Category FLIGHT and M ОТІOIM

In 1947, a WAC-Corporal rocket reached a height of 244 miles (390 kilometers) above the White Sands testing ground in New Mexico. This flight opened the door to space-and encouraged government interest-because it showed that rocket technology could now launch satellites. Ten years later, the Russians launched Sputnik 1, the first artificial satellite. So began the space race between the United States and the Soviet Union. Key figures
in the two rival space programs were Robert Gilruth (1913-2000), appointed to direct the U. S. Mercury astronaut pro­gram in 1958, and Sergei Korolyov (1906-1966), who led the Soviet design team behind the Sputnik program.

Spaceflight was front-page news through the 1960s as the United States and the Soviet Union competed to send astronauts into orbit and probes to the planets. Public interest in space reached a peak during the Apollo Moon landings (1969-1972).

Since the 1970s, spaceflight has developed as a multinational scientific activity and a commercial business.

LIFE BEYOND EARTH

The Planetary Society was founded in 1980 by Carl Sagan, Bruce Murray, and Louis Friedman. Its aim is to "inspire and involve the world’s public in space exploration" and to search for extraterrestrial life (life beyond Earth). A worldwide program known as SETI (Searching for Extra-Terrestrial Intelligence) aims to collect evidence of life on other worlds through detecting radio signals and other forms of transmissions. Currently, Earth is the only planet known to support life, although scientists spec­ulate that life could exist on Earth – type planets orbiting other stars.

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Most satellite launches, for example, are intended for communications and entertainment, such as TV broadcasting. Spaceflight has become almost routine, although tragedies-such as the losses of two U. S. Space Shuttles, Challenger in 1986 and Columbia in 2003-reminded people just how dangerous space can be. Robot space probes have made astonishing voyages, not only to planets but far beyond our solar system. In 1990, NASA’s Voyager 1 probe took a photograph of Earth from a distance of 4 billion miles (6.5 billion kilometers) more than twelve years after it set out on a voyage through space that may well last hundreds of years.

Since the end of the Apollo program in the early 1970s, the most significant manned spacecraft has been the U. S. Space Shuttle. First launched in 1981, the Space Shuttle flies regularly into orbit, delivering supplies to the International Space Station.

The future of spaceflight will proba­bly see a return of astronauts to the Moon and possibly a manned explo­ration trip to Mars. A lunar base might be in existence before the middle of the twenty-first century, and the discovery of water on Mars could even make a Martian colony a possibility.

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SEE ALSO:

• Apollo Program • Astronaut

• Future of Spaceflight • Rocket

• Satellite • Space Probe

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space probe is a robot spacecraft sent far into space. To probe means to investigate, and that is what space probes do. Scientists have sent space probes to the Moon, to the planets, and beyond the solar system into deep space. A probe equipped with sensors, cameras, computers, and a radio transmitter can-within a few hours-discover more about a distant planet than has been gathered in cen­turies of Earth-based astronomy.

A robot space probe needs no air, water, or fuel during its journey through space. Its power comes from tiny nuclear plants or from solar cells that convert sunlight to electrical energy. Once set on its course, a probe can con­tinue to travel through space for years, sending images and data back to Earth.

Flyby probes pass close to their tar – get-a planet, a comet, or an asteroid. Orbital probes go into orbit around a planet or the Sun. Landers descend through the atmosphere to the surface.

Spacelab was a reusable laboratory designed for the Space Shuttle. It allowed scientists to perform experi­ments while orbiting Earth. The labora­tory, mounted inside the Space Shuttle’s cargo bay, was used on many missions. Many experiments tested the effects of weightlessness and space on living things. Spacelab missions have included life science experiments involving human astronauts as well as animals taken into space for scientific research. On April 17, 1998, more than 2,000 living creatures joined the seven crew members of the Space Shuttle Columbia (STS-90) for a sixteen-day mission called Neurolab. During the mission, twenty – six experiments focused on studies of the nervous system and how it develops and functions in space. Test subjects included crew members as well as rats, mice, crickets, snails, and fish. This was Spacelab’s last scheduled flight.

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Shuttle Missions

On a standard mission, the crew com­prises five to seven members. It includes a commander, a pilot, payload special­ists, and mission specialists. The special­ists could be engineers in charge of a piece of equipment or scientists con­ducting experiments. On a rescue mis­sion, a Space Shuttle could be flown by three astronauts to bring back all seven crew members from another Space Shuttle that was in trouble.

The Space Shuttle can be used to launch satellites, to repair faulty equip­ment, to transport supplies and crew to space stations, and to perform experi­ments in space. Its cargo bay can hold up to five satellites. A satellite that needs to be placed in a high orbit above the Space Shuttle’s maximum operating altitude of 400 miles (640 kilometers) is boosted by a small rocket motor. The cargo bay also can carry a space labora­tory, inside which scientists can work comfortably.

The Space Shuttle has performed many significant missions. Scientific experiments performed on board have increased knowledge about space travel, microgravity, and how these affect humans and other living things. Space Shuttles have transported satellites into space, transforming our ability to com­municate and broadcast information. The Space Shuttle is used to carry com­ponents and crew to the International Space Station. Space Shuttle missions have installed, maintained, rescued, and repaired numerous space facilities,

mostly notably the Hubble Space Telescope, which the Shuttle carried into space in 1990.

stall is a sudden loss of lift that can be experienced by an air­craft in some circumstances. Pilots are trained to understand why a stall can happen, how to recognize the early signs of a stall, and how to recov­er from a stall if one occurs.

How It Happens

When a fixed-wing aircraft slows down, the speed of the air flowing over its wings decreases, and the wings produce

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Separated (turbulent) flow

less lift. While flying slowly, the pilot can increase lift by raising the plane’s nose. As the wings tip up, they produce more lift and more drag. The angle of tilt of a wing is called its angle of attack. If the pilot keeps raising a plane’s nose, the angle of attack becomes so great that the air flowing smoothly over the wings suddenly breaks away from them and changes into turbulent, swirling flow. This angle is called the critical angle of attack. When the smooth airflow over the wing breaks down, lift is suddenly lost, and the aircraft drops downward. If one wing stalls before the other, the plane may roll into a spin.

Stall also affects helicopters. When a helicopter’s main rotor spins, the blades moving in the same direction as the air­craft are called the advancing blades, and the blades traveling in the opposite direction are called the retreating blades. Air flows over the advancing blades faster than it flows over the retreating blades, so the advancing blades experi­ence greater lift. If the airflow over the retreating blades is slow enough, they can stall. The helicopter experiences a sudden loss of lift called a retreating blade stall, but only on one side. The advancing blades still produce lift, so the helicopter rolls over to one side.

Recovering from a Stall

A pilot can recover from a stall in two ways. Pushing the control stick forward lowers a plane’s nose, so that it dives and picks up speed. Air flows smoothly over the wing again, and lift returns.

When a piston engine stops unex­pectedly, it is said to have stalled, but this is completely different from the aerodynamic stall that happens to wings. If a piston engine in an air­craft stalls, the plane does not drop like a stone. It becomes a glider. As it glides down, the pilot can look for a suitable landing spot while trying to restart the engine.

Jet engines can suffer from a problem called compressor stall. The spinning compressor blades inside the engine work like small wings.

Just like wings, they can stall. If the smooth airflow entering a jet engine is disturbed, the compressor blades may stall. A common cause of com­pressor stall is a bird strike, when a bird is sucked into an engine. When a compressor stall happens, the engine makes a loud bang and loses thrust, and the aircraft turns toward the affected side.

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The pilot then can raise the nose and fly straight and level again. The other way to recover from a stall is to increase engine power. When a stalled aircraft accelerates, it lowers its nose, and smooth airflow over its wings is restored. The two methods can be used together. A stall-as well as the recovery

from it-always causes some loss of alti­tude, so a stall near the ground can be particularly dangerous.

Large aircraft are equipped with sys­tems that sense when a stall is about to happen. They warn the pilot by shaking the control stick and sounding a warn­ing. If the pilot does nothing, the system may push the control stick forward to automatically lower the plane’s nose.

A helicopter’s tail has no rudder or elevators. Its main rotor controls alti­tude, so elevators are not needed. Its tail rotor controls yaw, so a rudder is not needed either. The sideways thrust of the tail rotor stops the helicopter from spin­ning in the opposite direction to the main rotor. Increasing or decreasing the tail rotor thrust makes the helicopter turn, or yaw.

Not all helicopters have a tail rotor. A NOTAR (short for NO TAil Rotor) heli­copter has a jet thruster at the end of its
tail boom. It blows air out of a slot in the side of the boom. Some helicopters do not have a tail at all. These helicopters have two main rotors instead of one, and the two rotors spin in opposite directions. The turning forces they apply to the helicopter are equal and opposite. No overall turning force, or torque, is applied to the helicopter, and so no tail rotor or thruster is needed.

If an object with a mass of 132 pounds (60 kilograms) is weighed, the scales show a weight of 132 pounds (60 kilograms). If the same object is taken to the Moon and weighed there, it weighs only

О Gravity is weaker on the Moon than on Earth because the Moon is smaller and has less mass. Astronauts on Apollo missions set up scientific experiments on the Moon to find out about its force of gravity and other aspects of its environment.

22 pounds (10 kilograms), because the Moon’s gravity is only one-sixth the strength of Earth’s gravity. However, the object’s mass has not changed. It is still 132 pounds (60 kilograms).

The pound mass and the pound of weight, or pound-force, are therefore different. The pound mass never changes, but the weight of the pound mass depends on the strength of gravity acting upon it. In the metric system, the unit of mass is the kilogram, and the unit of force is the newton. Gravity acts on a mass of 1 kilogram with a force of 9.8 newtons. So, a 1-kilogram mass actually weighs 9.8 newtons. It is impor­tant to know the weight of an aircraft or rocket because it shows how much lift it must generate to take off.

WEIGHTLESSNESS

The strength of Earth’s gravity weak­ens with distance. The farther that something is from the center of Earth, the weaker the force of gravi­ty it experiences, and so it weighs less. This means that airline passen­gers and astronauts in space weigh less the higher they go.

This does not explain why astro­nauts are able to float about in space. Astronauts are weightless not because the force of gravity has fall­en to zero where they are. In fact, the force of gravity acting on astronauts in Earth orbit is just a fraction less than the force of gravity at Earth’s surface. Orbiting astronauts float about because they are in a state of free fall, like skydivers.

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Pilots and generals soon realized that planes could do more than just fly over the battlefield firing at one another. They also could drop bombs. The first air bombs were little bigger than grenades and were dropped by hand. Bombs, with fins to stabilize them as they fell, grew steadily bigger: from 10 pounds (4.5 kilograms) in 1914 to 1,600 pounds (726 kilograms) in 1918. Bombs were carried in racks and were dropped using bomb – sights that took into account the plane’s height and speed.

At first, bombs were dropped on military tar­gets only, but in 1915 German Zeppelin airships began bombing London and other British cities.

О Handley Page two-engine bombers were used to fly long distances and attack German ground targets and warships.

These bombings were the first air raids on civilians. The Zeppelins scared many people, but the giant aircraft were vulnerable to fighter planes once they were intercepted. Their size made them an easy target for machine guns.

Some news reports about the flight appeared, but the details were often wrong. The Wrights issued a statement but gave few details, hoping to protect their work. They already were planning a better machine.

In the spring of 1904, the Wrights launched a model named the Flyer II near Dayton. They made many flights that summer, becoming more skilled at piloting. On September 20, 1904, Wilbur had a spectacular flight. He traveled more than 3 miles (4.8 kilometers), made circles in the air, and stayed aloft for more than 1/2 minutes.

The following year, the brothers flew another new model. On October 5, 1905, the Flyer III covered more than 24 miles (39 kilometers) and was airborne for nearly 40 minutes. It would be a further three years before a European matched these achievements.

О This is the telegram that arrived in the Wright brothers’ family home in Dayton, Ohio, announcing the first successful powered flight on December 17, 1903.

Most probes are launched by a multi­stage rocket from the ground. There are three ways to send spacecraft into space using a rocket: sounding trajectory, Earth orbit, and Earth escape.

Sounding rockets were often fired into space during the 1940s and 1950s and are still used today. A sounding rocket can be fired to an altitude of about 100 miles (160 kilometers), at a

HIGH-SPEED LAUNCH

The fastest space launches have all involved space probes. In 1972 NASA’s Pioneer 10 was launched toward Jupiter at 32,400 miles per hour (52,130 kilo­meters per hour). In 1990, the probe Ulysses, on a mission to study the Sun, reached 34,450 miles per hour (55,430 kilometers per hour) during launch. New Horizons, launched in 2006 toward Pluto, was boosted to 35,800 miles per hour (57,600 kilometers per hour), as it left Earth’s orbit for deep space.

О A NASA sounding rocket is fired in 1988. Sounding rockets only reach the fringes of space, but they offer an inexpensive way of gathering data.

maximum speed of about 5,000 miles per hour (8,050 kilometers per hour). After its engine burns out, the rocket begins its descent back to Earth. Scientific instruments in the nose of the sounding rocket send information to the ground by telemetry (radio) or may be retrieved by parachute.

To enter Earth orbit, a rocket trajec­tory must be at an angle so that it flies parallel to Earth’s surface. When its booster motors cut out, the top­most stage of the rocket must be going fast enough to enter orbit and not fall back to the ground under the pull of Earth’s gravity.

To escape completely from Earth’s gravity and become a planetary probe, a spacecraft must reach a velocity of around 25,000 miles per hour (40,200 kilometers per hour). It will then fly away from Earth, gradually slowing down. It may go into orbit around the Sun, or it may be attracted by the gravitational pull of a planet, such as Mars or Jupiter.

At the end of its orbital mission, the Space Shuttle comes back to land on Earth. During reentry, the craft adopts a nose-up angle, and heat-absorbent tiles on the spacecraft’s underside shield the crew from the intense heat. As it descends, the Space Shuttle switches to horizontal flight, dropping fast through the air toward the landing strip. With no engine power during landing, pilots have described the Space Shuttle during air flight as a “flying brick.” A Shuttle

SHUTTLE FACTS

• Most Space Shuttle missions last between five and sixteen days.

• The longest orbital mission to date was STS-80, which lasted 17.5 days in November 1996.

• Early missions carried two-person crews, but the usual crew is seven. The Space Shuttle has room for ten.

• More than 800 people have flown into space on Space Shuttles.

• Each Space Shuttle mission is given a number preceded by the letters STS, which stands for Space Transportation System.

• The energy released by the Space Shuttle’s three main engines is equivalent to the output of thirteen Hoover Dams.

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pilot has only one opportunity to land the spacecraft-because it has no engine power for landing, the craft cannot fly around for a second try. Space Shuttle landings are usually made at the Kennedy Space Center in Florida or at Edwards Air Force Base in California. At Kennedy Space Center, the Space Shuttle lands on a 2.8-mile (4.5-kilometer) run­way, one of the longest in the world.

tealth is the ability to move in secret. A stealth airplane is designed to fly unseen, evading detection by enemy radar. Stealth tech­nology uses a combination of design factors, including materials, engines, and shape. A stealth strike aircraft can attack its target without warning. It also can fly reconnaissance missions without being detected.

Early Research

The research for stealth airplanes began in the 1950s. Air defense radar was developed during World War II (1939-1945). By the 1950s, air defenses had progressed so rapidly that almost any airplane flying over hostile territory was likely to be detected by radar. It then could be tracked and shot down with missiles. This was the era of the Cold War, when the United States and the Soviet Union were engaged in an arms race, during which both countries built up weapons supplies and advanced their military technology. Both sides used espionage, including spyplanes, to discover the other’s secrets.

At first, American strategists hoped that a high-flying airplane such as the U-2, developed by the Lockheed Corp­oration’s Skunk Works design team, could evade detection. This theory was disproved in 1960 when a U-2 spy plane was shot down over the Soviet Union. Later, expensive projects-such as the XB-70 Valkyrie bomber-were canceled

when it was realized that such airplanes left a large “blip” on radar screens, mak­ing them easy targets for missiles. By the 1970s, surface-to-air (SAM) missiles had

become so effective that few airplanes could escape being targeted once spotted on enemy radar.

Scientists did not give up, however. All airplanes, especially metal planes with heat-emitting jet engines, leave a track, called a signature, on a radar screen. The answer to escaping detection appeared to lie in finding a way to “cloak” the plane, thereby making it invisible to radar. Engineers looked for ways of reducing an aircraft’s radar sig­nature so that it would leave a smaller blip or not show up at all.

Mathematicians came up with a com­puter program, called Echo, that was able to predict the radar signature left by different airplane shapes. Studies showed that a body shape made of flat panels, or facets, could take almost all the radar energy that was hitting it and radiate that energy away from the ground, making the airplane virtually invisible to defense radars. The trick was to design an airplane of this shape, somewhat like a flying diamond, that could fly fast enough and high enough to be effective.