page_title: Nike-X
section_title: Sprint
hierarchical_section_title: Nike-X / Description / Sprint
caption_attribution_description: Sprint Antiballistic Missile
context_page_description: Nike-X was an anti-ballistic missile system designed in the 1960s by the United States Army to protect major cities in the United States from attacks by the Soviet Union's intercontinental ballistic missile fleet during the Cold War. The X in the name referred to its experimental basis and was supposed to be replaced by a more appropriate name when the system was put into production. This never came to pass; in 1967 the Nike-X program was canceled and replaced by a much lighter defense system known as Sentinel.
  The Nike-X system was developed in response to limitations of the earlier Nike Zeus system. Zeus' radars could only track single targets, and it was calculated that a salvo of only four ICBMs would have a 90% chance of hitting a Zeus base. The attacker could also use radar reflectors or high-altitude nuclear explosions to obscure the warheads until they were too close to attack, making a single-warhead attack highly likely to succeed. Zeus would have been useful in the late 1950s when the Soviets had only a few dozen missiles, but would be of little use by the early 1960s when it was believed they would have hundreds.
context_section_description: Sprint was the primary weapon of Nike-X as originally conceived; it would have been placed in clusters around the targets being defended by the MAR system. Each missile was housed in an underground silo and was driven into the air before launch by a gas-powered piston. The missile was initially tracked by the local MSR, which would hand off tracking to the MAR as soon as it became visible. A transponder in the missile would respond to signals from either the MAR or MSR to provide a powerful return for accurate tracking.
  Although a primary concern of the Sprint missile was high speed, the design was not optimized for maximum energy, but instead relied on the first stage (booster) to provide as much thrust as possible. This left the second stage (sustainer) lighter than optimal, to improve its manoeuvrability. Staging was under ground control, with the booster cut away from the missile body by explosives. The sustainer was not necessarily ignited immediately, depending on the flight profile. For control, the first stage used a system that injected Freon into the exhaust to cause thrust vectoring to control the flight. The second stage used small air vanes for control.
  The first stage accelerated the missile at over 100 g, reaching Mach 10 in a few seconds. At these speeds, aerodynamic heating caused the airframe's outer layer to become hotter than an oxy-acetylene welding torch. The required acceleration required a new solid fuel mixture that burned ten times as fast as contemporary designs such as the Pershing or Minuteman. The burning fuel and aerodynamic heating together created so much heat that radio signals were strongly attenuated through the resulting ionized plasma around the missile body. It was expected that the average interception would take place at about 40,000 feet (12,000 m) at a range of 10 nautical miles (19 km; 12 mi) after 10 seconds of flight time.
  Two warheads were designed for Sprint starting in 1963, the W65 at Livermore and the W66 at Los Alamos. The W65 was entering Phase 3 testing in October 1965 with a design yield of around 5 kT, but this was cancelled in January 1968 in favor of the W66. The W66's explosive yield was reported to have been in the "low kiloton" range, with various references claiming it was anywhere from 1 to 20 kT. The W66 was the first enhanced radiation bomb, or neutron bomb, to be fully developed; it was tested in the late 1960s and entered production in June 1974.
caption: Sprint was the centerpiece of the original Nike-X concept, but it was relegated to a secondary role in Sentinel.
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