Category FLIGHT and M ОТІOIM

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.

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.

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During World War II, fighter pilots sometimes found their planes behaving oddly in a high-speed dive. The plane shook violently, and the controls seemed to become locked and ineffective. Some pilots were able to regain control. Others
were not so lucky, and they crashed. Some aircraft were shaken so violently that they broke up. There were more mysterious crashes when early jet planes were being tested at high speed. This gave rise to the idea of the sound barrier-an invisible wall that an aircraft had to break through.

The first plane to fly faster than sound in level flight was the Bell X-1 experimental rocket plane in 1947, with Captain Chuck Yeager at the controls. He experienced the same violent shaking and loss

О Originally designed for aerial combat, the F-100 Super Sabre was a supersonic fighter bomber. An F-100 is seen here firing rockets at a target in the Vietnam jungle below in 1967.

TEC

F-100D SUPER SABRE

Length: 49 feet (15 meters). Wingspan: 39 feet (12 meters). Engine: J57 turbojet.

Takeoff weight: 34,000 pounds (15,400 kilograms).

Top speed: 905 miles per hour (1,460 kilometers per hour). Range: 1,985 miles (3,190 kilometers).

Service ceiling: 48,000 feet (14,630 meters).

of control as earlier pilots. As the plane accelerated beyond the speed of sound, however, the shaking faded away and flight became smoother again.

Flying speeds increased rapidly in the years after Yeager’s flight. The F-100 Super Sabre was the first fighter to be designed from scratch for supersonic flight. It went supersonic during its first flight on May 25, 1953, and set a new world airspeed record of 755 miles per hour (1,215 kilometers per hour) five months later. The first Mach 2 flight was made in 1953 and the first Mach 3 flight was made in 1956.

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

An 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.

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.

Early wind tunnel tests sometimes produced results that did not agree with measurements taken from real aircraft in flight tests. Researchers found that more accurate results were often obtained by increasing the air pressure inside the wind tun­nel. If a model one-fifth the size of a real aircraft was tested, the results would be more accurate if the air pressure was increased fivefold. The first high-pressure wind tunnel was used at the Langley Research Center (now part of NASA) in 1923.

There also are refrigerated wind tunnels. The air is chilled to sub-zero temperatures to study the problem of icing, when ice builds up on an aircraft’s wings and air inlets.

The world’s biggest wind tunnel is at NASA’s Ames Research Center. Its test section is big enough for aircraft with a wingspan of 100 feet (30 meters). Air is blown through the tunnel by six fans, each as tall as a four-story building.

VERTICAL WIND TUNNELS

Vertical wind tunnels blow air straight upward. These wind tunnels are not used for aerodynamic testing. They are used by people who want to practice or just enjoy the sensation of skydiving without having to jump out of an aircraft. The skydiver is held aloft by the air blasting upward. Some vertical wind tunnels are completely enclosed and recirculate the same air. Others are outside, and the sky – diver floats in open air. The airspeed is usually adjustable, up to about 140 miles per hour (225 kilometers per hour), to match the ability of the skydiver.

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SEE ALSO:

• Aerodynamics • Aircraft Design

• Pressure • Speed • Wright, Orville and Wilbur

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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.

Such attacks highlighted a new threat to air travel and the need for tighter securi­ty at airports. The Hague Convention of 1970, an international agreement signed by more than 130 nations, was drawn up to combat skyjacking and stop terrorists from escaping to “friendly” countries.

From 1973, the Federal Aviation Administration in the United States has required all airlines to screen passengers and their baggage to prevent people from carrying weapons-or objects that might be used as weapons-onto flights. Airports tightened security procedures, especially at check-in and during bag­gage handling. Armed guards, called sky marshals, traveled on some flights.

When an airplane is hijacked, mili­tary craft may escort it to a landing field
agreed to by the authorities. After it has landed, troops and police will surround the hijacked aircraft while skilled nego­tiators try to talk the skyjackers into releasing the hostages and surrendering. Armed assault also may be used. In 1976, following the hijacking of an Air France flight, Israeli commandos flew in to attack the Palestinian hijackers, who were holed up at Entebbe Airport in Uganda, Africa. The commandos rescued more than 100 hostages. In most hijack­ing situations, however, airport and law enforcement agencies usually try to avoid a gun battle, which risks injuring or even killing innocent hostages.

Skyjacking incidents decreased in the United States during the 1980s and 1990s, but violent terrorist incidents continued to take place in other parts of the world. Some of these skyjackings resulted in airplanes crashing. In 1996, a stolen Ethiopian airliner crashed into the Indian Ocean. About fifty passengers

managed to survive, but the crash killed 125 of the people onboard.

NASA provides up-to-date information on its current space probe missions through its Web sites. The Jet Propulsion Laboratory provides updates on missions in progress and on future missions. NASA’s Web sites also display the latest photos taken by space probes.

Robot probes will continue to play an important part in twenty-first-century

space exploration. Some already have set out on their long journeys. The Messenger probe left Earth in 2004 and will arrive at Mercury in 2011. The New Horizons probe, launched in 2006, should reach Pluto in 2015.

Space probes continue their journeys into infinity, long after they have ceased to communicate with Earth. Scientists calculate that by the year 34,593, Pioneer 10 will have reached a star called Ross 248, 10.3 light years distant from Earth.

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The Soviets had been developing power­ful rocket motors for some time, and they originally had hoped to launch a large satellite packed with scientific instruments. They scaled down their plan when they learned how small Vanguard was (the U. S. satellite weighed only 3.5 pounds, or 1.5 kilograms).

To ensure success, the Soviets opted to start by launching Sputnik 1, an “artificial moon” simpler and smaller than their science satellite, but still much bigger and heavier than its U. S. rival. Soviet space scientists were confi­
dent of putting this small satellite into orbit, even if its scientific value would be limited.

Sputnik 1 was designed and built in conditions of great secrecy by a team of Soviet scientists and engineers led by Sergey Korolev (1907-1966), chief designer of the Soviet space bureau. Korolev had helped design the long – range ballistic missiles from which the R-7 satellite launcher rocket was devel­oped. After successful R-7 test flights in the summer of 1957, a modified version of the R-7 was prepared to launch Sputnik 1 .

It is easy to tell if a plane is flying faster than sound because a supersonic plane makes a telltale boom as it flies past. The sound of an aircraft travels away from it in all directions through the air. Sound
travels faster than a subsonic plane, so a plane such as a jumbo jet can be heard coming before it passes overhead. A supersonic plane flies faster than its own sound, so it passes silently overhead before its sound arrives.

Supersonic aircraft compress, or squash, the air ahead of them, producing a high-pressure wave called a shock wave. Several shock waves form on var­ious parts of the aircraft. As a plane nears the speed of sound, a shock wave forms in the middle of each wing. The shock wave forms over the wing first because the air flowing over the top of the wing speeds up. The speed of the wing relative to the air is therefore high­er than the speed of other parts of the
aircraft relative to the air. So even when a plane is flying just below the speed of sound, the tops of its wings may be supersonic relative to the air, and that is where the first shock waves appear.

The biggest shock wave forms on an aircraft’s nose. It makes a cone shape, with the aircraft’s nose at the cone’s tip. This shock wave spreads out into the surrounding air and travels all the way down to the ground. As it sweeps across the ground, the sudden change in air pressure it causes sounds like a boom to anyone below the shock wave.

The intensity of this sonic boom depends on an aircraft’s altitude. The higher it is, the more time the shock wave has to spread out into the sur­rounding air, reducing its intensity. A supersonic plane flying at an altitude of more than 35,000 feet (10,700 meters) makes a loud, thunderlike sonic boom. The same plane flying at the same speed, but at an altitude of less than 10,000 feet (3,050 meters), produces a sonic boom powerful enough to shatter windows. For this reason, Concorde was only allowed to fly at supersonic speeds when at high altitude and over water.

When something falls through the air toward the ground, the force of gravity makes it accelerate. As it accelerates, the drag (air resistance) it experiences increases. If it falls for long enough, its weight is exactly balanced by drag, and it stops accelerating. This velocity is called its terminal velocity.

A large but very light object, such as a feather, reaches its terminal velocity very quickly. A heavier object of the same size has a higher terminal velocity, because a higher speed is needed to cre­ate enough drag to balance its weight.

In the usual skydiving position­falling with arms and legs held out-a skydiver’s terminal velocity is about 120 miles per hour (195 kilometers per hour). With arms and legs pulled in, however, there is less drag, and the skydiver accelerates. Terminal velocity increases to about 200 miles per hour (320 kilo­meters per hour) before weight and drag are once again balanced.

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SEE ALSO:

• Gravity • Laws of Motion

• Relativity, Theory of • Skydiving

• Speed

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