Double-Base Propellants during and Soon after World War II

At the beginning of recent solid-propellant development during World War II, the vast majority of rockets produced for use in com­bat employed extruded double-base propellants. These were limited in size by the nature of the extrusion process used at that time to produce them. In extrusion using a solvent, nitrocellulose was sus­pended in the solvent, which caused the nitrocellulose to swell. It was formed into a doughlike composition and then extruded (forced) through dies to form it into grains. This process of production lim­ited the size of the grains to thin sections so the solvent could evap­orate, and the elasticity of the grain was too low for bonding large charges to the motor case. With a solventless (or dry) process, there 232 were also limitations on the size of the grain and greater hazards of Chapter 6 explosion than with extrusion using a solvent.

These factors created the need for castable double-base propel­lants. But before a truly viable process for producing large castable propellants could be developed, the United States, because it was at war, needed a variety of rockets to attack such targets as ships (including submarines), enemy fortifications, gun emplacements, aircraft, tanks, and logistical systems. The development of these weapons did not lead directly to any launch-vehicle technology, but the organizations that developed them later played a role in furthering that technology. Two individuals provided the leader­ship in producing the comparatively small wartime rockets with extruded grains. One was Clarence Hickman, who had worked with Goddard on rockets intended for military applications during World War I. He then earned a Ph. D. at Clark University and went to work at Bell Telephone Laboratories. After consulting with God­dard, in June 1940 Hickman submitted a series of rocket proposals to Frank B. Jewett, president of Bell Labs and chairman of a divi­sion in the recently created National Defense Research Committee (NDRC). The upshot was the creation of Section H (for Hickman) of the NDRC’s Division of Armor and Ordnance. Hickman’s section had responsibility for researching and developing rocket ordnance. Although Section H was initially located at the Naval Proving Ground at Dahlgren, Virginia, it worked largely for the army.

Hickman chose to use wet-extruded, double-base propellants (em­ploying a solvent) because he favored the shorter burning times they afforded compared with dry-extruded ones. He and his associates worked with this propellant at Dahlgren, moved to the Navy Pow­der Factory at Indian Head, Maryland, and finally to Allegany Ord­nance Plant, Pinto Branch, on the West Virginia side of the Potomac

River west of Cumberland, Maryland. There at the end of 1943 they set up Allegany Ballistics Laboratory, a rocket-development facility operated for Section H by George Washington University. By using traps, cages, and other devices to hold the solvent-extruded, double­base propellant, they helped develop the bazooka antitank weapon, a 4.5-inch aircraft rocket, JATO devices with less smoke than those produced by Aerojet using Parson’s asphalt-based propellant, and a recoilless gun.22 Under different management, ABL later became an important producer of upper stages for missiles and rockets.

Hickman’s counterpart on the West Coast was physics professor Charles Lauritsen of Caltech. Lauritsen was vice chairman of the Division of Armor and Ordnance (Division A), and in that capacity he had made an extended trip to England to observe rocket devel­opments there. The English had developed a way to make solvent­less, double-base propellant by dry extrusion. This yielded a thicker grain that would burn longer than the wet-extruded propellant but required extremely heavy presses for the extrusion. However, the benefits were higher propellant loading and the longer burning time that Lauritsen preferred.

Convinced of the superiority of this kind of extrusion and be­lieving that the United States needed a larger rocket program than Section H could provide with its limited facilities, Lauritsen argued successfully for a West Coast program. Caltech then set up opera­tions in Eaton Canyon in the foothills of the San Gabriel Moun­tains northeast of the campus in Pasadena. It operated from 1942 to 1945 and expanded to a 3,000-person effort involving research, development, and pilot production of rocket motors; development of fuses and warheads; and static and flight testing. The group pro­duced an antisubmarine rocket 7.2 inches in diameter, a 4.5-inch barrage rocket, several retro-rockets (fired from the rear of airplanes at submarines), 3.5- and 5-inch forward-firing aircraft rockets, and the 11.75-inch “Tiny Tim" rocket that produced 30,000 pounds of thrust and weighed 1,385 pounds. (This last item later served as a booster for the WAC Corporal.)

By contrast with Section H, Section L (for Lauritsen) served mainly the navy’s requirements. In need of a place to test and eval­uate the rockets being developed at Eaton Canyon, in November 1943 the navy established the Naval Ordnance Test Station (NOTS) in the sparsely populated desert region around Inyokern well north of the San Gabriel Mountains. Like the Allegany Ballistics Labora­tory, NOTS was destined to play a significant role in the history of U. S. rocketry, mostly with tactical rockets but also with contribu­tions to ballistic missiles and launch vehicles.

One early contribution was the “White Whizzer" 5.0-inch rocket developed by members of the Caltech team who had already moved to NOTS but were still under direction of the university rather than the navy. By about January1944, combustion instability had become a problem with the 2.25-inch motors for some of the tactical rock­ets. These rockets used tubular, partially internal-burning charges of double-base propellant. Radial holes in the grain helped solve se­vere pressure excursions—it was thought, by allowing the gas from the burning propellant to escape from the internal cavity. Edward W. Price, who had not yet received his bachelor’s degree but would later become one of the nation’s leading experts in combustion in­stability, suggested creating a star-shaped perforation in the grain for internal burning. He thought this might do a better job than the 234 radial holes in preventing oscillatory gas flow that was causing the Chapter 6 charges of propellant to split. He tested the star perforation, and it did produce stable burning.

In 1946, Price applied this technique to the White Whizzer, which featured a star-perforated, internal-burning grain with the outside of the charge wrapped in plastic to inhibit burning there. This ge­ometry allowed higher loading of propellant (the previous design having channels for gas flow both inside and outside the grain). And since the grain itself protected the case from the heat in the internal cavity, the case could be made of lightweight aluminum, providing better performance than heavier cases that were slower to accelerate because of the additional weight. Ground-launched about May 1946, the White Whizzer yielded a speed of 3,200 feet per second, then a record for solid rockets. The internal-burning, aluminum-cased design features later appeared in the 5.0-inch Zuni and Sidewinder tactical missiles. The internal-burning feature of the design also came to be applied to a great many other solid rock­ets, including ballistic missiles and stages for launch vehicles. This apparently was the first flight of a rocket using such a grain design in the United States, preceding JPL’s use of a similar design, known as the Deacon, and also flight testing of the first member of the Vicar family to be flown.23