Category FLIGHT and M ОТІOIM

The first satellite, Sputnik 1, carried a radio transmitter. In 1957 the only way to tell if the satellite really had made it into space and was orbiting Earth was to listen for the bleeps that its radio trans­mitted as it passed overhead.

The frequencies of radio signals used to communicate with spacecraft have to be chosen carefully because some radio signals will not travel through Earth’s atmosphere into space. Radio signals used for space communications today are mainly in the super high frequency (SHF) band. Radio signals in this band have frequencies from 3 gigahertz to 30 gigahertz. (A gigahertz is equal to 1 bil­lion hertz, or waves per second.)

In the early days of spaceflight, a ground station could communicate with a spacecraft only while it was above the horizon. When it passed over the ground station and disappeared below the hori­zon again, contact was lost. Ground sta­tions had to be set up all around the world to stay in contact with early manned spacecraft.

Various types of drone are in service. Some, such as the Dragon Eye, operate

at low altitude. Others, such as the EQ-4 Global Hawk, can fly at high altitudes, staying in the air for 24 hours. The Global Hawk is capable of very long flights: in 2001, a Global Hawk craft flew 7,500 miles (12,068 kilometers) nonstop across the Pacific from the United States to Australia. The Global Hawk is as big as a small airplane, 44 feet (13.4 meters) long with a wingspan of 116 feet (35.4 meters). It can cruise at

around 400 miles per hour (644 kilometers per hour) at a height of

65,0 feet (19,812 meters). Using its radar, cameras, and other sen­sors, the Global Hawk can scan an area the size of the state of Illinois in a period of 24 hours.

The smaller MQ-1 Predator is used by the U. S. Joint Forces Command. The M stands for multi-role missions; Q means it is unmanned. Predator is normally flown at medium alti­tude on long-endurance missions. The aircraft and its control system are portable-they can be loaded into a freight plane, such as a C-130 Hercules, and airlifted anywhere in the world. The Predator drone does, however, need a runway to take off and land.

Drones can be made very small. The Israelis have some aircraft that can fly in through an open window and out again on spying missions. Known as Birdy, the smallest Israeli spy drone weighs only about 3 pounds

(1.4 kilograms). Israel uses this minia­ture airplane and other slightly larger drones (all of which look like model air­planes) to take photographs of sensitive areas. The aircraft are small enough to be carried by a soldier and can be oper­ated from a laptop computer.

In 2006 the Los Angeles Sheriff’s Department announced that it was using drones. Its SkySeer is a small robot pro­peller airplane that weighs 4 pounds (1.8 kilograms) and is battery driven. An officer can carry the kit in a backpack and can assemble the drone in as little as 5 minutes. At the touch of a button, the engine whirrs, and the plane takes off. The drone carries a video camera and can fly over a crime scene (such as a burglary) to scan the rooftops of surrounding buildings. It also can help locate people lost in inaccessible terrain—a ravine or forest, for example—
using low-light or infrared cameras to detect the heat given off by a body.

One advantage of drones over manned helicopters is their cheapness—a SkySeer kit costs around $30,000. Another asset is the speed with which the “eye in the sky” can be deployed when the need arises. Their size, in addi­tion, gives them access to places where larger aircraft cannot go.

SEE ALSO:

• Aircraft, Military • Control

System • Radar • World War II

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The ramjet is a jet engine for very high­speed aircraft. It has no fan or compres­sor. The engine has to be moving at about 600 miles per hour (965 kilome­ters per hour) before it starts working. At that speed, air rams into the engine so fast that a compressor is not needed to compress it. The shape of the engine enables this to happen. With no fan or compressor, there is no need for a tur­bine. Ramjets work best in aircraft flying at more than twice the speed of sound.

SEE ALSO:

• Aircraft Design • Fighter Plane

• Jet and Jet Power • Propeller

• Rocket • Thrust

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TECH^TALK

EXTRA THRUST

Some aircraft are able to swivel their engine exhaust nozzles to point in different directions. This action is called thrust vectoring. It was invent­ed for aircraft such as the Harrier Jump Jet, which takes off straight up in the air by pointing its engine nozzles downward; it then swings the engine nozzles backward to fly normally. Some fighter planes use thrust vectoring to help them maneuver fast in air battles. The engine nozzles of the F-22 Raptor, for example, swivel in this way.

A fighter plane also sometimes needs a sudden burst of power or speed to take off or to escape trou­ble in an air battle. Fighters do this by using an afterburner, which sprays fuel into the jet engine’s exhaust nozzle. The fiery, hot jet of gas leaves the engine, and the fuel instantly burns and gives the plane an extra push. Afterburners are normally used only for short periods because they use up fuel very quick­ly. The F-22 Raptor was designed to fly at supersonic speeds for long periods without using afterburners.

This ability, called supercruise, gives the fighter plane an advantage over an enemy plane that may run out of fuel in mid-combat.

fuel is a substance used to pro­duce heat or power. Fuels con­tain energy that is usually obtained by burning the fuel. Aircraft and spacecraft use fuel to produce power. When fuel is burned inside an engine, it produces a lot of gas. The heat makes the gas expand rapidly, and this provides the power to propel the air­craft through the air. A variety of different fuels are used in aviation and spaceflight.

Aviation Fuels

There are many aviation fuels, each one a different mixture of chemicals. Extra chemicals called additives are included in the mixture to make it burn smoothly instead of exploding and to stop it from freezing solid or growing bacteria.

Early aircraft used the same sort of gasoline fuel as automobiles. When new types of engines were developed, new fuels were produced specially for them. Today, aircraft with piston engines (like automobile engines) use a type of gaso­line called Avgas. The first jet engines built in Germany used gasoline, too. Modern jet engines burn a different fuel, called kerosene.

The first fuel produced especially for jet engines was called Jet Propellant 1, or JP-1. When fuels were created for new military aircraft, each new fuel was given a JP number: JP-2, JP-3, etc. The U. S. Navy, for example, wanted to develop an aircraft fuel that would not

FUEL TANKS

Planes usually store fuel in tanks inside their wings. The Boeing 747­400 jumbo jet’s giant wings hold an enormous amount of fuel. There are three fuel tanks in each wing, anoth­er tank in the space where the wings join the fuselage, and another tank inside the horizontal stabilizer, or tailplane. When the tanks are all full, they hold more than 57,000 gallons (about 216,000 liters). This huge amount of fuel enables the 747-400 to fly a distance of more than 8,000 miles (12,872 kilometers) before it has to land and refuel.

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catch fire as easily as JP-1, so that it could be stored more safely on board ships. This new fuel was named JP-5.

Fuels for nonmilitary jets have differ­ent names. The most widely used fuels for commercial jets are Jet A-1 (most common worldwide) and Jet A (most used in the United States). A different jet fuel, Jet B, is sometimes used in the coldest parts of the world, including Canada and Alaska. Jet B is a mixture of gasoline and kerosene-the gasoline helps the fuel burn in very cold air.

When superfast spy planes were built in the 1960s, they were unable to use the same fuel as other jet planes. They flew at more than three times the speed of sound. At such a high speed, air rubbing
against a plane’s body heats it up. The wings of the new spy planes became so hot that fuel stored inside them could explode.

Chemists created a new fuel, JP-7, that could be heated to very high tem­peratures without exploding. It is said that a burning match dropped into JP-7 will actually go out.

Glenn became the space hero that NASA officials and the American people so wanted. He was invited to speak to a joint session of Congress and was hon­ored with parades across the country. Four million people turned out for Glenn’s parade in New York City. A smaller but even more appreciative crowd turned out in his hometown of New Concord, Ohio.

After his return to NASA, Glenn was assigned to work on Project Apollo, the space program aimed at sending American astronauts to the Moon. He left NASA in 1964, however, and began working in business. Ten years later, Glenn won election to the U. S. Senate, where he served for the next twenty-four years. He won

О Seated between President John F. Kennedy (left) and General Leighton Davis (right), John Glenn (center) rides in a celebratory parade in Florida after his historic spaceflight in 1962.

reelection three times. Glenn tried to win the Democratic nomination for president in 1984, but his campaign never got off the ground. In 1997, he announced that he would retire from the Senate.

Modern hang gliders often are launched in the same way that Otto Lilienthal launched himself in the 1890s, by run­ning down a hillside. The pilot holds the glider over his or her head and takes

VARIO/ALTIMETERS

Glider pilots, including hang glider pilots, look for rising air to help them fly higher. The vario/altimeter is an electronic instrument that shows the pilot when the glider is rising or sink­ing. This instrument has a visual dis­play and also gives audio signals in the form of beeps. A typical vario/altimeter includes a height and airspeed indicator and may have a GPS navigation function. This useful aid helps a hang glider pilot find an updraft of air, or thermal, and stay within it.

swift paces down the windward slope (the side of the hill against which the wind is blowing) until the glider catches enough air to lift off.

An alternative launch method is to be towed by a truck at the end of a towrope or by a boat across a lake or ocean. When the pilot has reached a safe height, usually around 400 feet (120 meters), he or she releases the towrope. Experienced fliers can choose from even more dramatic launch techniques. These methods include being towed into the
air by a powered airplane, taking off under power using a small motor attached to the harness, or being dropped from a hot air balloon.

The wing of a typical hang glider resembles that of a toy stunt kite, but it has a span of about 30 feet (9 meters). The hang glider’s wing is kept rigid by a metal frame. To make the glider go where the pilot wants, he or she shifts his or her own body position and oper­ates a control bar attached to the glider.

A hang glider flies on the same prin­ciples as a fixed-wing glider. The aircraft fly best in rising drafts of air, for example when the wind hits the side of a hill or a sea cliff. Long flights can be achieved if the pilot flies into the updrafts of air known as thermals. Rising air also is found along mountain ridges. By good use of rising air drafts, hang gliders have made flights of more than 435 miles (700 kilometers).

In the 1960s, NASA launched two small stargazing satellites, called Orbital Astronomical Observatories, into orbit around Earth. The first was launched in 1966 and the second in 1968. Other space probes and satellites also were sent on astronomy missions.

Astronomers still wanted a large space telescope. In 1977, the U. S. Congress approved the building of a space telescope. This time, the project went ahead. Some twelve countries and many contractors and specialists were involved in the design and construction of the observatory. By 1985, the space telescope was ready.

There was then a delay before Hubble could be sent into space. In 1986, the disastrous and fatal loss of the Space Shuttle Challenger led to the grounding of the Space Shuttle fleet for two years. It was 1990 before Hubble went into space, carried in the cargo bay of the Space Shuttle Discovery. On April 25, 1990, Hubble finally drifted free into orbit, ready to begin observations.

Personal hygiene is a matter of considerable interest to everyone on board. Water, heavy to transport from Earth, is precious. For this rea­son, all water in space is recycled. The space station recycling system cleans and reuses wastewater from hydrogen fuel cells. It also condenses water from humidity in the air. The space toilet works on a suction system to remove waste, and urine is recycled (solid waste is stored and removed with the garbage). Even animals, such as labo­ratory rats taken into space for research purposes, help in the recy­cling regime: seventy-two rats can provide as much recycled water, from their urine, as one astronaut! Recycled “space water” is cleaner than the water coming out of a faucet in the United States.

To reduce waste, water pressure onboard the ISS is only half that found in a standard bathroom or kitchen on Earth. Astronauts wash their hands by wetting a washcloth

with a spray nozzle, and then using the cloth. They normally bathe every day after exercising, showering in a special economy shower unit. A space station shower uses less than 1 gallon (4.5 liters) of water, compared with an average of 11 gallons (50 liters) used by a person showering on Earth.

The second of Newton’s laws explains how the motion of an object changes when a force acts on it. It says that the rate of change of an object’s momentum (which is its mass multiplied by its velocity) depends on the size of the force acting on the object.

If a force acts on a mass for a period of time, it produces a change in veloci­ty. A change in velocity is the same as acceleration. Newton’s second law can be written as: Force = mass x accelera­tion. The bigger the force acting on an object, the faster it accelerates.

The connection between force and acceleration works in either direction. Force produces acceleration, and accel­eration produces force. The thrust of an airliner’s engines makes the plane accel­erate along a runway for takeoff. This is an example of force producing accelera­tion. Inside the airplane, the passengers feel themselves being pushed back in their seats. This is an example of accel­eration producing force.

Usually, more than one force acts on an object. When two or more forces act

О Newton’s second law of motion: When different forces act upon the same mass, more force produces more acceleration. When the same force acts upon different masses, the greater mass accelerates less. So the racecar with the larger engine (more force) will acceler­ate faster than the same racecar with a smaller engine. But the lighter racecar will accelerate faster than the heavier racecar (more mass) with the same size engine.

in the same direction, they combine to produce a stronger force. This is called the resultant force. When forces act in opposite directions, the resultant force is the difference between them. If the resultant force acting on a mass is not zero, it produces acceleration.

An airliner is built from millions of parts—6 million for a Boeing 747 and more than 3 million for a Boeing 767 or 777. Boeing airliners are built in the world’s largest building in Everett, Washington, about 30 miles (about 48 kilometers) north of Seattle. Parts arrive every day from all fifty U. S. states and from all over the world. Ensuring that the right number of correct parts arrive on time at the relevant production line is an incredibly complex task.

Each aircraft is built in sections. It is vital that these sections are exactly the right shape and size so that they fit together precisely. The sections are built on very accurately made frames called jigs. Overhead cranes move finished sec­tions together for assembly on the pro­duction line. Highly skilled workers swarm over the airplane, installing the wiring, hydraulics, avionics, engines, fuel system, and countless other parts.

Modern airliners contain so many electrical and electronic systems that every Boeing 747 needs 171 miles (275 kilometers) of wiring to connect it all together. When all the equipment and systems have been installed in the air­liner, they are checked to make sure that

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SPACECRAFT MATERIALS AND STRUCTURES

Materials and structures are vital to spacecraft. The design of a spacecraft depends on whether it is manned or unmanned and whether it will land or stay in space. The first manned spacecraft for traveling only in space was the lunar module that landed astronauts on the Moon. Its spidery, boxlike shape, and flimsy structure would not have survived reentering Earth’s atmosphere, but it was perfectly designed for its task.

Building a spacecraft begins with a strong frame to which the other parts of the craft are attached. Aluminum metal is commonly used for this because it can be formed into a strong structure that also is lightweight. The Space Shuttle has a skeleton-like frame made of aluminum covered with a thin aluminum skin.

Manned spacecraft must be protected from the heat of reentry, so they are covered

with heat-resistant materials. Space cap­sules usually have a heat shield that can be used only once. The Space Shuttle’s heat protection can be used again and again.

New lightweight materials, such as car­bon fiber, are replacing some of the metal parts of spacecraft, but aluminum is still used for the main structure of large, manned craft. The biggest and newest space structure, the International Space Station, is made mainly from aluminum.

О NASA workers prepare the Mars Pathfinder lander for its journey into space by closing up its metal "petals." The Pathfinder landed on Mars in 1997. Its small Sojourner rover (visible in place on the foremost petal) then traveled over Mars’ surface.

everything works properly. The final production lines—two for 777 airliners,

tasks are to install the seating in the lay­out and to paint the airplane in the cus­tomer’s chosen colors.

As each plane is assembled at the factory, it moves along the production line toward the giant doors where the finished airliners leave. The factory is so big that there is enough room for four
one for 747s, and one for 767s.

SEE ALSO:

• Aerodynamics • Aeronautics • Air and Atmosphere • Aircraft Design

• Airship • Biplane