Category Science

Earth’s atmosphere is made up of minuscule particles of rock and gas. When an orbiter re-enters the atmosphere, it impacts with these particles, heating up because of friction. Parts of the Shuttle can reach up to 1500°C (2732°F), which is hot enough to cause them to melt. Because of this, the nose tip and wing edges are protected by heat-absorbing tiles that prevent the orbiter from getting too hot.

Spacecraft re-entry is tricky business for several reasons. When an object enters the Earth’s atmosphere, it experiences a few forces, including gravity and drag. Gravity will naturally pull an object back to earth. But gravity alone would cause the object to fall dangerously fast. Luckily, the Earth’s atmosphere contains particles of air. As the object falls, it hits and runs against these particles, creating friction. This friction causes the object to experience drag, or air resistance, which slows the object down to a safer entry speed. 

This friction is a mixed blessing, however. Although it causes drag, it also causes intense heat. Specifically, shuttles face intense temperatures of about 3000 degrees Fahrenheit (about 1649 degrees Celsius). Blunt-body design helps alleviate the heat problem. When an object — with blunt-shaped surface facing down — comes back to Earth, the blunt shape creates a shock wave in front of the vehicle. That shock wave keeps the heat at a distance from the object. At the same time, the blunt shape also slows the object’s fall. The Apollo program, which moved several manned ships back and forth from space during the 1960s and 1970s, coated the command module with special ablative material that burned up upon re-entry, absorbing heat.

Unlike the Apollo vehicles, which were built for one-time use, space shuttles are reusable launch vehicles (RLVs). So instead of merely using ablative material, they must incorporate durable insulation. On the next page, we’ll delve more deeply into the modern re-entry process for shuttles.

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The Space Shuttle was a partially reusable low Earth orbital spacecraft system operated by the U.S. National Aeronautics and Space Administration (NASA). Its official program name was Space Transportation System (STS), taken from a 1969 plan for a system of reusable spacecraft of which it was the only item funded for development. Operational missions launched numerous satellites, conducted science experiments in orbit, and participated in construction and servicing of the International Space Station (ISS). The first of four orbital test flights occurred in 1981, leading to operational flights beginning in 1982.

Unfortunately there are many risks relating to space travel. With the tremendous forces involved, accidents inevitably occur. In 1986, the Challenger orbiter exploded when a joint between two segments of one of the boosters came loose. Tragically, everybody on board died.

From 1981 to 2011 a total of 135 missions were flown, all launched from Kennedy Space Center (KSC) in Florida. During that time period the fleet logged 1,322 days, 19 hours, 21 minutes and 23 seconds of flight time. The longest orbital flight of the Shuttle was STS-80 at 17 days 15 hours, while the shortest flight was STS-51-L at one minute 13 seconds when the Space Shuttle Challenger broke apart during launch. The shuttles docked with Russian space station Mir nine times and visited the ISS thirty-seven times. The highest altitude (apogee) achieved by the shuttle was 350 miles (560 km) when servicing the Hubble Space Telescope. The program flew a total of 355 people representing 16 countries. The Kennedy Space Center served as the landing site for 78 missions, while 54 missions landed at Edwards Air Force Base in California and one mission landed at White Sands, New Mexico.

The first orbiter built, Enterprise, was used for atmospheric Flight but future plans to upgrade it to orbital capability were ultimately canceled. Four fully operational orbiters were initially built: Columbia, Challenger, Discovery, and Atlantis. Challenger and Columbia were destroyed in mission accidents in 1986 and 2003 respectively, killing a total of fourteen astronauts. A fifth operational orbiter, Endeavour, was built in 1991 to replace Challenger. The Space Shuttle was retired from service upon the conclusion of STS-135 by Atlantis on 21 July 2011.

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After extensive preparation, the STS lift off from the launch tower. After eight seconds, the rocket is travelling at 160km/h (100mph), but it only takes one minute to reach 1600km/h (1000mph). At a height of 45km (28 miles), the solid rocket boosters are jettisoned. They fall back to Earth, using parachutes. When the fuel in the external tank is used up, it too is jettisoned, burning up in Earth’s atmosphere. Once the orbiter reaches a low-Earth orbit, it stays there for up to two weeks before beginning the dangerous return trip.

The space shuttle was developed by the National Aeronautics and Space Administration, more commonly known as NASA. The vehicle consists of a winged orbiter, two solid-rocket boosters, and an external fuel tank. As with previous spacecraft, the shuttle is launched from a vertical position. Liftoff thrust is derived from the orbiter’s three main liquid-propellant engines and the boosters. After two minutes, the boosters use up their fuel, Separate from the Spacecraft, and after deployment of parachutes are recovered following splashdown. During this time, the speed of the shuttle is about 1400 meters per second.

After about eight minutes of flight, the orbiter’s main engines shut down; the external tank is then jettisoned and burns up as it reenters the atmosphere. The orbiter meanwhile enters orbit after a short burn of its two small Orbiting Maneuvering System (OMS) engines. At this time, its top speed is an amazing 8,000 meters per second! To return to earth, the orbiter turns around, fires its OMS engines to reduce speed, and, after descending through the atmosphere lands like a glider.

After four orbital test flights (1981-1982) of the space shuttle Columbia, operational flights began in November of 1982. On January 28, 1986, a shuttle exploded shortly after takeoff, killing all seven astronauts. Shuttle flights were suspended until September 1988, while design problems were corrected, and then resumed on a more conservative schedule; NASA was forced to reemphasize expendable rockets to reduce the cost of placing payloads in space. By the end of 2000, 102 missions had been completed and five different orbiters had been seen in service.

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The orbiter is the most important section of the Space Shuttle. Although it looks a great deal like a small plane, it is actually a high-tech laboratory and storage area, with facilities to hold up to seven crew members for over two weeks. The front end of the orbiter is comprised of three levels: the flight deck, the mid-deck, where the crews live whilst in space, and the lower deck, which contains vital life-support equipment. Most of the orbiter is taken up by a vast payload bay.

The Orbiter is both the brains and heart of the Space Transportation System. About the same size and weight as a DC-9 aircraft, the Orbiter contains the pressurized crew compartment (which can normally carry up to seven crew members), the huge cargo bay, and the three main engines mounted on its aft end. 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.

The cockpit, living quarters and experiment operator’s station are located in the forward fuselage. This area houses the pressurized crew module and provides support for the nose section, the nose gear and the nose gear wheel well and doors.

The 65.8-cubic-meter (2,325-cubic-foot) crew station module is a three-section pressurized working, living and stowage compartment in the forward portion of the Orbiter. It consists of the flight deck, the middeck/equipment bay and an airlock. Outside the aft bulkhead of the crew module in the payload bay, a docking module and a transfer tunnel with an adapter can be fitted to allow crew and equipment transfer for docking, Spacelab and extravehicular operations. The two-level crew module has a forward flight deck with the commander’s seat positioned on the left and the pilot’s seat on the right.

The flight deck is designed in the usual pilot/copilot arrangement, which permits the vehicle to be piloted from either seat and permits one-man emergency return. Each seat has manual flight controls, including rotation and translation hand controllers, rudder pedals and speed-brake controllers. The flight deck seats four. The on-orbit displays and controls are at the aft end of the flight deck/crew compartment. The displays and controls on the left are for operating the Orbiter, and those on the right are for operating and handling the payloads. More than 2,020 separate displays and controls are located on the flight deck.

Six pressure windshields, two overhead windows and two rear-viewing payload bay windows are located in the upper flight deck of the crew module, and a window is located in the crew entrance/exit hatch located in the midsection, or deck, of the crew module.

The middeck contains provisions and stowage facilities for four crew sleep stations. Stowage for the lithium hydroxide canisters and other gear, the waste management system, the personal hygiene station and the work/dining table is also provided in the middeck. The nominal maximum crew size is seven. The middeck can be reconfigured by adding three rescue seats in place of the modular stowage and sleeping provisions. The seating capacity will then accommodate the rescue flight crew of three and a maximum rescued crew of seven.

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The STS is comprised of four main parts: the orbiter is the main section of the Shuttle, housing the crew, the control centre and the payload. The orbiter is the only part of the Shuttle to reach orbit, after which it returns to Earth, landing like a plane. An external fuel tank contains the liquid hydrogen and liquid oxygen needed for propulsion. Two solid rocket boosters propel the orbiter to a height of 45km (28 miles) before they are jettisoned.

Orbiter: Each orbiter is 121 feet long, with a wingspan of 78 feet and a tail height of 57 feet. Constructed mainly of aluminum, 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 varies from mission to mission and ranges from 200,000 pounds to 230,000 pounds. Each orbiter is designed for a lifetime of about 100 space missions. 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 (OMS), the reaction control system (RCS) pods, the wing aft spar, and the attach point for the vertical tail.

Main Engines: The main engines operate on a mixture of liquid oxygen and liquid hydrogen, each engine producing a sea level thrust of 375,000 pounds and a vacuum thrust of 470,000 pounds. The engines can be throttled over a thrust range of 65 to 109 percent, allowing a high power setting during liftoff and initial ascent, and a power reduction during final ascent to keep acceleration of the orbiter at three earth gravities. The engines are gimbaled (movable) to control pitch, yaw, and roll. Normal engine operating time on each flight is about 8.5 minutes. Each engine is designed for about 7.5 total operating hours.

External Tank: The external tank is 154 feet long and 28.6 feet in diameter. It is 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 Fahrenheit and generates a liftoff 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 28 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.

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Most rockets either burn up in Earth’s atmosphere or are decommissioned after they have completed their mission. A new rocket has to be built from scratch for the next launch. All but one part of NASA’s Space Shuttle returns to Earth intact. After these parts have been checked for damage, they are ready to be used again, therefore saving the cost of rebuilding.

The U.S. space shuttle consisted of three major components: a winged orbiter that carried both crew and cargo; an external tank containing liquid hydrogen (fuel) and liquid oxygen (oxidizer) for the orbiter’s three main rocket engines; and a pair of large, solid-propellant, strap-on booster rockets. At liftoff the entire system weighed 2 million kilograms (4.4 million pounds) and stood 56 metres (184 feet) high. During launch the boosters and the orbiter’s main engines fired together, producing about 31,000 kilonewtons (7 million pounds) of thrust. The boosters were jettisoned about two minutes after liftoff and were returned to Earth by parachute for reuse. After attaining 99 percent of its orbital velocity, the orbiter had exhausted the propellants in the external tank. It released the tank, which disintegrated on reentering the atmosphere. Although the orbiter lifted off vertically like an expendable rocket launcher, it made an unpowered descent and landing similar to a glider.

The space shuttle could transport satellites and other craft in the orbiter’s cargo bay for deployment in space. It also could rendezvous with orbiting spacecraft to allow astronauts to service, resupply, or board them or to retrieve them for return to Earth. Moreover, the orbiter could serve as a space platform for conducting experiments and making observations of Earth and cosmic objects for as long as about two weeks. On some missions it carried a European-built pressurized facility called Spacelab, in which shuttle crew members conducted biological and physical research in weightless conditions.

The space shuttle launched like a rocket. But it landed like a glider airplane. The solid rocket boosters and the main engines on the orbiter helped the shuttle blast off from Earth like a rocket. The two boosters dropped off the shuttle two minutes after launch. They fell into the ocean. A special boat picked the boosters out of the ocean. They were used again for another flight. The external tank dropped off the orbiter after it had used all the fuel in the tank. The external tank would burn up over Earth. So the tank could not be used again.

When the shuttle orbiter returned to Earth, it came down from the sky like an airplane. Wheels came out from underneath the orbiter. It rolled to a stop on a runway. Then NASA would prepare it to fly on another mission.