|2018||144"||Space Launch Sys|
|1962||31" x 4||RT-1|
Composite solid propellant is a mechanical mixture of fine, solid particles of oxidizer and powdered metal or metal hydride evenly distributed in an organic polymer, and the composite contains up to 10 to 12 components. It uses oxygen-rich nitrates and perchlorates and organic nitro compounds as oxidizers. Metals in the form of high-dispersion powders constitute the primary fuel.
In the United States, a group of researchers at the Guggenheim Aeronautical Laboratory at Caltech (which formed the nucleus of what became JPL in 1944) was working on jet-assisted takeoff units. In June of 1942, the chemist John Parsons had the idea of combining asphalt (as a binder and fuel) with potassium perchlorate (as an oxidizer) to make the first castable composite solid propellant. At Atlantic Research Corporation, working under contract with the US Navy, engineers Keith Rumbel and Charles Henderson found that the addition of large amounts of aluminum significantly increased the specific impulse of a castable composite propellant. A significant part of the history of American rocketry involves the full details of how ammonium perchlorate successfully came to be used and how the various ingredients in the Polaris motors came to be combined in the proportions that ultimately were employed.
Thiokol introduced PBAN, a co-polymer of butadiene and acrylic acid, which offered better physical properties as a cured polymer binder, in 1954. Used in Minuteman missiles, Space Shuttle solid rocket boosters, and Poseidon missiles, PBAN has accumulated the largest production tonnages in the industry. Colleagues at Atlantic Research apparently had the proper mix of skills and knowledge to employ the correct procedures for testing the effects of a 21-percent concentration of aluminum combined with 59 percent ammonium perchlorate and a binder of 20 percent plasticized polyvinyl chloride in test stands at Atlantic Research. Aerojet later verified their findings in an actual 100-lb rocket in early 1956.
By the late 1950s the Americans showed great consistency when they concentrated their efforts on the development and successive replacement of generations of one basic type of solid-propellant missiles on land - Minuteman - and similarly set about replacing generations of solid-propellant missiles on submarines - Polaris. In the US, design of the solid-propellant Minuteman I missile was under way in 1957–58.
At the end of World War II solid propellant rockets, while used in some minor weapons applications, were still in their development infancy. But during the 1950's solid propellant technology accumulated gains in metallurgy, chemistry and high temperature materials. By 1957, large solid rocket motors up to 60 inches in diameter, containing as much as 25,000 pounds of propellant, had been assembled and successfully fired. Contracts were awarded for an advanced "second generation" intercontinental ballistic missile, the Minuteman. The Navy was developing the Polaris solid propellant intermediate range missile at about the same time. Validity of the concept was demonstrated on 1 September 1959 when the first large size solid propellant, flight weight motor, over 24 feet long and over five feet in diameter, weighing over 50,000 pounds, was successfully fired. Minuteman production began in 1959, and in 1961, silo launchers with these missiles went into service.
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