The Space Shuttle is an American spacecraft operated by the National Aeronautics and Space Administration (NASA) for orbital human spaceflight missions. The Space Shuttle is part of the Space Transportation System (STS). Space Shuttles are one of the most talked about aircrafts. The Shuttle is a reusable launch and reentry vehicle that saves on the costs that were once required to carry out a space mission. The Shuttle can also remove objects from orbit when their missions or lifetime has ended.
Major missions consisted of launching numerous satellites and interplanetary probes, conducting space science experiments, and servicing and construction of space stations. A typical Shuttle mission lasts seven to eight days, but can go up to 14 days depending on what the mission was for. Although designs and construction of the Space Shuttle began in the 1970s, the concept of a spacecraft returning from space to a horizontal landing began with NACA, in 1954, in the form of an aeronautics research experiment later named the X-15.The NASA space program really began working when President Nixon signed the approval for the development of the Space Shuttle in 1972. The Space Shuttle development was a group effort by all groups at NASA. The first Shuttle produced was the Enterprise and its main goal was to practice entering the upper atmosphere and returning to earth with a safe landing.
The first fully functional Space Shuttle was the Colombia and it did its first mission in 1981. The United States funded STS development and Shuttle operations.The Shuttle has been used for orbital space missions by NASA, the U. S. Department of Defense, the European Space Agency, and Germany. Each Space Shuttle is a reusable launch system that is composed of three main parts: the reusable Orbiter Vehicle (OV), the expendable external tank (ET), and the two reusable solid rocket boosters (SRBs).
Only the orbiter enters orbit shortly after the tank and boosters are jettisoned. The vehicle is launched vertically like a conventional rocket, and the orbiter glides to a horizontal landing like an airplane, after which it is refurbished for reuse.The SRBs parachute to splashdown in the ocean where they are towed back to shore and fixed for later shuttle missions. The orbiter can be used in conjunction with a variety of add-ons depending on the mission. The main function of the Space Shuttle external tank is to supply the liquid oxygen and hydrogen fuel to the Space Shuttle main engines.
It is also the backbone of the launch vehicle giving attachment points for the two Solid Rocket Boosters and the Orbiter. The external tank is the only part of the shuttle system that is not used over again.Two solid rocket boosters (SRBs) each provide thrust 83 percent of the thrust needed at liftoff. The SRBs are jettisoned two minutes after launch and then deploy parachutes and land in the ocean to be recovered. The shuttle was one of the earliest craft to use a computerized fly-by-wire digital flight control system.
This means no mechanical linkages connect the pilot's control stick to the control surfaces or reaction control system thrusters. A big concern with digital fly-by-wire systems is reliability. A lot of research went into the shuttle computer system.Four computers run specialized software called the Primary Avionics Software System (PASS). A fifth backup computer runs separate software called the Backup Flight System (BFS).
All together they are called the Data Processing System (DPS). The design goal of the shuttle's DPS is fail-operational/fail-safe reliability. After one failure, the shuttle can still continue the mission. After two failures, it could still land safely. The four general-purpose computers operate essentially in lockstep, checking each other.
If one computer fails, the three functioning computers "vote" it out of the system. This separates it from vehicle controls. If a second computer of the three that are left fails, the two functioning computers vote it out. The Backup Flight System (BFS) is separately developed software running on the fifth computer. The Backup Flight System is only used if the entire four-computer main system fails.
The BFS was created because although the four main computers are hardware redundant, they all run the same software, so a generic software problem could crash all of them.The Space Shuttle has received many upgrades and modifications since the 1970s for improvements ranging from performance and reliability to safety. Inside, the shuttle still is largely similar to the original design, with the exception of the improved avionics computers. The Space Shuttle Main Engines (SSMEs) have had several improvements to enhance reliability and power. The vision of the future is to establish a long term orbiting space station that will be greatly aided by the use of the Shuttles or by a newly designed shuttle type vehicle.
The system is scheduled to be retired from service in 2011 after 135 launches.
