|
Overview
NASA space shuttles are the main element of America's Space Transportation System
(STS) and are used for space research and space applications. They are the world's first reusable
spacecraft, and the first spacecraft in history that can carry large satellites both to and from
orbit. A shuttle launches like a rocket, maneuvers in Earth orbit like a spacecraft and lands like
an airplane.
Space shuttles are primarily 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. The shuttles are also
used place satellites in orbit or to rendezvous with orbiting satellites so that repairs can be
made. When required, satellites can be returned to Earth in space shuttles for refurbishment.
History
In September 1969, two months after the first manned lunar landing, a Space Task
Group appointed by the President of the United States to study the future course of U.S. space
research and exploration made the recommendation that "....the United States accept the basic goal
of a balanced manned and unmanned space program. To achieve this goal, the United States
should....develop new systems of technology for space operation....through a program directed
initially toward development of a new space transportation capability...."
In early 1970, NASA initiated extensive engineering, design, and cost studies of
a space shuttle. These studies covered a wide variety of concepts ranging from a fully reusable
manned booster and orbiter to dual strap-on solid propellant rocket motors and an expendable liquid
propellant tank. Each concept evaluated development risks and costs in relation to the suitability
and the overall economics of the entire system.
On 5 January 1972, President Richard M. Nixon announced that NASA would proceed
with the development of a reusable low cost space shuttle system. NASA and its aerospace industry
contractors continued engineering studies through January and February of 1972; finally on 15 March
1972, NASA announced that the shuttle would use two solid propellant rocket motors.
In the post-Apollo era, the Space Shuttle was intended to make access to space
"routine" and less expensive. To meet these goals, it had to be reusable and economical to develop
and operate. Thus, the design of the Shuttle was shaped not only by engineering considerations but
also by interests of the White House, Congress and Department of Defense.
The First Shuttle
On 17 September 1976, the first orbiter spacecraft, Enterprise (named
after the famed starship in the television series Star Trek),
was rolled out. A total of thirteen test flights were performed. The Enterprise was built
as a test vehicle and was not equipped for space flight.
The main role of this test vehicle was to check the Shuttle's flight
characteristics and performance. NASA conducted the Approach and Landing Test Program from February
through November 1977 at the Dryden Flight Research Center. Ground tests included taxi tests with
Enterprise mounted atop the Boeing 747 Shuttle Carrier Aircraft
(SCA) to determine loads, control characteristics, steering, and braking of the mated vehicles. Five
captive flights with Enterprise attached to the SCA were conducted, with the Shuttle unmanned
and its systems inert, to assess structural integrity and performance of the mated craft in flight.
Three manned captive-flights followed, with an astronaut crew aboard the Shuttle (still attached to
the SCA) operating and evaluating its activated systems in flight. Finally, two astronaut crews took
turns piloting the 150,000-pound Shuttle test vehicle from an altitude of 19,000 to 26,000 feet to
five free-flight landings at Edwards Air Force Base under conditions simulating a return from space.
For all of the captive flights and the first three free flights, the orbiter
was outfitted with a tailcone covering its aft section to reduce aerodynamic drag and turbulence.
The final two free-flights were made without the tailcone, and the three simulated space shuttle
main engines and two orbital maneuvering system engines were exposed aerodynamically.
On 18 November 1985, Enterprise was ferried from Kennedy Space Center to
Washington, D.C. and became the property of the Smithsonian Institution.
The First Launch
The second orbiter, Columbia, was the first to fly into space. Perched atop
NASA's SCA, Columbia arrived at Kennedy Space Center from Dryden Flight Research Facility on 25 March
1979 to be readied for the its first flight on 12 April 1981. This first shuttle mission (STS-1),
flown by John Young (Commander) and Robert Crippen (Pilot), lasted 54 hours, 21 minutes.
Each of the five space shuttle orbiters — Columbia, Challenger, Discovery, Atlantis
and Endeavour — were designed to fly at least 100 missions.
| Orbiter |
Notes |
| Enterprise |
Shuttle prototype. Approach and Landing test vehicle; never launched into space. First free-flight on 12 August 1977. Officially retired on 18 November 1985. |
| Columbia |
First launched on 12 April 1981. Broke apart during re-entry on 1 February 2003, killing the entire crew of seven. |
| Challenger |
First launched on 4 April 1983. Exploded 73 seconds after liftoff on 28 January 1986, killing the entire crew of seven. |
| Discovery |
First launched on 30 August 1984. |
| Atlantis |
First launched on 3 October 1985. |
| Endeavour |
First launched on 7 May 1992. Built as a replacement for Challenger. |
|
|
Features
The Space Shuttle consists of three major components: the orbiter which
houses the crew; a large external fuel tank that holds fuel for the main engines; and two
solid rocket boosters which provide most of the Shuttle's lift during the first two minutes of
flight. All of the components are reused except for the external fuel tank, which burns up in the
atmosphere after each launch.
Orbiter
The cockpit, living quarters and experiment operator's station are located in the
forward fuselage of the orbiter vehicle. Payloads are carried in the mid-fuselage payload bay, and
the orbiter's main engines and maneuvering thrusters are located in the aft fuselage.
External Fuel Tank
The external tank is 154 feet (46.9 m) long, 28.6 feet (8.7 m) in diameter, and has an
empty weight of 78,100 pounds. When filled and flight ready, it 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 tank is also the "backbone" of the shuttle during the launch,
providing structural support for attachment with the solid rocket boosters and orbiter.
At liftoff, the external tank absorbs the total thrust loads of the three main engines
and the two solid rocket motors. When the solid rocket boosters separate at an altitude of approximately
28 miles (45 km), the orbiter, with its main engines still burning, carries the external tank piggyback
to near orbital velocity, approximately 70 miles (113 km) above the earth. Approximately 8.5 minutes into
the flight, with its propellant used, the empty tank is jettisoned and falls in a preplanned trajectory
with the majority of it disintegrating in the atmosphere and the rest falling into the ocean. It is the
only major part of the STS which is not reusable.
Solid Rocket Boosters
The STS 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 (35.4 m) long, 12 feet
(3.7 m) 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 (38.6 km), 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.
Space Shuttle Main Engines
The three main engines of the Space Shuttle, in conjunction with the solid rocket
boosters, provide the thrust to lift the orbiter off the ground for the initial ascent. The main
engines continue to operate for 8.5 minutes after launch, the duration of the Shuttle's powered
flight.
After the solid rockets are jettisoned, the main engines provide thrust which
accelerates the Shuttle from 3,000 mph (4,828 km/h) to over 17,000 mph (27,358 km/h) in just six
minutes to reach orbit. 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. Each engine has a designed lifetime of about 7.5 operating hours.
Mission Sequence
The orbiter processing area is several miles from the Kennedy Space Center launch
pads. After the orbiters are readied for flight they are mated with the external fuel tank and solid
rocket boosters then receive final detailed systems checks before they are moved to the launch pad.
The orbiter's main engines and 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 fuel 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.
In orbit, Space Shuttles circle the earth at a speed of about 17,500 mph (28,164
km/h). Each orbit is about 90 minutes long and the crew sees a sunrise or a sunset every 45 minutes.
Orbital altitudes for Shuttle missions range from as low as 155 miles (250 km) to as high as 600
miles (966 km), 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.
After the Space Shuttles began flights in April 1981, Edwards AFB, CA, the
location of NASA's Dryden Flight Research Center, was the primary landing site. The Shuttles used
the main 15,000-foot runway, or 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. The landing speed of the orbiters ranges from 205 to 235 mph (330-378 km/h), based on the
weight of the vehicle.
Among improvements to the orbiters since flights began have been the 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 to 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 FRC in California.
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. 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's fuselage. Ferry flights back to the Kennedy Space Center usually
take one to two days, based on weather along the route.
Back to top 
|
