Science: Solid Progress

At last week’s Washington meeting of the American Rocket Society, a 90-ft. Titan missile stood outside the building; often discussed at the meeting were other liquid-fuel rockets. These types are dominant in the U.S. and probably in Russia. Their great advantage: they work. But also discussed at the meeting was the progress being made in solid-fuel rockets.

The solid-fuel rocket is like the monoplane in the early years of aviation. Biplanes were then the established type. They were easy to build because their double wings, braced by crisscrossed wire and struts, strengthened each other. But they were inefficient aerodynamically, and they had to be fooled with continually to keep their complex structure in proper order. The single wings of monoplanes were hard to make strong enough, but everyone knew that when they could be built, their efficiency and simplicity would make them dominant.

The solid-fuel rocket, too, is simple and vastly promising—but difficult. Chief problem is to get the fuel to burn dependably in such a way as to provide a precalculated, controllable thrust. In the liquid rocket this is done by an intricate system of gas generators, pumps, valves, turbines and tubing. But this advantage is also a source of trouble, because failure of one or more of these intricate parts is the usual reason for the frequent liquid-rocket misfires.

Minuteman. Most promising solid-fuel rocket is the Minuteman, the Air Force’s long-range (6,300 miles) missile. Not much has been revealed officially, but an air of success hangs around men who are working on it. Much smaller than its rivals, the liquid-fuel Atlas and Titan, it has three stages filled with fuel made mostly of a rubbery plastic holding together crystals of an oxygen-supplying material, such as ammonium perchlorate. The ingredients are first blended to form a semiliquid mass like peanut butter. This is pumped with extreme care into the rocket casing and cured by gentle heat to turn it into an elastic solid. Then a mandrel in the center is pulled out, leaving a roughly star-shaped cavity on whose surface the fuel will start to burn when the rocket is fired.

If all goes well, the fuel burns evenly, acts as an insulator to protect the vulnerable metal casing from the searing heat of its flame. As the fuel is consumed, the cavity becomes nearly cylindrical, so when the flame reaches the outside wall not enough fuel is left to soften the metal. A well-made solid-fuel rocket engine can be touched with bare fingers just after firing on the test stand.

Always Ready. Solid fuel can also be stored in the vehicle. Thus the rocket is always ready. Liquid fuels are so combustible and dangerous to handle that the)’ must be pumped in at the last moment. This means a delay of many minutes or even hours between an alert and firing time, also involves costly storage tanks and pumps. In contrast, Minuteman should be able to wait quietly, year after year, in a cylindrical hole in the ground, then take off on a 6,000-mile flight on a few seconds’ notice.

Another Minuteman boast is that its surprisingly small size (one guess: 60 ft. long by 5 ft. thick at the base, v. the Atlas’ 80 ft. by 10 ft.) and its ruggedness allow it to be carried around on a railroad car. A plan under active development is to mount Minutemen and their crews on railroad cars, keep them circulating ceaselessly on the railroad tracks of the U.S. Like oldtime warships sailing with sealed orders, they would not know where they are going until the command arrives. Enemies of the U.S. would not know either, so they could not destroy the Minutemen before they were able to retaliate awesomely.

Minutemen will be cheap. Air Force General Ben I. Funk has stated that a Minuteman in its hole, alert and ready to go, will cost only $1,000,000. This has been estimated as being about one twenty-fifth of the cost of rival long-range missiles with their expensive crews, liquid oxygen plants and bases.

Space Ahead. Even before the Minuteman has been proved in flight (its test schedule is secret), solid-fuel enthusiasts are promising bigger things. Vice President Harold Ritchey of Thiokol Chemical Corp., which makes the first-stage engine of the Minuteman, thinks that big, solid-fuel boosters are the quickest and surest way to match or surpass the threat of Russia’s space rockets.

To scale up the thrust of a liquid-fuel engine is an intricate and formidable job. Every increase in thrust requires a proportionate increase in the capacity of turbines, pumps, valves, and all the other tricky accessories that supply floods of fuel to the thirsty engine. Novel designs must often be used, and these must be tested over and over to ensure reliability. Scaling up a solid-fuel booster is much simpler. Little or no plumbing is needed. The metal casing will be bigger, but since it need not hold more pressure, it will not have to be stronger.

Ritchey insists that a reliable booster with 10 million Ibs. of thrust can be built in three years. Such a rocket, with proper upper stages, could put a 120,000-lb. payload in orbit, which should be enough weight allowance for a long-lived, manned satellite. Though other experts point out that the first big solid-fuel rocket has yet to fly, Ritchey insists that all the program needs for success is enough money.