Category FLIGHT and M ОТІOIM

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

к

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

The momentum of an aircraft or space­craft traveling in a straight line is called linear momentum. The momentum of something that spins is called angular momentum. An object’s total angular momentum stays the same if no other

forces act on it. This is also known as the law of conservation of angular momen­tum. It can be used to control the move­ment of a satellite in space.

The direction in which a satellite points is known as its attitude. Devices called momentum wheels, or reaction wheels, are often used to control a satel­lite’s attitude. Inside the satellite, three wheels at right angles to each other are spun by motors. If a wheel is made to spin in one direction, then—to conserve angular momentum—the spacecraft must spin in the opposite direction.

The advantage of using momentum wheels to turn a satellite is that they use no fuel. If rocket thrusters or gas jets were used for attitude control, the satel­lite could only be controlled for as long as the fuel or gas lasted. After that time, the satellite would be out of control.

Momentum wheels should keep working as long as the satellite because they are powered by electricity generated from sunlight by solar panels.

Momentum wheels can turn a satel­lite to point at a precise part of the sky. The Hubble Space Telescope can take several hours to make an image of a very distant star or galaxy. It must point in exactly the same direction, without wavering, to capture a sharp image while it orbits Earth. The telescope uses momentum wheels to achieve this. Most Earth-orbiting satellites use momentum wheels to keep their antennae, solar panels, cameras, and other instruments pointing in the right direction.

N

SEE ALSO:

• Force • Gravity • Hubble Space

Telescope • Laws of Motion • Rocket

• Satellite •Speed

_______ I_________ J

The only manned spacecraft that have navigated through space and into an orbit other than Earth’s were those of the Apollo mission, when nine space­craft went into orbit around the Moon. The Apollo program also landed twelve astronauts on the Moon between 1969 and 1972. On the way to the Moon, the spacecraft’s inertial guidance system figured out its position by sensing changes in its speed and direction. The position was double-checked by taking sightings of stars using a sextant and telescope. Thirty-seven stars were used as guides to navigate the spacecraft. The sextant, telescope, inertial guidance sys­tem, and guidance com­puter provided Apollo’s primary guidance, naviga­tion, and control system (PGNCS). The astronauts called it “Pings.”

О Timing and precision are crucial to space navigation. Scientists successfully launched the probe Deep Impact to intercept the comet Tempel 1 in 2005. The probe released an impactor to create a crater, so releasing debris to gain informa­tion about the comet’s interior.

The most precise Apollo navigation system was not in the spacecraft at all. It was on Earth. The huge radio dishes of NASA’s Deep Space Network were trained on the spacecraft and relayed communications between Apollo mis­sions and Earth. Tracking a spacecraft using these dishes showed exactly where it was. This information was sent up to the spacecraft and used to correct any errors in its own guidance system. If the spacecraft lost radio contact with Earth, its own guidance system would be cor­rect and could guide it until contact with Earth was restored. Some losses of con­tact were expected. While the spacecraft

——————————— N

SEE ALSO:

• Bird • Communication • Global

Positioning System • Radar

• Space Probe

_____________________________________________ /

was in orbit around the Moon, it lost touch with Earth every time it disap­peared around the far side of the Moon. NASA still uses the dishes of the Deep Space Network in California, Spain, and Australia to communicate with space probes in all parts of the solar system.

r

AN EXPENSIVE ERROR

When navigation goes wrong, the results can be catastrophic. In 1998 NASA sent a probe named the Mars Climate Orbiter to Mars. It was sup­posed to orbit Mars, but instead it entered the planet’s atmosphere and burned up. An inquiry found that some of the navigation data was calculated using U. S. standard units (feet/pounds/seconds), and this became mixed up with data calcu­lated in metric units (meters/ kilograms/seconds). The navigational error resulted in the loss of the multimillion-dollar spacecraft.

Military pilots fly with the U. S. Air Force, U. S. Navy, U. S. Marine Corps, U. S. Army, U. S. Coast Guard, and the Air National Guard. In the U. S. Air Force, the Air Education and Training Command (AETC) is based at Randolph Air Force Base near San Antonio, Texas. Personnel hoping to become pilots receive up to 25 hours of initial flight training from civilian instructors. Selected candidates move on to further training by military instructors. Student pilots learn to fly on fairly slow training airplanes, such as the turboprop T-6II, moving up to the twin-jet T-37, and then to a supersonic jet such as the T-38.

All students learn basic flight skills. Then they are selected for one of sever­al advanced training tracks, depending on the type of aircraft they will fly. Helicopter pilots, for example, receive
special training, on the UH-1 Huey heli­copter. Student airlift (transport) and tanker pilots train on the T-1A Jayhawk, and others fly the T-44 to learn how to pilot a multi-engine, turboprop airplane such as the C-130 Hercules.

Pilots complete their training at U. S. Air Force bases around the country. For example, fighter pilots qualifying from the T-38 course at Randolph Air Force Base go on to fly the F-15 Eagle at Tyndall Air Force Base, Florida, or the F-16 Fighting Falcon at Luke Air Force Base, Arizona. On completion of their military service, many pilots continue to fly as civilian pilots.

N

SEE ALSO:

• Barnstorming • Bleriot, Louis

• Coleman, Bessie • Curtiss, Glenn

• Earhart, Amelia • Lindbergh,

Charles • Night Witches

________________ J

Many home security systems have motion detectors that sense when someone is moving around in a room. Some of these detectors work by picking up the heat of the person’s body, but others use radar. They flood the room with microwaves that bounce back to the detector. If someone enters the room, the steady pattern of reflec­tions is disturbed, and an alarm sounds.

Some of the cameras used to monitor the speed of vehicles on highways work by radar. The radar system measures the speed of the vehicles. If a vehicle is moving faster than the speed limit, the radar system triggers a camera that photographs the car, includ­ing its license plate, so it can be traced to the speeding owner.

Archaeologists use a variety of methods to map structures under­ground and ground-penetrating radar is one of these methods. Radar can probe down to 33 feet (10 meters) deep and show buried features of ancient buildings such as walls and floors.

Science satellites carry out a range of tasks to observe objects and phenomena in space. They have transformed many scientists’ views of the universe. Science satellites’ instruments often measure radiation in various forms. IRAS (Infrared Astronomical Satellite) was launched in 1983. In its ten-month lifespan, it discov­ered 20,000 galaxies (including a new kind called a starburst galaxy), 130,000 stars, and a comet. In 1999, the Space Shuttle Columbia launched an X-ray observatory named Chandra. It has an unusual elliptical orbit that brings it to

SPACE JUNK

Old satellites and leftover pieces of satellite launch vehicles end up as trash drifting in space. Space junk is heaviest at a height of around 530 miles (850 kilometers), where most satellites orbit. After a half-century of space launches, there is now a lot of space junk. Scientists have recorded at least 11,000 objects larger than 4 inches (10 cen­timeters) in diameter. The junk includes used-up rocket stages, tools lost by astronauts, and lumps of solidified fuel. Space junk is a potential hazard, since a lump of fist-size debris, traveling at more than 21,000 miles per hour (33,800 kilometers per hour), can make a serious hole in an expensive spacecraft.

within 6,000 miles (9,650 kilometers) of Earth and then swings out to 86,000 miles (about 138,400 kilometers)-about a third of the way to the Moon. Each orbit takes 64 hours. Being so far out means Chandra keeps clear of the belts of charged particles that surround Earth and so provides astronomers with longer peri­ods of clear observation time.

SEE ALSO:

• Gravity • Rocket • Space Probe

• Space Race

_________________ J