The huge, orange External Tank (ET) that will help launch Space Shuttle Discovery on its next mission isn't glitzy like the crystal New Year's ball in Times Square. But its journey from NASA's Michoud Assembly Facility marks something special for 2005: the Year of Return to Flight.

The tank, designated ET-120, rolled out on its transporter and was loaded onto a covered barge today at Michoud, in New Orleans, for shipment to NASA's Kennedy Space Center, Fla. The barge will take four to five days to travel from the Mississippi River-Gulf of Mexico Outlet to Florida's Banana River, which flows into the Atlantic Ocean. Shipping the tank is an important milestone, particularly for the NASA team that spent 23 months working on modifications to make it safer.

During a launch, the ET delivers 535,000 gallons of liquid hydrogen and oxygen propellants to the three main engines, which power the Shuttle to orbit. It is covered by polyurethane-like foam, with an average thickness of about one inch. The foam insulates the propellants, keeps ice from forming on the tank's exterior, and protects its aluminum skin from aerodynamic heat during flight.

Modifications to the tank address the Columbia Accident Investigation Board's recommendation to reduce the risk to the Shuttlring Columbia's launch in January 2003, insulating foam from the bipod area, near the front of the craft where the ET attaches to the orbiter, fell off the and damaged the left wing.

ET-120 incorporates several safety improvements, including an improved bipod fitting that connects it to the orbiter; a video camera mounted on the liquid oxygen feed line to document liftoff; reversed bolts on the flange of the tank's mid-section and a new spraying procedure for the thermal protection required there; a redesign of three bellows on the liquid oxygen feed line, the 70-foot pipe feeding liquid oxygen to the main engine; and a more defined spray procedure on the longeron, a structural support for the tank's aft, orbiter attachment struts.

The ET is the largest element of the Shuttle system, which also includes the orbiter, main engines and Solid Rocket Boosters. It measures 27.6 feet wide and 154 feet tall. Despite the tank's size, the aluminum skin covering it is only one-eighth-inch thick in most areas. Yet, it still withstands more than 6.5 million pounds of thrust during liftoff and ascent. The tank is the only Shuttle component that cannot be reused.

Image Courtesy of Robert Pearlman and  collectSPACE.com

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