Nike-X
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.
The key concept that led to Nike-X was that the rapidly thickening atmosphere below altitude disrupted the reflectors and explosions. Nike-X intended to wait until the enemy warheads descended below this altitude and then attack them using a very fast missile known as Sprint. The entire engagement would last only a few seconds and could take place as low as. To provide the needed speed and accuracy, as well as deal with multi-warhead attacks, Nike-X used a new radar system and building-filling computers that could track hundreds of objects at once and control salvos of many Sprints. Many dozens of warheads would need to arrive at the same time to overwhelm the system.
Building a complete deployment would have been extremely expensive, on the order of half the total yearly budget of the Department of Defense. Robert McNamara, the Secretary of Defense, believed that the cost could not be justified and worried it would lead to a further nuclear arms race. He directed the teams to consider deployments where a limited number of interceptors might still be militarily useful. Among these, the I-67 concept suggested building a lightweight defense against very limited attacks. When the People's Republic of China exploded their first H-bomb in June 1967, I-67 was promoted as a defense against a Chinese attack, and this system became Sentinel in October. Nike-X development, in its original form, ended.
Although ultimately cancelled, testing performed during Nike-X and earlier Nike Zeus programs would prove vital for later ballistic missile protection programs such as Safeguard, the Ballistic Missile Defense Organization, the Strategic Defense Initiative, and the current Missile Defense Agency.
History
Nike Zeus
In 1955 the US Army began considering the possibility of further upgrading their Nike B surface-to-air missile as an anti-ballistic missile to intercept ICBMs. Bell Labs, the primary contractor for Nike, was asked to study the issue. Bell returned a report stating that the missile could be upgraded to the required performance relatively easily, but the system would need extremely powerful radar systems to detect the warhead while it was still far enough away to give the missile time to launch. All of this appeared to be within the state of the art, and in early 1957 Bell was given the go-ahead to develop what was then known as Nike II. Considerable interservice rivalry between the Army and Air Force led to the Nike II being redefined and delayed several times. These barriers were swept aside in late 1957 after the launch of the R-7 Semyorka, the first Soviet ICBM. The design was further upgraded, given the name Zeus, and assigned the highest development priority.Zeus was similar to the two Nike SAM designs that preceded it. It used a long-range search radar to pick up targets, separate radars to track the target and interceptor missiles in flight, and a computer to calculate intercept points. The missile itself was much larger than earlier designs, with a range of up to, compared to Hercules'. To ensure a kill at altitude, where there was little atmosphere to carry a shock wave, it mounted a 400 kiloton warhead. The search radar was a rotating triangle wide, able to pick out warheads while still over away, an especially difficult problem given the small size of a typical warhead. A new transistorized digital computer offered the performance needed to calculate trajectories for intercepts against warheads traveling over.
The Zeus missile began testing in 1959 at White Sands Missile Range and early launches were generally successful. Longer range testing took place at Naval Air Station Point Mugu, firing out over the Pacific Ocean. For full-scale tests, the Army built an entire Zeus base on Kwajalein Island in the Pacific, where it could be tested against ICBMs launched from Vandenberg Air Force Base in California. Test firings at Kwajalein began in June 1962; these were very successful, passing within hundreds of yards of the target warheads, and in some tests, low-flying satellites.
Zeus problems
Zeus had initially been proposed in an era when ICBMs were extremely expensive and the US believed that the Soviet fleet contained a few dozen missiles. At a time when the US deterrent fleet was based entirely on manned bombers, even a small number of missiles aimed at Strategic Air Command's bases presented a serious threat. Two Zeus deployment plans were outlined. One was a heavy defensive system that would provide protection over the entire continental United States, but require as many as 7000 Zeus missiles. McNamara supported a much lighter system that would use only 1200 missiles.Technological improvements in warheads and missiles in the late 1950s greatly reduced the cost of ICBMs. After the launch of Sputnik, Pravda quoted Nikita Khrushchev claiming they were building them "like sausages". This led to a series of intelligence estimates that predicted the Soviets would have hundreds of missiles by the early 1960s, creating the so-called "missile gap". It was later shown that the number of Soviet missiles did not reach the hundreds until the late 1960s, and at the time they had only four.
Zeus used mechanically steered radars, like the Nike SAMs before it, limiting the number of targets it could attack at once. A study by the Weapons Systems Evaluation Group calculated that the Soviets had a 90 percent chance of successfully hitting a Zeus base by firing only four warheads at it. These did not even have to land close in order to destroy the base; an explosion within several miles would destroy its radars, which were very difficult to harden. If the Soviets did have hundreds of missiles, they could easily afford to use some to attack the Zeus sites.
Additionally, technical problems arose that appeared to make the Zeus almost trivially easy to defeat. One problem, discovered in tests during 1958, was that nuclear fireballs expanded to very large sizes at high altitudes, rendering everything behind them invisible to radar. This was known as nuclear blackout. By the time an enemy warhead passed through the fireball, about above the base, it would only be about eight seconds from impact. That was not enough time for the radar to lock on and fire a Zeus before the warhead hit its target.
It was also possible to deploy radar decoys to confuse the defense. Decoys are made of lightweight materials, often strips of aluminum or mylar balloons, which can be packed in with the reentry vehicle, adding little weight. In space, these are ejected to create a threat tube a few kilometers across and tens of kilometers long. Zeus had to get within about to kill a warhead, which could be anywhere in the tube. The WSEG suggested that a single ICBM with decoys would almost certainly defeat Zeus. A mid-1961 staff report by ARPA suggested that a single large missile with multiple warheads would require four entire Zeus batteries, of 100 missiles each, to defeat it.
Nike-X
The Advanced Research Projects Agency was formed in 1958 by President Dwight Eisenhower's Secretary of Defense, Neil McElroy, in reaction to Soviet rocketry advances. US efforts had suffered from massive duplication of effort between the Army, Air Force, and Navy, and seemed to be accomplishing little in comparison to the Soviets. ARPA was initially handed the mission of overseeing all of these efforts. As the problems with Zeus became clear, McElroy also asked ARPA to consider the antimissile problem and come up with other solutions. The resulting Project Defender was extremely broad in scope, considering everything from minor Zeus system upgrades to far-out concepts like antigravity and the recently invented laser.Meanwhile, one improvement to Zeus was already being studied: a new phased-array radar replacing Zeus' mechanical ones would greatly increase the number of targets and interceptors that a single site could handle. Much more powerful computers were needed to match this performance. Additionally, the antennas were mounted directly in concrete and would have increased blast resistance. Initial studies at Bell Labs started in 1960 on what was then known as the Zeus Multi-function Array Radar, or ZMAR. In June 1961, Western Electric and Sylvania were selected to build a prototype, with Sperry Rand Univac providing the control computer.
By late 1962 a decision on whether or not to deploy Zeus was looming. Bell began considering a replacement for the Zeus missile that would operate at much shorter ranges, and in October sent out study contracts to three contractors to be returned in February. Even before these were returned, in January 1963 McNamara announced that the construction funds allocated for Zeus would not be released, and the funding would instead be used for development of a new system using the latest technologies. The name Nike-X was apparently an ad hoc suggestion by Jack Ruina, the director of ARPA, who was tasked with presenting the options to the President's Science Advisory Committee. With the ending of Zeus, the ZMAR radar effort was renamed MAR, and plans for an even more powerful version, MAR-II, became the central part of the Nike-X concept.