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.

External Tank 120, the tank that will return the shuttle to flight, rolls out at Michoud Assembly Facility in New Orleans on Dec. 31. Credit: Lockheed Martin/NASA Michoud

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.

"Our team of contractors and civil servants has worked hard developing, testing and implementing improvements that will reduce the risk to the orbiter during liftoff and ascent," said Sandy Coleman, manager of the External Tank Project, an element of the Space Shuttle Propulsion Office at NASA's Marshall Space Flight Center in Huntsville, Ala. "This will be the safest, most reliable tank NASA has ever produced."

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 Shuttle from falling debris during ascent.

During 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.

External Tank 120 is loaded onto its covered barge at Michoud Assembly Facility in New Orleans for shipment to KSC. Credit: Lockheed Martin/NASA Michoud

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.

"Clearly, the modifications to the External Tank are at the heart of our Return to Flight work," said Michael Kostelnik, deputy associate administrator for the International Space Station and Space Shuttle Programs. "Seeing this tank begin its journey to the Kennedy Space Center, where it will be prepared for launch, makes it clear how far we've come in making the Shuttle a safer spacecraft for our astronauts," he said.

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.

A seven-member Discovery crew will fly the Return to Flight mission, designated STS-114, to the International Space Station. The major mission objectives are testing and evaluating new procedures for flight safety.

Returning the 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 Shuttle will be used to complete assembly of the International Space Station. The Station is 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 Marshall manages the tank project. Lockheed Martin Space Systems Co., in New Orleans, is the primary contractor.