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Theodore Von
Karmán |
Meanwhile rocketry was developing in the US, quite apart from Robert Goddard's efforts. One noted pioneer was Theodore Von Karmán, a native of Hungary and the graduate of the Minta, one of the famed high schools of Budapest from which came a remarkable number of distinguished scientists. Karmán became an authority on aerodynamics and in the 1930s served as professor of aeronautics at Caltech, the California Institute of Technology in Pasadena, California.
Together with Frank Malina, one of his graduate students, Karmán began designing and building rockets at Caltech's Guggenheim Aeronautical Lab (supported by the Guggenheim family which also financed Goddard's work). Because rockets had a dubious "far out" connotation, they referred to their work as "jet propulsion." Ultimately Karmán and Malina established at Caltech a laboratory devoted to rocket work, the Jet Propulsion Laboratory (JPL); today JPL is virtually part of NASA, a large lab specializing in the exploration of the solar system beyond Earth. Another distinguished student of Karmán was Hsue Shen Tsien, who later returned to China and helped establish that country's spaceflight effort.
Karmán's group built both solid-fuel and liquid-fuel rockets. During World War II one of the problems was getting heavily loaded seaplanes into the air, Karmán and his engineers solved this by designing the JATO rocket, for "Jet Assisted Take Off." It originally burned a mixture of roofing tar and perchlorate, an oxygen-rich compound similar to the one used by chemistry teachers for producing oxygen in classroom demonstrations: the tar was the fuel and the perchlorate provided the oxygen. (Robert Goddard designed an alternate liquid-fuel JATO rocket, but it was not successful. )
Later they designed the solid-fuel "Private" for military use, and a bigger liquid-fuel rocket, the "Corporal. " The latter was adapted for high-altitude research as the "WAC Corporal" (WAC stood for Women's Auxiliary Corps) which, with a thrust of 6700 newtons, reached in 1945 a height of 70 km; later a larger scientific rocket was developed from it, the Aerobee.
Military Uses
Apart from the V-2, the various armies in WW II used solid-fuel artillery rockets much in the way that Congreve had used them, for massive bombardments, to cover attacks or beach landings; the Russian army, for instance, had its famed "Katyusha".
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The X-1 rocket airplane, the first
airplane to pass the speed of
sound. Effects of shock waves
are seen in the rocket exhaust. |
In addition Germany developed rocket-powered fighter planes, whose engines only burned long enough to enable them rise and intercept American bombers, after which they glided to Earth, to land without any engine. These, however, were weapons of desparation, and the war ended before they could be used. After the war, in 1947, the US built and flew a rocket airplane, the X-1, and it became the first airplane to exceed the speed of sound in level flight, on 14 October 1947. The X-1, too, can be seen in the Smithsonian museum.
Rocket Staging and Technology
Each of the above rockets had a single engine, on which it rose until it ran out of fuel. A better way to achieve great speed, however, is to place a small rocket on top of a big one and fire it after the first has burned out.
Suppose one wanted to use a V-2 rocket to send a small payload--e.g., 10 kilograms--as high as possible. The usual payload of the V-2 rocket was one ton (1000 kg), and with that a height of about 100 km was possible. Reducing the payload to 10 kg would increase that height somewhat, but not by much, since the empty rocket, weighing about 3 tons, would also have to be raised to the full height.
The US army, which after the war used captured V-2s for experimental flights into the high atmosphere, used a more effective way. It replaced the payload with another rocket, in this case a "WAC Corporal," which was launched from the top of the orbit. Now the burned-out V-2, weighing 3 tons, could be dropped, and using the smaller rocket, the payload reached a much higher altitude. Such was the "Bumper" rocket (on the right) which in February 1949 reached an altitude of 393 km.
Today of course almost every space rocket uses several stages, dropping each empty burned-out stage and continuing with a smaller and lighter booster. Explorer 1, the first artificial satellite of the US which was launched in January 1958, used a 4-stage rocket. Even the space shuttle used two large solid-fuel boosters which were dropped after they burned out (the "Challenger" disaster in 1986 occured when one of them failed).
The fuel for the shuttle's own engines--liquid hydrogen and oxygen--came from a huge detachable tank. As that fuel was used up, the boosted mass decreased, and by Newton's 2nd law, the acceleration increased steadily (it is hard to reduce the engine's thrust, though the shuttle could do so to a limited degree). To reduce the acceleration and save the astronauts and the vehicle from excessive stress, at a chosen point in the flight two of the three engines were shut down. Even then, when the last fuel in the tank wass burned, the acceleration reached about 6g, pressing each astronaut down with an added force 6 times his or her body weight.
The Atlas Rocket
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Launch of an
Atlas-Centaur. |
Persons not familiar with spaceflight rarely realize that almost all of a rocket's launch mass consists of fuel. The launch mass of the V-2 was about 75% fuel and 25% rocket, but as high as that may seem, it is not nearly good enough for spaceflight. In a 1948 article in the American Journal of Physics, titled "Can We Fly to the Moon? " the authors answered their question with a resounding "no! " They extrapolated the V-2 technology to larger rockets, estimated that 80% of the weight would be fuel, and concluded that a payload of 10 kg might be sent to the moon, but never a human being.
Flights to the moon were only made possible by a technology in which the fuel formed a much bigger fraction of the mass. Of the mass of the Atlas missile, built in the 1950s and used by the first astronauts, about 97% was fuel. That rocket has been described as a "stainless steel balloon," keeping its shape with the help of pressurized gas in its interior, also used in pushing out the fuel. That was the vehicle with which on February 20, 1962 John Glenn became the first American to orbit the Earth. Because the fuel tank was so light, the Atlas only dropped two of its rocket engines at the end of the first stage of its flight, and like the shuttle continued on a third.
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S-5.Waves & Photons
