Category FLIGHT and M ОТІOIM

Glenn made history one more time. After he announced his retirement from politics, Glenn was asked by NASA if he would like to go into space one more time, on a Space Shuttle mission. The gesture was made partly to honor him and partly to study the effects of space­flight on older people—Glenn was in his seventies at the time. Glenn jumped at the chance to join the mission.

On October 29, 1998, Glenn left Earth once again. It was almost thirty-seven years since his first flight. Things had changed. This time, he was on board the Space Shuttle Discovery and had six crewmates instead of being the lone astronaut. The flight took more than nine days, whereas his previous flight

INSPIRATION FOR THE FUTURE

"The most important thing we can do is inspire young minds and to advance the kind of science, math, and technology education that will help youngsters take us to the next phase of space travel."

John Glenn, speaking as spokesperson for National Space Day, 2000

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had lasted just over 4 hours. For Glenn, going into space again was an enormous thrill.

After the flight, Glenn retired from public life. He and his wife Annie settled back in Ohio. Both served on the board of trustees at Muskingum College, where they had studied so many years before. Glenn opened a center at Ohio State University to encourage young people to start careers in public service.

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SEE ALSO:

• Astronaut • NASA • Pilot

• Spaceflight • Space Race

• Supersonic Flight

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Hang gliders can fly at speeds of up to 90 miles per hour (145 kilometers per hour), and they can encounter some rough weather conditions. They also can be tricky to fly. For these reasons, trainee pilots learn basic hang gliding skills on the ground and during brief “hops” into the air. Pilots in training will often

О A well-positioned platform sticking out from a hill also makes a good launching pad for a hang glider.

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PARAGLIDERS

A paraglider flies in a way similar to a hang glider. The difference is that a paraglider looks more like a parachute and has no rigid frame. The pilot sits in a seat harness

suspended beneath the canopy. The term paraglider was first used by aviation scien­tists in the 1960s. The sport paraglider was developed in the 1970s by French enthusi­asts, who were inspired by new, advanced parachute designs. French pilots made paragliding popular, and France still has the largest number of paragliders.

The paraglider is easy to pack and light enough to be carried, which is useful when a flight ends with the pilot landing miles away from the takeoff area. The paraglider trainee can learn most skills in the air.

The aircraft is easy to launch and fly in light winds, but it does not glide as well as a hang glider. For this reason, it usually cannot fly such long distances, although some paragliders have flown as far as 250 miles (400 kilometers).

fly tandem (two at a time) with an expe­rienced instructor.

The United States Hang Gliding Association provides licenses to hang glider pilots. This official body also issues certificates to instructors and enforces safety regulations that all pilots are expected to observe. Hang gliding is often thought to be a risky sport by peo­ple not involved in it. Although modern materials are both light and strong, a hang glider is a flimsy airplane that is
easily damaged. Accidents can happen, often as a result of unpredictable wind currents or weather changes. Hang glid­er pilots can carry a parachute in their harnesses for emergencies.

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SEE ALSO:

• Air and Atmosphere • Bird

• Glider • Global Positioning System

• Lilienthal, Otto • Wing

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Hubble’s precision optics make the most of its unique location beyond Earth’s atmosphere. The atmosphere, the blanket of gases that makes life possible on our

planet, is a hindrance to astronomy. By orbiting in space, above the gases, Hubble gets a much clearer view of the universe. Hubble also can be aimed very accurately to study a specific target, such as a star billions of miles away.

Right after its launch, engineers dis­covered there was something wrong with the telescope. There was a flaw in the optics of the main (primary) mirror. As a result of the flaw, the images Hubble received were not as clear as sci­entists had hoped. The cause of the problem was that the primary mirror had been ground to the wrong shape, in spite

of the care that had been taken to make it accurate. It was too flat at the edges by a microscopic amount, but this was enough to produce what scientists called “severe spherical aberration.” Light reflecting from the edge of the mirror was focused on a different point than the light reflecting off its center, so the picture was blurred.

A Space Shuttle flight in 1993 solved this problem. Astronauts fitted a com­
plex pack of five pairs of smaller mirrors to correct the aberration in the main mirror. It was like fitting a new lens in a person’s eyeglasses to sharpen his or her eyesight. It worked, and Hubble started to send back to Earth astounding images of the distant universe. In 1994, the space telescope was able to send back sharp images of Jupiter during the plan­et’s collision with a comet named Shoemaker-Levy 9, an event that hap­pens only once every few hundred years.

The views from space are stunning, but astronauts live in cramped accommoda­tion. There are two small crew cabins— each is only big enough for one person. Each cabin contains a sleeping bag and has a large window through which the occupant can enjoy the view of Earth while off duty. In space, there is no up or down and no gravity. The weightless astronauts on the ISS can sleep right way up or upside down as they wish.

Space station crews usually bed down inside the sleeping bag. If all three ISS astronauts are sleeping, the third member of the crew can sleep anywhere, as long as the sleep­ing bag is fastened to the floor or wall

О Cosmonaut Gennady Padalka, commander of ISS Expedition Nine, juggles with fruit in the Zvezda service module.

of the crew compartment. No one wants to float around while they are asleep.

Astronauts onboard the space station get into a routine of an 8-hour sleep period at the end of each mission day. Some astronauts report difficulty in sleeping, either because of excitement during the first days of a mission or due to the space sickness that some people suffer. As a space vehicle moves in Earth orbit, the Sun rises about every 90 min­utes! Glaring sunlight shining through a window can disturb sleepers unless they wear a sleep mask.

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Newton’s third law of motion is often stated as, “To every action there is an equal and opposite reaction.” This means that when one object applies a force (the action) to a second object, the second object pushes back in the oppo­site direction with the same force (the reaction). When a rocket stands on its launch pad, for example, its weight
(the action) pushes down on the launch pad. The launch pad pushes up against the rocket with an equal and opposite force (the reaction).

Action-reaction forces should not be confused with the forces that make objects accelerate. Action-reaction forces are always equal and opposite. Whether or not an object accelerates depends on the forces acting only on that object.

The example of a rocket can be used again to illustrate this law. When a rock­et standing on a launch pad fires its engine, the jet of gas from the engine pushes up against the rocket (action), and the rocket pushes down against the gas with equal force (reaction). These forces are equal and opposite, but whether or not the rocket takes off depends on the forces acting only on the rocket itself.

Momentum is a property of all moving objects. It is equal to the mass of an object multiplied by its velocity. The more mass an object has and the faster it moves, the more momentum it has. A heavy airliner has more momentum than a small fighter plane flying at the same speed because the airliner has more mass. In addition, a plane flying at 1,000 miles per hour (1,600 kilometers per hour) has twice the momentum of the same plane fly­ing at 500 miles per hour (800 kilome­ters per hour).

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Planet’s Orbit

О Kepler’s first law stated that a planet’s orbit follows the shape of an ellipse with the Sun at one focus. Most planets have regular, almost circular orbits, but some comet orbits form very "eccentric" ellipses, as shown here.

The force of gravity pulls the rocket down, and the thrust of its engine push­es it up. If the thrust upward is greater than the force of gravity acting on the rocket, the resultant downward force will make the rocket accelerate upward.

microlight is a very light, pow­ered aircraft used for recreation­al flying. Some microlights look like regular light airplanes, but smaller. Others resemble a kite or flying wing with an engine. There are even micro­light amphibians and floatplanes (or seaplanes) that can land on water.

Certain types of microlight aircraft are known as ultralights. In the United States, an ultralight is defined as a single­seat microlight airplane that weighs less than 235 pounds (107 kilograms) when empty and has a top speed of 63 miles per hour (101 kilometers per hour). An ultralight is permitted to fly only during daylight hours and over unpopulated areas of the country.

Slightly heavier, faster microlight aircraft are known as light-sport air­planes, a category introduced by the

U. S. Federal Aviation Administration (FAA) in 2004. Another term sometimes used to describe microlights is recre­ational aircraft.

Building Microlights

Lightweight sports flying became popu­lar in the 1970s, a time when a growing number of people were interested in fly­ing for fun and at low cost. Hang gliders also became popular around this time. It was a fairly simple task to fit a small engine and propeller to a hang glider frame to make a powered aircraft that was fun to fly and for which no pilot’s license was required.

Most microlights are now made by specialty companies, but many have been constructed by individuals who get pleasure from designing and building airplanes. People who build aircraft at home recapture some of the pioneering excitement of the early days of aviation in the early 1900s, when people built planes powered by motorcycle engines.

Older homemade microlights were built from plywood and spruce, covered with cotton fabric. Today, even amateur aircraft builders are more likely to use aluminum for the frame and dacron for the fabric. Some microlights are made of strong, lightweight composite materials, such as an epoxy resin coating contain­ing glass or carbon fiber molded over a plastic-foam body. There are many dif­ferent designs. Experts have said that it would be very difficult to design a new microlight in a way that has not already been tried.

О Building microlights is a popular pas­time. Some microlights, such as this one, are scaled-down, lightweight replicas of vintage military airplanes.

Dates of birth: Joseph-Michel: August 26, 1740; Jacques-Etienne: January 6, 1745. Places of birth: Joseph-Michel: Blaruc-les-Bains, France; Jacques-Etienne: Annonay, France.

Died: Joseph-Michel: June 26, 1810; Jacques-Etienne: August 2, 1799.

Major contributions: Invented the first successful lighter-than-air balloon; carried out first flight of a manned balloon. Awards: Order of Saint Michel.

he Montgolfier brothers were the sons of a prosperous paper manu­facturer from southern France.

Joseph-Michel was interested in science and had few business skills. Jacques – Etienne was trained to take over the family business.

During the early 1780s, Joseph – Michel noticed that a piece of paper rose in the hot air of a chimney. He started thinking about building a device that could use this effect to rise into the sky. Joseph-Michel built a small box of light­weight wood and covered it with fabric. He placed a wad of paper underneath the container and set the paper on fire. The container rose in the air until it hit the ceiling.

Joseph-Michel showed this discovery to his brother, and they began experi­menting. In December 1782 the Montgolfiers built a larger container and tested it outside. The object rose nearly 70 feet (21 meters) on heated air and stayed aloft for a minute or so. The Montgolfier brothers went on to have more successful experiments. They built two larger globe-shaped containers held down by long ropes. The globes rose when heated, although they did not fly because of the ropes.

The Montgolfiers then prepared a large balloon to show the public their invention. They made a sphere out of tough sackcloth, covered it with four fabric panels held together by buttons, and surrounded the entire structure with netting to keep everything in place. On June 4, 1783, the Montgolfiers brought their invention to a square in their hometown of Annonay and lit a fire underneath the balloon. As a crowd

О On September 19, 1783, the Montgolfier balloon rose over the French royal palace of Versailles, watched by the king and queen and a large crowd of spectators.

watched in amazement, the balloon rose. The brothers estimated that it reached 6,000 feet (1.8 kilometers). Carried by the wind, it traveled about 1.2 miles (2 kilo­meters) before coming back to land.

The Montgolfiers took their discovery to Paris, where Jacques-Etienne demon­strated another balloon for members of the Academy of Sciences in mid – September 1783. King Louis XVI and Queen Marie Antoinette asked to see the invention for themselves. Accordingly, on September 19, 1783, Jacques-Etienne sent another balloon aloft. This time he attached a basket that carried a sheep, a rooster, and a duck. The balloon rose and floated on air for nearly 10 minutes, landing more than 1 mile (1.6 kilome­ters) away.

The first person to reach the balloon after it landed was a physician, Jean – Frangois Pilatre de Rozier. Excited, he volunteered to go aloft. During the next few weeks, Jacques-Etienne built a bal­loon that measured 75 feet (23 meters) high and 46 feet (14 meters) across. It had a basket with a container that could hold and sustain a fire to keep the bal­loon aloft. The brothers tested it several
times with Jacques-Etienne or de Rozier. on board but with the balloon held down by ropes. Then, on November 1, 1783, de Rozier and a French army major entered the basket and lit the fire. Once the bal­loon was cut loose, it rose into the air. They cruised for 25 minutes, traveling about 5 miles (8 kilometers) over Paris.

The brothers continued experiment­ing. On January 19, 1784, Joseph – Michel went aloft along with de Rozier and five others. Thereafter, the Montgolfiers abandoned balloons and devoted themselves to other work. Joseph-Michel tinkered with some experiments not connected to flying. Jacques-Etienne returned to papermak­ing and invented a method for making vellum, a strong kind of paper.

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SEE ALSO:

• Aerodynamics • Aeronautics

• Balloon

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Date of birth: December 25, 1642. Place of birth: Woolsthorpe, England. Died: March 20, 1727.

Major contribution: First formulated the idea of gravity; expressed three key laws of motion; invented calculus, a branch of mathematics.

Awards: Named a Fellow and later President of the Royal Society; Order of Knighthood.

saac Newton had a difficult child­hood. His father died a few months before he was born. Newton was a sickly child who was not expected to live. When Newton was two, his mother remarried, and his stepfather sent him away to live with other relatives. Only when the stepfather died was Newton reunited with his mother.

Newton began studying at Trinity College, Cambridge, England, in 1661. He dedicated himself to new, emerging ideas in science and mathematics. Much of his study of the new science was done on his own and appeared only in his private notebooks. In 1665 Newton graduated from Trinity College and over the next two years, he reached conclusions that formed the basis of his later work.

In 1667, Newton returned to Cambridge as a professor. Using a pair of prisms, he broke white light into its different colors-those we see in a rainbow. Through this work, Newton proved that light is not a simple structure but a complex one. He also began to develop the

О Isaac Newton is one of the most important scientific figures in the history of the world. His view of physics prevailed until they were modified by Albert Einstein’s ideas in the early 1900s.

ideas that would become calculus, an advanced form of mathematics that makes it possible to describe the move­ments of objects.

Newton began to think about the orbit of objects around planets. He wrote an essay called On Motion in 1684 and expanded his ideas three years later in his masterwork Philosophiae Naturalis Principia Mathematica. With this work Newton established his three laws of motion and his theory of universal gravitation. Newton’s ideas gained wide acceptance fairly quickly, and his theories are the basis of much of modern physics.

In 1696 Newton was named Warden of the Royal Mint, which oversees the making of coins. He kept his professor­ship at Cambridge for a few more years, but most of his later life was spent in London. In 1704, Newton finally pub­lished a work about sight, light, and color entitled Opticks.

Although he did little new work in later years, Newton remained an impor­tant figure in the sciences. He became President of the Royal Society in 1703. In that role he helped sponsor the work of younger scientists who quickly rose to dominate the scientific community in England, further helping to spread Newton’s ideas. Two years later, Newton became the first scientist ever to be knighted by a British monarch.

Newton’s later life was marred by a major controversy. He had devised the basics of calculus back in the 1660s but had never published a detailed

NEWTON’S CANNON

Hundreds of years before it actually happened, Newton understood that a human-made object could orbit Earth, just as the Moon did. Imagine, he said, a mountain so tall that it extended above Earth’s atmosphere. Now imagine placing a cannon atop the mountain’s peak and firing a cannonball on a hori­zontal path. A powerful enough cannon could fire the ball so fast that it would never fall. At the same time, gravity would bend its path toward Earth. Never falling and never escaping Earth’s gravity, Newton theorized, the cannonball would orbit the planet indefinitely.

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description. In 1684, the German math­ematician Gottfried Wilhelm Leibniz published his work on calculus and gained renown as the inventor of a new system. Newton began a running battle with Leibniz that was carried out in print. Both men tarnished their names with their bitter attacks on one another. Newton died at the age of eighty-four.

SEE ALSO:

• Gravity • Laws of Motion

• Momentum • Satellite

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itch, roll, and yaw are the three ways in which aircraft and space­craft can change their direction of flight. Pitch, roll, and yaw are rotations. When something rotates, it turns around an imaginary line called an axis.

Defining Pitch, Roll, and Yaw

Imagine an airplane with a stick pushed through it from nose to tail, so the plane can spin on the stick. This type of rota­tion is called roll, and the stick is the roll axis. A stick pushed through a plane from wingtip to wingtip is the pitch axis. A stick pushed through a plane from top to bottom is the yaw axis. The position, or angle, of an aircraft-the amount of pitch, roll, and yaw it has-is called its attitude. In a standard airplane, the pilot generally can change the plane’s atti­tude by operating controls that move the elevators, ailerons, and rudder.

Changing an airplane’s pitch makes its nose tip up or down. The pilot changes the pitch by using the control stick to tilt the elevators, which are at the back of the tail. Pulling the stick back tilts the elevators up. Air flowing over them pushes the plane’s tail down and raises its nose. Pushing the stick for­ward has the opposite effect.

Rolling, or banking an aircraft to one side, enables it to turn. When it rolls, the lift produced by the wings tilts to one side instead of acting straight upward. The sideways part of the lift pulls the plane into a turn. A pilot makes a plane roll by pushing the control stick to one side or (on a larger airplane) turning the yoke on top of the control column. This control moves the ailerons, which are at the back of the wings. When the

О The B-2 Spirit Bomber (along with other flying wing aircraft) has elevons (circled) at the back of its wings that function as combined ailerons and elevators.

aileron on one wing tilts down, the wing rises. The aileron on the other wing tilts up, and the wing sinks.

Yaw is the name for the motion when a plane’s nose turns to the left or right.

Yaw is controlled by a rud­der, which is mounted on an airplane’s tailfin. The rudder is operated by a pair of foot pedals. Turning the rudder to one side pushes the plane’s tail to the opposite side and swings the nose around. When a plane rolls into a turn, the pilot also adjusts its pitch and yaw to keep the plane’s nose pointing in the right direction.

n the early 1900s Albert Einstein (1879-1955) produced two theories that caused a revolution in science. Together, they are known as the theory of relativity.

The first of Einstein’s relativity theo­ries is his Special Theory of Relativity of 1905. This states that:

(1) The laws of physics are the same for people moving at different speeds.

(2) The speed of light is always the same for all observers, no matter how fast they are moving.

These two simple principles produce some surprising effects when speeds close to the speed of light are involved.

There is no such thing as absolute rest anywhere in the universe. Someone standing still on Earth is actually moving because Earth is spinning. The planet also is orbiting the Sun. The Sun orbits the center of the Milky Way (our

galaxy), and the Milky Way moves through space among billions of other galaxies that also are moving. Any observer can say that he or she is at rest and everything else in the universe is moving in relation to—or relative to— him or her. This phenomenon gives relativity its name.

One of the most surprising effects of relativity is that times and lengths depend on who measures them. Imagine that one person stays on Earth while her twin goes on a long spaceflight almost as fast as the speed of light. The person on Earth would see the spacecraft become shorter as it accelerates toward the speed of light. This is called Lorentz contraction. Also, time runs more slow­ly as speed increases. When the astro­naut twin returns to Earth, she would be younger than her earthbound twin. This is known as the “twins paradox.”

The Special Theory of Relativity also predicts that as something goes faster, it becomes more and more difficult to make it go even faster. The more energy it has, the more inertia it has. Einstein also showed that energy

О The twins paradox illustrates Einstein’s theory that if two bodies at the same point accelerate to different speeds and then meet again, they will find that a different amount of time has elapsed for each of them.

and mass are linked. He produced his famous equation, E=mc2, to show how they are related. In this equation, “c” is the speed of light, a huge number, so even a tiny mass (m) is equivalent to an enormous amount of energy (E).

In 1915, Einstein produced a new theory, his General Theory of Relativity, which added the effect of gravity to the Special Theory. Nobody had been able to explain how gravity works. Einstein imagined that space is flat and all objects dent it, like heavy weights sitting on a stretchy sheet. In other words, mass bends space. The paths of moving objects curve toward massive objects, simply because space itself is curved there. Light also is bent by curved space.

Global Positioning System (GPS) navigation satellites fly around the world at 7,000 miles per hour (11,300 kilometers per hour). According to special relativity, their onboard clocks should run more slowly than clocks run on Earth. According to general relativity, the curving of space caused by Earth has the opposite effect. It makes the clocks run faster than clocks on Earth. The result of these two coun­teracting effects is that the satellite clocks run 38-millionths of a second faster every day than clocks on Earth. It is a tiny error, but GPS clocks have to be more than 1,000 times more accurate than this. So satellite clocks are deliberately set to run slow before they are launched, so that they are correct in orbit.

Relativity is not just a strange set of ideas and mathematics. Its effects are real. Observations and experiments have confirmed many of its predictions. Spacecraft designers and planners of space missions have to allow for them.

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SEE ALSO:

• Einstein, Albert • Global Positioning System • Spaceflight

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