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Space Shuttle, the world's first reusable spacecraft

Space Shuttle The US space shuttle, first launched in 1981, was the world's first reusable spacecraft. NASA ran the programme of 135 manned missions. Mission control was located at Johnson Space Center in Houston, Texas, while the shuttles themselves launched from Kennedy Space Center in Cape Canaveral, Florida.

There were originally five orbiter space planes: Atlantis, Challenger, Columbia, Discovery and Endeavour. Two of these, Challenger and Columbia, were destroyed in tragic accidents. Atlantis flew the last mission of the shuttle programme in July 2011.

The space shuttle was initially used to deploy satellites in orbit; to carry scientific experiments such as Spacelab, a modular arrangement of experiments installed in the shuttle's cargo bay; and to carry out military missions. As the program matured, the space shuttle also has been used to service and repair the International Space Station, orbiting satellites and to retrieve and return to the earth previously deployed spacecraft.

Of its three components - the orbiter space plane, rocket boosters and external fuel tank - only the fuel tank was not recovered after a mission. Special heat-resistant tiles prevented the orbiter from burning up when it re-entered the Earth's atmosphere. The remote manipulator arm in the orbiter's payload bay could put satellites into space, recapture them from space, and act as a stable platform for astronauts working in the bay.

The space shuttle carried a wide range of equipment, known as the payload, into space, ranging from communication, military, and astronomical satellites; space experiments for studying the apparent weightlessness (called 'microgravity') experienced aboard a shuttle flight; and human experimental facilities. Often NASA collaborated with other countries by allowing them to use shuttle cargo space for special projects.

Cargo Bay The space shuttle was designed to leave the earth as a vertically launched rocket weighing up to 2.0 million kg (4.5 million lb.) with 3 million kg (7 million lb.) of thrust from its multiple propulsion systems. The orbiter segment returned from space-withstanding the intense heat when entering the earth's atmosphere. Flown by the shuttle crew much like an aircraft, the shuttle would lands horizontally on a conventional airport runway.

The crew of the shuttle was an integral part of the system and was critical to the success of each mission. The flight crew was led by the commander and backed up by the pilot - both were professional astronauts and proven pilots with extensive space systems and operations training. Their primary responsibility was to fly the shuttle as a launch vehicle, spacecraft, and aircraft.

The remaining crew members - up to five more people - were responsible for the unique aspects of a particular space mission. The mission specialist was the lead astronaut and ensured that the mission met all the objectives. Payload specialists were experts in that mission's objectives and cargo, which were usually space experiments or artificial satellites. Often the payload specialists were astronauts from other countries on board to help with a project in which their country had an interest.

Spacecraft and Supporting Systems

Payload Bay The space-shuttle system, called the Space Transportation System (STS), was one of the most technologically advanced and complex machines on earth. It consisted of the orbiter, propulsion systems - two solid rocket boosters (SRBs) and three main engines, and an external fuel tank.

Space-Shuttle Orbiter

The orbiter was both the brains and heart of the STS, and it contained the latest advances in flight control, thermal protection, and liquid-rocket propulsion. About the same size and weight as a DC-9 aircraft (a fairly small two-engine jet aeroplane), the orbiter was composed of the pressurised crew compartment (which could carry up to seven crew members), the huge cargo bay, and the three main engines mounted on its aft, or rear, end.

The crew cabin had three levels: the flight deck, the mid-deck, and the utility area. Uppermost was the flight deck where the commander and pilot control the craft, surrounded by an array of switches and controls. During launch of a seven-member crew, two additional astronauts were positioned on the flight deck behind the commander and pilot. The three other crew members were in launch positions in the mid-deck, which was below the flight deck.

Spacewalk on the Shuttle The galley, toilet, sleep stations, and storage and experiment lockers were found in the mid-deck. Also located in the mid-deck were the side hatch for passage to and from the vehicle before and after landing, and the airlock hatch into the cargo bay and space beyond.

Astronauts would pass through this hatch to don their space suits and manoeuvring units (called Simplified Aid for EVA Rescue, or SAFER, these units strapped on an astronaut's back over the space suit and allowed an astronaut to move about in space without being tethered to the shuttle). This equipment prepared astronauts for extravehicular activities (EVAs), more popularly known as spacewalks. Below the mid-deck's floor was a utility area for air and water tanks.

The space shuttle's cargo bay was adaptable to hundreds of tasks. Large enough to accommodate a tour bus at 18 by 4.6 m (60 by 15 ft), the cargo bay carried satellites, spacecraft, and scientific laboratories for the modular Spacelab system to and from the earth's orbit. It also was a workstation for astronauts to repair satellites, a foundation from which to erect space structures, and a storage area for satellites retrieved from space to be returned to the earth.

Mounted on the port (left, as seen while facing the nose of the shuttle) side of the cargo bay behind the crew quarters was the remote manipulator system (RMS), developed and funded by the Canadian government. The RMS (about 15 m [50 ft] in length) was a robot arm and hand with three joints analogous to those of the human shoulder, elbow, and wrist. Two television cameras mounted near its elbow and wrist provided visual cues to the crew member who operated it from the rear station of the orbiter's flight deck. The RMS could move anything from satellites to astronauts to and from the cargo bay or to different points in nearby space. It was used on many missions, deploying and retrieving various scientific and communications satellites.

Lift Off! Thermal tile insulation and larger flexible sheets of insulating material (also known as the thermal protection system or TPS) covered the underbelly, bottom of the wings, and other heat-bearing surfaces of the orbiter to protect it during its fiery re-entry into the earth's atmosphere.

In contrast to earlier manned spacecraft such as the Apollo command module, which used material that burned and melted off in layers during re-entry and could never be used again, the shuttle's silicate fibre tiles were designed to be used for 100 missions before requiring replacement.

Some 24,000 individual tiles had to be installed by hand on the orbiter's surfaces. These tiles were incredibly lightweight, about the density of balsa wood, and dissipated heat so quickly that a white-hot tile with a temperature of 1260° C (2300° F) can be taken from an oven and held in bare hands without injury.

Propulsion Systems

The two SRBs, with their combined thrust of some 2.6 million kg (about 5.8 million lb), provided most of the power for the first two minutes of flight. The SRBs took the space shuttle to an altitude of 45 km (28 mi) and a speed of 4973 km/hr (3094 mph) before they separated and fell back into the ocean to be retrieved, refurbished, and prepared for another flight.

After the boosters fell away, the three main engines continued to provide thrust. These engines were clustered at the rear end of the orbiter and had a combined thrust of almost 540,000 kg (almost 1.2 million lb). The space shuttle's liquid-propellant engines were the world's first reusable rocket engines. They fired for only eight minutes for each flight, just until the shuttle reached orbit, and were designed to operate for 55 flights. The engines were very large - 4.2 m (14 ft) long and 2.4 m (8 ft) in diameter at the wide end of the cone-shaped nozzle at the rear of the orbiter.

Shuttle launchpad Another propulsion system took over once the space shuttle's main engines shut down as the ship approached the altitude at which it would begin orbiting around the earth, known as the orbital insertion point. Two orbital manoeuvring system (OMS) engines, mounted on either side of the aft fuselage, provided thrust for major orbital changes. For more exacting maneuvers in orbit, 44 small rocket engines (known as the reaction control system), clustered on the shuttle's nose and on either side of the tail, were used. They were proven indispensable in performing the shuttle's important work of retrieving, launching, and repairing satellites in orbit.

External Fuel Tank

The giant, cylindrical, external fuel tank, with a length of 47 m (154 ft) and a diameter of 8.4 m (27.5 ft), was the largest single piece of the space shuttle. It fueled the orbiter's three main engines. During launch, the external tank also acted as a support for the orbiter and SRBs to which it was attached.

Inside separate pressurised tanks, the external tank held the liquid hydrogen fuel and liquid oxygen oxidiser (which reacted with the hydrogen to produce combustion) that ran the shuttle's three main engines. During launch, the external tank fed the fuel under pressure through small ducts that branched off into smaller lines that fed directly into the main engines. Some 450 kg (1000 lb.) of fuel were consumed by each of the main engines each second.

Made from aluminum alloys, the space shuttle's external fuel tank was the only part of the launch vehicle that was not reused. After its 1.99 million litres (526,000 gal) of fuel were consumed during the first 8.5 minutes of flight, the external tank was jettisoned from the orbiter and broke up in the upper atmosphere, its pieces falling into remote ocean waters.

Challenger Disaster

On January 28, 1986, millions of television viewers all over the world watched in horror as the Space Shuttle Challenger exploded less than two minutes after its launch. It was totally destroyed, and all seven crew members were killed. One of the crew, Christa McAuliffe, was a teacher who had intended to conduct lessons from space. An inquiry into the disaster found that the seal between two sections of a booster rocket had failed, causing a gas leak, which then ignited. The Shuttle Program was grounded for nearly three years after the accident while its safety was improved.

Columbia Disaster

On January 16, 2003, the fate of the Shuttle Columbia was sealed savagely. During takeoff, a piece of insulated foam broke loose from the external tank and struck the underside of the orbiter’s left wing, causing damage that broke apart the orbiter upon its reentry on February 1. Caught in a big explosion that trailed across the daylight sky of the southern U.S., the seven astronauts were killed instantly, among them Ilan Ramon, the first Israeli to fly aboard a NASA Shuttle. The remaining Shuttles were kept away from the launch pad for a long time before resuming their normal routines; in the meantime, America and the world took time off to mourn their lost heroes and investigate the accident.

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Author: Marc Delehanty

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