Stacking the Shuttle's Boosters on the Mobile Launch Platform is a significant step to prepare Discovery for launch. The Mobile Launch Platform, a two-story tall, nine-million-pound steel structure, is the launch base for the Space Shuttle. Once the Shuttle vehicle is assembled, the platform is transported to the launch pad. The Shuttle vehicle is made up of the obiter, the Solid Rocket Boosters and the large External Tank.

"In our Return to Flight planning, we have systematically emphasized that our preparations for launch would be milestone driven," said Michael Kostelnik, deputy associate administrator International Space Station and Space Shuttle Programs. "Stacking of the Shuttle's Boosters is clearly one of those key milestones and indicative of the progress the program continues to make."

Assembly will continue this week until both the right and left Solid Rocket Boosters are stacked and ready to be connected with the External Tank and the Orbiter. The next step will be to join the External Tank to the Boosters.

"It's certainly great to see the assembly of the vehicle begin," said Michael Rudolphi, manager of Space Shuttle Propulsion Office at NASA's Marshall Space Flight Center in Huntsville, Ala. "This is an important milestone on the road back to U.S. human spaceflight."

The Solid Rocket Boosters are the largest solid rockets ever designed. Each is 149 feet high and 12 feet in diameter and produces 2.65 million pounds of thrust at liftoff. Each Booster consists of four segments of solid propellant, solid rocket motors, vertically stacked with a nose cone on top and the aft skirt, or base of the Booster, on which the entire vehicle weight rests prior to launch.

Stacking, or assembling the Reusable Solid Rocket Motors into the Booster, begins with transferring the aft skirt from the Rotation, Processing and Surge Facility to the Vehicle Assembly Building. Once the segment arrives, it is mounted on the Mobile Launch Platform. The segment is then bolted to the platform with four, 28-inch-long, 3.5-inch-diameter bolts.

Cranes are used to continue stacking the remaining fueled segments as well as the top of the booster, called the frustum, and the nose cone to form a complete Booster.

The Solid Rocket Boosters work with the main engines for the first two minutes of flight to provide the additional thrust needed for the Shuttle to escape the gravitational pull of the Earth. At an altitude of approximately 24 nautical miles, the Boosters separate from the External Tank, descend on parachutes, and land in the Atlantic Ocean. They are recovered by ships, returned to land and refurbished for reuse.

For more information about NASA's Return to Flight efforts, visit:

http://www.nasa.gov/returntoflight

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• Space Station
• Space Exploration
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• Spintronics

• Multistage rocket
• Solid-fuel rocket
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