Discovery's seven astronauts will fly to the International Space Station on STS-121, the second mission in NASA's Return to Flight sequence. The previous mission, STS-114, also involved Discovery in a 13-day flight to the ISS last July. In the new flight, Discovery's crew is scheduled to test new equipment and procedures designed to increase shuttle safety, and to deliver supplies and make repairs to the station.

The barge is expected to take five to six days to travel from the Mississippi River-Gulf of Mexico Outlet to Florida's Banana River, which flows into the Atlantic Ocean.

At Kennedy, the tank will be delivered to the Vehicle Assembly Building for final checkout and attachment to the twin solid rocket boosters and Discovery for its flight to the ISS. The tank feeds 535,000 gallons of liquid propellants - hydrogen and oxygen - to the shuttle's three main engines, which lift it into orbit.

For the first time, NASA said in a statement, the tank will fly without Protuberance Air Load ramps. The ramps attached to the tank to protect a cable tray and two pressurization oxygen and hydrogen lines during the dynamic portion of launch, which includes liftoff through about the first three minutes of the climb to orbit.

There are two PAL ramps on the external tank, one at the top of the liquid oxygen portion of the tank, which is 14 feet long and consists of 14 pounds of foam. The other is a liquid hydrogen PAL ramp 38 feet long containing 21 pounds of foam.

Following last summer's shuttle mission, STS-114, engineers at Michoud performed detailed inspections, engineering analysis and testing on external tanks, NASA said. As a result, they determined the PAL ramps were not necessary and, in fact, safety would improve if the remaining shuttle missions were flown without the ramps on the tank.

Wind-tunnel testing using the data is scheduled to begin in mid-March and continue through April to corroborate the conclusions about the ramps.

Additional work to the tank included minor redesign of the ice/frost ramps - the foam segments that cover support brackets at various locations along the pressurization lines. These ramps were partially covered by the PAL ramps and were left exposed after the ramp was removed.

Engineers also completed work on the tank's bipod fittings that connect the external tank to the orbiter through two forward attachment struts.

They removed electrical harnesses that service the bipod heaters and temperature sensors and replaced them with improved versions designed to reduce the potential for nitrogen leakage from the intertank through the cables into the cryogenic region near the bipod fittings.

To prevent nitrogen leakage beneath the cables, they eliminated void spaces by using an improved bonding procedure to ensure complete adhesive coverage.

NASA's Space Shuttle Propulsion Office at Marshall Space Flight Center in Huntsville, Ala., manages the tank project, and Lockheed Martin Space Systems Co. is the primary contractor for the tank.

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