After years of speculation and careful planning, the US military initiated the creation of an anti-ballistic missile (ABM) aimed at intercepting Soviet re-entry vehicles (RVs). Known as the “Sprint missile,” this weapon became operational within the US Army between 1975-76, showcasing an impressive capability to attain remarkable speeds within seconds.
Unfortunately, the effectiveness of this ABM was short-lived, as policy changes eventually led to its discontinuation.
Last-ditch defensive strategy
As early as the 1940s, the US military initiated exploratory efforts to devise a weapon capable of intercepting theater ballistic missiles (TBMs). In 1955, the Army awarded a contract to Bell Telephone Laboratories to tackle this challenge. The company’s assessment revealed that developing an anti-ballistic missile tailored to thwart TBMs was technologically feasible, with minor adaptations to the Nike Hercules surface-to-air missile (SAM).
The development of the Nike Zeus began in 1955 under Bell’s guidance. This undertaking involved a number of enhancements, including robust radar systems designed to detect intercontinental ballistic missiles (ICBMs) well in advance, enabling effective countermeasures. Additionally, it incorporated faster and more advanced computer technology.
Rigorous testing of the Nike Zeus took place in 1959 and, three years later, a base was established on Kwajalein Island. The anti-ballistic missile demonstrated its success by intercepting test missiles and precisely targeting low-flying satellites.
Issues with the Nike Zeus
During development of the Nike Zeus, it became clear the ABM had quite a few issues that made it easy to defeat.
As it used 1950s-era mechanical radar, the number of targets it could track were limited. A report at the time even suggested that four warheads had a 90 percent chance of destroying a Nike Zeus base. This initially didn’t seem like a big issue, but, as ICBMs became less expensive to produce, the threat of the Soviet Union using them against the United States became more probable.
Over time, even more problems presented themselves. After nuclear testing in space in 1958, it was found radiation from warhead detonations would blanket large areas, blocking radar signals above an altitude of 60 km. If the Soviets caused an explosion above a Nike Zeus site, they could prevent observation until it too late to launch a counterattack.
Additionally, they could use radar reflectors on their warheads, which created multiple false targets.
Replacing the Nike Zeus with the Nike-X
At the behest of then-Secretary of Defense Neil H. McElroy, the Advanced Research Projects Agency (ARPA) was tasked with investigating pertinent issues. Their findings revealed that both high-altitude nuclear explosions and radar decoys ceased to be effective in the lower atmosphere due to thickening. To address this challenge, the recommendation was to await the warhead’s descent below 60 km, at which point radar detection could resume.
However, a new obstacle emerged. The warheads, hurtling at speeds of Mach 24, necessitated the deployment of similarly high-speed missiles to intercept them before reaching their targets.
Subsequently, Secretary of Defense Robert McNamara, who succeeded McElroy, proposed to President John F. Kennedy that funds allocated to the Nike Zeus be redirected toward developing the ARPA’s system. His argument swayed JFK and paved the way for the creation of the Nike-X.
Introducing the Sprint missile
The Sprint missile became the focal point of the Nike-X program. Equipped with a W66 thermonuclear warhead, it was designed to attack re-entry vehicles (RVs) at 60 kilometers.
The Sprint was 27 feet in length and weighed 7,500 pounds. To successfully launch, the cover was blown off the silo in which the missile was held, after which it was ejected by an explosive-driven piston. Once clear of the silo, it angled itself toward its target, after which it was controlled by ground-based radio command guidance. This tracked incoming RVs using phased array radar and guided the missile to its target, destroying it through neutron flux.
The performance had be incredible. As such, the missile was developed to accelerate at 100 g and reach Mach 10 in just five seconds. As the missile reached such a high velocity at relatively low altitudes, its skin temperature could reach up to 6,200 degrees Fahrenheit. An ablative shield was used to counter this, and a unique plasma was formed around the missile that caused it to glow white as it flew.
Powerful radio signals were required to penetrate the plasma and guide the weapon to its target.
HIBEX missile
The High Boost Experiment (HIBEX) missile is considered a kind of predecessor to the Sprint missile, as well as its competitor. It was another high-acceleration missile designed in the early 1960s, and it actually provided a technological transfer to the Sprint development program.
Unlike the Sprint missile, the HIBEX had a high initial acceleration rate of nearly 400 g. Its role was to intercept RVs at an even lower altitude – as low as 20,000 feet. Unlike the Sprint, it featured a star-grain “composite modified double-base propellant” that was created by combining zirconium staples with aluminium, double-base smokeless powder and ammonium perchlorate.
Sprint II missile and the end of the Nike-X program
Over time, the Nike-X evolved into the Safeguard Program, prompting the Los Alamos National Laboratory to explore alternative warheads for a fresh design. Subsequently, efforts were directed toward enhancing the Sprint II missile.
By 1971, the Sprint II became an integral part of the Safeguard Program, serving as a protective measure for Minuteman missile fields. Its interceptor boasted a slightly reduced launch dispersion, compared to its predecessor, which enhanced hardness and minimized miss distance for improved accuracy.
Despite ongoing optimization efforts by Los Alamos to refine the design, the operational lifespan of both missiles was relatively brief.
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During the 1970s, shifts in the ABM policies of both the US and the Soviet Union raised doubts about the effectiveness of the Safeguard Program. It was deemed unnecessary and expensive, leading to its cancellation. The official discontinuation date is unclear, but reports persisted until 1977.
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