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Sprint missile in flight
|Place of origin||United States|
|Weight||7,700 pounds (3,500 kg)|
|Length||26.9 feet (8.20 m)|
|Diameter||53 inches (1.35 m)|
|Warhead||W66 nuclear low kt|
|25 miles (40 km)|
|Flight ceiling||19 miles (30 km)|
|Speed||12,250 kilometres per hour; 7,610 miles per hour; 3,403 metres per second (Mach 10)|
|Radio command guidance|
The Sprint was a two-stage, solid-fuel anti-ballistic missile (ABM), armed with a W66 enhanced radiation thermonuclear warhead. It was designed to intercept incoming reentry vehicles (RV) after they had descended below an altitude of about 60 kilometres (37 miles), where the thickening air stripped away any decoys or radar reflectors and exposed the RV to observation by the radar. As the RV would be travelling at about 5 miles (8.0 km) per second, Sprint had 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 in 5 seconds. Such a high velocity at relatively low altitudes created skin temperatures up to 6,200 °F (3,430 °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.
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 itself 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 then emerging MIRV warheads of the Soviet Union, resulted in a very short operational period.
Some work on an improved Sprint II was carried out in the early 1970s, but was cancelled as US ABM policy changed.
The conical Sprint was stored in and launched from a silo. To make the launch as quick as possible, the cover was blown off the silo by explosive charges; then the missile was ejected by an explosive-driven piston. As the missile cleared the silo, the first stage fired and the missile was tilted toward its target. The first stage was exhausted after only 1.2 seconds, but produced 650,000 pounds-force (2,900 kilonewtons) of thrust. On separation of the spent first stage, it disintegrated due to aerodynamic forces. The second stage fired within 1 to 2 seconds of launch. Interception at an altitude of one to eighteen miles' altitude (1.5 to 30 km) took at most 15 seconds.
The Sprint was armed with an enhanced radiation nuclear warhead with a yield reportedly of a few kilotons, though the exact number has not been declassified. The warhead was intended to destroy the incoming reentry vehicle primarily by neutron flux.
The "HIBEX" (HIgh Boost EXperiment) missile is considered to be somewhat of a design predecessor and competitor to the Sprint missile, as it was a similar high acceleration missile in the early 1960s, with a technological transfer from that program to the Sprint development program occurring. Both were tested at the White Sands Launch Complex 38. Although HIBEX's initial acceleration rate in G's was higher at near 400 G, its role was to intercept reentry vehicles at a much lower altitude than Sprint, 6,100 m, and it is considered to be a last ditch anti-ballistic missile "in a similar vein to Sprint". HIBEX employed a star-grain "composite modified double-base propellant", known as FDN-80, created from the mixing of ammonium perchlorate, aluminium, and double base smokeless powder, with zirconium staples (0.125 inches in length) embedded or "randomly dispersed" throughout the matrix.
The first stage's Hercules X-265 engine is believed to have contained alternating layers of zirconium "staples" embedded in nitrocellulose powder, followed by gelatinizing with nitroglycerine, thus forming a higher thrust double-base powder.
17 November 1965 First guided SPRINT flight test took place at WSMR
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