By Liz White, UT staffKennedy Space Center, Florida-The US space agency NASA has grounded its fleet of space shuttles, following the launch of its 'return to flight' Discovery mission on 27 July. But officials have stressed that the Discovery vehicle itself seems safe, despite some apparent damage to two of its heatshield tiles. Examination of video footage and pictures taken by the astronauts-during the launch and in flight-showed that two pieces of the polyurethane foam insulation on Discovery's external fuel tank had again fallen off. But this foam did not seem to hit the shuttle itself, and officials have not identified the source of the tile damage. It was damage to insulating tiles on the Shuttle Columbia, caused by foam debris from the fuel tank, that led to craft's disastrous break up during re-entry, with the loss of all seven astronauts on board, in February 2003. Following initial jubilation at the successful launch on 27 July came the gradual realisation that debris had again come away from the massive external fuel tank. The many procedures-still and video cameras on the tank itself, the shuttle and at NASA, set up to record events-allowed NASA to rapidly identify what had happened. It is clear that we shouldn't have started this mission," said Bill Parsons, space shuttle programme manager. "I personally am disappointed … on other hand it didn't harm the orbiter," he said at a 27 July press conference. It seems that a 60-85 cm piece of foam came off the tank's PAL (protuberance air load) ramp as well as a 15cm chunk from the tank's liquid hydrogen intertank flange. Regular readers of Urethanes Technology may remember that during several months of tank redesign, particular attention was paid to these areas of insulation to try and prevent debris falling from them during lift-off (see UT Feb/Mar 2005 p30). The picture, taken from the Discovery, shows the tank as it was jettisoned, with the missing foam from the PAL circled in white. "
