By Matt McClellan, UT Akron BureauHuntsville, Alabama-In an attempt to prevent future accidents, NASA is using a heated copper plate to replace some of the polyurethane foam insulation that protects the space shuttle's fuel tanks from freezing.The agency has been concerned about chunks of foam damaging the shuttle ever since the shuttle Columbia disintegrated during re-entry 1 Feb 2003, killing all seven astronauts on board. NASA believes the accident was caused by a foam bipod ramp that peeled off during the strain of launch. The loose foam hit the left wing of the orbiter and ripped a hole in it, so the shuttle could not withstand the pressure of re-entry.Polyurethane foam has been used since the beginning of the space shuttle programme to insulate the fuel tanks. It is needed because ice can build up while the shuttle sits on the launch pad filled with extremely cold liquid hydrogen fuel.The loss of foam during flight has been a problem for decades, NASA officials said, but its importance was only realised after the Columbia disaster. The wedge-shaped foam structures can do a lot of damage with the speed of launch and space travel, despite measuring only 30 by 14 by 12 inches (76x36x30 cm). The foam is being replaced by four rod heaters placed below each of the three bipod fittings in a copper plate. The bipods connect the orbiter to the external fuel tank."