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The Greatest Engineering Achievements of the 20th Century is a collaborative project led by the National Academy of Engineering. The achievements, nominated by 29 professional engineering societies, were selected and ranked by a distinguished panel of the nation’s top engineers. This is the third of five articles highlighting the top 20 achievements. Source:

Top 20 Greatest Engineering Achievements,
Nine through Twelve

In the 20th century, engineers began transforming a fledgling technology of copper wire, wooden poles and primitive transmitters into a complex system of fiber optics, satellites and digital technology. They carry images, computer data and conversations with unprecedented accuracy and reliability at lightning speed.

Long-distance technology had arrived in 1892 with the invention of a signal amplifier, but many innovations were necessary before telephoning would truly cover long distances. The triode vacuum tube, invented in 1906 by American Lee De Forest, further amplified electrical signals to make long distance feasible. By 1915, the east and west coasts of the United States were connected.

The technical focus for the next several decades was on improving transmission quality and expanding automatic switching systems. Innovations included high quality insulated wire and coaxial cable technology. Direct distance dialing further reduced the need for operators. From the 1970s on, engineers began transforming the telephone into an invaluable multifunctional tool.

In 1975 engineers developed the first commercial continuous-wave semiconductor laser. Smaller than a grain of sand, this remarkable device made it possible to transmit optically encoded telephone conversations over fiber-optic cables. A single optical fiber combined with amplifiers can carry tens of millions of phone conversations in one thousandth of a second.

Today, new digital exchanges route some 1.5 million calls per hour. The switch from analog systems to digital has overcome many of the problems associated with sending electrical signals over long distances. In remote places in India and Africa, solar cells make it possible to have phones without a large-scale electrical distribution system.

Mobile phones were introduced in St. Louis in 1945. Today, hexagonal base stations are central to cellular phones. Every 15 minutes each base station beams out a message asking all the activated handsets within its cell to report in. This enables the central computers to know where to route a call when a handset is phoned. Systems that use radio waves for transmission via a network of satellites and terrestrial-based antennas allow people to use a digital telephone anywhere on Earth.

Thomas Edison once noted that the telephone had “annihilated time and space, and brought the human family in closer touch.” What would Edison think of human potential now?

Life changed immensely in the 20th century, as air conditioning and refrigeration systems became more efficient, controllable and even mobile.

It took the pioneering genius of Willis Carrier to work out the basic principles of cooling and humidity control. Carrier’s invention made many technologies possible, especially in fields that require highly controllable environments, such as scientific research, product testing, computer manufacturing and space travel.

Carrier claimed that while he was standing in a Pittsburgh train station one night in 1902, he realized that air could be dried by saturating it with chilled water to induce condensation. He built the first air conditioner that year for a Brooklyn printer who couldn’t print a decent color image because of heat and humidity problems. It had the cooling power of 108,000 pounds of ice a day.

The use of ice for refrigeration was widespread until shortly before World War I, when mechanical refrigerators became available. In 1927, General Electric introduced a refrigerator with a “monitor top” containing a hermetically sealed compressor. The 14-cubic-foot refrigerator sold for $525, affordable to just a few, and made GE the industry leader by 1930. By 1939, the cost of a household refrigerator had dropped to nearly $150.

Single-phase electric motors were perfected and reliable by 1920. Frigidaire manufactured the first individual room cooler in 1929, using technology from the household refrigerator. The invention of halocarbon refrigerants by Thomas Midgley in 1928 provided a safe alternative to toxic, flammable refrigerating fluids. The Frigidaire division of General Motors adopted Freon 12 (dichlorodifluoromethane) refrigerant gas, and most other refrigerator makers followed suit. But as chlorofluorocarbons demonstrated signs of destroying the Earth’s ozone layer, production of these chemicals began to be phased out.

The first air-conditioned automobile, a Packard, was engineered in 1938. The first successful window air conditioner was marketed in 1938 by Philco-York. Mass production of window air conditioners after World War II lowered costs to the point where they were accessible to mass consumers, as were refrigerators.

Refrigeration technology led to the creation of the frozen food industry. In 1914, Clarence Birdseye was fishing in Canada when he noticed that fish caught through the ice froze stiff the instant they were exposed to the air, and they tasted almost fresh when defrosted and cooked weeks later. By 1925, Birdseye and Charles Seabrook developed a deep-freezing process for cooked foods. Five years later, Birds Eye Frosted Foods were sold in stores for the first time.

At the end of the 20th century, nearly 70 percent of U.S. households had air conditioning and 99.5 percent of households had at least one refrigerator. Climate control had grown from an invisible luxury to a common necessity.

Highways provide one of our most cherished assets — the freedom of personal mobility. Thousands of engineers built the roads, bridges and tunnels that connect our communities and enable goods and services to reach remote areas.

By 1921 there were 387,000 miles of paved roads in the United States. There were no national standards for size, weight restrictions or signage. During World War I, roads throughout the country were nearly destroyed by the weight of trucks.

When General Eisenhower returned from Germany in 1919, after serving in the U.S. Army’s first transcontinental motor convoy, he noted: “The old convoy had started me thinking about good, two-lane highways, but Germany (the Autobahn) made me see the wisdom of broader ribbons across the land.”

It would take another war before the federal government acted on a national highway system. During World War II, a tremendous increase in trucks and new roads were required. Thirteen percent of defense plants received all their supplies by truck, and almost all other plants shipped more than half of their products by vehicle.

By then, local control of highways had led to a bewildering array of design standards. Even federal and state highways did not follow basic standards. Some states allowed trucks up to 36,000 pounds, while others restricted anything over 7,000 pounds. The Federal-Aid Highway Act of 1944 called for strict, centrally-controlled design criteria.

The interstate highway system, one of the greatest engineering public works projects of the century, was launched in 1956. To build its 44,000-mile web of highways, bridges and tunnels, hundreds of unique engineering designs and solutions had to be worked out. Innovative designs of roadways, tunnels, bridges, overpasses and interchanges that could traverse or bypass urban areas soon began to weave their way across the country, forever altering the face of America. Traffic control systems and methods of construction developed under the interstate program soon influenced highway construction around the world.

The interstate system has been an essential element of the nation’s economic growth in terms of shipping and job creation. More than 75 percent of the nation’s freight deliveries arrive by truck, and most products that arrive by rail or air use interstate highways for the last leg of the journey.

Today, the interstate system links every major U.S. city and connects to highways in Canada and Mexico. Fatality rates on U.S. highways are half that of all other roads. Built with safety in mind, the highways have wide lanes and shoulders, dividing medians or barriers, long entry and exit ramps, curves engineered for safe turns and limited access.

In 1957, Sputnik I pierced the atmosphere, shocked the world, and started a space race that launched the greatest engineering team effort in American history. “We have a long way to go in this space race,” said President John F. Kennedy in 1962. “But this is the new ocean, and I believe the U.S. must sail on it and be second to none.”

Early human space flight leading up to the Apollo program required the integration of numerous technologies on a scale never before undertaken. The launch and return of spacecraft, from Apollo to the Shuttle, is one of the monumental engineering triumphs in all of human history. The space program spawned technological advances in numerous fields and the development of more than 60,000 products.

The first spacecraft to be launched were Earth-orbiting satellites that began a revolution in global communications. Eventually they would be instrumental in weather forecasting, national defense, navigation, environmental and scientific research and wireless communications systems.

In the late 1950s, engineering advances with liquid hydrogen led to the RL-10 rocket engine. The RL-10 has launched an array of sophisticated unpiloted spacecraft, including Viking, Mariner and Pioneer, without a single engine failure. The RL-10 led to the development of larger hydrogen-fueled engines that made the lunar landing possible.

Wernher von Braun and his team played a crucial role in the space program by outlining the basic technology that would achieve the first major space goal: the moon landing. Von Braun devised the most powerful rocket ever built. The Saturn V was more than 360 feet long and weighed 3,000 tons. Its lift-off engines delivered an incredible 7.5 million pounds of thrust and burned more than 10 tons of fuel each second.

John Glenn’s historic first flight in 1962 took him around the Earth three times, proving the capsule’s material and structure could withstand the enormous temperatures of re-entry. The space docking between two Gemini spacecraft in 1965 was another significant step toward the Apollo program because it solved the problem of the amounts of fuel needed to get to the moon. The actual moon landing in 1969 was an astounding technological and cultural achievement.

During the 1970s the U.S. space program de-emphasized piloted flights and stressed instead fully automated missions that sent spacecraft close to the surfaces of Mercury, Mars, Jupiter and Saturn. In 1982 the Soviets succeeded in landing an exploration craft on Venus, where it successfully transmitted pictures back to Earth.

In the 1980s the Space Shuttle program was launched, heralding a new era in aviation design and technology. Shuttle flights have conducted hundreds of scientific experiments and medical tests and carried satellites and the Hubble telescope into space.

Seven years after Kennedy’s inspiring words, Neil Armstrong stepped onto the lunar landscape. As Armstrong declared the moment a “giant leap for mankind,” a note was placed on JFK’s grave to honor his vision. The note read: “Mr. President, the Eagle has landed.”

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