Category FLIGHT and M ОТІOIM

A satellite’s orbit depends on the task for which it is designed. Most satellites are launched in the same direction as Earth is spinning, and this is called a prograde orbit. To launch in the opposite direction, like throwing a ball into the wind, requires more booster power and fuel.

О A polar-orbiting satellite is prepared for launch in 2000. The satellite joined the polar – orbiting operational environmental satellite (POES) program, which provides data about the global climate and weather.

Scientists choose various orbits for their satellites, depending on the loca­tion of the launch site and the task of the satellite. Orbits fall into three types: high geostationary orbit, Sun – synchronous polar orbit, and low orbit.

A high geostationary orbit keeps a satellite always in the same position with respect to Earth. The satellite makes one orbit in the same period of time as Earth makes one rotation (23 hours, 56 minutes, 4.09 seconds). To do this, it must orbit at a height of about 22,300 miles (about 35,900 kilometers) above Earth’s surface. By orbiting in tandem with Earth, the satellite appears station­ary, or synchronous (in time), with respect to the rotation of the planet.

A Sun-synchronous polar-orbiting satellite travels above the North and South poles. It flies at a height of about 540 miles (about 870 kilometers) and passes the Equator and each of Earth’s latitudes at the same time each day. Being Sun-synchronous means the satellite passes overhead at the same solar time through the year, so it can transmit data (on weather, for example) at consistent times. Its data can be com­pared year by year.

Low-orbiting satellites fly at a height of 200-300 miles (320-485 kilometers). A low orbit requires the least rocket

power and is often chosen for observa­tory satellites, such as the Hubble Telescope. Hubble orbits Earth at a height of about 375 miles (600 kilome­ters), making one orbit every 97 minutes.

Some orbits are circular, while others are elliptical (egg-shaped). The length of time a satellite takes to make one orbit is called its orbital period.

A satellite’s initial velocity is high enough to counter the force of gravity and keep it in orbit, but friction (from Earth’s atmosphere and from the Sun’s energy) gradually slows the satellite’s speed. Its orbit begins to decay. Eventually, as the satellite descends into the thicker layers of the atmosphere, it burns up or breaks up.

Military Satellites

Military satellites include spy or reconnaissance satellites. These satellites are fitted with scanning devices and cameras that can detect objects on the ground. Some of these objects may be as small as a truck hundreds of miles below the spacecraft. Spy satellites also can detect missiles being fired. The first military satellite able to detect missile launches was Midas 2, launched by the United States in 1960. Early spy satel­lites took photographs on film that were returned to Earth in small capsules that landed by parachute. Modern spy satel­lites are equipped with digital imaging systems, and they relay their images directly from space.

A number of countries have military satellites. Military navigation satellites are used by aircraft, submarines, surface ships, and land vehicles. Anti-satellite weapons, known as “killer” or “suicide” satellites, are designed to track, locate, and destroy other satellites or orbital weapons systems.

Although accidents do happen, skydiv­ing and parachute sports have a good safety record. Accidents are most com­mon when people jump in poor weather conditions, such as unpredictable winds. Jumping from buildings, cliffs, or other high structures (known as BASE jump­ing) is especially dangerous. Because the modern parachute can be steered, there is little chance of the parachutist landing accidentally in a lake or a tree, as was often the fate of parachutists in the past.

Drop zones in the United States and Canada are required to have an experi­enced person who acts as a safety offi­cer. In most countries, skydivers are required to carry a reserve parachute that has been packed and inspected by a certified parachute rigger. In the United States, certification is provided by the Federal Aviation Administration (FAA).

Many countries have national para­chuting associations, affiliated to the Federation Aeronautique Internationale (FAI). In the United States, skydiving permits and ratings are issued by the United States Parachute Association.

EXTREME SKYDIVING

Specialized forms of skydiving and parachuting include:

• Accuracy landing: Aiming to land on or very near a drop zone target.

• Blade running: Like slalom skiing with a parachute.

• Formation skydiving: Also called relative work (RW).

• Paraskiing: Landing on a snowy mountain on skis.

• Skysurfing: Landing with a surfboard strapped to the feet.

• Stuff jumping: Jumping with

an object, such as a bicycle, which is ridden through the air before the sky – diver lets go and opens the parachute.

The history of aeronautics began long before people understood the principles of flight. The Italian explorer Marco Polo (1254-1324) was one of the first Europeans known to have gone to China. When he returned to Europe in 1295, he told stories of people who flew using giant kites. Kites may have been built in China as long ago as 1000 b. c.e. They are the world’s first aerial vehicles.

Even before Marco Polo, there were people who believed they would fly if they strapped a pair of wings to their arms and flapped like a bird. They tested their ideas by jumping from towers and mountains. Without any real understanding of lift, gravity, or the properties of air, they fell to the ground much faster than expected. Injuries and death were common.

О Samuel Perkins tested man-lifting kites for observational uses by the U. S. Army during World War I. This 1910 photograph shows five Perkins kites holding a man aloft at Harvard Aviation Field in Atlantic, Massachusetts.

One of the most famous of these early “jumpers” was Abbas Ibn Fimas (810-887 c. e.). He lived in Andalusia, now part of Spain. Firnas was an inven­tor who studied chemistry, astronomy, and physics. In 875, when he was sixty – five years old, Firnas built a glider. He made a successful flight, which was seen by a large number of people, but he was injured when the glider hit the ground. This happened about 1,000 years before modern aeronautical pioneers started making successful glider flights.

In the year 1010, an English monk named Eilmer tried to fly from the top of a tower with wings fastened to his arms and feet. Eilmer managed to glide for about 650 feet (200 meters), but he landed badly and broke his legs.

Many of the wings used by early fliers copied the wing shape or flapping action of birds’ wings. Even the great Italian artist and inventor Leonardo da Vinci (1452-1519), who drew designs for flying machines more than 500 years ago, thought the first successful flying machine would have flapping wings.

The atmosphere does not have a defined top, like the surface of land or ocean. Air becomes thinner with altitude until it is too thin to measure. Scientists chose an altitude within the atmosphere where they consider space begins. The most widely used definition for the beginning of space is 62 miles (100 kilometers) above sea level, in the thermosphere. In the United States, however, a person is defined as an astronaut when traveling above 50 miles (80.45 kilometers).

Space scientists and engineers defined the beginning of space at a dif­ferent altitude in the thermosphere. They chose an altitude of 400,000 feet (121,920 meters), or about 76 miles (122 kilometers), and they call it the entry interface. This is the altitude where the air is thick enough to begin heating up a spacecraft as it returns from space.

The air doesn’t stop suddenly at this altitude. There is still some air higher up, where spacecraft orbit Earth. In fact, there is enough air at those levels to slow down a spacecraft.

Commercial aircraft are built for strength and safety rather than speed, although many can travel at just below the speed of sound. A modern airliner can fly nonstop from San Francisco to Sydney, Australia; from Washington, D. C., to Rome, Italy; or from New York

City to Tokyo, Japan. It can cruise high above the clouds at over 600 miles per hour (965 kilometers per hour).

Most airliners have turbofan engines, powerful enough to lift a payload of 400 tons (363 metric tons) or more. Each engine of a Boeing 747, for example, generates about 50,000 pounds (22,700 kilograms) of thrust-about the same as the two engines of an F-15 fighter. Four engines provide insurance against engine failure, but modern engines are so powerful and reliable that many modern airliners, such as the Boeing 777, make do with two.

Commercial airplanes with piston or turboprop engines are still used, too. Propeller planes, although slower than jet planes, are quieter and cheaper to run. They can also take off and land from small airports.

Private airplane owners fly light air­planes, carrying between two and ten people, for business and pleasure. U. S. manufacturers, such as Beech, Cessna, and Piper, have built many of the world’s most successful light aircraft. Modern business planes, with jet engines, carry five to ten passengers, and they cruise at much the same speeds as jet airliners.

One of the most important decisions to make is how fast a new aircraft will fly, because this affects its shape and the engine power it needs. It may also affect the choice of materials from which a plane will be built. Aircraft speeds are divided into bands that cover the slowest to the fastest: low speed, medium speed, high speed, super­sonic, and hypersonic. These speed bands are also known as regimes of flight.

О The C-5 Galaxy transport plane is the U. S. Air Force’s largest aircraft. It was designed specifically to accommodate huge cargo, such as this container being loaded at an air force base in Delaware.

An airplane designed to fly well at very high speeds is not generally good at flying slowly, so the designer must choose which is more important. Some aircraft have to perform well at both low speeds and high speeds, however. One way of achieving this is to make the plane change shape. The F-14 Tomcat and Tornado fighter bombers have wings that stick straight out to the side at low speeds but then swivel back as the plane goes faster. These aircraft are variable geometry, or swing-wing, planes. Swing-wing planes are not very common, because the machinery that moves the wings adds extra weight to the aircraft.

Dates of birth: Alcock: November 6, 1892; Brown: July 23, 1886.

Places of birth: Alcock: Manchester, United Kingdom; Brown: Glasgow,

United Kingdom.

Died: Alcock: December 18, 1919;

Brown: October 4, 1948.

Major contribution: Flew the first nonstop flight across the Atlantic Ocean, 1919.

Awards: Alcock: Distinguished Service Cross and Knight Commander of the British Empire; Brown: Knight Commander of the British Empire.

ohn Alcock was raised just outside the large English city of Manchester and trained to become an auto mechanic when he finished school. His employer encouraged the young Alcock in his interest in airplanes. Alcock was then hired by French aviator Maurice Ducrocq to be a mechanic. Ducrocq taught him how to fly, and Alcock obtained a pilot’s license at age twenty.

Prisoners of War

When World War I began in 1914, Alcock joined the Royal Naval Air Service. At first, he was a flight instruc­tor, but he soon became a pilot. In Europe in 1917, Alcock shot down two German planes, for which he won a Distinguished Service Cross. Later the same day, on another mission, his own plane suffered engine trouble. Alcock was forced to crash land in Germany and was captured. He remained a German prisoner until the war ended in November 1918.

There were some striking similarities in the early lives of Alcock and Brown even though their beginnings were dif­ferent. Arthur Whitten Brown was born to American parents in Scotland, part of the United Kingdom. His family then moved to Manchester, where Alcock was raised. Trained as an electrical engineer, Brown became interested in aviation and joined the Royal Flying Corps early in World War I. Brown was shot down over Turkey in 1915 and he lived as a prisoner of war for two years.

An astronaut is a person who travels in space. The word astro­naut means “star traveler.” The Russians (who, as part of the Soviet Union, led the way in manned space­flight in the early 1960s) use the name cosmonaut for their space travelers.

Astronaut Profile

Almost all people who have traveled in space are trained to be professional astronauts. A few people fly as passen­gers, however, after a short period of preparation for spaceflight. Most of the first astronauts came from a military background, but astronauts today include civilian specialists in engineer­ing, space medicine, electronics, and other fields of science. Most astronauts today fly in the Space Shuttle or are sta­tioned aboard the International Space Station (ISS).

The United States and the former Soviet Union have sent more astronauts into space than any other nation. A number of other nations’ astronauts have flown on U. S. or Soviet missions. A few countries, such as China, have launched their own astronauts.

Astronauts must be well educated and physically fit. Many astronauts are experienced aviation pilots. During space training, they experience weight­lessness (being without gravity) to get used to conditions in space. Before every mission, the selected crew of astronauts and their backup crew practice the tasks

TYPES OF ASTRONAUT

Space Shuttle astronauts are desig­nated in one of three categories: pilots, mission specialists, or payload specialists. Pilots are highly trained flight professionals with jet aircraft experience who are in charge of the spacecraft. They operate and navi­gate the spacecraft and keep its occupants safe. A mission specialist carries out tasks and operates onboard equipment. Mission special­ists, for example, will use robotic arms or even leave a spacecraft to perform repairs. They take care of any payload, such as scientific equipment, that is being taken into space. Payload specialists are usually scientists rather than professional astronauts, and they are in space to perform a particular experiment or task.

that will be carried out in space. This training often takes place in simulators that use computerized virtual displays to give astronauts some experi­ence handling situations that might occur during a spaceflight. Trainee astronauts also work inside a full-size model of their spacecraft to familiarize themselves with its layout and fea­tures. When fully trained, an astronaut may have to wait a long time before being assigned to a mission.

There are world and national champion­ships for both hot air and gas balloons. Like airplane pilots, balloon pilots in the United States must be licensed by the Federal Aviation Administration.

In 1978, Ben Abruzzo of the United States and two companions made the first flight in a balloon across the Atlantic Ocean, in the helium balloon Double Eagle II. In 1981, Abruzzo also became the first balloon pilot to fly the Pacific Ocean, in his Double Eagle V.

The Pacific crossing of 5,768 miles (9,310 kilometers) took 84 hours and 31 minutes. The first Atlantic crossing by a hot air balloon was made in 1987, by Richard Branson of Britain and Per Lindstrand of Sweden. They also made the first trans-Pacific flight in a hot air balloon, in 1991.

The first balloonists to circle Earth were Bertrand Piccard of Switzerland and Brian Jones of Britain. They made the record-breaking flight of 26,602 miles (42,802 kilometers) between March 1 and March 20, 1999, in their balloon Breitling Orbiter III.

SEE ALSO:

• Airship • Montgolfier, Jacques-

Etienne and Joseph-Michel

• Parachute

Gliding uses less energy than flapping. The bird stretches its wings and coasts through the air, as gulls do when return­ing to their cliff-top roosts at sunset. Gliding birds can also soar (rise high) by seeking out rising currents of air, or thermals. Vultures using thermals circle effortlessly for hours at a time, and they can soar very high-one African vulture collided with an airplane at 37,000 feet (11,280 meters). Birds soar, too, on uplifts of air pushed up by a hillside or cliff or formed where blocks of warm and cold air meet.

Seabirds, such as gulls, make use of the different wind speeds in the air above the ocean. Over the sea, wind speed is reduced close to the water because of friction with the waves. The fastest wind speeds are usually between 50 and 100 feet (15 and 30 meters) above the waves. Some seabirds, such as fulmars, use these faster-moving winds to pick up speed and then glide down with the wind behind them to skim low above the water. Their momentum takes them up again into the wind. For such maneuvers, long wings provide stability as well as high speed.

Hovering

Some birds can hover in the air, using their wings and tail to maintain posi­tion. They hover usually to feed or spot prey below. Kestrels and terns can do this, but the hovering champion is the hummingbird, which not only hovers, but is the only bird able to fly backward.

Hummingbirds hover by beating their wings backward and forward so fast that they produce lift without propulsion. In this way, the bird stays in one place when feeding from flowers. Kestrels use a slightly different hovering technique. This bird flies into the wind at exactly the same speed as the wind, so that one force balances the other.