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.

Coming Back to Earth

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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Coming Back to Earthpilot 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.

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.

Helicopters

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.

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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Airships and Bombs

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.

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.

Staying on Course

The calculations involved in space navi­gation are complex. The launch base (Earth), the space probe, and the probe’s target (a moon of one of the giant plan­ets, perhaps) are all moving through space. Ground controllers must calculate

Staying on Course

launch speed and course precisely. If necessary, they make midcourse correc­tions by using computers to fire small rocket motors onboard the spacecraft. In this way, scientists can send a probe on voyages that will last for years.

When deciding on a launch date for a planetary probe, scientists choose a favorable “window,” usually when the target planet is at its closest. Moving between planets in space seldom involves traveling in a straight line. Keeping a space probe on the right course requires smart computing and

Staying on Course

О A conceptual illustration by NASA shows how samples could be launched from the surface of Mars in a capsule that would bring them back to Earth as part of future missions to Mars.

accurate gyroscopes on the spacecraft. The gyroscopes are used for inertial guidance to keep the space probe on course without reference to the Sun or stars. Instruments measure the slightest change in the spacecraft’s acceleration so that computers can calculate any adjust­ment to the course. When planning a multiplanet mission, scientists may be able to send the probe on a “slingshot” trajectory. This takes the probe around one planet and then uses the planet’s gravitational pull to accelerate it off to the next target. Pioneer 11 did this in 1975, swinging around Jupiter onto a path that took it to Saturn.

Aboard the Space Shuttle

The Space Shuttle is about the same size and weight as a medium-size airliner, but crew conditions inside are cramped. The cargo bay takes up the middle of the spacecraft. The main engines and orbital maneuvering systems are in the tail sec­tion. The flight deck and living quarters, are confined to the forward fuselage. On the flight deck, two pilot seats are fitted with manual controls in addition to the automatic systems. The pilots have more than 2,000 separate displays and controls on the flight deck to monitor. The mid-deck area con­tains four crew sleep stations, the waste management system, a personal hygiene station, and a table used for work and meals.

The mid-deck also contains an area for scientific experiments.

О A large truss (support) for the International Space Station arrives at the Kennedy Space Center in 1999. The Space Shuttle carried the truss in its cargo bay to the space station, where it was installed by astronauts.

To carry out extravehicular activity (EVA), or spacewalks, the crew exits the Space Shuttle through an airlock, wear­ing spacesuits. The airlock has room for two crew members to change spacesuits. An EVA that involves a complex task in the payload bay may last up to 6 hours. One of the tools that Space Shuttle astronauts may use is the Remote Manipulator System (RMS), a 50-foot (15-meter) articulating arm, remotely controlled from the flight deck. The arm has a video camera near its tip, so the operator can see clearly when doing delicate assembly or repair work.

Developing the F-117

In 1977, Lockheed began the top-secret Have Blue project for the Defense Advanced Research Projects Agency (DARPA), the central research and devel­opment organization of the U. S. Depart­ment of Defense. Skunk Works came up with a design that looked like a pyramid with wings and two tails. It was almost invisible to radar when mounted on a pole on the ground, but would it fly? The plane’s unusual shape made it unstable, and it could not have flown successfully without the aid of comput­er technology. Computerized fly-by-wire systems were already in use on planes such as the F-16, constantly adjusting the flight controls to prevent the plane from losing stability and crashing. The secret stealth plane, designated the F-117, was equipped with such a system.

The F-117 was test flown in the Nevada desert in 1981. It was like no other plane. Anything that gave off a radar trace was eliminated from the air­craft, so antennae and sensors were designed to retract into the fuselage. The F-117 had no radar system of its

TECH ‘kTALK

THE F-117

The F-117 Nighthawk is a single-seat airplane powered by two General Electric turbofan engines. It flies at just below the speed of sound (Mach 1). Its principal weapons are two 2,000-pound (907-kilogram) laser-guided bombs, or air-to-surface missiles. The wings and fuselage are aerodynamically blended. They are made of a conventional material, aluminum, but are coated with spe­cial radar-absorbent materials. The Nighthawk weighs about 52,000 pounds (about 23,000 kilograms) when fully loaded.

Подпись: О The Tacit Blue was a research aircraft built to demonstrate that curved surfaces could avoid radar. It flew first in 1982 after several years of development and was retired in 1985.

own to betray its position. The cockpit was coated with a reflective material that radar beams bounced off in all directions. The engine intakes were screened, and exhaust gases were cooled by heat absorbers so that little trace showed on heat sensors.

Initially, the F-117 was not an easy aircraft to fly. Two early prototypes crashed, in 1978 and 1980, but the pro­gram continued with two more test air­craft. The first F-117A was handed over to the U. S. Air Force in 1982 and went operational the following year. It was still top secret, flying only at night. The public became aware of the mystery plane, named the Nighthawk, in 1989, when it took part in operations against Panama. F-117s also flew missions against Iraq during the Gulf War in 1991.