GAM-87 Skybolt
The Douglas GAM-87 Skybolt (AGM-48 under the 1962 Tri-service system) was a hypersonic air-launched ballistic missile (ALBM) developed by the United States during the late 1950s. The basic concept was to allow US strategic bombers to launch their weapons from well outside the range of Soviet defenses, as much as 1,000 miles (1,600 km) from their targets. To do this in an air-launched form, a lightweight thermonuclear warhead was needed. Initially, the W47 from the Polaris missile was selected, but it was later replaced by the W59 from the Minuteman missile.
This article is about the ballistic missile. For the biplane, see Steen Skybolt. For the sounding rocket, see Starchaser Industries. For the French-Canadian film, see La Guêpe (film).GAM-87 Skybolt
11,000 pounds (5,000 kg)
38 feet 3 inches (11.66 m)
35 inches (890 mm)
5 feet 6 inches (1.68 m)
1,150 miles (1,850 km)
300 miles (480 km)
9,500 miles per hour (15,300 km/h; Mach 12)
Aircraft
The UK joined the Skybolt program in 1960, intending to use it on their V bomber force. When the design added a star tracker in addition to its inertial navigation system (INS) this meant that it could only be carried externally where the tracker could see the sky. This requirement along with the required ground clearance on takeoff limited it to the Avro Vulcan bomber. Several design decisions in the W47 led the RAF to question its safety, so they intended to use their own Red Snow warheads. This was a heavier warhead and would reduce the range to about 600 miles (970 km), meaning the bombers would have to cross the Soviet coastline to attack Moscow.
Testing began in 1962 and was initially marked by a string of failures. These failures, along with a lack of mission after the successful development of submarine-launched ballistic missiles (SLBMs), led to its cancellation in December 1962.[1] The UK had decided to base its entire 1960s deterrent force on Skybolt, and its cancellation led to a major disagreement between the UK and US, known today as the "Skybolt Crisis". This was resolved by a series of meetings that led to the Royal Navy gaining the UGM-27 Polaris missile and construction of the Resolution-class submarines to launch them.
History[edit]
Background[edit]
The US Air Force had built up an enormous fleet of strategic bombers during the 1950s, only to see them threatened by the possibility of a surprise attack by Soviet ICBMs. As the US bombers were located at only a small number of air bases, a relatively small fleet of missiles could attack all of them at once. The US had been developing its own ICBMs as well, but early models, like the SM-65 Atlas, required some time to prepare to launch from their surface launchers and were vulnerable to sneak air attack. A carefully timed attack from Soviet bombers against US missiles and their ICBMs against US bomber fields could inflict serious damage.[2]
The one weapon system that was not open to attack was the US Navy's Polaris missile system. The Polaris equipped submarines could cruise in large areas of the Atlantic or Pacific where the Soviet fleet was unable to find them, and launch their missiles with impunity. If the goal of the nuclear force was to maintain deterrence by ensuring that a counterstrike would be launched, Polaris met this goal in a way the existing Air Force fleet could not. This fact was more worrying to the Air Force than the Soviet arsenal and generated a number of internal reports on how to deal with this threat to their dominance in the strategic field.[2]
WS-199 and WS-138[edit]
In response, in 1957 the Air Force began studying solutions to the "Puzzle of Polaris" under the WS-199 program. WS-199 was a grab-bag effort, studying anything that might improve the survivability of the Air Force strike capability. Primary among the concepts were two air-launched ballistic missiles, Bold Orion and High Virgo. These systems would give the Air Force a method somewhat similar to the Navy's; in times of high alert, the bomber force would be sent to holding positions far outside the range of any Soviet defenses, and then launch their missiles on command. Using aerial refueling, a bomber might be expected to be able to loiter for as long as a day.
This system had a major advantage compared to Polaris, as the aircraft could be sent radio instructions to retarget the missiles before launch. In theory, the bombers could be used as a second-strike weapon, attacking only those targets that had been missed in a first-strike, or alternately, being switched from counterforce to countervalue targets or vice versa. Ground-based systems like Atlas and Polaris lacked this ability, and could only be retargeted with a significant amount of effort. Even the latest Air Force design, the LGM-30 Minuteman, required changes in targeting data to be loaded from magnetic tape in a process that took several weeks.[3]
WS-199 was generally successful, but the two ALBMs had a shorter range than desired. The Air Force tendered bids for a longer-range version in early 1959. Douglas Aircraft received the prime contract in May, and in turn subcontracted to Northrop for the guidance system, Aerojet for the propulsion system, and General Electric for the reentry vehicle. The system was initially known as WS-138A and was given the official name GAM-87 Skybolt in 1960.
Description[edit]
The GAM-87 was powered by a two-stage solid-fuel rocket motor. The missile was fitted with a tailcone to reduce drag while on the pylon, which was ejected shortly after being dropped from the plane. After first stage burnout, the Skybolt coasted for a while before the second stage ignited. First stage control was by eight movable tail fins, while the second stage was equipped with a gimballed nozzle.
Guidance was entirely by inertial platform. The current position was constantly updated from the host aircraft through accurate fixes, meaning that the accuracy of the platform inside the missile was not as critical.
B-52s were to carry four missiles, two under each wing on the weapons pylon with a dual launcher adapter with the missiles slightly staggered (inboard missile slightly ahead of the outboard missile).[10] The Vulcan carried two missiles, one each on smaller underwing pylons.