The term “boost-phase intercept” (BPI) refers to programs, strategies, and systems designed to intercept ballistic missiles during the course of their initial phase of flight, beginning with ignition and lasting through that period of time during which the missile’s stages are firing and providing thrust. The boost phase can last anywhere from 20 to 240 seconds, depending on the type and range of the missile. From the point of view of developing an effective missile defense system, there are distinct advantages to attempting to intercept a missile during this phase, but there also are daunting technical challenges involved. The advantages include the fact that a ballistic missile is traveling at its slowest speed while accelerating, the missile’s exhaust plume is bright and hot against the atmosphere and the surface of the Earth and thus more easily detected and tracked, and any countermeasures the missile might be carrying will not yet have been deployed. In many respects, a ballistic missile is at its most vulnerable during its boost phase. Having the capability to intercept missiles during this phase can contribute to a layered defense; if a missile fails to be intercepted during this phase, there remain the midcourse and terminal phases during which additional attempts can be made to intercept it.

Achieving an intercept during the boost phase is technologically very challenging. Since this phase of the missile’s flight is so short, there is very little time available for the process, which includes detecting its launch, tracking its flight, determining whether it is hostile, deciding whether to launch an interceptor missile or initiate some other interception method (such as using an airborne laser), and actually reaching the ascending and accelerating missile with another missile or kill mechanism. This approach thus places maximum stress on command and control systems and on the acceleration capacities of interceptor missiles, since their acceleration often must be many times that of the missiles they are intended to intercept. To be effective, a BPI system probably needs to be located very close to the bases from which the targeted missiles are launched.

Sea-based BPI systems have the advantage of mobility; they can be deployed off the shores of a hostile nation and relocated as circumstances require. They can also be deployed closer to the launch point, making early interception during the boost phase more likely. The United States is currently developing a very fast acceleration missile for deployment on navy ships intended as a boostphase interceptor. Sea-based systems, however, would be ineffective against missiles launched from deep within a hostile nation’s territory.

Space-based BPI systems, if developed, could orbit over any part of the Earth’s surface, providing global reach. The United States is pursuing long-range research and development into both a kinetic kill space-based intercept capability (designed to physically ram hostile missiles) and a directed energy space-based system (which would employ laser beams or focused X-rays to destroy a missile). But the first tests of prototypes for such systems are ten to twelve years off, and their effectiveness has yet to be validated.

References

Garwin, Richard L., “Boost-Phase Intercept: A Better Alternative,” Arms Control Today, September 2000, available at http://www.armscontrol.org/act/ 2000_09/bpisept00.asp.

Lamb, Frederick K., and Daniel Kleppner et al., “Boost- Phase Intercept Systems for National Missile Defense,”American Physical Society Report, July 2003, available at http://www.aps.org/public_affairs/ popa/reports/nmdexec.pdf.

“Missile Defense Systems and Boost-Phase Intercept,” Raytheon Corporation, available at http://raytheonmissiledefense.com/boost/.

An F-15 Eagle launches the ASM-135 during the final test, which destroyed the Solwind P78-1 satellite.

Anti-satellite (ASAT) weapons are designed to attack satellites in orbit. Potential destruction and disruption mechanisms for ASAT weapons include nuclear warheads, high explosives, directed energy, kinetic energy, and electronic warfare.

The United States became concerned about countering the potential for nuclear weapons delivery systems in orbit soon after the beginning of the space age. It first tested an air-launched ASAT weapon from a B-47 bomber under the U.S. Air Force’s Bold Orion program in 1959, and in the early 1960s the U.S. Navy tested systems launched by F-4 fighters. All of these earliest ASAT systems would have used nuclear warheads as the kill mechanism, but none of them became operational. In the early 1960s, Secretary of Defense Robert S. McNamara authorized development and deployment of limited numbers of two ground-based, nuclear tipped ASAT systems. The army’s Program 505 system used a Nike-Zeus launcher to conduct seven tests from Kwajalein Island in the Pacific between 1964 and 1966. Program 437, the U.S. Air Force system, used a Thor booster from Johnson Island and was tested sixteen times from 1964 to 1970. The indiscriminate nuclear kill mechanism on these systems could have destroyed or disabled all satellites in low-Earth orbit by pumping up radiation belts.

Both the Soviet Union and the United States began work on more discriminating ASAT systems during the 1960s.The Soviets developed a radar and optical guided co-orbital system with a high-explosive warhead that was launched from a Tsyklon-2 (SL-11) booster and tested it at least twenty times between 1968 and 1982. U.S. efforts during this period culminated in the successful September 13, 1985, test of the Miniature Homing Vehicle (MHV), a direct-ascent kinetic kill ASAT launched from an F-15 fighter.

Some analysts argued that these systems undermined strategic stability, and they were quite controversial in the United States. Congressional restrictions on testing led the administration of President Ronald Reagan to cancel the MHV system in 1988. The superpowers also attempted to address ASAT issues through formal arms control efforts, holding three rounds of dedicated ASAT negotiations in 1978–1979 and discussing the issue in the Defense and Space Talks from 1985 to 1991.None of these negotiations produced an agreement, an illustration of the considerable challenges surrounding efforts to control ASAT capabilities.

There has been no testing of dedicated ASAT systems by any nation since the 1980s, and there are no operational systems deployed today. There is, however, a large amount of residual ASAT capability worldwide, including nuclear-tipped ballistic missiles and ballistic missile defense systems, ground and air-based lasers, and a wide range of electronic capabilities to spoof, disrupt, degrade, or destroy satellites.

References

Carter, Ashton B., “Satellites and Anti-Satellites: The Limits of the Possible,” International Security, vol. 10, Spring 1986, pp. 46–98.

Cooper, Henry F., “Anti-Satellite Systems and Arms Control: Lessons from the Past,” Strategic Review, vol. 17, Spring 1989, pp. 40–48.

Stares, Paul B., The Weaponization of Space: U.S. Policy, 1945–1984 (Ithaca, NY: Cornell University Press, 1985).

U.S. Department of Defense, “Report to the Congress on U.S. Policy on ASAT Arms Control,” 31 March 1984, available at http://www.securitypolicy. org/papers/other/ASAT-0384.html.

Wilson, Tom, “Threats to United States Space Capabilities,” Space Commission Staff Background Paper, 11 January 2001, available at http://armedservices.house.gov/Publications/107thCongress/article05.pdf

The Vietnam air war changed dramatically on 24 July 1965 when a Soviet SA-2 [(Russian С-75, NATO reporting name SA-2 Guideline] missile downed an Air Force F-4 and damaged three others. Proving this shoot down was no fluke, two days later an SA-2 destroyed an American drone. US reconnaissance spotted construction of the first SAM site in early April and watched it and three other sites progress throughout the spring. But the decision makers would not permit the airmen to attack the missile sites, one of the many political restrictions on the air war. Secretary of Defense Robert McNamara argued that if the airmen attacked the SAM sites, they must also attack the MiG fields, which would be a major escalation of the air war. The leaders also feared that such attacks might cause Soviet casualties. Besides, one of McNamara's chief assistants, John T. McNaughton, believed that the SAMs only represented a bluff and would not be used.

The Soviet antiaircraft missile evolved from German World War II programs. The first Soviet SAM, the SA-1 [Soviet designation S-25 Berkut, NATO reporting name is SA-1 Guild], was inspired by the German Wasserfall [1] with ground (command) guidance. It became operational in early 1954. The West first saw its successor, the SA-2, in 1957. The Soviets designed this missile to defend against high-flying, essentially non-maneuvering, strategic bombers. The SA-2 measured 35 feet in length and weighed 4,875 pounds with its booster. It could carry a 288-pound warhead at Mach 3 .5 out to a slant range of 24-25 miles and was effective between 3,000 and 60,000 feet. The SA-2 first achieved prominence by knocking down an American U-2 over the Soviet Union in the spring of 1960 and downing another U-2 over Cuba in October 1962.

Despite knowledge of the missile since 1957, and its potential (similar to the Nike Ajax), the United States made only mixed progress with countermeasures. Tight budgets in the late 1950s hampered these efforts. Airmen assigned high priority to countermeasures against the SA-2 in budgets for fiscal years 1964 and 1965, but had nothing effective in hand when the need arose. As a result, in 1964, some airmen believed that aircraft could not operate in SAM protected areas. Although it is easy and partially correct to blame the tight funding, it is also true that the airmen underestimated the requirement for countermeasures. Although the US Air Force equipped strategic bombers with warning and jamming devices in the late 1950s, it did not similarly equip tactical fighters and bombers. Whatever the reason-money, obsession with nuclear weapons delivery, electrical power requirements, trust in fighter maneuverability and speed-the tactical air forces were unprepared for combat.

The potential SAM threat grew as the North Vietnamese incorporated more missiles into their inventory. North Vietnamese SAM battalions increased from one in 1965 to 25 the next year, to 30 in 1967, and to 35-40 in 1968. This growth in units permitted the North Vietnamese to increase their missile firings from 30 per month in the first 11 months of operation to 270 per month between July 1966 and October 1967. The latter month, with between 590 and 740 SAMs fired, was the peak month of firing until the Linebacker II operations of 1972. From October 1967 to the bombing halt on 1 April 1968, SAM firings averaged 220 per month. During this period, the American airmen observed 5,366-6,037 SAMs, which downed 115-128 aircraft.

Despite the increase in SAM firings, their direct effectiveness declined. In 1965 it took almost 18 SAMs to down each American aircraft, a figure that rose to 35 in 1966, to 57 in 1967, and to 107 in 1968. A number of factors contributed to this decline.

The airmen quickly learned that the SA-2 could be outmaneuvered. The Soviets designed the SA-2 to destroy highflying, non-maneuvering, strategic bombers; but until 1972 it engaged primarily low-flying, very maneuverable, tactical fighters. On clear days, alert airmen could spot SA-2 launches as the missile was large, described by most flyers as a flying telephone pole, and left a visible smoke trail.

The pilots would rapidly dive toward the missile, and when it changed direction to follow the aircraft, the pilot would pull up as abruptly and as sharply as possible. The SA-2 just could not follow such maneuvers. But such action required sufficient warning, proper timing, and, of course, nerve and skill. To give pilots adequate time to maneuver, procedures prohibited the pilots from flying too close to clouds between them and the ground. Later, the airmen received electronic devices that gave a visual and aural warning when a SAM radar was tracking (painting) an aircraft.

The American airmen also directly took on the missiles. On 27 July, 46 US Air Force fighter-bombers attacked two missile sites, met disaster, and according to a CIA report, hit the wrong targets. North Vietnamese gunners downed three aircraft while a midair collision accounted for two others. Nevertheless, the anti-SAM attacks continued. In the first nine months of 1966, the airmen launched 75 strikes against 60 sites and claimed to have destroyed 25 and damaged 25. Such attacks proved unprofitable because of the mobility of the SAMs-they could be relocated within hours.

One effort to counter North Vietnamese SAMs was standoff ECM: aircraft crammed with electronics gear that orbited a distance from the defenses and interfered with Communist radar and SAM signals. The Marines employed EF-1011s in this role between April 1965 and 1969. The Douglas Skyknight was ancient, having first flown in 1948 and seen action in the Korean War as a night fighter. It was joined in the ECM role in late 1965 by another Douglas product, the Skywarrior, which first flew in 1952. The Navy employed the Skywarrior as an electronic warfare aircraft designated as the EKA-3B. The Air Force adopted the Navy aircraft and also used it in the ECM role as the EB-66C, which carried a crew of seven, including four ECM operators in a crew compartment fitted in the bomb bay. Joined by other ECM versions of the B-66, it served throughout the war. However, the North Vietnamese moved their SAMs, forcing the EB-66 in turn to move away from North Vietnam to orbits over both Laos and the Gulf of Tonkin. In January 1968 a Vietnamese MiG downed an EB-66C (fig. 63). In late 1966 the Marines introduced the EA-6A in the jamming role.

A third American measure against the SAMs was codenamed Wild Weasel. The Air Force installed radar homing and warning (RHAW), electronics equipment that could detect SAM radar and indicate its location, into F-100Fs, the two-seat trainer version of its fighter-bomber. Wild Weasel I went into action in November 1965, flying with and guiding conventionally armed F-105s against SAM positions. These operations, known as Iron Hand (SAM suppression), preceded the main force by about five minutes, attacked and harassed the SAMs and thus permitted operations at 4,000-6,000 feet above the light flak into which the SAMs had forced the American aircraft.

In April and May of 1966 the American airmen first used the Navy's AGM-45A Shrike missiles. Now the anti-SAM crews had a standoff weapon that homed in on the SAM's radar signal. However, the Shrike had limited range and maneuverability and could be confused. These liabilities reduced the anti-radiation missile's (ARM) effectiveness as did Communist countermeasures. The North Vietnamese crews soon learned that by limiting emissions and coordinating several radars, they could still operate the SAMS and yet limit their vulnerability to the Wild Weasels. Just as the North Vietnamese used decoys to neutralize and ambush American air strikes, SAM operators sometimes turned on their radar to provoke an ARM launch and then turned it off before missile impact. The Shrike's kill rate declined from 28 percent of those launched by Air Force and Navy crews in 1966 to 18 percent in the first quarter of 1967. In the fall of 1967 SA-2 crews began using optical aiming, which rendered American ECM efforts useless; however, optical aiming required visual conditions, which also reduced SAM effectiveness. In March 1968 the Americans introduced the longer-range and more capable AGM-78 Standard ARM. Although it was constrained by reliability and size problems, nevertheless, the AGM-78 gave American airmen another weapon against the SAM.

In the summer of 1966 Wild Weasel III appeared in the form of the two-seat F-105 trainer, re-designated F-105G. Iron Hand operations were now easier as compatible aircraft were flying together. In late 1966 US airmen began using cluster bomb units (CBU-antipersonnel munitions) against North Vietnamese positions. But in the period following the 1968 bombing halt, 1969 until summer 1972, free-fall munitions were removed from Iron Hand aircraft, degrading their effectiveness. By then, however, the airmen had another weapon with which to combat the SAMs.

The Navy in mid-1966 and the US Air Force in October tested ECM pods carried beneath the fighters. A formation of fighters using the pods, the Navy's ALQ-51 and the Air Force's QRC-160-redesignated ALQ-71-seriously inhibited radar-directed defenses. The pods permitted operations between 10,000-17,000 feet, above the reach of light and medium flak. Put into service in January 1967, the pods further neutralized Communist defenses. But unfortunately for the airmen, the formation required for the best ECM results made the aircraft vulnerable to MiG attack. The various jamming devices forced the SAM operators to adopt a new procedure, track-on jamming. They fired the SA-2s at the jamming signal, but as it gave azimuth and not range information, it proved much less accurate than the normal method.

[1] The Wasserfall was most effective in providing a baseline for postwar US and Soviet SAM designs.

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