Category FLIGHT and M ОТІOIM

satellite is an object in space that orbits another body, such as a planet. The Moon is a natural satellite of Earth. An artificial satellite is a small spacecraft sent into orbit from Earth.

Artificial satellites are used for com­munication, weather forecasting, navi­gation, military surveillance, and scien­tific research. A satellite remains in orbit because of the gravitational pull of the larger body around which it travels. Any spacecraft orbiting Earth is technically a satellite, although manned spacecraft are not usually referred to as satellites. The International Space Station is the biggest artificial satellite. The Hubble

Space Telescope also is a satellite. There are about 2,500 satellites orbiting Earth, and others have been placed in orbit around the Moon, Venus, and Mars.

kydiving is a sport in which a parachutist falls through the air, performing various maneuvers, before opening his or her parachute. Free-falling in this way is the closest that a human comes to flying like a bird.

Parachutists in the early 1900s opened their parachutes within a second or two of jumping. As parachuting developed, however, bolder jumpers delayed pulling the ripcord. They expe­rienced free fall for a few seconds before the parachute opened and slowed their descent. This was the start of skydiving.

In the 1930s, parachuting began to develop as an international sport. The first world championships were held in 1951, and today there are competitions for accuracy, style, and team jumping.

Many people enjoy the thrill of skydiv­ing as a recreational sport.

Scientists who specialize in aerody­namics are known as aerodynamicists.

They put a lot of time and effort into reducing drag because drag wastes fuel. A plane’s engines have to burn fuel to generate the power necessary to over­come drag. Improving a plane’s aerody­namics can enable it to fly farther with­out burning any more fuel. Because drag acts like a brake, reducing drag also enables the fastest airplanes to go even faster. Improving a glider’s aerodynamic design enables it to stay aloft longer.

One way to study aerodynamics is to use a wind tunnel. Air is blown through a tunnel with a model aircraft inside. As the air flows around the model, the forces acting on it are measured.

Scientists would like to be able to calculate precisely how a plane will per­
form in the air instead of having to build models to test every design and every change in a design. Such calculations, however, present a formidable task. That task involves calculating the aerody­namic forces acting on every part of an aircraft as it flies through the air at all angles and speeds. To do this, the air flowing around the aircraft is divided into tiny packets called cells. The forces acting on each and every cell must be calculated to figure out how each cell moves and how it affects the aircraft. Each cell affects all the cells around it. In turn, they affect other cells, which affect yet others, making the problem incredi­bly complicated.

The method of using computers, numbers, and mathematical equations to figure out how air flows around an object is known as computational fluid dynamics (CFD). Only the fastest super­computers have the ability to use CFD to tackle complicated aerodynamics.

The atmosphere is not the same all the way up from the ground. It is divided into four layers: the troposphere, strato­sphere, mesosphere, and thermosphere.

The lowest layer is the troposphere. It extends from Earth’s surface up to a height of about 4 miles (6.4 kilometers) at the poles and 11 miles (17.7 kilome­ters) at the equator. Most weather and clouds occur in the troposphere. Temperature falls with height, dropping to about -112°F (-80°C) at the top. Clouds are produced by water vapor ris­ing into the colder air and changing into water droplets or ice crystals.

Jet streams are fast air currents found near the top of the troposphere. They are studied by meteorologists, because they affect the weather below them. The jet streams’ winds blow from west to east. The wind speed is normally 35 to 75 miles per hour (56 to 121 kilometers per hour), but speeds of more than 250 miles per hour (402 kilometers per hour) have been recorded. An airliner using the jet stream to fly eastward can fly faster without burning any more fuel.

The layer above the troposphere is the stratosphere. The stratosphere is drier and less dense than the layer below it. It goes up to a height of about 31 miles (50 kilometers) above Earth’s sur­face and contains the ozone layer. Ozone is a type of oxygen with three atoms instead of the usual two. This gas soaks up harmful ultra-violet radiation from the Sun. Because of this, the temperature rises with height in the stratosphere, up to about 32°F (0°C) at the top.

The next layer is the mesosphere. It goes from about 31 miles (50 kilometers) above Earth’s surface up to about 53 miles (85 kilometers). Less is known

О This diagram shows the layers of the atmos­phere and the exosphere. Some satellites orbit Earth in the exosphere; others are out in space.

about the mesosphere than the lower layers because it is too high for most air­craft to fly in and too low for most spacecraft to orbit in. Temperature falls yet again in the mesosphere, down to about -148°F (-100°C).

In the early days of aviation, airplanes were small and flew slowly. The public showed little interest in air travel, and businesses did not consider air freight as a way to move their goods around. Not until 1912 did an airplane exceed 100 miles per hour (160 kilometers per hour) to match a railroad train or automobile. Planes were faster than ships, but they could not cross the wide oceans. Nor could they carry more than one or two people at a time.

The first known freight flight took place in 1910, when the Ohio company Morehouse-Martens hired Philip O. Parmalee to fly two packages of silk between its stores in Columbus and Dayton, Ohio. This was a publicity stunt, but the practice of carrying mail by air seemed a good idea and soon caught on.

AIRMAIL

Airmail flights began in September 1911, when the U. S. Postmaster-General awarded pilot Earl L.

Ovington the title of Air Mail Pilot Number One.

On May 15, 1918, the U. S.

Postal Service introduced a daily airmail service between New York City,

Washington, D. C., and Philadelphia. For the first few months, army avia­tors flew the airmail routes. Civilian pilots were then trained, and

the airmail service was gradually expanded. The first coast-to-coast airmail was delivered in the United States in 1921. The mail left San Francisco at 4:30 a. m. on February 22 and reached Long Island, New York, at 4:50 the following afternoon. Soon, regular flights operated between New York and San Francisco. In 1927, the Postal Service turned its airmail network over to the newly emerging airlines.

In 1912, there were only 2,400 licensed pilots in the world, more than 900 of whom were in France. There were fewer than 200 pilots in the United States. Things changed rapidly after World War I (1914-1918). Aircraft were bigger, faster, and more reliable. There were many more pilots available, trained as military fliers and now released from service. Record-breaking flights, such as the first crossing of the Atlantic Ocean in June 1919 by John Alcock and Arthur

Whitten Brown, showed that long­distance flight was no longer a dream.

The Japanese navy built a number of air­craft carriers, gaining experience in their use during the nation’s war with China that began in 1937. Japanese carriers led the attack on the U. S. naval base at Pearl Harbor in December 1941 that brought the United States into World War II. The U. S. Navy’s Pacific Fleet’s carriers, which were at sea at the time, escaped damage in this attack, and their aircraft went on to help the United States win the key Pacific air-sea battles of the war. In April 1942 the first U. S. air raid on the Japanese capital of Tokyo was made by B-25s launched from the USS Hornet.

After World War II, heavier, faster jets came into naval service. The first jet aircraft to land on an aircraft carrier was a British De Havilland Vampire, which touched down on the HMS Ocean in December 1945. The first U. S. jet plane to operate from an aircraft carrier soon followed, when a McDonnell FH-1 Phantom flew from the USS Franklin D. Roosevelt in July 1946. U. S. Navy jets saw combat for the first time during the Korean War, when a Grumman F9F-2 Panther shot down an enemy MiG-15 jet fighter on November 9, 1950.

New aircraft carriers had angled flight decks and steam catapults to help land and launch the new generation of airplanes. The U. S. Navy’s first carrier with an angled flight deck was the USS Antietam (1953). The Navy’s first nuclear-powered aircraft carrier was the Enterprise (1960).

From 1964 onward, naval air power played an important part in the Vietnam War. McDonnell F-4 Phantom jets,

О The U. S. Navy’s Nimitz-class carriers have angled deck landing areas, visible here on the USS Harry S. Truman. The angle allows aircraft that are unable to stop before the end of the landing area to become airborne again for another try without the risk of hitting anything on deck.

flying from the USS Midway, scored the first combat victories against MiG-17 fighters in June 1965. Carrier-based aircraft also took part in the Gulf War of 1991 and the Iraq War of 2003.

During World War I (1914-1918), Germany built a fleet of more than sixty Zeppelins. The airships were used to patrol European waters and to drop bombs on London and other cities in England. The airships were a little slow­er than the fighter planes of the time. By flying high, however, they made it diffi­cult for fighter pilots to catch them.

The first Zeppelin shot down in air combat was LZ-37, in June 1915. While bombing the French town of Calais, this airship was attacked by a British plane. The pilot flew above the Zeppelin and dropped six bombs; the sixth bomb exploded. The airship caught fire and plunged to the ground. The British pilot, Flight Sub-Lieutenant Reginald A. J. Warneford, became a national hero, but he was killed twelve days later when his airplane crashed.

After World War I, airships stayed in the news. In 1919, the British airship

R-34 flew across the Atlantic Ocean from Scotland to New York (July 2-6 ) and then back to England (July 9-13). In 1926, the Italian-built airship Norge —with Roald Amundsen as one of its passengers—flew over the North Pole. Amundsen had been the first explorer to reach the South Pole, in 1911.

The Apollo program continued until 1972. In November 1969, the Apollo 12 mission, crewed by Charles Conrad and Alan Bean, made a second Moon landing. During this mission, the astro – nauts inspected an earlier unmanned probe, Surveyor 3. The subse­quent mission, Apollo 13, nearly ended in dis­aster. On its way to the

О President Richard Nixon visited the Apollo 11 astro­nauts while they were held in quarantine after their return to Earth on July 24, 1969.

Moon, the spacecraft was damaged when an oxygen tank in the command module blew up. This seriously reduced the supply of oxygen and electrical power. The crippled spacecraft flew on around the Moon and headed back to Earth. Astronauts James A. Lovell, Jr., Fred Haise, and Jack Swigert used the little lunar module as their “lifeboat,” making use of its power and oxygen supplies during the three-day return trip. They returned to the command module before making a safe landing.

The last four Apollo missions carried out explorations at different sites. Apollo 15 astronauts David Scott and James Irwin were the first people to explore the Moon riding in a four­wheeled, battery-driven Lunar Rover.

THE LUNAR ROVER

On the last three Apollo landings, American astronauts drove the elec­tric Lunar Rover, or Moon buggy. This remarkable vehicle was steered by a T-shape control stick instead of a steering wheel. Apollo 15 astronauts David Scott and James Irwin found the buggy hard to drive—it took a little time to get used to driving in gravity that is only one-sixth of that on Earth. The Lunar Rover had four – wheel drive to cope with the bumpy Moon surface and a top speed of 7 miles per hour (11 kilometers per hour). When the astronauts returned to Earth, the Moon buggies from the three missions were left behind on the Moon.

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In 1782 French silk maker Joseph- Michel Montgolfier made a model hot air balloon. Montgolfier burned scraps of wool or straw to warm the air inside his balloon. Because the hot air was less dense than the surrounding air, the bal­loon rose successfully. Montgolfier and his brother Jacques-Etienne then flew a larger balloon in the town square. Next, they set off for the French capital of Paris, where scientist Jacques Charles was working on a rival balloon. This balloon was to be filled with hydrogen, the lightest of all gases. Naturally light gases work in the same way as hot air – they rise because they are lighter than the air surrounding them.

Charles demonstrated the hydrogen balloon (without a passenger) on August 27, 1783. It rose to about 3,000 feet (915 meters). Undeterred, the Montgolfiers brought out their own balloon. It was 72 feet (22 meters) high and 43 feet (13 meters) in diameter. On September 19, 1783, watched by King Louis XVI and other amazed spectators, the balloon rose in the air, carrying a sheep, a duck, and a chicken. It flew for eight minutes, traveled 2 miles (3.2 kilometers), reached an estimated altitude of 1,500 feet (457 meters), and landed safely.

Jean-Frangois Pilatre de Rozier vol­unteered to ride on the next flight, and he ascended to 84 feet (25.6 meters). The balloon was tethered to the ground with a rope. On November 21, 1783, de Rozier rose into the air again, accompa­nied by the Marquis d’Arlandes. This

time there was no rope tether, and the men flew for 25 minutes, traveling 5 miles (8 kilometers) and rising to 3,000 feet (914 meters). For the first time, people had taken to the air and stayed in flight. In December 1783 Charles flew in his hydrogen bal­loon for about 26 miles (42 kilo­meters).

irds are warm-blooded vertebrates with wings instead of forelimbs or arms. Birds are the only animals with feathers. These strong but delicate structures keep a bird warm and help it to fly.

The Study of Flight

The first people to dream of flying undoubtedly gazed at birds. Birds are truly masters of the air, although other animals, such as insects and bats, also fly. Scientists of old must have watched a bird or a bee and puzzled over how these creatures flew. Today’s scientists have analyzed the aerodynamics of the bumblebee and are amazed that this insect can even get off the ground!

People in ancient times thought they could imitate bird flight. It looked so easy-if a swan or a goose could fly simply by flapping its wings, why not a human? So inventors tried to fly by strapping feathery wings to their arms and leaping from high towers, waving their arms. Sadly, like Icarus in the ancient Greek myth, they crashed to the ground. A machine called an ornithopter can fly by flapping its wings, but a person cannot.