By Steam To The Moon
AFTER THIS MAGA zine published my article on Jules Verne’s novel From the Earth to the Moon (“A Manned Moon Shot—in 1865”), in Spring 1994, a curious letter appeared in the next issue. A fellow Ohio engineer, Paul Williams, had written to tell about an early-1960s scheme to launch rockets from a huge gun that bore uncanny parallels to the one in the Verne book. After his letter appeared, Paul called me to arrange a lunch. He later put me in touch with Jules Gram, who had dreamed up the idea with a colleague while working at Babcock & Wilcox (B&W). I learned that the story of B&W’s venture was absolutely fascinating.
In 1961 Gram was the manager of prototype products for B&W, a company that had been making steam boilers since 1867. He was working at the time on supercritical high-temperature boilers, ones that operate above the critical point of saturated steam: 705.4 degrees Fahrenheit and a pressure of 3206.2 pounds per square inch (psi). Above these values water no longer undergoes a phase change from liquid to gas. Engineers call the resulting medium “water substance.”
Contractors like B&W saw plenty of opportunities in the defense business, because the early 1960s was a grim period in the Cold War. The United States was convinced that the Soviet Union had a substantial lead in the development of intercontinental ballistic missiles. Some aspects of the “missile gap” turned out to be exaggerated, but in terms of launch readiness the threat was real. By the end of the 1960s, after the moon shot Verne had foreshadowed a century earlier, the United States would be clearly in the lead, but at the beginning of the decade, things looked much different.
The space race began in earnest on October 4,1957, when the Soviet Union shocked the United States with its successful launch of the world’s first artificial satellite, Sputnik . Within weeks the Soviets were orbiting payloads weighing several tons. The United States finally managed to launch its Explorer I in January 1958, and in theory it was not hard to imagine launching heavier vehicles deeper into space by similar means. Practical problems arose when engineers looked at exactly how much fuel would be needed to escape the earth’s gravity.
As the 1962 World Book explained: “It may take a rocket that weighs nearly a thousand times the weight of its payload to put a satellite into orbit or to put a probe into space. But scientists believe that some day they will be able to design a satellite rocket that will need to weigh less than a hundred times its payload.” Even allowing for technical advances, it seemed that launching anything large enough to be useful would require an impossibly unwieldy—and expensive—mass of fuel.
Reducing the cost of the first stage was a critical problem. The B&W proposal would have done so by reusing the launch apparatus, but plenty of even wilder schemes were discussed. For example, there was a rumor in the early 1960s that the Soviets were launching huge payloads with small amounts of propellant by putting the missile on a dolly that ran down a mountainside on rails, then looped upward like a roller coaster, hurling the space vehicle skyward. An analysis of such a scheme quickly reveals that, as any high school physics student could explain, it would have no advantage over merely moving the launch site to the top of the mountain.
AMID SUCH AN ATMOSPHERE JULES GRAM AND another B&W engineer, Charles Smith, were given an assignment. Could they figure out a way to use steam as an assist for launching space vehicles, thus reducing the amount of fuel they would have to carry? The answer, they soon realized, would be negative if they were limited to steam alone, because a gas can’t expand any faster than the speed of sound. At 1,000 degrees Fahrenheit the speed of sound in steam is about 2,350 feet per second (fps). At 2,000 degrees it goes up to 2,800 fps, and at 3,000 degrees the figure is 3,400 fps—less than one mile per second (mps). Escape velocity is more than 7 mps, so a big rocket booster would still be needed. What’s more, there would be a substantial pressure drop between the bottom of the launching tube and the top.
But plain steam was not the only answer. In March 1961 B&W submitted a confidential proposal to NASA entitled “A Steam-Hydrogen Mass Accelerator for Launching Space Vehicles.” (The document’s confidentiality became moot when U.S. Patent 3,131,597 was issued to Gram and Smith in 1964.) The proposal described a system that would accelerate a 250,000pound missile to 8,000 fps without exceeding 100 Gs of acceleration. Rockets could then be fired to achieve escape velocity, as in a conventional multistage missile.
The breakthrough in the inventors’ thinking came when they realized that, as their patent explains, “hydrogen has a sonic velocity at 100O0F of 7073 fps, at 2000°F 9069 fps, and at 3000°F over 10,000 fps.” If high-pressure steam could be used to compress the hydrogen, thereby increasing its temperature, the higher-velocity hydrogen could be used to propel the missile. Moreover, they reasoned, “because hydrogen is so light in weight, the frictional resistance and pressure drop in the launching tube will be well within practical limits.”
The arrangement they proposed was of epic proportions. A vertical gun tube 21 feet in diameter and 10,000 feet long would be sunk into a mountain at least two miles high. Access to the breech of the space cannon would be provided by a tunnel several miles long drilled horizontally into the side of the mountain. Near the inside end of the tunnel, not far from the bottom of the launching tube, would be a chemical plant capable of manufacturing hydrogen from natural gas, together with a mammoth steam plant. Downstream from its generator the hydrogen would be heated to at least 1,000 degrees on its way to the launch mechanism.
A quarter-mile below the launching tube, a steel sphere 312 feet in diameter would accumulate the steam, building up to a pressure of 7,500 psi at 1,000 degrees. Above this vessel, whose requisite burst strength would be achieved by fitting it tightly into a concentric sphere hollowed out of the bedrock of the mountain, would be a container for the hydrogen. This container was to be a vertical cylinder 85 feet in diameter with rounded ends, giving it the appearance of a huge Tylenol capsule nearly 1,400 feet long. Between the hydrogen capsule and the giant steam ball would be a ring of seventy fast-opening steam valves, each three feet in diameter. A similar ring of seventy fast-opening hydrogen valves, each four feet in diameter, would be provided between the top of the hydrogen cylinder and the base of the launching tube. As the steam rushed into the hydrogen capsule, its greater density would keep it from rising upward and mixing with the much lighter hydrogen. At full compression the hydrogen would reach a temperature of 3,150 degrees and a pressure of 4,700 psi.
The base of the space vehicle would rest on a platform that Gram and Smith called a “sabot.” The term was borrowed from the days of muzzle-loading field artillery, when a sabot was a wooden sealing disk inserted between the cannonball and the powder charge to better seal in the gases of combustion and thus increase the muzzle velocity. Above this sabot piston the tall rocket would be laterally stabilized and centered in the launch tube by blocks of plastic foam. The top of the cannon would be sealed by a diaphragm, and the gun tube would be evacuated (by being filled with steam, which would then be condensed) to reduce air resistance.
B&W estimated the cost of building such a space gun at $270 million. The facility would have been capable of a launch every three or four days. Such an investment, the company reckoned, would reduce the $5 million cost of a first-stage booster for the Saturn rocket, with its 1.5 million pounds of thrust, to a mere $100,000. Cost per pound in orbit would drop from $1,000 to about $190.
To prove that the system would work, the inventors suggested building a one-tenth-scale prototype in an abandoned mineshaft. NASA demurred. Considering the investment it had already made in conventional rocket technology, $270 million was more than the agency was prepared to spend at the time. More important, perhaps, 100 Gs seemed considerably more than most astronauts were prepared to endure—even for the two and a half seconds it would take to get out of the launching tube.
BUT THE CONCEPT OF GUN-LAUNCHED SATELLITES fired the imagination of other scientists and engineers. By 1964, the year the Gram-Smith patent was issued, a U.S. Army-funded team from Montreal’s McGill University was shooting atmospheric probes to a height of 125 miles. At Lawrence Livermore National Laboratory in California, John Hunter, a physicist, is currently launching small missiles at 6,800 miles per hour (about 10,000 feet per second) from a $2.8 million prototype that uses burning methane to compress hydrogen. He hopes it will lead to a two-mile, $1.5 billion supergun, from which he proposes to shoot unmanned space capsules to the moon. Other engineers have proposed gentler accelerations for space rockets using the kind of magnetic propulsion found in “maglev” vehicles.
Such ideas pale, however, in comparison with the Gram-Smith space gun. Those who remember Verne’s 900-foot Columbiad cannon, which launched three astronauts and two dogs in From the Earth to the Moon (a book neither Gram nor Smith had read at the time), cannot forget the author’s description of the cacophony: “An appalling, unearthly retort followed instantly, such as can be compared to nothing whatever known, not even to the roar of thunder, or the blast of volcanic explosions! No words can convey the slightest idea of the terrific sound! An immense spout of fire shot up from the bowels of the earth as from a crater.”
The Gram-Smith gun would have made a similar racket. Each launch, the inventors calculated, would consume 192,000 pounds of hydrogen, which would emerge from the mountaintop at 8,000 fps at red heat, instantly bursting into flame as it encountered the oxygen of the air. Like a cosmic blowtorch, a pillar of fire of biblical proportions would shoot up through the clouds, burning from the outside in as it turned into 1.7 million pounds of water. A firestorm-induced tornado similar to those sometimes seen in Western forest fires could develop. Seconds later a roaring geyser containing 54 million pounds of steam—enough to make Old Faithful look like a squirt gun—would erupt from the mountain peak. Lifting the flaming pillar into the mushroom cloud forming in the stratosphere and mixing with combustion products, the expanding steam would begin to condense, producing a torrential rain quite possibly accompanied by thunder and lightning. The colossal cloud would dump some 28,000 tons of water—almost a million cubic feet, or seven million gallons—onto the surrounding countryside.
Jules Verne would have loved it. So, perhaps, would Enrico Fermi, a Verne fan who once suggested shooting a rocket to the moon by exploding an atomic bomb at the bottom of a deep pit. However appealing it may have been, the plan was much too harsh and unwieldy to be practical, so the U.S. space program got to the moon by more conventional, if less spectacular, means.