AN UNLlKELY LOOKING FLYING MACHINE stands on its tail above the watery, thicketed Florida landscape. The time is the mid-1980s, and the Space Shuttle preparing for launch is one of a fleet of four that now plies routinely, about one round trip a week, between the United States and Earth orbit.
The first true aerospace vehicle, the Shuttle takes off like a rocket, operates in orbit as a spacecraft, and lands like an airplane. To do this takes a complex configuration of three main elements: the Orbiter, a delta-winged spacecraft-aircraft, about the length of a twin-jet commercial airliner, but much bulkier, and built to last for at least 100 flights; a dirigible-like expendable External Tank, containing half a million gallons of propellants, secured to the Orbiter's belly; and, attached to the sides of the tank, a pair of reusable Solid Rocket Boosters, each longer and fatter than a railway tank car.
The countdown clocks blink to zero on the consoles in Launch Control at the Kennedy Space Center, in Mission Control at the Johnson Space Center, Texas, and in the Shuttle's cabin. Three main engines in the Orbiter's stern ignite, gulping liquid hydrogen and liquid oxygen from the External Tank through feedlines thicker than a man's body. As they build to 90 percent of full power, in about four seconds, the two Solid Rocket Boosters begin firing in a storm of flame and smoke. The w hole assemblage rises from the same mobile launching platform that was once used for Saturn V rockets that sent Apollo astronauts to the Moon.
Clear of the servicing tower, the Shuttle turns toward its destination in space and begins arcing over on its back-the crew heads-down, the tank and boosters on top of the upsidedown Orbiter-and slants up over the open Atlantic, its direction controlled by slight swiveling of the engines and rocket nozzles. In their spacious cabin up front, the crew of three astronauts and a scientist feel no more acceleration than a comfortable three times normal gravity. They wear ordinary clothes, work at room temperature, and breathe normal air at sea-level pressure.
After two minutes of flight, 50 kilometers (31 miles) up, the two solid-fuel boosters, their work done, burn out, are cut loose from the tank by explosive separation devices, and are pushed clear by small rocket motors. The spent boosters coast upward to about 67 kilometers, then drop back toward the sea. At 4.7 kilometers each discards its nose cap and ejects a small parachute; this pulls out a larger chute that, in turn,  pulls out three bigger main chutes. These lower the burnedout rocket case, nozzle first, into the ocean about 280 kilometers ( 175 miles) from the launch site. Waiting tugs collect the parachutes, attach lines to the rocket cases, and pump in air so that they float horizontally while being towed ashore to be repacked with propellant for reuse.
The Orbiter's three main engines continue firing until about eight minutes into flight, then shut doss n just before orbital velocity is reached. Ten to fifteen seconds later the big External Tank, almost empty, is cast off, like the booster rockets....
....earlier, and follows a ballistic trajectory 18500 kilometers down range. Unlike the boosters, it breaks up reentering the atmosphere, its surviving fragments falling into a remote ocean area-the only main element of the Shuttle that doesn't return to Earth to be used again.
Free of the tank, the Orbiter, after coasting for a short time, fires its two small maneuvering engines-fed from internal tanks-for about 105 seconds to reach orbital velocity of 7847 meters a second ( 17 500 mph). The initial elliptical orbit ranges from 110 km (60 n.mi.) at its lowest point to....
 ....280 km ( 150 n. mi. ) at the apogee. A second firing of 95 seconds, half way around the world from the launch site, reshapes the egg-shaped flight path to a circular orbit, and the Space Shuttle is ready to go to work.
From forward-facing seats, much like those in an airliner cockpit, the NASA astronauts serving as ship commander and pilot now shift to occupy orbital work stations facing aft. The commander, on the left as usual, handles the Orbiter's maneuvering and attitude controls. The pilot directs the motions of a triple-jointed, 15-meter (50-ft) mechanical arm in the cargo hold that lifts payloads out and in. An astronaut mission specialist and a scientist payload specialist, seated behind the commander and pilot during ascent and maneuvering, now work at stations on either side of the flight deck, conducting checks and other chores concerned with experiment packages carried in the hold and with satellites to be deployed, retrieved, or serviced in orbit.
Over Australia, an hour after liftoff, a pair of clamshell doors, split along the top of the fuselage and hinged at the sides, swing outward to open the full length of the cargo bay, as big as a trailer truck. On this flight the payload to be deployed is another in a series of the oldest kind of workaday spacecraft, a communications satellite for relaying telephone calls and television programs between continents. Attached to it is a solid-fuel rocket, called an upper stage, that will propel the satellite into a higher, geosynchronous transfer orbit. There, at 35 900-kilometers (22 300 mi) altitude after the apogee motor is fired, velocity will exactly match Earth's rotation, keeping the satellite always over the same area of land or ocean.
After a final on-board check-out, the satellite and attached upper stage are nudged out of the bay by ejection springs and left free to drift in space. When the crew has determined that the satellite and its upper stage are precisely aimed, and the Orbiter has moved off to a safe distance, the upper stage is ignited by radio signal from the Orbiter as all cross the equator over South America.
Next day-if one can measure time by days in a world where the Sun rises every hour and a half-the crew change orbit to rendezvous with a 9100-kg ( 10-ton) space telescope 14 meters (46 ft) tall that was brought up on an earlier Shuttle flight. This huge and powerful observatory has been designed both to be serviced in orbit and periodically brought....
....back to Earth for overhaul and relaunch over a lifetime of fifteen to twenty years. Above the hazy, turbulent atmosphere that blurs the view of telescopes on Earth, the space telescope, its five extremely sensitive instruments aimed and focused by radio, can see into several hundred times the volume of space viewed by the largest ground-based ones, observing objects so far away that their light has taken billions of years to reach us. The data, transmitted by radio and shared by U.S. and European astronomers, are used, among other things, to study events that happened soon after the universe was created, to watch for new galaxies being formed, and to see whether other stars like our Sun also have planets.
When the Shuttle's flight path has been matched precisely with the telescope's, the manipulator arm is extended to capture the satellite and stand it upright into the cargo bay. The pilot and mission specialist put on space suits and crawl into the bay through an airlock that lets them out while keeping the air in the cabin at sea-level pressure. In the first of two six-hour work periods they inspect and photograph the telescope, open its access doors, and make minor corrections and adjustments while the scientist, a woman astronomer with no formal astronaut or pilot training, watches from the flight deck and talks with them by intercom.
In a second six hours next day, after having gone back to the Orbiter cabin to eat and sleep, the pilot and mission specialist, again in their space suits, reenter the bay, remove one of the telescope's instruments, and replace it with an improved model that hadn't been ready for the original launch. After they have returned again to the cabin, the telescope's various circuits and mechanisms are tested remotely by the astronomer on the flight deck and by ground controllers. It is then powered up, lifted out of the hold by the manipulator arm, and set free again in orbit. The Orbiter stands by while the crew make sure all is working properly, then pulls away to prepare for its next task.
After the crew relaxes, eats, and sleeps, the Shuttle's small engines are fired briefly to readjust the orbit and rendezvous with a free-flying spacecraft-also brought up on an earlier flight-that has no maneuvering ability, attitude controls, power supply, data-collecting equipment, communications, or instruments of its own. This is the Long Duration Exposure Facility: an empty aluminum canister resembling a huge Japanese lantern, 9.14 meters (30 ft) tall and polygon  shaped, its outer surfaces divided into bays that hold shallow trays, seventy-two of them around the periphery and two on each end. The trays, 3 to 8 centimeters ( 1 to 3 in.) deep, some open and some closed over, contain experiments provided by scientists and engineers of U.S. and foreign government agencies, universities, and industrial companies. Their purpose is to expose various instruments, materials, electronic parts, and dust collectors to the space environment-high vacuum, near-zero gravity, solar radiation, cosmic rays, micrometeoroids-for six months or more.
The Orbiter moves close to the passive free-flyer, grasps it with the manipulator, and hauls it into the cargo hold. The crew take breaks for meals and sleep. Then they close the cargo-bay doors, move into their seats, fasten their belts like any airline passengers, and prepare to head home.
Half way around the world from the Florida base, the small attitude-control thrusters are fired in short bursts to turn the spacecraft tail-first. The larger orbital maneuvering engines then are fired for about two minutes to slow the ship and lower its flight path in a slow curve toward Earth. Half an hour later, about 150 kilometers up and the ship again flying nose-first, the crew begin to feel the drag of the thin top layer of the atmosphere.
Now begins the most critical and demanding part of the voyage. Why this is so was explained by the director of the Space Shuttle Program, Myron S. Malkin, in a vivid account of the last half hour of a Shuttle flight from here to touchdown:
The Orbiter must change from a spacecraft to an aircraft while slowing from its orbital speed of nearly 8,000 meters a second ( 18,000 mph) to about 100 meters a second (225 mph ) for landing. Above the atmosphere, maneuvering is done by firing small rockets in the nose and tail; in the atmosphere, attitude and direction are controlled by a conventional aircraft rudder and flaps. At middle speeds and altitudes, during reentry into the atmosphere, rocket and aerodynamic controls must be skillfully blended. The commander and pilot are aided in this tricky task by five computers on board that decide which rockets should be fired and for how long, and how much to move the control surfaces, to keep the craft steady and headed in the right direction.
Edging into the atmosphere, the pilot uses the attitude-control thrusters to angle the nose up so that the craft pushes
 ....into the thickening blanket of air at about a 40-degree angle of attack, the term aeronautical engineers use to describe the upward slant of an aircraft's lifting surfaces in relation to its direction of movement. Air friction heats the Orbiter's heavily insulated underside to more than 1000 C, and ionization of the surrounding atmosphere blacks out communication with the ground for some seconds. At about 93 kilometers ( 58 mi) altitude the air becomes dense enough so that aerodynamic controls take hold, and the Orbiter becomes a heavy glider.
(Without fuel for its main engines, the craft wouldn't be able to go around for a second landing approach in case of a miscalculation, as an airliner could; it can, however, shift as....
....much as 2000 kilometers (1200 mi) to the right or left of its entry path to make an emergency landing at any of several U.S. airports or military air bases. In such an event, it would be ferried to its home base on the back of a specially fitted NASA 747 air transport.)
About 48 kilometers above Earth, the Orbiter's nose is pushed down to reduce the angle to about 14 degrees. At 24 kilometers (15 mi) height the final approach begins, with the craft about 92 kilometers (57 mi) from the Kennedy Space Center. The great glider dives for the runway nose down at 22 degrees and an airspeed of about 158 meters a second (355 mph). At 520 meters (1700 ft) the pilot begins to flatten the glide to only 1.5 degrees, extends the speed brakes, and settles the ship for a landing. At 90 meters (300 ft) the landing gear goes down, and seconds later the tires touch the 4572-meter (15 000 ft) concrete strip-just thirty busy minutes from the smooth, silent weightlessness of space.
Immediately after the landing, ground cooling equipment like that used for airliners is attached, and the Orbiter is towed into a servicing building. Leftover propellants are drained from the tanks and feedlines, and any unused explosive actuators are removed. The cargo doors are opened, the Long Duration Facility is hoisted out, and the experiment trays are distributed to the scientists who will study how the contents were affected by their stay in space. After general maintenance work on the Orbiter, a new payload is lowered into the bay. For the coming flight it is the Spacelab, a completely fitted-out laboratory, designed and built by members of the European Space Agency, in which four scientists can work for a week to a month in an Earth-like atmosphere but in the zero gravity of orbit.
The Orbiter, with its new payload, is next towed to the Vehicle Assembly Building originally designed for stacking Saturn/Apollo vehicles. Here it is rotated to a vertical position and mated with a new External Tank and reloaded Solid Rocket Boosters on the mobile launching platform.
Erect on the platform, as big as a baseball diamond and carried by four enormous crawler tracks, the space vehicle moves slowly to the launching pad. More than 700 tons of super-chilled propellants are pumped into the tank, a new crew of three astronauts and the four scientists board, and the Space Shuttle is ready, two weeks after its landing, for another working voyage.