By Jason Lea, UT Akron Bureau New Orleans, Louisiana-NASA (the US National Aeronautics and Space Administration) is considering new options for foam insulation on the space shuttle external fuel tank, according to a contractor involved with the project.Four pieces of polyurethane foam fell off the space shuttle Discovery during liftoff July 26. Discovery is now scheduled to return early Aug. 9.PU foam problems with Discovery follow similar difficulties in 2003, when space shuttle Columbia disintegrated during re-entry. The problem was traced toa large chunk of foam falling from its external tank on lif-off which damaged the shuttle's left wing. Following that disaster, and a two-year project costing over $2 million, NASA engineers redesigned the external tank so it would use less PU. They also added four rod-shaped heaters to help the foam keep the outside of the tank warm and prevent ice build-up as the shuttle stands on the launch pad.New designs for the external tank are not finished, but it would not be surprising if the foam were better-anchored to the tank or partially replaced on future missions, according to an Aug. 4 e-mail from Lockheed Martin Corp. spokesman Harry Wadsworth.Lockheed Martin manufactures NASA's external tanks, including the foam, at its NASA Michoud facility in New Orleans. The site is government-owned but run by Lockheed Martin.In the case of Discovery, four pieces of PU fell during lift-off, and one piece struck the wing. The shard was 7 inches long and 2 inches wide (about 18 x 5 cm) and struck the wing with one-tenth the force necessary to cause an accident, according to a NASA statement.The largest piece of foam to fall was between 24-33 inches long (61-84cm), 10-14 inches wide (25-26) and 2.5-8 inches (3.3-20 cm) tall, but it did not touch the shuttle. The foam was jarred when the external tank hit the orbiter during launch.NASA has declared that there will be no more flights until it finds a satisfactory fix to its foam woes.The PU was initially put on the tank to stabilise temperature of the propellants, liquid oxygen and liquid hydrogen, at -183 and -252°C, respectively, and to prevent ice forming on the outside. "The [PU] foam on the external tank maintains propellant quality and insulates the tank from extreme cold and hot temperatures," Wadsworth explained."