LIM-49 Nike Zeus
|Nike Zeus B|
Nike Zeus B test launch at White Sands.
|Place of origin||United States|
|Used by||US Army|
|Weight||2,259 pounds (1,025 kg) total,
1,051 pounds (477 kg) sustainer,
1,208 pounds (548 kg) booster
|Length||48 feet 3 inches (14.71 m)|
|Diameter||14.6 inches (370 mm) sustainer,
16.2 inches (410 mm) booster
|Engine||450,000 pounds-force (2,000,000 N) booster,
Thiokol TX-238 2nd,
Thiokol TX-239 3rd
|Wingspan||50 inches (1,300 mm) sustainer,
76 inches (1,900 mm) booster
|Speed||greater than Mach 4 (ca. 2,800 miles per hour (4,500 km/h) arbitrary)|
XLIM-49 Nike Zeus was an anti-ballistic missile (ABM) system developed during the late 1950s and early 1960s. It was developed by Bell's Nike team, and was initially based on the earlier Nike Hercules anti-aircraft missile. The original Zeus A was designed to intercept warheads in the upper atmosphere, and mounted a 25 kiloton W31 nuclear warhead to guarantee a "kill". During development it was greatly enlarged and extended into a totally new design, Zeus B, intended to intercept warheads at ranges of hundreds of miles using the 400 kiloton W50 warhead. In several successful tests, the B model proved itself able to intercept warheads, and even satellites.
Throughout its development critics raised serious concerns about its real-world capabilities and cost effectiveness. From the start it was noted that the price of the system would be more than the ICBMs it would attack. More worrying was the inability of the radar systems to distinguish warheads from decoys, in spite of considerable effort to develop solutions to this problem. It was also discovered during development that a nuclear explosion in space would blind radars from detecting objects at high altitudes, rendering the entire concept of exo-atmospheric interceptions questionable.
Attention turned to the Nike X concept, a layered system with more than one type of missile. The Zeus missile underwent further upgrades to the Zeus EX, and was later renamed as Spartan (keeping the same tri-service identifier). Nike X also added a shorter-range missile, the Sprint, and greatly improved radars and computer systems that provided defence over a wide area. Nike X eventually emerged as the Sentinel Program and then the Safeguard Program, which was operational only for a few months.
During World War II the US Army Air Force (USAAF) concluded that existing anti-aircraft guns, only marginally effective against existing generations of propeller-driven aircraft, would not be effective at all against the emerging jet-powered designs. Like the Germans and British before them, they decided that a successful defense system would have to use guided weapons.
As early as 1944 the US Army started exploring anti-aircraft missiles, examining a variety of concepts. They split development between the Ordnance department and the Army Air Force based on whether or not the design "depend[ed] for sustenance primarily on the lift of aerodynamic forces" or "primary on the momentum of the missile". Official requirements were published in 1945; Bell Laboratories won the Ordnance contract for a short-range line-of-sight weapon under Project Nike, while Boeing won the contract for a long-range design known as "Ground-to-Air Pilotless Aircraft", or GAPA. In 1946 the USAAF also started two early research projects into anti-missile systems in Project Thumper and Project Wizard.
In 1953, Project Nike delivered the world's first operational anti-aircraft missile system, the Nike I. Nike tracked both the target and the missile using separate radars, used a simple computer to calculate the impact point, and sent commands encoded in the tracking radar signal to commanding the missile into a collision with the target. Nike was initially deployed at military bases starting in 1953, especially Strategic Air Command bomber airfields, and general deployment then followed at US cities, important industrial sites, and then overseas bases. Similar systems quickly emerged from other nations, including the S-75 Dvina (SA-2) from the USSR, and the English Electric Thunderbird in the UK.
By the mid-1950s aircraft performance had improved so much that the Nike had limited capability to successfully attack the aircraft before they would be within weapons launching range. The interception could be made even more difficult, or impossible, through the use of stand-off weapons that allowed the aircraft to drop its bomb load while still outside the missile's ~30 miles (48 km) range. There were also concerns that the system's relatively low resolution radars would make it difficult to pick out targets flying in formation, leading to an outright miss.
An obvious solution to the accuracy problem was to use a nuclear warhead, and Bell proposed two updated versions of the missile to carry one. The "Ajax" version used the existing missile with a gun-type warhead, while the "Hercules" was enlarged to carry a more efficient but rounder implosion-type device. The Army chose the Hercules option, which was initially known as Nike B.[N 1] Soon after starting work, the decision was made to eliminate liquid fuels, and the missile underwent a major redesign into a much larger solid fuel form. The new missile used four of the Ajax's solid rocket boosters to get it into the air quickly, and flew at higher speeds to interceptions as far away as 75 miles (120 km) and altitudes over 100,000 feet (30 km). In 1956 both missiles were renamed using Bell's code names, Nike I becoming the MIM-3 Nike Ajax and Nike B the MIM-14 Nike Hercules.
Hercules was designed from the start to operate from Ajax bases. It protected a much greater area, so not as many sites were needed to provide coverage of potential targets. Early deployments starting in 1958 were on new sites, but Ajax units started converting as well. Conversions were largely complete by 1960, leaving only a few Ajax sites in use. The last active Nike Ajax batteries were relieved of their mission in December 1961, followed by the last Army National Guard unit in May 1964.
At first considered invulnerable, improvements in computer tracking systems and radars appeared to make an ICBM interception possible, albeit difficult. As early as February 1955, the Army concluded that missile systems had advanced enough to attack ICBMs, and in March they contracted Bell's Nike team to begin a detailed 18-month study of the problem under the name Nike II.
Bell returned an initial study in January 1956 that demonstrated the need to intercept the incoming warheads at 100-mile (160 km) altitude, and suggested that this was within the abilities of an upgraded version of Hercules. The 5-mile (8.0 km)-per-second approach speed of the ICBM warhead, combined the several minutes that it took for the Nike missile to climb to the warhead's altitude, required that the warhead be initially detected at about 1,000 miles (1,600 km) range in order to leave enough time to it to be intercepted. Warheads are relatively small and have limited radar cross sections, so this requirement demanded radars of extremely high power.
As the interceptor lost maneuverability as it climbed out of the atmosphere and its aerodynamic surfaces became less effective, the interceptor should be directed onto the target as rapidly as possible, leaving only minor fine tuning later in the engagement. This required that accurate tracks be developed for the both the warhead and outgoing missile very quickly, in comparison to a system like Hercules where the guidance could be updated throughout the engagement. This demanded new computers and tracking radars with much higher processing rates than the systems used on earlier Nikes. After running 50,000 simulated intercepts on analog computers, Bell returned a final report on the concept in October 1956, indicating that the system was within the state of the art.
While the Army was carrying out its ABM work with the Nike team, the Air Force and Navy were also involved in ABM research. The Navy was proposing developments of its Talos missile system and some consideration was given to a land-based Talos in this role. The Air Force had cancelled Thumper in 1949 and use those funds to further development of GAPA. When this continued to have problems, the Wizard team joined them, and the missile became the CIM-10 Bomarc. Work on the theoretical aspects of anti-missile defense continued within the Wizard project throughout.[N 2]
At this point a fight broke out between the Air Force and Army over who had precedence to develop land-based ABM systems. After the war, the Army used its large stocks of anti-aircraft artillery to set up defensive rings around US cities and other sites, and then supplanted these with Ajax missiles as they became available. The Air Force concentrated primarily on long-range fighters and missiles, including Bomarc. This separation of duties eventually became semi-formalized, with the Army given the task of defending "point" targets at short ranges while the Air Force was tasked with providing "area" defense.
When the Army introduced its Jupiter IRBM missile, which offered performance similar to the Air Force's Thor, fighting broke out between the two forces over who should have precedence for developing long-range missiles. The argument expanded to include Hercules, whose longer range threatened the still-not-deployed Bomarc. The Air Force began a policy of publicly denigrating the Hercules and agitating for the missile defense program to be handed to them, going so far as to claim the Army was "unfit to guard [the] nation" in the New York Times. With the introduction of the Zeus these arguments grew more strident, with the Air Force noting that the long range of the system meant that ABMs should be considered area weapons, and therefore part of the Air Force's mission. The Army noted that the definition of "point" specifically mentioned weapons being sited near the targets they were defending. This was the case with Zeus, whose long range was intended to improve reaction time, not defensive range. They also pointed out that the defense role had been theirs since the war.
The argument was eventually decided by the US Secretary of Defense, Charles Erwin Wilson. Wilson considered a wide range of problems between the Army and Air Force and sided with the Air Force on most of them. Among the many issues considered in his 26 November 1956 memorandum, he limited the Army to weapons with 200-mile (320 km) range, and those involved in ground-to-air defense to only 100 miles (160 km). This forced the Army to turn over its Jupiter systems to the Air Force, and to limit the range of their ABM and advanced anti-aircraft developments.
Wilson's decision was highly controversial, and led Army Colonel John Nickerson Jr., to publicly denounce Wilson in the press, while leaking details of their latest missile design, the Pershing. Pershing's 600-mile (970 km) range put it well into the area that Wilson's memo forbade. The resulting flap led to calls for Nickerson to be court-martialed and was compared to the Billy Mitchell court-martial in the 1920s.[N 3]
In 1957 the Bell team was given the go-ahead to develop Nike II, now known as Nike Zeus. Douglas Aircraft were once again selected to build the actual missiles, known to them as the DM-15. This was essentially a slightly scaled-up Hercules with an improved, more powerful single-piece booster replacing Hercules' cluster of four smaller boosters. Intercepts would take place at the limits of the Wilson requirements, at ranges and altitudes of about 100 miles (160 km). Prototype launches were planned for 1959. For more rapid service entry there had been some consideration given to an interim system based on the original Hercules missile, but these efforts were dropped. Likewise, early requirements for a secondary anti-aircraft role were also eventually dropped.
In August 1957 the Soviets successfully launched their R-7 Semyorka (SS-6) ICBM, and followed this up with the successful launch of Sputnik 1 in October. Wilson's concerns about inter-service rivalry were swept aside, and a fresh look at the Army and Air Force projects followed. By this point the Army was already planning Zeus tests and deployment, while the Air Force had failed to deliver the Bomarc even in the anti-aircraft role. In January 1958, Secretary of Defense Neil McElroy re-directed the AF's Wizard solely to radar research, overturned the Wilson Memo, and gave the Army free hand to develop the Zeus system as they saw fit. The National Security Council gave Zeus "S-Priority", the highest national priority. Additional funds were requested to the Zeus program to ensure an initial service date in the fourth quarter of 1962, but these were denied, delaying service entry until some time in 1963.
Freed of constraints, the Army re-designed the system to be the system they wanted instead of the one they were limited to. A new missile design emerged with a much enlarged upper fuselage and three stages, more than doubling the launch weight. This version greatly extended the range of the system, with interceptions taking place at over 200 miles (320 km) range and over 100 miles (160 km) in altitude. An even larger booster took the missile to hypersonic speeds while still in the lower atmosphere, so the missile fuselage was covered over completely with a phenolic ablative heat shield to protect the airframe from melting.[N 4] The new DM-15S Nike Zeus B (the earlier model retroactively becoming the A) received a go-ahead for development on 16 January 1958. The entire system, including the new 120 foot wide radar systems, required 200 acres to deploy.
Test firings of the original A models of the missile began in 1959, mostly at White Sands Missile Range. The first attempt on 26 August 1959 was of a live booster stage and dummy sustainer, and broke up shortly before booster/sustainer separation. A similar test on 14 October was a success, followed by the first two-stage attempt on 16 December. The first complete test of both stages with active guidance and thrust vectoring was successfully carried out on 3 February 1960. Data collected from these tests led to changes to the design to improve speed during the ascent. The first test of the Zeus B took place in May 1961, and on 14 December a Zeus passed within 100 feet (30 m) of a Nike Hercules being used as a test target.
Many test firings followed over the next three years, but White Sands was too close to its own launch sites to truly test an ICBM flight profile. Consideration was given to using Point Mugu in California, which would launch against missiles flying from Cape Canaveral, but range safety requirements placed limits on the potential tests. The Atlantic Test Range, to the north-east of Canaveral, had a high population density and little land available for accurate downrange tracking stations. Eventually Kwajalein Island was selected, as it was 4,800 miles from California, perfect for ICBMs, and already had a US Navy base with considerable housing and an airstrip.
The Zeus site, known as the Kwajalein Test Site, was officially established on 1 October 1960. As it grew in size, it eventually led to the entire island complex being handed over to the Army from the Navy on 1 July 1964. The site took up a considerable amount of the empty land to the north side of the airfield. On 26 June 1962 the system attempted to intercept the warhead from an SM-65 Atlas missile fired from Vandenberg AFB, but the radar system malfunctioned and the test failed. A second test on 19 July was a success, with the Zeus passing within 2 kilometres (1.2 mi) of the target, close enough that its 400 kilotons of TNT (1,700 TJ) warhead would have destroyed it. Another test on 12 December 1962[N 5] was a complete success, with the Zeus passing only 200 metres (660 ft) from its target. Of the fourteen tests carried out over the two-year test cycle, ten of them were successful in bringing the Zeus within its lethal range.
In spite of tremendous capabilities, and successful tests, Nike Zeus was becoming outdated even faster than it could be developed. By the early 1960s the ICBM stockpiles of both the US and USSR were growing at a rapid rate, and attacks would now consist of hundreds of warheads. The Zeus system could only attack one target at a time,[N 6] so unless hundreds of bases were set up, some warheads would "leak through" the system while it was busy with other targets.
Another serious issue was system cost, a problem that was shared by any ground-based interceptor. While an ICBM could target any location in the US, the limited radar sight range of the ABMs meant they could only defend a small area, limited by the local radar horizon. That meant that each ABM site would, theoretically, have to have enough interceptors to shoot down every Soviet ICBM, so any widespread system would cost much more than the ICBM force. Deploying an even marginally effective system initially called for about 60 Zeus bases with 50 missiles each, at a price of $10 billion (78 billion today). This would protect only major Strategic Air Command and military communication sites to ensure the US ability to counterattack. A system of 120 sites would be required to extend some protection to cities and industry as well. At $1 million per missile, Zeus was more expensive than the ICBMs it faced.
Through the late 1950s a number of new effects related to high altitude nuclear explosions also demonstrated serious concerns with the system. Nuclear fireballs are opaque to radar, and ones at very high altitudes could expand anywhere from 100 to 1,000 kilometres (62 to 621 mi) across, the exact size being an area of considerable uncertainty. Given the 2 mile lethal range of the Zeus warhead, this meant that a single fireball from any warhead, even the Zeus' own, would render the system unable to attack other warheads anywhere in the area, at least until the fireball cooled after some time. Even after the fireball became transparent again, the huge volume of heated and shocked air filled with charged particles acted as radio frequency lenses, which refracted the radar signals too much to be useful for aiming. Other effects included electromagnetic pulse (EMP) which might disturb communications and radio, and the Christofilos Effect, which appeared to allow large swaths of the sky to be blanketed with a semi-opaque layer that might persist for long periods. It was known that higher frequencies mitigated some of these effects to a degree, but the uncertainties surrounding them were enormous, and radars of the era were already stretching the state of the art at the S-band.
These effects presented an almost trivial way to attack the Zeus bases, using two ICBM warheads following the same rough trajectory but a few moments apart in time. Given the 5 mile-per-second speeds of the and the approximate 2 mile lethal radius of the Zeus warhead, the attacking warheads could be positioned as little as one second apart. The first warhead would either allow itself to be attacked by Zeus, or deliberately explode just outside the Zeus' maximum range. This would produce a large area where the radars could not see the second warhead as it approached. When it finally cleared the fireball only a few moments later, it would be so close to the base that it would be impossible for the Zeus to reach it while it was still in the upper atmosphere. This timing effect can be magnified using a "lofted" trajectory which allows the warheads to descend almost vertically onto the bases, further limiting reaction time, or by using a low-altitude "fractional orbital" trajectory that makes the warhead appear on radar only a few hundred kilometres from the base.
The issue of decoys and other radar countermeasures became a serious issue during development. This problem was first alluded to in 1958 in public talks that mentioned Zeus' inability to discriminate targets. Decoys are very light, so they can be launched in large numbers along with a warhead. Once deployed in space, these present credible radar returns that look, to some degree or another, like the return of the warhead. For a system like Zeus, as long as the decoys spread out over several miles during their flight, several missiles will be required to attack them and guarantee that the warhead hiding among the decoys will be destroyed. This leads to the possibility of an all-decoy attack which uses up the stock of interceptor missiles for little cost to the attacker. Several test programs, notably DAMP and PRESS, were expected to demonstrate how to tell warheads from decoys at long ranges. While most of the results of these experiments remain classified, some level of the difficulties encountered have been discussed and generally suggest that early-stage discrimination is not easily accomplished.[N 7]
The only reliable way to "declutter" the decoys is to wait until they hit the upper atmosphere and begin to slow down due to drag. The warhead is fairly small and dense, so it suffers relatively low drag until it hits the lower atmosphere. The decoys, much lighter and less dense, begin to rapidly slow while still in the upper atmosphere. As the package begins re-entry, these changes in relative velocity cause the warhead to overtake the decoys and eventually emerge in front of them. Due to the nature of the Zeus' interception profile, the package would have been travelling through the upper atmosphere for some time before the Zeus reached them. To speed the decluttering process, a special radar that looked for differences in velocity was used, so that by the time the package came into attack range, the faster moving warhead was picked out. However, the attacker could compress this time window by using a lofted trajectory; this meant the targets spent much less time in the atmosphere, to the point where decluttering was too late for the Zeus to respond.
One could also make heavier decoys that do not slow as much, but only at the cost of being able to carry fewer of them for any given ICBMs throw-weight. But a particularly worrying type of "decoy" could be created by attaching a small explosive device to the missile's upper stage, causing it to fragment after reaching space. These fragments had a higher density than something like a metalized balloon or chaff, and would not declutter until well within the atmosphere. Commenters felt that a much shorter-range and faster reacting system would be needed to effectively deal with warheads hidden among decoys of this type, an interceptor that operated within the lower atmosphere where the decluttering would be complete no matter what type of decoy was used.
Throughout development, Zeus was the focus of "fierce controversy" in both the press and military circles. Even as the testing was being carried out, it was unclear if development would continue. President Eisenhower's defense secretaries, Neil H. McElroy (1957–59) and Thomas S. Gates, Jr. (1959–61), were unconvinced that the system was worth the cost. Eisenhower remained skeptical throughout, questioning whether an effective ABM system could even be developed in the 1960s. Another harsh critic on cost grounds was Edward Teller. He pointed out that while a system may be technically feasible, the increased cost to an enemy of penetrating an ABM screen would be less than the cost of strengthening the screen to prevent penetration.
In 1961, the incoming administration of President Kennedy and Secretary of Defense Robert McNamara agreed to continue development funding through FY62, but declined to provide funds for production. McNamara summed up both the positives and the concerns this way:
Successful development [of Zeus] may force an aggressor to expend additional resources to increase his ICBM force. It would also make accurate estimates of our defensive capabilities more difficult for a potential enemy and complicate the achievement of a successful attack. Furthermore, the protection that it would provide, even if for only a portion of our population, would be better than none at all ...
There is still considerable uncertainty as to its technical feasibility and, even if successfully developed, there are many serious operating problems yet to be solved. The system, itself, is vulnerable to ballistic missile attack, and its effectiveness could be degraded by the use of more sophisticated ICBMs screened by multiple decoys. Saturation of the target is another possibility as ICBMs become easier and cheaper to produce in coming years. Finally, it is a very expensive system in relation to the degree of protection that it can furnish.
These earlier concerns about cost and effectiveness, as well as new difficulties in terms of attack size and decoy problems, led McNamara to eventually cancel the Zeus project in January 1963. In its place they decided to continue work on a greatly improved system, Nike-X.
While reporting to the Senate Armed Services Committee in February, McNamara noted that they expected the Soviets to have an initial ABM system deployed in 1966, and then later stated that the Nike-X would not be ready for use until 1970. Noting a "defensive gap", Strom Thurmond began an effort to deploy the existing Zeus as an interim system. On 11 April 1963, Thurmond led the Congress in an effort to fund deployment of Zeus. In the first closed session of the Senate in twenty years, Zeus was debated and the decision was made to continue with the planned development of Nike-X with no Zeus deployment. The Army continued the testing program until December 1964 at White Sands Missile Range, and May 1966 at Kwajalein Missile Range.
Nike-X, Sentinel, Safeguard
Through the late 1950s, the newly formed ARPA had been working on a major study of ABM systems under "Project Defender". As part of these studies they examined Zeus in depth. They concluded their studies in 1961, outlining four development paths for the Zeus system. The most basic was to continue deployment of the existing Zeus. Two plans outlined modifications featuring newer radars, or newer radars and computers. The final plan, NX, called for an updated Zeus, new radars and computers, and a new high-velocity missile for lower-altitude interception. The Department of Defense chose the NX plan, and started work on what they called Nike-X.
Nike-X featured a new enormously powerful phased array radar able to locate targets simultaneously throughout a large volume of space, working at higher frequencies that would help see though the blanking caused by high-altitude explosions. New computers with hundreds of times the performance of the Zeus models would interpret this data and develop tracking information for hundreds of targets, which included incoming warheads, decoys and outgoing interceptors. Each site would now be able to attack several targets at once. To address the problem of decoys that could not be discriminated at high altitude, and the potential blinding of long-range radar even at higher frequencies, the new Sprint missile was used for in-atmosphere interceptions, accelerating at up to 90 gee. To increase range, Zeus B was further upgraded to the much larger Zeus EX, and later renamed Spartan.
Under Nike-X, Zeus' role was greatly diminished. Assuming most attacks would include decoys, Zeus (and Spartan) was seen as a secondary system for attacking satellites, missiles approaching from the south, submarine-launches while still offshore, and providing defense over a larger area of lower population density. It was also thought that salvos of Zeus' might be used against highly cluttered targets to help declutter them prior to attack by Sprint. Zeus would have little role in an attack by the USSR with sophisticated decoys, and the defense was almost entirely up to a number of Sprint sites distributed around the cities. Small radars at each site would allow the central computer to build a composite picture to "see around" the fireballs and attack warheads approaching behind them.
In the end, even these developments proved to be too little for the task. The introduction of MIRV technology in the late 1960s meant that the USSR could overwhelm even the Nike-X system by placing more warheads on existing missiles. Warheads were far less expensive than the missiles needed to shoot them down, so the simplest solution to the presence of ABM systems was to greatly increase the number of warheads in everyone's inventory. Doing so would have numerous spin-off effects in terms of security concerns. This worrying development led to the ABM Treaty of the early 1970s.
After the project's cancellation some work with the Zeus continued as an experimental anti-satellite system. There were concerns that the Soviets might develop satellites that were armed with nuclear weapons, which it could drop without the tell-tale signs of a rocket launch. McNamara formed Project Mudflap in April 1962 to address this, using the Zeus missile as an interceptor. The first test firing of the Mudflap concept was carried out at White Sands in December 1962, with the Zeus reaching an altitude of over 150 km.Testing was then moved to Kwajalein, and on 24 May 1963 the system was successful against an instrumented Agena D target. The Kwajalein site was officially active between 1964 and 1967, where it was known as Program 505. In 1967 it was replaced by a Thor-based system, Program 437.
Nike Zeus was originally intended to be a straightforward development of the earlier Hercules system giving it the ability to hit ICBM warheads at about the same range and altitude as the maximum performance of the Hercules. In theory, hitting a warhead is no more difficult than an aircraft; the interceptor does not have to travel any further or faster, the computers that guide it simply have to select an intercept point farther in front of the target. In practice, the difficulty is detecting the target early enough that the intercept point is still within range of the missile. This demands much larger and more powerful radar systems, and faster computers.
The key development for the new system was the Zeus Acquisition Radar, or ZAR, which provided wide-area early warning and initial tracking information. This enormously powerful radar was driven by multiple 1.8 MW klystrons and broadcast through three 80-foot (24 m) wide antennas arranged as the outside edges of a rotating equilateral triangle. The signal was so powerful that it was considered dangerous to people within 330 feet (100 m), so the entire system was surrounded by a 65-foot (20 m) high fence located 350 feet (110 m) away from the antenna. The signal was received on separate set of three antennas, situated at the centre of an 80 foot diameter Luneburg lens, which rotated synchronously with the broadcaster under a 120-foot (37 m) diameter dome. Around the receiver dome was a large field of wire mesh, forming a reflector.
Targets picked out by the ZAR were then illuminated by the Zeus Discrimination Radar (ZDR). The name describes the purpose of this radar, to discriminate the warhead from nearby decoys. The ZDR watched for differences in velocity as the warheads and decoys decelerated in the upper atmosphere, which is a function of the decoy weight, which implies that you would face larger numbers of lighter decoys or a small number of heavier ones. ZDR was designed to discriminate lightweight decoys, 2% of warhead weight, at altitudes up to 200,000 feet (61,000 m). Once the warhead had been picked out, information was passed to the Target Tracking Radar (TTR), the missile launched and tracked by the Missile Tracking Radar (MTR). The computers examined the trajectories of the warhead and the Zeus, and guided Zeus to an interception using radio commands modulated in the MTR signal. Running all of this was the Target Intercept Computer (TIC), which used twistor memory for ROM and core memory for RAM.
A single Zeus installation would normally consist of six launcher sites, each with sixteen missiles, two TTRs and one MTR. All of these would be fed initial information from a single ZAR and ZDR shared across the entire installation. This would allow an installation to attack six targets at a time, and two missiles would normally be fired at each target. It was expected that the ZAR would take 20 seconds to develop a track and hand off a target to one of the TTRs, and 25 seconds for the missile to reach the target. With these sorts of salvo rates, a Zeus installation was expected to be able to successfully attack 14 "bare" warheads per minute. Its salvo rate against warheads with decoys is not recorded, but would depend on the ZDR's processing rate more than any physical limit.
The original D-15 Zeus A was similar to the original Hercules, but featured a revised control layout and gas "puffers" for maneuvering at high altitudes where the atmosphere was too thin for the aerodynamic surfaces to be effective. The Zeus B interceptor was longer at 14.7 metres (48 ft), 2.44 metres (8 ft 0 in) wide, and 0.91 metres (3 ft 0 in) in diameter. This was so much larger than the earlier Hercules that no attempt was made to have them fit into the existing Hercules/Ajax launchers. Instead, the B models were launched from silos, thus the change of numbering from MIM (mobile surface launched) to LIM (silo launched). Since the missile was designed to intercept its targets in space, it did not need large maneuvering fins of the A model. Rather, it featured a third rocket stage with small control jets to maneuver in space. Zeus B had a maximum range of 250 miles (400 km) and altitude of 200 miles (320 km).
Zeus A was designed to attack warheads through shock effects, like the Hercules, and was to be armed with a relatively small nuclear warhead. As the range and altitude requirements grew, along with better understanding of weapons effects at high altitude, the Zeus B intended to attack its targets through the action of neutron heating. This relied on the interceptor's warhead releasing a huge number of high-energy neutrons (similar to the neutron bomb), some of which would hit the enemy warhead. These would cause fission to occur in some of the warhead's own nuclear fuel, rapidly heating the "primary", hopefully enough to cause it to melt. For this to work, the Zeus mounted the W50, a 400 kt enhanced radiation warhead, and had to maneuver within 2 km of the target warhead.
When Zeus B was upgraded into the Zeus EX that worked at even higher altitudes and longer ranges, a new type of attack became possible. In the vacuum of space, where the EX operated, x-rays travel long distances and can be used for an attack over a wide area, larger than a practical neutron weapon. To fill this need a much larger gold-tampered warhead was developed, the 5 Mt W71. For the short-range Sprint that operated closer to the ground, the much smaller W66 was created, operating much the same way as the Zeus' W50 but with a much lower (still classified but ~1 kt) yield. The W66 is widely reported as the first neutron bomb, although any differences compared to the W50, other than yield, are unclear.
- Different sources appear to confuse measures between the Zeus A, B and Spartan. These are taken from US Strategic and Defensive Missile Systems 1950–2004 unless otherwise noted:
|Missile||Nike Zeus A||Nike Zeus B||Spartan (LIM-49A)|
|Length||44 ft 3 in (13.5 m)||48 ft 3 in (14.7 m)||55 ft 1 in (16.8 m)|
|Diameter||3 ft 0 in (0.91 m)||3 ft 0 in (0.91 m)||3 ft 7 in (1.09 m)|
|Fin span||9 ft 9 in (2.98 m)||8 ft 0 in (2.44 m)||9 ft 9 in (2.98 m)|
|Mass||10,980 lb (4,980 kg)||22,700 lb (10,300 kg)||28,900 lb (13,100 kg)|
|Maximum speed||Mach 4 > (ca. 2800+ mph; 4,900 km/h arbitrary)|
|Range||200 mi (320 km)||250 mi (400 km)||460 mi (740 km)|
|Ceiling||?||170 mi (280 km)||350 mi (560 km)|
|First stage||Thiokol TX-135
400,000 lbf (1,800 kN)
450,000 lbf (2,000 kN)
500,000 lbf (2,200 kN)
|Second stage||?||Thiokol TX-238||Thiokol TX-454|
|Third stage||None||Thiokol TX-239||Thiokol TX-239|
|Warhead||W31||W50 (400 kt)||W71 (5 Mt)|
- The naming of the improved design is confusing, especially in light of the Nike II being a different design. It may be that the "improved Nike" that became Hercules was originally known as the Nike IB (as opposed to Nike B). This naming appears in some of the sources below, but not others.
- Both Talos and Bomarc used ramjet air-breathing engines in their upper stages, giving a maximum altitude around 80,000 feet. This would be useful only against short-range missiles of the V2 type, not against ICBM warheads flying at much higher altitudes.
- One of the more roundabout effects of the Wilson memo was to greatly aid the Apollo Moon landings. Limited to short-range weapons, the Army's rocket development team in Huntsville began considering non-weapon concepts. To fill a perceived need for a heavy satellite launcher, they designed a series of much larger rockets based on various combinations of existing designs. One of these, combining Jupiter and Redstone parts, became the Saturn I. See the article on the Saturn (rocket family) for complete details.
- The outer layer of the missile can be seen turning black in the Bell Labs film.
- Some sources say 22 December.
- One target at a time per launcher, with the normal launch site having six launchers. This implies that an attack of, say, 10 warheads spaced within the 20 second response time will result in several "leakers".
- Available references for the PRESS system in particular give strong credence to the failure to distinguish warheads from decoys above the atmosphere. In Historical Review this appears in two places. In the first, it notes ARPA's interest in interceptions at very low altitudes in order to declutter, including the HIBEX experiment that was intended to attack at altitudes as low as 20,000 feet. In the section on the Arecibo telescope, they note that the tests resulted in their interest in the telescope changing from characterization of the F-layer of the ionosphere to studies of effects below it. These, and other references, all suggest that the idea of high-altitude decluttering failed.
- Zeus 1962, p. 165.
- Walker, Bernstein & Lang 2003, p. 39.
- Walker, Bernstein & Lang 2003, p. 20.
- Leonard 2011, pp. 3–4, 18.
- "Thunderbird". Flight International: 295–299, 302–303. 25 September 1959. ISSN 0015-3710. Retrieved 18 May 2013.
- Zeus 1962, p. 166.
- "Nike Hercules (SAM-N-25) (MIM-14/14A/14B)". Federation of American Scientists. Retrieved 18 May 2013.
- Leonard 2011, pp. 315–317.
- Leonard 2011, p. 180.
- Kaplan 2006, p. 4.
- "Air Force Calls Army Unfit to Guard Nation". New York Times. 21 May 1956. p. 1.
- Larsen, Douglas (1 August 1957). "New Battle Looms Over Army's Newest Missile". Sarasota Journal. p. 35. Retrieved 18 May 2013.
- Walker, Bernstein & Lang 2003, pp. 27–30, 37.
- "Nickerson Accuses Wilson Of 'Grave Errors' On Missiles". The News and Courier. 28 June 1957. p. B-14. Retrieved 18 May 2013.
- "Army Weights Court-Martial Over Missiles". St. Petersburg Times. 25 February 1957. p. 1. Retrieved 18 May 2013.
- Kaplan 2006, p. 5.
- Leonard 2011, p. 183.
- Kaplan 2006, p. 7.
- Leonard 2011, p. 182.
- Zeus 1962, p. 170.
- Berhow & Taylor 2005, p. 31.
- Gibson 1996, p. 205.
- Walker, Bernstein & Lang 2003, p. 42.
- Walker, Bernstein & Lang 2003, p. 44.
- Walker, Bernstein & Lang 2003, p. 41.
- Stephen Moeller, "Vigilant and Invincible", ADA Magazine, US Army Missile Command, May–June 1995, p. 7.
- Baucom 1992, p. 21.
- Baucom 1992, p. 19.
- Consumer Price Index (estimate) 1800–2014. Federal Reserve Bank of Minneapolis. Retrieved February 27, 2014.
- Richard Garvin and Hans Bethe, "Anti-Ballistic-Missile Systems", Scientific American, March 1968, pp. 29–30.
- Bethe 1969, p. 277.
- Leonard 2011, pp. 186–187.
- Zeus 1962, p. 167.
- "Defender Anti-Ballistic Missile", DARPA Technical Accomplishments Volume II: A Historical Review Of Selected DARPA Projects, April 1991, Section I: PRESS.
- Kaplan 2006, p. 6-8.
- Daniel Papp, "From Project Thumper to SDI", Airpower Journal, Winter 1987–88
- "Ballistic Missile Defence and post-Cold War American Foreign Policy: Origins, Influences and Motives". All Academic. Retrieved 8 May 2013.
- Kaplan 2006, p. 13.
- Kaplan 2006, p. 14.
- Baucom 1992, p. 92.
- Kaplan 2006, pp. 12–13.
- "Spartan". Nuclearabms.info. Retrieved 18 May 2013.
- "Nike-X System"", Chapter 2 of ABM Research and Development at Bell Laboratories, Bell Labs, October 1975
- Baucom 1992, pp. 30–39.
- Leonard 2011, pp. 221–223.
- Hubbs, Mark (February 2007). "Where We Began – the Nike Zeus Program". The Eagle. p. 14.
- "Program 505". Encyclopedia Astronautica. Retrieved 18 May 2013.
- "Program For Deployment Of Nike Zeus", 30 September 1961
- Zeus 1962, pp. 167,170.
- "Nike Zeus". Encyclopedia Astronautica. Retrieved 18 May 2013.
- Kaplan 2006, p. 12.
- Wm. Robert Johnston, "Multimegaton Weapons", 6 April 2009.
- Mark Berhow, "US Strategic and Defensive Missile Systems 1950–2004", Osprey Publishing, 2012, p. 32.
- Bethe, Hans (1969). ABM; an evaluation of the decision to deploy an antiballistic missile system. Harper & Row.
- Berhow, Chris; Taylor (2005). US Strategic and Defensive Missile Systems 1950–2004. Oxford: Osprey. ISBN 978-1-84176-838-0. OCLC 62889392.
- Baucom, Donald (1992). The Origins of SDI, 1944–1983. Lawrence, Kansas: University Press of Kansas. ISBN 978-0-7006-0531-6. OCLC 25317621.
- Gibson, James (1996). Nuclear Weapons of the United States: An Illustrated History. Atglen, Pennsylvania: Schiffer Publishing. ISBN 978-0-7643-0063-9. OCLC 35660733.
- Kaplan, Lawrence (2006). Nike Zeus: The U.S. Army's First ABM. Falls Church, Virginia: Missile Defense Agency. OCLC 232605150. Retrieved 13 May 2013.
- Leonard, Barry (2011). History of Strategic and Ballistic Missile Defense: Volume II: 1956–1972. DIANE Publishing. Retrieved 13 May 2013.
- Walker, James; Bernstein, Lewis; Lang, Sharon (2003). Seize the High Ground: The U. S. Army in Space and Missile Defense. Washington, D.C.: Center of Military History. ISBN 978-0-16-072308-7. OCLC 57711369. Retrieved 13 May 2013.
- Technical Editor (2 August 1962). "Nike Zeus". Flight International: pp. 165–170. ISSN 0015-3710. Retrieved 13 May 2013.
- "Nike Zeus". Nuclearabms.info. Retrieved 18 May 2013.
- Bell Labs movie on the Zeus system
- The Range Goes Green, movie of a Zeus test launch at White Sands