Sprint (missile)

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The Sprint was a two-stage, solid-fuel anti-ballistic missile (ABM), armed with a W66 enhanced-radiation thermonuclear warhead used by the United States Army during 1975–76. It was designed to intercept incoming reentry vehicles (RV) after they had descended below an altitude of about 60 kilometres (37 mi), where the thickening air stripped away any decoys or radar reflectors and exposed the RV to observation by radar. As the RV would be traveling at about 5 miles per second (8,047 m/s; 26,400 ft/s; Mach 24), Sprint needed to have phenomenal performance to achieve an interception in the few seconds before the RV reached its target. Sprint accelerated at 100 g, reaching a speed of Mach 10 (12,000 km/h; 7,600 mph) in 5 seconds. Such a high velocity at relatively low altitudes created skin temperatures up to 6,200 °F (3,400 °C), requiring an ablative shield to dissipate the heat. The high temperature caused a plasma to form around the missile, requiring extremely powerful radio signals to reach it for guidance. The missile glowed bright white as it flew. Sprint was the centerpiece of the Nike-X system which concentrated on placing bases around large cities to intercept Soviet warheads. The cost of such a system quickly became untenable as the Soviets added more ICBMs to their fleet, and Nike-X was abandoned. In its place came the Sentinel program, which used Sprint as a last-ditch defense against RVs that evaded the much longer-ranged LIM-49 Spartan. Sentinel was changed to become the Safeguard Program, which was operational only for a few months from October 1975 to early 1976. Congressional opposition and high costs linked to its questionable economics and efficacy against the emerging MIRV warheads of the Soviet Union resulted in a very short operational period. During the early 1970s, some work was carried out on...