LIM-49 Spartan

LIM-49A Spartan
Type	Anti-ballistic missile
Place of origin	United States
Service history
In service	1975
Production history
Manufacturer	Western Electric & McDonnell Douglas
Specifications
Weight	29,000 lb (13,100 kg)
Length	55 ft 2 in (16.8 m)
Diameter	3 ft 7 in (1.08 m)
Warhead	W71 nuclear; 5 Mt
Engine	1st Stage: Thiokol TX-500 (2200 kN); 2nd Stage: Thiokol TX-454; 3rd Stage: Thiokol TX-239
Wingspan	9 ft 9.6 in (2.98 m)
Operational range	460 mi (740 km)
Flight altitude	350 mi (560 km)
Speed	>Mach 4
Guidance system	Radio command
Launch platform	Silo

The LIM-49A Spartan was a United States Army anti-ballistic missile, designed to intercept attacking nuclear warheads from Intercontinental ballistic missiles at long range and while still outside the atmosphere. For deployment, a defensive five-megaton atomic warhead was planned to destroy the incoming ICBM. It was part of the Safeguard Program.

Spartan was the ultimate development in a long series of missile designs from the team of Bell Laboratories and Douglas Aircraft Company that started in the 1940s with the Nike. Spartan was developed directly from the preceding LIM-49 Nike Zeus, retaining the same tri-service identifier, but growing larger and longer ranged, from the Zeus' 250 miles (400 km) to about 450 miles (720 km).

Spartan was initially developed as part of the Nike-X project, later becoming the Sentinel Program. This was eventually cancelled and replaced with the much smaller Safeguard Program. Spartans were deployed as part of the Safeguard system from October 1975 to early 1976.

History

Zeus

The US Army started their first serious efforts in the anti-ballistic missile arena when they asked the Bell Labs missile team to prepare a report on the topic in February 1955. The Nike team had already designed the Nike Ajax system that was in widespread use around the US, as well as the Nike Hercules that was in the late stages of development as the Ajax's replacement. They returned an initial study on Nike II in January 1956, concluding that the basic concept was workable using a slightly upgraded version of the Hercules missile, but requiring dramatically upgraded radars and computers to handle interceptions that took place at thousands of miles an hour.

Work began on the resulting LIM-49 Nike Zeus system in January 1957, initially at a low priority. However, several developments that year, including the development of the first Soviet ICBMs and the launch of Sputnik I, caused the schedule to be pushed up several times. In January 1958 Zeus was given "S-Priority", the highest national priority, with aims to deploy the first operational sites in 1963.

To fully test the system, the Army took control of Kwajalein Island from the US Navy, and began building an entire Zeus site on the island. By 1962 the system was ready for testing, and after some initial problems, demonstrated its ability to intercept warheads launched from California. Eventually fourteen "all up" tests were carried out over the next two years, with ten of them bringing the missile within the lethal radius of its warhead, sometimes within a few hundred meters.

Cancellation

In spite of Zeus' smooth testing program and successful interceptions, it was becoming increasingly clear that the system would not be effective in a real war scenario. This was due primarily to two problems; decoys would shield the warhead from detection until it was too late to intercept it, and the rapid increase in the number of ICBMs threatened to overwhelm the system.

The former problem was becoming increasingly obvious from about 1957. Missiles designed to carry a specific warhead found themselves with excess throw-weight as warhead physics improved and they became smaller and lighter. Even a small amount of excess capacity could be used to throw radar decoys or chaff, which are very light weight, and would provide additional radar returns that would make it difficult to pick out the warhead. As long as the decoys spread out or blocked an area larger than the lethal radius of the interceptor, several interceptors would have to be launched to guarantee the warhead would be hit. Adding more decoys was extremely inexpensive, requiring very expensive ABMs to be added in response.

At the same time, both the US and USSR were in the midst of introducing their first truly mass produced ICBMs, and their numbers were clearly going to grow dramatically during the early 1960s. Zeus, like Hercules and Ajax before it, used mechanically directed radar dishes that could track only one target and one interceptor at once. It was planned that Zeus bases would actually consist of several launcher sites connected to a central control, but even in this case the site might be able to guide perhaps four to six missiles at once. With the ICBM fleet reaching hundreds even before Zeus could become operational, it would be easy to simply overwhelm the defense by flying enough warheads over it that it couldn't guide interceptions rapidly enough.

Nike X

The solution to both of these problems is to improve speed, both of the defending missiles and the defense system as a whole.

Decoys are less dense than warheads, and not aerodynamic. Therefore they are subject to more deceleration when they begin the re-enter the upper atmosphere. The warhead, which is dense and streamlined, experiences less deceleration from air resistance, eventually flying out in front of the decoys. The rate at which this happens depends on the types of decoys used, but the warhead will have pulled past even advanced types by the time it is between 250,000–100,000 feet (76,000–30,000 m). At that point the warhead is open to attack, but leaves only 5 to 10 seconds before impact. To handle these scenarios, a very high speed missile was required. Zeus was simply not fast enough to perform such an attack, it was designed for interceptions lasting about two minutes.

Likewise, the solution to dealing with massive numbers of warheads was to use faster computers and radars, allowing many interceptors to be in flight at once. Zeus was being developed just as digital computers were starting a massive improvement in performance through parallel processing, and radar systems were likewise introducing the first phased array radar (Passive electronically scanned array) systems. Combining the two would allow hundreds of warheads and interceptors to be tracked and controlled at once. As long as the interceptor missile wasn't significantly more expensive than the ICBM, which was likely given to their relative sizes, overwhelming such a system would be a losing proposition.

Studying all of this, ARPA outlined four potential approaches to an ABM system. The first was Nike Zeus in its current form. The second was Zeus combined with a new radar system, the third included new radars and computers. Finally, the "X" plan called for all of these changes, as well as a new short-range missile. As the shorter range missile would overlap with Zeus, X also called for Zeus to be modified for even greater range as Zeus EX. After considerable debate, the decision was made to cancel the existing Zeus deployment and move ahead with the X plan.

Testing

The first test-launch of the Spartan occurred at Kwajalein Missile Range on 30 March, 1968.

Survivors

• The Air Defense Artillery museums at Fort Bliss, Texas and the ADA park at Fort Sill, Oklahoma, have both Safeguard missiles on display, the Sprint and Spartan.

Photo gallery

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See also

• Sprint (missile)
• Nike-Hercules missile
• Nike Zeus

Aircraft of comparable role, configuration and era

• PGM-17 Thor

Related lists

• List of military aircraft of the United States
• List of missiles

External links

• Directory of U.S. Military Rockets and Missiles
• a further development of the Nike Zeus B missile
• index of pictures
• Mickelsen Safeguard Complex
• W71 nuclear warhead for the Spartan