Rockets trace their ancestry back about 800 years to the Chinese, who used them against invading Mongol hordes in the year 1232. Not much is known about these early Asian devices; they are described simply as "arrows of flying fire."1 Centuries passed with little improvement in the design of these early black powder rockets, but those versed in the "black art" kept the science alive through the ensuing centuries. By the early nineteenth century Sir William Congreve of the British Army made several notable improvements, including larger size and range, improved propellant-packing techniques, sheet-metal casings, and portable center-guide sticks.2 Congreve rockets were used at the battle of Fort McHenry during the War
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of 1812, and are immortalized as "the rockets' red glare" in the national anthem of the United States. William Hale later made further improvements, notably the addition of exhaust vanes, which gave the rockets a stabilizing spin. With the advent of longer range artillery shells and better aiming methods, rockets almost faded entirely from the scene until the early twentieth century (Fig. 4.1).
I t was not until 1926 that a pioneering American physicist, Dr. Robert Hutchings Goddard, built and flew the first liquid-fueled rocket (Fig. 1.2). The advantage of all liquid-fueled rockets is that they can be throttled. They can be turned off or throttled down for various reasons, giving them a distinct advantage over solid rockets. They also tend to be more efficient, especially at high altitudes. Within 20 years, Walter Dornberger and his team of German rocket scientists, including Dr. Wernher von Braun, had developed a series of liquid-propellant rockets culminating in the famous V-2 of World War II. All subsequent liquid-fueled rockets can trace their ancestry back to the V-2 (Fig. 4.2).
Liquid-propellant rocket engines are marvels of engineering. They may use a range of cryogenic or storable, inert or hypergolic, toxic or nontoxic chemicals in their operation. Typically high pressures are required as two liquid propellants - a fuel and an oxidizer - are admitted into the combustion chamber. The high pressures are delivered either by pressurized propellant tanks or by high-pressure turbopumps, depending on the design.
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