Category FLIGHT and M ОТІOIM

Leaving Earth

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.

Leaving Earth

О Pioneer 10, launched in 1972, was the first spacecraft to fly through the asteroid belt that lies between Mars and Jupiter, into the outer regions of the solar system.

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.

Stealth

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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

Stealth

О After testing was completed, fifty-seven F-117s were made for the U. S. Air Force. Military planners were delighted with the plane’s ability to travel undetected and attack targets with pinpoint accuracy.

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.

Weight

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

WeightО 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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Later Efforts

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.

NASA Advances

The Soviet successes pushed the U. S. government into funding the $20 billion Apollo program that aimed to land

THE PRESIDENT’S CHALLENGE

"I believe this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the Moon and returning him safely to the Earth. No single space project. . . will be more exciting, or more impressive to mankind. . . and none will be so difficult or expensive to accomplish."

President John F. Kennedy addressing Congress, May 25, 1961

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NASA Advances

О The United States launched its first satellite, Explorer 1, on a Jupiter rocket at Cape Canaveral, Florida, in January 1958. The Soviets had launched their first satellite a few months before.

astronauts on the Moon before the end of the 1960s. NASA successes and failures, broadcast live on television and radio, were very public. Soviet flights were revealed only after a successful launch. The Soviets made more headlines with the first two-person spacecraft, the first woman astronaut, and the first space­walk. With the U. S. Gemini program, however, NASA demonstrated essential space techniques, such as docking. U. S. computer and ground-tracking systems also were far ahead of Soviet electronics at the time.

THE HUMAN COST OF THE SPACE RACE

There were human casualties of the space race. Three U. S. astronauts were killed in a fire in January 1967 when they were trapped in their capsule as it caught fire during testing. The men were Apollo 1 crewmen Virgil Grissom, Roger Chaffee, and Edward White. Soviet cosmonaut Vladimir Komarov was killed in Soyuz 1 in April 1967. Three other Soviet cosmonauts (Georgi Dobrovolski, Viktor Patsayev, Vladislav Volkov) died in Soyuz 11, in 1971.

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By the mid-1960s, manned space­flights attracted huge public interest. The promise of Apollo overshadowed scientific missions by robot probes to the planets Mars and Venus, which were launched by both the Soviet Union and the United States.

By 1969, the Americans had a rocket to match the Soviet boosters: the mighty Saturn V, built to send Apollo to the Moon. Each Apollo test flight aroused high public excitement. The world was watching when, on July 20, 1969, the Apollo 11 lunar lander touched down on the Moon, and Neil Armstrong radioed a message to Earth: “Houston, Tranquility Base here. The Eagle has landed.”

Synthetic Vision System

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synthetic vision system (SVS) provides pilots with a clear image of the view from their air­craft in all weathers, flying conditions, and visibility levels. A typical system is composed of databases of information that create a virtual reality display in the cockpit. The systems, still in develop­ment, are being created to help pilots fly more safely.

Developing a Solution to Poor Visibility

A pilot’s mental image of his or her plane moving in relation to the ground is called situational awareness. If the pilot’s mental image is not the same as what is actually happening in the real world, the pilot has lost situational awareness. When an aircraft is near the ground, or flying near other air traffic, loss of situational awareness can prove
to be deadly. It can cause a plane to fly into an obstacle or lead to a midair col­lision. It can make a fighter pilot delay ejecting from an aircraft, which can be fatal. If an aircraft flies into an obstacle, or water, while under control, this is called Controlled Flight into Terrain, or CFIT. In general aviation, CFIT is the leading cause of accidents.

Synthetic vision systems are being developed to give the pilot a clear view of the surrounding ground, no matter how bad the visibility is. The research and development work is being carried out jointly by four NASA establish­ments—Langley Research Center, Ames Research Center, Dryden Flight Center, and Glenn Research Center in partner­ship with the FAA (Federal Aviation Administration) and the aviation indus­try. The research aims to cut fatal acci­dents by 80 percent in ten years and by 90 percent in twenty-five years by mak­ing every flight as safe and easy as a flight on a clear, sunny day.

An SVS improves a pilot’s situation­al awareness by creating a three­dimensional (3D) image of the ground below. The image is not from a camera—it is generated from a computer database stored in the aircraft. The database uses

О Poor visibility is a common factor in air accidents. A pilot often cannot see the ground clearly because of low cloud, fog, rain, or darkness. In such conditions, it is possible to fly dangerously close to moun­tains or other obstacles.

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MEASURING EARTH’S SHAPE

The Space Shuttle Radar Topography Mission measured the shape of about 80 percent of Earth’s surface. It creat­ed an image of the ground below by using radar instead of light. Radar was used because it can see through clouds and make images at night. Two radar images of the same spot on the ground were taken every 100 feet (30 meters). The images were taken from slightly different points using two radar antennae. One was inside the Space Shuttle’s payload bay. The other was at the end of a 195-foot (59- meter) mast that extended from one side of the Space Shuttle. The differ­ences between the two images allowed the height of the ground to be calculated. This process is called inter­ferometry. The information allows a computer to generate a detailed map of Earth’s surface that shows the shape and height of the ground.

information that was collected by the Space Shuttle during the Space Shuttle Radar Topography Mission in 2000.

Creating Virtual Reality

The synthetic vision database does not just show Earth’s surface shape. It also contains details of obstacles such as bridges, towers, and pylons. A full-color

moving image appears on a flat panel display, like a computer screen, in the cockpit. The screen display looks like an image from a flight simulator computer game, but SVS is much more advanced than a game. It generates a 3D view of the ground in real time. As a plane flies along, GPS satellite navigation tells the synthetic vision system where it is. The image of the ground moves past just like the real view from the plane’s window, but the SVS image is always bright and clear whatever the weather conditions or time of day.

Weather information can be added to the image to show nearby storms. The screen also can display the correct approach path to an airport. This can make a difficult approach to an airport easier and safer to fly. When a plane is on the ground at an airport, the display

shows a plan of the airport. When the pilot is given permission to taxi, the ground controller’s directions can be sent straight to the plane’s synthetic vision system via a radio link. If the plane should stray off the taxiway or onto a runway by mistake, the system automatically sounds a warning in the airplane’s cockpit.

Supercritical Wings

When researchers found it difficult to accelerate experimental aircraft through the sound barrier, they looked at the shape of the airplane’s wings. As a normal wing nears the speed of sound, a high-pressure shock wave forms on top

of it. This causes drag, which makes it difficult for an aircraft to go faster with­out using a lot more engine power. It also makes an aircraft harder to control.

Simply by changing the shape of the airfoil, the shock waves can be made smaller. Airfoils changed in this way are called supercritical wings. In a supercrit­ical wing, the upper surface is flattened

WINGLETS

The high-pressure air below a wing tries to flow around the wingtip into the low – pressure air above the wing. This makes the air spin off the wingtips and trail behind the plane. The spinning trails are called vortices. The vortices behind a big airliner are powerful enough to flip over a small plane flying behind it. Wingtip vortices also cause extra drag. Some air­planes have wingtips that are specially shaped to reduce the drag caused by vor­tices. Many aircraft use turned-up wingtips called winglets for this purpose.

Supercritical Wings

О The Learjet, the first jet plane in produc­tion to use winglets, found increased range and stability with this wingtip device.

EXPERIMENTAL WINGS

 

A few planes have been built with wings that sweep forward to increase maneuver­ability. The first forward-swept wing airplanes were built in the 1940s, but their metal wings could not be made stiff enough, and so they bent. When new materials such as carbon fiber were developed, designers looked at forward-swept wings again. An experimental jet-powered aircraft with forward-swept wings, the Grumman X-29, was built in the 1980s. In Russia, the manufacturer Sukhoi has produced an experi­mental forward-swept wing supersonic fighter, the Su-47 Golden Eagle.

The Wright brothers solved the problem of how to steer a plane by making its wingtips bend, which is called wing warping. By twisting the wingtips on one side of the plane in one direction and the wingtips on the other side in the opposite direc­tion, more lift was produced on one side and less on the other side, so the plane rolled into a turn. Since then, most airplanes have used ailerons instead of wing warping.

Today’s designers are still working on flexible wings, however. They now are called aeroelastic wings. The X-53 is an experimental plane with flexible wings. When wings bend, the result is usually more drag, which is not wanted. The X-53’s wings and the positions of its flaps and ailerons have been designed so that when the wings bend, the result is more lift. One advantage of flexible wings is that they can be up to one – fifth lighter than stiff wings. Flexible wings may enable future aircraft to burn less fuel, carry heavier cargo, or fly farther.

C With its forward – swept wings, the X-29 had a better lift-to-drag ratio than other aircraft, but not enough to be developed into a production model.

 

Supercritical WingsSupercritical Wings

Подпись: О The C-17 Globemaster III has supercritical wings to give extra lift to the heavy cargo plane.

and the curve at the trailing edge is increased. Planes with supercritical wings can go faster with less engine power. Although supercritical wings were developed for supersonic aircraft, they also can produce a lot of lift at low speeds, so they are used by cargo aircraft. The extra lift is good for getting heavy loads off the ground at low speeds.

Sputnik

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putnik is the Soviet word for trav­eling companion, and Sputnik 1 was the first space traveler from Earth. The world’s first artificial satellite, it was launched by the Soviet Union on October 4, 1957.

International Geophysical Year

After World War II brought advances in rocket technology, interest in launching artificial satellites grew, in both the United States and the Soviet Union. The world’s science organizations designated 1957 to 1958 as International Geo­physical Year. Committees were formed to observe such phenomena as cosmic rays, gravity, and solar activity. It was hoped that the period also would see the launch of the first satellite.

The United States prepared two satel­lites, Explorer and the smaller Vanguard. No one was entirely sure that a satellite launch would work. For that reason, Vanguard was a tiny spacecraft, designed to test the theory that it was
possible to launch a satellite on top of a multistage rocket. Unlike the Soviets, the Americans had relatively small launch rockets. Also unlike the Soviets, they released details of their space program to the public.

Very little information had been released about Soviet space plans, although some details of space radio links had been made public, suggesting that the Soviets had a satellite program. This was the era of the Cold War, when the United States and the Soviet Union were building up their supplies of large rockets for military use as well as for scientific study. Rockets used as ballistic missiles could potentially deliver nuclear weapons over ranges of thousands of miles. Both sides kept their military developments secret, and the Soviet Union extended this secrecy to its devel­opment of space technology.

Sputnik

TECH’^TALK

SPUTNIK 1

The satellite Sputnik 1 was fairly sim­ple. It was an aluminum sphere pres­surized by nitrogen gas. Inside the sphere were batteries providing elec­trical power for two radio transmit­ters. Attached to the outside of the sphere were four whip-like radio antennae.

Launch date: October 4, 1957.

Size: 23 inches (58 centimeters) in diameter.

Weight: 183 pounds (83 kilgrams). Speed: About 18,000 miles per hour (28,960 kilometers per hour).

Orbital height: 143-584 miles (230-940 kilometers).

Orbital time: 96 minutes.

Подпись: о An "exploded" view of Sputnik 1 shows that the world's first satellite was a simple device. 4_________________________ У

Velocity

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elocity is speed in a particular direction. Velocity changes when speed or direction, or both, are altered. An airplane flying north at 500 miles per hour (805 kilometers per hour) has a speed of 500 miles per hour (805 kilometers per hour) and a velocity of 500 miles per hour (805 kilometers per hour) north. If two airplanes are flying in the same direction at the same speed, they have the same velocity. If the two planes are flying at the same speed but in different directions, they have differ­ent velocities.

Velocity and Change

The direction of velocity need not be a straight line. An object moving in a circle-such as an airplane turning or a spacecraft orbiting Earth-is said to have angular velocity. Anything that moves with a steady, unchanging veloc­ity is described as having a uniform velocity. According to Newton’s first law of motion, an object stays at rest or moves at a uniform velocity unless a force acts upon it.

When a spacecraft fires a rocket to go faster or change its orbit, its change in velocity is called delta-v. The Greek let­ter delta is often used by mathema­ticians and physicists to mean a change in something. In this case, it is the velocity (v) that changes.

Velocity also can be defined as the rate of change in displacement. Distance is the length of the path taken by a
vehicle. Distance is a number, so it is a scalar quantity. Displacement is the length of the straight line between the start point and end point of a vehicle’s journey. It is distance in a certain direc­tion, so it is a vector quantity. (A vector is something that has magnitude and direction.)

HYPERVELOCITY

VelocityAn extremely high velocity, higher than about 6,700 miles per hour (about 11,000 kilometers per hour), is known as hypervelocity. Spacecraft returning to Earth enter the atmo­sphere at hypervelocity. According to Einstein’s theory of relativity, the highest velocity possible in the universe is the velocity of light. Light travels through space at a speed of

186,0 miles (about 300,000 kilo­meters) per second.

Velocity

О Meteoroids (small space rocks) enter

Earth’s atmosphere at hypervelocity and become meteors (shooting stars).

Velocity

Подпись: O A skydiver's terminal velocity depends on body position in freefall. Extending out arms and legs decreases the terminal velocity, whereas pulling in arms and legs increases it. An airplane that takes off and flies 200 miles (320 kilometers) in a circle, landing back on the same runway where its journey began, travels a distance of 200 miles (320 kilometers), but its change in dis­placement is zero.

Its average speed is the distance traveled divided by the flight time, or 200 miles per hour (320 kilometers per hour). Its average velocity is its change in displacement divided by the flight time. As the plane’s change in displacement is zero, its average velocity for the whole flight is also zero.

Air-to-Air Combat

The main weapons in air-to-air combat were machine guns and cannons. The Spitfire fighter was armed with eight wing-mounted machine guns; an

Me-109 had two machine guns and twin cannons; and a P-51 Mustang was equipped with six machine guns.

Fighter-bombers carried small bombs and rockets as well as guns. German fighters fired salvos of air-to-air rockets into formations of U. S. bombers. Allied fighter-bombers used rockets against ground targets, such as railroad trains and road convoys, during the 1944 battles in Normandy, France. Extra-fast airplanes such as the British Mosquito fighter-bomber flew without defensive armament, relying on speed to evade the enemy.