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Two Plus One Makes History
June Malone
Marshall Space Flight Center, Huntsville, Ala.
(Phone: 256.544.0034)
News release: 05-024

What do two Space Shuttle Solid Rocket Boosters plus one External Tank equal?

Together, the fuel in the Boosters and Tank can generate 6.5 million pounds of thrust. That's exactly enough to power Space Shuttle Discovery on its Return to Flight mission to the International Space Station, targeted for launch as early as May 15.

On Monday, Feb. 28, NASA successfully "mated," or attached, the External Tank designated ET-120 to twin Solid Rocket Boosters at Kennedy Space Center, Fla., marking yet another important milestone on the road to return the Shuttle safely to flight. Lifted by a giant crane and then joined to the already assembled, or "stacked," Solid Rocket Boosters in NASA's Vehicle Assembly Building, the Shuttle's newly redesigned External Tank is the largest element of the Space Shuttle system. At 27.6 feet wide and 154 feet tall, the Tank holds a combined volume of 73,000 cubic feet of fuel. That's enough liquid hydrogen and liquid oxygen to fill about six 1,600 square foot homes. The fuel is used to power the Space Shuttle's three Main Engines, which initially provide 1.2 million pounds of thrust.

Add the Shuttle's twin Solid Rocket Boosters, the largest solid fuel rockets ever designed, and you've got power. At 149 feet high and 12 feet in diameter, each Booster produces 2.65 million pounds of thrust at liftoff and burns about 4.5 tons of fuel per second. Sound like a lot? Well, it equals about 40 million horsepower, or the same energy as 14,700 diesel locomotives speeding on the same track. The mating of the towering rockets and fuel tank takes place in NASA's Vehicle Assembly Building, one of the world's largest buildings, covering eight acres and standing nearly twice the height of the Statue of Liberty.

During mating, the left and right Solid Rocket Boosters are bolted to the Tank at both the forward, or top, and the aft, or tail, ends. At the forward end, a vertical bolt mechanism attaches each booster to the tank at what's known as the "intertank" area. At approximately two minutes into launch, the boosters begin to separate from the tank when pyrotechnic devices fire to break the 25-inch, 62-pound steel bolts. One half of each bolt is caught in a canister-like "bolt catcher" located on the Tank. The other half remains with the boosters.

Discovery will also fly with a modified bolt catcher. The new bolt catcher has been modified from a two-piece welded design to a one-piece machined design. By eliminating the weld, the modified bolt catcher is stronger structurally than the original design. At the aft end, there are three attachment points on each Booster's External Tank Attach Ring--two lateral braces and a diagonal strut--that bolt to the Tank. Pyrotechnic devices are fired to break these bolts when the Booster separates during ascent. The newly redesigned tank will fly with several modifications, including two new forward bipod fittings, the fittings that connect the Tank to the Orbiter at the Shuttle's two forward attachment struts. NASA and Lockheed Martin Space Systems Co., in New Orleans, spent nearly two years modifying the Tank to make it safer.

The next Shuttle mission, STS-114, is targeted for launch during a window that begins May 15 and ends June 3. The window accommodates daylight launch attempts and ensures the most detailed and clear photography of the External Tank. The seven-member STS-114 crew will deliver supplies to the International Space Station, but the major focus of their mission will be testing and evaluating new Space Shuttle flight safety, which includes new inspection and repair techniques.

Returning the Space Shuttle to flight is the first step in the Vision for Space Exploration, which calls for a "stepping stone" strategy of human and robotic missions to achieve new exploration goals. The Space Shuttle will be used to complete assembly of the International Space Station, a vital research platform for human endurance in space and a test bed for technologies and techniques that will enable longer journeys to the Moon, Mars and beyond.

The Space Shuttle Propulsion Office at NASA's Marshall Space Flight Center in Huntsville, Ala., directs the External Tank and the Solid Rocket Booster projects. Lockheed Martin Space Systems Co., in New Orleans, is the primary contractor for the Tank. United Space Alliance is the primary contractor for the Boosters and for readying the Shuttle for flight.