes to the seekers to allow them to operate with shipboard radars, and the new Mark 25 trainable launcher system, based on the ASROC launcher, to align the seeker head with the target before launch. Combined with a Mark 115 manned fire control director it was known as the Basic Point Defense Surface Missile System (BPDSMS) or just BPDMS.


As a surface-to-air system, the Sparrow has a number of disadvantages. For one, the missile steers with its mid-mounted wings, which initially made them unfoldable. For this reason the missile takes up much more room than it would have to if the wings could be folded. Additionally the engine is optimized for flight time, as opposed to fast acceleration, which makes sense when launched from an aircraft moving at high speed at a target at long range. In the surface-to-air role, however, one would rather have very high acceleration in order to allow it to intercept sea-skimming targets as soon as possible. Furthermore, the Sea Sparrow possesses a shorter range than its air-to-air counterpart. Some estimates indicate that it may be effective only to 10 nm, about one quarter of the range of the AIM-7 Sparrow.

As part of the NATO Sea Sparrow Missile system (NSSM) the launcher size was reduced by folding the mid-mounted wings, resulting in the Mark 29 NSSM launcher. The older manned directors were replaced by unmanned AN/SPS-65 radars, part of the Mark 91 Fire control system. NSSM replaced BPDMS on Aircraft Carriers and was used on other ships such as Spruance class destroyers.

In order to address these issues, a consortium of many Sea Sparrow users joined together to create the Evolved Sea Sparrow Missile (ESSM). The new design uses the tail-fins for steering, allowing the wings to fold. This allows the missile body to increase in size while still fitting into the same launchers, growing to 10 inches in diameter and offering far higher performance. Additionally the wing-based maneuvering of the older design is designed to save energy during the long gliding period of the missile, while the tail-fin based steering of the ESSM uses up more energy but offers considerably higher maneuverability while the engine is still firing.

Another recent development is the Jet Vane Control (JVC) unit, which can be added to the base of the missile to allow it to be vertically launched. After being "popped" from the launch cell the JVC rotates the missile to bring the seeker onto the target and level the flightpath in that direction. It is then jettisoned. Vertical launching allows a single cell to cover the entire area around the ship, because the seeker can be pointed in any direction by the JVC after launch. Additionally the time needed to point the launcher is eliminated. Another major advantage of the ESSM is that it uses a Mk 25 quad-pack canister allowing four missiles to be loaded into a Vertical Launch System (VLS), instead of just one, quadrupling capacity.1

Though initially employed by the United States Navy and other NATO countries, there are now numerous navies that use variants of the Sea Sparrow.

See also

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