THE SPACE SHUTTLE
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image.
 Space Shuttles are the main element of
America's Space Transportation System and are used for space research and
space applications. The shuttles are the first vehicles capable of being
launched into space and returning to earth on a routine basis.
Space shuttles are used as
orbiting laboratories in which scientists and mission specialists conduct
a wide variety of scientific experiments, and study and photograph stars,
galaxies, the planets, and other bodies in and beyond the universe.
Crews aboard
space shuttles place satellites in orbit. They also rendezvous with
satellites to carry out repairs and return them to orbit. Satellites are
also returned to earth in space shuttles for refurbishment and
reuse.
A True Aerospace Vehicle
 The space shuttles are true aerospace vehicles. They leave earth
and its atmosphere under rocket power provided by three liquid-fueled main
engines and two solid-fuel boosters attached to an external liquid fuel
tank.
After their missions in orbit end,
the shuttles streak back through the atmosphere and are maneuvered to land
like an airplane. The shuttles, however, are without power and they land
on runways like a glider.
Other rockets can place heavy
payloads into space, but they are used only once. Space shuttles are
designed to be used 100 times.
Space shuttles are used to transport
complete scientific laboratories into space. The laboratories remain
inside the payload bay throughout the mission. They are removed after the
orbiter returns to earth and can be prepared for another
flight.
Some of these laboratories, like the
Spacelab developed by the European Space Agency, provide facilities for
several specialists to conduct experiments in such fields as medicine,
astronomy, and materials manufacturing.
 Among the types of satellites
the shuttle can orbit and service in space are those involved in
environmental and resources protection, weather forecasting, navigation,
oceanographic studies, and other fields useful to citizens throughout the
world.
Interplanetary spacecraft can be
placed into orbit by space shuttles with the use of a propulsion unit
called the Inertial Upper Stage (IUS). After the satellite or spacecraft
is deployed from the shuttle payload bay, the IUS is ignited to accelerate
the spacecraft deep into space. The IUS is also used to boost satellites
into an orbit higher than the space shuttle's maximum altitude of 600
miles.
Now, space shuttles can be used to
carry into orbit the structural components that are assembled and become
the space station, a permanent facility in which crews of astronauts work
for extended periods of time in space. The space station has its own solar
power units and astronauts carry out a wide range of scientific
activities. Space shuttles are not only be used to help construct the
space station, but are also used to ferry crew members and supplies
between it and earth.
Development
History
 In 1969, shortly after the
first moon landing of the Apollo program, the President's Space Task Group
recommended that the United States initiate a program to develop a new
space transportation system. In 1970 NASA initiated engineering, design,
and cost studies dealing with the concept of a reusable manned spacecraft
that utilized strap-on solid propellant rockets and an expendable liquid
fuel/oxidizer tank.
On Jan. 5, 1972, President Richard M.
Nixon gave NASA authority to proceed with development of this type of
reusable space system. NASA selected the Space Transportation Systems
Division of Rockwell International, Downey, Calif., to build the orbiters.
Rockwell's Rocketdyne Division builds the three main engines used on each
orbiter. Morton Thiokol, Brigham City, Utah, makes the solid rocket
booster motors, and Martin Marietta Corp., New Orleans, La., makes the
external fuel tank.
A Typical Shuttle
Mission
 Space shuttles are launched from
the NASA John F. Kennedy Space Center in Florida.
The orbiter processing area is
several miles from the launch pads. After the orbiters are readied for
flight they are mated with the external fuel tank and the solid rocket
boosters and the assembled components receive final detailed systems
checks before they are moved to the launch pad.
The orbiter's main engines and the
booster rockets ignite simultaneously to lift the shuttle and its crew
away from earth and into space. About two minutes after launch, the solid
rocket boosters complete their firing sequence and separate from the
external tank and, by parachute, fall back into the ocean where they are
recovered and used again. The orbiter continues its flight into space with
the main engines furnishing ascent power for another eight minutes before
they are shut down, just before achieving orbit. The external tank, now
empty, separates and falls back into the atmosphere and breaks up over a
remote area of the ocean. It is not reusable.
In orbit, space shuttles circle the
earth at a speed of about 17,500 mph. Each orbit is about 90 minutes and
the crew sees a sunrise or a sunset every 45 minutes.
Orbital altitudes
for shuttle missions range from as low as 155 miles to as high as 600
miles, based on mission requirements. The flight paths are within a region
over earth extending from 57 degrees north to 57 degrees south of the
equator.
 Missions
usually last up to 10 days, but the crew has food, fuel, and other
supplies to remain in orbit several days longer than planned in case they
cannot come back on time due to bad weather at the landing
sites.
The crew size
varies and can be as many as eight people, although up to 10 can be
carried under special conditions. The crew includes the commander, the
pilot, and enough mission specialists and payload specialists to carry out
the specific mission. Mission specialists are responsible for equipment
and resources supporting the payloads during the flight, while the payload
specialists are in charge of the specific payload equipment. The mission
commander, pilot, and mission specialists are NASA astronauts and assigned
by NASA. Payload specialists may or may not be astronauts, and are
nominated for the mission by the payload sponsor.
When the mission ends
and the orbiter begins to glide back through the atmosphere, special
insulation covering the outside portions of the vehicle acts as a heat
shield to keep it from getting too hot from air friction and damaged by
the heat. Most of the insulation used to protect the orbiter in places
where it gets extremely hot is shaped like small tiles. The tiles, about
six inches square and made of silica, shed heat so well that one
side is cool enough to hold in bare hands while the other side is red hot
and withstands temperatures of 2300 degrees (F). Some tiles get damaged
during launch or landing and are replaced.
After the space
shuttles began flights in April 1981 Edwards Air Force Base, Calif., the
location of NASA's Dryden Flight Research Center, was the primary landing
site. The shuttles used the main 15,000-foot runway, or on Rogers Dry
Lake, which has seven designated runways on the natural clay surface. The
Kennedy Space Center is now the primary landing site, with Edwards
remaining as an alternate.
When certain
developmental tests on orbiter systems are being carried out, Edwards is
an excellent landing site because of the safety margin presented by the
lakebed and the number of runways from which mission controllers and
shuttle crews can choose.
The landing speed
of the orbiters ranges from 205 to 235 mph, based on the weight of the
vehicle.
Among improvements
to the orbiters since flights began have been installation of a drag
parachute at the aft end of the fuselage.  They are deployed when the orbiters land
to help lower rollout speed to reduce tire and brake wear. Endeavour, the
newest orbiter, was the first to have the drag chute system installed.
They have been retrofitted on the three other vehicles.
Post-Landing Operations
As soon
as the landing occurs, a team of space shuttle recovery operations
specialists carefully inspect the orbiter to be sure no gases or fuels are
present that may be toxic. This clears the way for the shuttle crew to
power down the vehicle while other ground operations personnel begin
connecting up ground support equipment and prepare to tow the spacecraft
from the landing site to the space shuttle deservicing area at either the
Kennedy Space Center in Florida or at Dryden.
 Hoses from two large mobile units are
attached to the orbiter during the towback from the landing site. One is a
large air conditioning unit to direct cool air into the orbiter's aft
fuselage, payload bay, wings, vertical stabilizer, and orbital
maneuvering-reaction control system pods to dissipate heat generated by
atmospheric reentry. The other unit is a Freon coolant system to protect
the flight crew area and avionics systems from excessive heat during
post-landing systems checks.
When
the orbiters land at Dryden, they are towed to the Mate-Demate Device
(MDD). It is a large gantry-like structure where the orbiters receive
post-flight servicing and are prepared for the ferry flights back to the
Kennedy Space Center with the NASA 747 Shuttle Carrier Aircraft (SCA).
Before the ferry flights begin, all orbiter systems are checked thoroughly
and certain fuel lines and tanks are purged.
Post-flight servicing and ferry flight preparations at
the MDD normally take about five days. When the orbiter is ready for the
ferry flight, it is lifted by the MDD and placed on special mounts atop
the SCA fuselage. Ferry flights back to the Kennedy Space Center usually
take one to two days, based on weather along the route.
 Component
Descriptions
The
space shuttle system is composed of several large components: the orbiter,
the main engines, the external tank , and solid rocket boosters. The gross
launch weight is about 4.5 million pounds (varies based on payload weight
and consumable supplies).
Orbiter: Each orbiter is 121 feet long, has a wingspan
of 78 feet, and a height of 57 feet. It is about the size of a DC-9
commercial airliner, and can carry a payload of 65,000 pounds into space.
The payload bay is 60 feet long and 15 feet in diameter. The landing
weight will vary from mission to mission and ranges from 200,000 pounds to
230,000 pounds. Most of its basic construction, like an aircraft, is of
aluminum. The forward fuselage houses the cockpit and crew cabin and crew
work areas. The mid-fuselage area consists of the payload bay, and the
wing and main landing gear attach points. The aft fuselage houses the main
engines, the orbital maneuvering system, the reaction control system pods,
the wing aft spar, and the attach point for the vertical tail. Each
orbiter is designed with a lifetime of about 100 space
missions.
 Main Engines:
Each main engine, operating on a mixture of liquid oxygen and liquid
hydrogen, produces a sea level thrust of 375,000 pounds and a vacuum
thrust of 470,000 pounds. They can be throttled over a thrust range of 65
to 109 percent, allowing a high power setting during liftoff and initial
ascent, but a power reduction to limit acceleration of the orbiter to 3Gs
during final ascent. The engines are gimbaled (movable) to provide pitch,
yaw, and roll control during ascent phases of flight. Normal engine
operating time on each flight is about 8.5 minutes. Each engine has a
designed lifetime of about 7.5 operating hours.
External Tank: Each external tank is 154 feet long and
28.6 feet in diameter. They are constructed primarily of aluminum alloys.
Empty weight of an external tank is 78,100 pounds. When filled and flight
ready, each has a gross weight of 1,667,677 pounds and contains nearly 1.6
million pounds (143,060 gallons) of liquid oxygen and more than 226,000
pounds (526,126 gallons) of liquid hydrogen. The external tank is the only
major part of the space shuttle system not reused after each
flight.
Solid
Rocket Boosters: The space shuttle solid rocket boosters are the largest
solid propellant motors ever built and the first to be used on a manned
spacecraft. Each motor is made of 11 individual weld-free steel segments
joined together with high-strength steel pins. Each assembled motor is 116
feet long, 12 feet in diameter, and contains more than l million pounds of
solid propellant. The propellant burns at a temperature of 5,800 degrees
(F) and generates a lift-off thrust of 2.65 million pounds. The exhaust
nozzles are gimbaled to provide yaw, pitch, and roll control to help steer
the orbiter on its ascent  path. The solid propellant is made of
atomized aluminum powder (fuel), ammonium perchlorate (oxidizer), iron
oxide powder (catalyst), plus a binder and curing agent. The boosters burn
for two minutes in parallel with the main engines during initial ascent
and give the added thrust needed to achieve orbital altitude. After two
minutes of flight, at an altitude of about 24 miles, the booster casings
separate from the external tank. They descend by parachute into the
Atlantic Ocean where they are recovered by ship, returned to land, and
refurbished for reuse.
Major Subsystems
Orbital
Maneuvering System (OMS): Two rocket units at the orbiter's aft end, at
the base of the vertical tail, are used to place the vehicle onto its
final orbital path and they are used for extended maneuvering while in
space. The OMS is also used to slow the vehicle's speed in orbit at the
end of the mission. When the orbiter slows down, gravity begins pulling it
back into the atmosphere and it glides back to earth for a runway landing.
The OMS uses nitrogen tetroxide and monomethyl hydrazine for fuel. Each
engine produces 6,000 pounds of thrust.
 Reaction Control System (RCS): This
system consists of 44 nozzles on both sides of the nose and each side of
the aft fuselage pod near each OMS engine. The RCS is used throughout the
mission to move or roll the orbiter as the crew carries out tasks which
require the vehicle to be pointed certain ways for experiments or
photography. The RCS uses the same types of fuel as the OMS. Thirty-eight
of the thrusters produce 870 pounds of thrust each. The six others each
produce 25 pounds of thrust.
Electrical Power: Three fuel cells supply electrical
power on the orbiter during all phases of a mission. The units are located
in the mid-body area of the payload bay. Electrical power is produced by
the chemical reaction of hydrogen and oxygen, which are supplied
continuously as needed to meet output requirements. A by-product of this
reaction is drinking water used by crew. Each fuel cell is connected to
one of three independent electrical distribution systems. During peak and
average power loads, all three systems are used. During minimum loads,
only two are used and the third is on standby, but can be brought back on
line instantly if needed. The system provides up to 24 kilowatts of power,
ranging from 27.5 to 32.5 volts of direct current.
Hydraulic Power: Three auxiliary power units (APU)
furnish power to operate hydraulic systems on the orbiters such as the
main engine gimbaling controls, the nose and main landing gear and brake
systems, and the rudder, speed brake, and elevon flight control  surfaces. The APUs are fueled by
hydrazine which is changed into a hot gas by a granular catalyst. The
momentum of the expanding gas spins turbine blades and this energy is
transferred to gearboxes on the hydraulic pump units. All three APUs
operate during launch, but only two are needed for reentry and
landing.
Environment Control and Life Support System: The
orbiter's environmental control and life-support system purifies the cabin
air, adds fresh oxygen, keeps the pressure at sea level, heats and cools
the air, and provides drinking and wash water. The system also includes
lavatory facilities. The cabin is pressurized to sea level (14.7 psi) with
21 percent oxygen and 79 percent nitrogen, comparable to earth's
atmosphere. The air is circulated through lithium hydroxide/charcoal
cannisters which remove carbon dioxide. The cannisters are changed on a
regular basis. Heat from the cabin and flight-deck electronics is
collected by a circulating coolant water system and transferred to
radiator panels on the payload bay doors where it is dissipated. The fuel
cells produce about seven pounds of water each hour. It is stored in
tanks, and the excess water is dumped overboard when the tanks are full.
The lavatory unit collects and processes body waste, and also collects
wash water from the personal hygiene station. The lavatory unit, located
in the mid deck area, operates much like those on commercial airlines but
is designed for a weightless space environment.
 Thermal Protection: The thermal
protection system is designed to limit the temperature of the orbiter's
aluminum and graphite epoxy structures to about 350 degrees (F) during
reentry. There are four types of materials used to protect the orbiter.
Reinforced carbon-carbon is a composite of a layer of graphite cloth
contained in a carbon matrix. It is used on the nose cap and wing leading
edges where temperatures exceed 2,300 degrees (F). High-temperature
reusable surface insulation consists of about 20,000 tiles located mainly
on the lower surfaces of the vehicle. They are about six inches square and
made of a low-density silica fiber insulator bonded to the surface in
areas where temperatures reach up to 1,300 degrees (F). Low-temperature
reusable surface insulation also consists of tiles. There are about 7000
of this variety on the upper wing and fuselage sides where temperatures
range from 700 to 1,200 degrees (F). Flexible reusable surface insulation
(coated Nomex felt) is sheet-type material applied directly to the payload
bay doors, sides of the fuselage and upper wing areas where heat does not
exceed 700 degrees (F).
Photo credits:
NASA |
