BGM-75 WS 120A Advanced ICBM
The Minuteman's successor was given the general label of an “advanced ICBM” and between 1966 and 1968 fell within the program known as WS-120A. On 01 November 1966, OSD began a new strategic weapon study, STRAT-X, to evaluate the air force proposal for a new strategic missile (WS-120A). The proposed missile was larger than Minuteman III and carried ten to twenty warheads. The BGM-75 AICBM was to be a solid-propellant missile designed for use in fixed silo and mobile train configurations.
The preferred deployment mode was hardened and dispersed launch facilities, but Aerospace also investigated various mobile options, including an off-road version and defended dispersed modes. Mobility characteristics are considered essential to make it a difficult target for hostile ICBMs. Martin/Denver will conduct a preliminary design for an off-road transporter/launcher. The weapon will have a 20-minute alert time, high survivability, and a 7,000 nautical mile range.
On 02 February 1966 Headquarters USAF established a schedule for preparation of documentation and submission of a Preliminary Technical Development Plan for an Advanced ICBM program which was subsequently designated Weapon System 120A. On 25 March 1966 Headquarters AFSC authorized the formation of an Advanced ICBM (WS 120A) task group at Headquarters Ballistic Systems Division. In July Ballistic Systems Division completed the Preliminary Technical Development Plan for the Advanced ICBM (WS 120A).
Air Force Contract AF33(615)-2998, "Development of a ManufacOuring Process and Associated Equipment to Improve Internal Core Forming in Solid Propellant Rocket Motors," and Modifications S/A 1, 2, and 3 was awarded in response to Thiokol Chemical Corporation Proposals HP-39-65, dated March 1965, and HP-39A-65, dated April 1965. The period of performance for the basic contract was 15 July 1965 through 15 October 1966. Modification S /A 1 to the basic contract authorized disposition of tooling after expiration of the period of performance.
Phase I effort was completed during the period 15 July 1965 to 15 October 1966. No work was performed from 15 October 1966 to July 1967 pending redirection from the Air Force. It was decided during this period to investigate further the casntible combustible core concept with special emphasis on the WS-120A system. The scope of work was revised and formally presented in Modification S/A 2 of the contract. Erosive burning would be no problem in the Space Booster motor, while it appeared to be a real problem in the WS-120A system. Launch energy for the WS-120A system from material within the motor could be achieved by tailoring the primary propellant grain accordingly or using a bipropellant grain with the secondary propellant having the same modulus of elasticity as the primary propellant.
The completed Advanced ICBM (WS 120A) Alternate Basing Study was submitted to AFSC, Headquarters USAF, and Secretary of the Air Force Dr. Harold Brown in July 1967. In late 1967, to the chagrin of those researching WS 120A, the air force, given the needs of the Vietnam War, the deployments of Minuteman II and III, and a belief that Soviet ICBMs could not threaten the existing or planned ICBM force for several years, cancelled further study of WS 120A.
By October 1967 Headquarters USAF planners began to move away from the concept of the WS 120A Advanced ICBM missile system and toward the concept of a dual-capable silo for the Minuteman III weapon system. Using the basing concept devised for WS 120A, the new approach was to concentrate on the development of a silo that could hold the Minuteman III when it became operational and could later accommodate an advanced ICBM.
The Advanced ICBM (WS 120A) Provisional System Program Office (SPO) at Norton was dissolved in March 1968, and most of its personnel were transferred to the Minuteman SPO as the core cadre for the Hard Rock Silo (HRS) development program. The Hard Rock Silo was considered as a technique for rebasing Minuteman missiles in the late 1960s. The concept was similar to Minuteman, one missile in one vertical silo, except that the silos were to be located in granite outcroppings in the western United States. This design approach was chosen to achieve the highest possible hardness level for a surface-flush silo launcher.
The Hard Rock Silo was to be compatible with the Minuteman III missile or with the next generation ICBM- at that time designated WS 120A - a 10-foot diameter, 70-foot long missile. The facility was to be generally similar to a Minuteman silo with a launch tube and annular equipment room. The launch tube was 16 feet in diameter and 90 feet deep. The approach was to drill the silo cavity in a surface rock outcropping and line the excavation with reinforced concrete. The resulting hardness was estimated to be about 3000 psi. This hardness level is no longer judged to be adequate to cope with the existing Soviet threat, and it is not technically feasible to design them to adequate levels of hardness.
On December 1, 1967 The Secretary of Defense recommended continuing Advanced Development of an Advanced ICBM, but recommended against starting Contract Definition in FY 69. The JCS recommended completion of Contract Definition in FY 69, and dependent upon favorable review, full-scale development of the missile element of the Advanced ICBM (WS–120A), with the objective of an IOC in FY 73. They also recommended delaying a decision on expenditures unique to a specific deployment mode until study results are available. The Secretary of the Air Force recommended beginning Contract Definition in FY 69 at a cost of $79 million.
Subsequently the Secretary of Defense and the Secretary of the Air Force agreed to develop silos that are capable of accepting either Minuteman III or the WS–120A missile; the program would support a deployment date of Minuteman in such silos in FY 72 and an Advanced ICBM IOC in FY 74. Of the $207 million total hard silos R&D program, the Secretary of Defense will authorize $40 million in FY 69. This includes $38 million R&D money for the dual-capable silo and $2 million for site surveys. An additional $10 million was authorized for advanced ICBM technology.
On July 29, 1968 Secretary of Defense Clifford disapproved the JCS recommendation for Contract Definition of the advanced ICBM system (WS–120A). This missile was found to provide little improvement over Minuteman. The 10-year cost of developing, procuring, and operating a force of 280 missiles would be $9.1 billion.
In its final form, the ninety-two inch diameter MX weighed more than 192,000 pounds, nearly 114,000 pounds more than Minuteman III but significantly less than ICBM-X or WS 120A.
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