Polaris and Minuteman

Jupiter, Thor, and Atlas marked a huge step forward in the matura­tion of U. S. rocketry, but before the technology from those missiles came to significant use in launch vehicles, the navy’s development of the Polaris inaugurated a solid-propellant breakthrough in mis­sile technology that also profoundly affected launch vehicles.82 Un­til Polaris A1 became operational in 1960, all intermediate-range and intercontinental missiles in the U. S. arsenal had employed liq­uid propellants. These had important advantages in terms of perfor­mance but required extensive plumbing and large propellant tanks that made protecting them in silos difficult and expensive. Such factors also virtually precluded their efficient use onboard ships, especially submarines. Once Minuteman I became operational in 1962, the U. S. military began to phase out liquid-propellant stra­tegic missiles. To this day, Minuteman III and the solid-propellant fleet ballistic missiles continue to play a major role in the nation’s strategic defenses because they are simpler and cheaper to operate than liquid-propellant missiles.

Because of the higher performance of some liquid propellants and 40 their ability to be throttled as well as turned off and on by the use of Chapter 1 valves, they remained the primary propellants for space-launch ve­hicles. However, since solid-propellant boosters could be strapped on the sides of liquid-propellant stages for an instant addition of high thrust (because their thrust-to-weight ratio is higher, allowing

faster liftoff), solid-propellant boosters became important parts of launch-vehicle technology. The technologies used on Polaris and Minuteman transferred to such boosters and also to upper stages of rockets used to launch satellites. Thus, the solid-propellant break­through in missiles had important implications for launch-vehicle technology. By the time that Polaris got under way in 1956 and Minuteman in 1958, solid-propellant rocketry had already made tremendous strides from the use of extruded double-base propel­lants in World War II tactical missiles. But there were still enor­mous technical hurdles to overcome before solid-propellant missiles could hope to launch strategic nuclear warheads far and accurately enough to serve effectively as a deterrent or as a retaliatory weapon in case of enemy aggression.83

With a much smaller organization than the army or air force, a navy special projects office under the leadership of Capt. (soon-to-be Rear Adm.) William F. Raborn pushed ahead to find the right tech­nologies for a submarine-launched, solid-propellant missile, a daunt­ing task since a solid propellant with the necessary performance did not yet exist. Capt. Levering Smith—who, at the Naval Ord­nance Test Station (NOTS), had led the effort to develop a 50-foot solid-propellant missile named “Big Stoop" that flew 20 miles in 1951—joined Raborn’s special projects office in April 1956. Smith contributed importantly to Polaris, but one key technical discovery came from the Atlantic Research Corporation (ARC), a chemical firm founded in 1949 with which the Navy Bureau of Ordnance had contracted to improve the specific impulse of solid propellants (the ratio of thrust a rocket engine or motor produced to the amount of propellant needed to produce that thrust).84

ARC’s discovery that the addition of comparatively large quan­tities of aluminum to solid propellants significantly raised perfor­mance, together with the work of Aerojet chemists, led to successful propellants for both stages of Polaris A1. The addition of aluminum to Aerojet’s binder essentially solved the problem of performance for both Polaris (and, as it turned out, with a different binder, for Minuteman). Other key technical solutions relating to guidance and an appropriate warhead led to the directive on December 8, 1956, that formally began the Polaris program.85

Flight testing of Polaris at the air force’s Cape Canaveral (be­ginning in 1958 in a series designated AX) revealed a number of problems. Solutions required considerable interservice cooperation. On July 20, 1960, the USS George Washington launched the first functional Polaris missile. The fleet then deployed the missile on November 15, 1960.86

The navy quickly moved forward to Polaris A2. It increased the range of the fleet ballistic missile from 1,200 to 1,500 miles. Flight testing of the A2 missiles started in November 1960, with the first successful launch from a submerged submarine occurring on Octo­ber 23, 1961. The missile became operational less than a year later in June 1962. Polaris A3 was still more capable, with a range of 2,500 miles. It incorporated many other new technologies in both propulsion and guidance/control, becoming operational on Septem­ber 28, 1964. All three versions of Polaris made significant contri­butions to launch-vehicle technology, such as the Altair II motor, produced by the Hercules Powder Company under sponsorship of the Bureau of Naval Weapons and NASA and used as a fourth stage for the Scout launch vehicle.87

While Polaris was still in development, the air force had officially begun work on Minuteman I. Its principal architect was Edward N. Hall, a heterogeneous engineer who helped begin the air force’s involvement with solid propellants as a major at Wright-Patterson AFB in the early 1950s. As Karl Klager, who worked on both Polaris and Minuteman, has stated, Hall “deserves most of the credit for maintaining interest in large solid rocket technology [during the mid-1950s] because of the greater simplicity of solid systems over liquid systems." Hall’s efforts “contributed substantially to the Polaris program," Klager added, further illustrating the extent to which (unintended) interservice cooperation and shared informa­tion contributed to the solid-propellant breakthrough. Hall moved to the WDD as the chief for propulsion development in the liq­uid-propellant Atlas, Titan, and Thor programs, but he continued his work on solids, aided by his former colleagues back at Wright – Patterson AFB.88

Despite this sort of preparatory work for Minuteman, the mis­sile could not begin its formal development until the air force se­cured final DoD approval in February 1958, more than a year later than Polaris. Hall and others at WDD had a difficult job convincing Schriever in particular to convert to solids. Without their heteroge­neous engineering, the shift to solids might never have happened. They were aided, however, by development of Polaris because it provided what Harvey Sapolsky has dubbed “competitive pressure" for the air force to develop its own solid-propellant missile.89

Soon after program approval, Hall left the Ballistic Missile Divi­sion. From August 1959 to 1963, the program director was Col. (soon promoted to Brig. Gen.) Samuel C. Phillips. Hall and his coworkers deserve much credit for the design of Minuteman and its support by the air force, whereas Phillips brought the missile to completion.

Facing many technical hurdles, Phillips succeeded as brilliantly as had Levering Smith with Polaris in providing technical manage­ment of a complex and innovative missile. Often using trial-and – error engineering, his team working on the three-stage Minuteman I overcame problems with materials for nozzle throats in the lower stages, with firing the missile from a silo, and with a new binder for the first stage called polybutadiene-acrylic acid-acrylonitrile (PBAN), developed by the contractor, Thiokol Chemical Corpora­tion. Incorporating substantial new technology as well as some bor­rowed from Polaris, the first Minuteman I wing became operational in October 1962.90

Minuteman II included a new propellant in stage two, known as carboxy-terminated polybutadiene and an improved guidance/con – trol system. The new propellant yielded a higher specific impulse, and other changes (including increased length and diameter) made Minuteman II a more capable and accurate missile than Minute – man I. The newer version gradually replaced its predecessor in mis­sile silos after December 1966.91

In Minuteman III, stages one and two did not change from Min – uteman II, but stage three became larger. Aerojet replaced Hercules as the contractor for the new third stage. With the larger size and a different propellant, the third stage more than doubled its total impulse. These and other modifications allowed Minuteman IIIs to achieve their initial operational capability in June 1970. As a result of the improvements, the range of the missile increased from about 6,000 miles for Minuteman I to 7,021 for Minuteman II, and 8,083 for Minuteman III.92

The deployment of Minuteman I in 1961 marked the completion of the solid-propellant breakthrough in terms of its basic technol­ogy, though innovations and improvements continued to occur. But the gradual phaseout of liquid-propellant missiles followed almost inexorably from the appearance on the scene of the first Minuteman. The breakthrough in solid-rocket technology required the extensive cooperation of a great many firms, government laboratories, and uni­versities, only some of which could be mentioned here. It occurred on many fronts, ranging from materials science and metallurgy through chemistry to the physics of internal ballistics and the mathematics and physics of guidance and control, among many other disciplines. It was partially spurred by interservice rivalries for roles and mis­sions. Less well known, however, was the contribution of interser­vice cooperation. Necessary funding for advances in and the sharing of technology came from all three services, the Advanced Research Projects Agency, and NASA. Technologies such as aluminum fuel,

methods of thrust vector control, and improved guidance and con­trol transferred from one service’s missiles to another. Also crucial were the roles of heterogeneous engineers like Raborn, Schriever, and Hall. But a great many people with more purely technical skills, such as Levering Smith and Sam Phillips, ARC, Thiokol, and Aerojet engineers made vital contributions.

The solid-propellant breakthrough that these people and many others achieved had important implications for launch vehicles as well as missiles. The propellants for the large solid-rocket boosters on the Titan III, Titan IVA, and the Space Shuttles were derived from the one used on Minuteman, stage one. Without ARC’s dis­covery of aluminum as a fuel and Thiokol’s development of PBAN as a binder, it is not clear that the huge Titan and shuttle boosters would have been possible. Many other solid-propellant formula­tions also used aluminum and other ingredients of the Polaris and Minuteman motors. Although some or all of them might have been developed even if there had been no urgent national need for solid – propellant missiles, it seems highly unlikely that their development would have occurred as quickly as it did without the impetus of the cold-war missile programs and their generous funding.