entry, killing all seven astronauts. Richard Gilbrech, head of a NASA team working to find out what caused the foam to drop from Discovery's tank, said one likely cause was repeated contact with the foam by workers during assembly, though he said there was no evidence of negligence. The foam dropped from a part of the tank known as the PAL ramp, and Gilbrech noted that an improved foam insulation was sprayed on the front section of the ramp, but not on the rear section -- which was the source of the falling foam chunk. The external tank slated to boost the next shuttle into orbit is now at the Michoud assembly plant, where the biggest hindrance to shuttle-related work has been damage to roads, infrastructure and workers' homes. "We will have lost equivalent of three months' work based on the effects of hurricanes," Hale said. With 500 workers now at the plant, Hale said the full workforce of about 2,000 would be on the job by December. The shuttle fleet is scheduled to retire in 2010, to be replaced by a new Apollo-like capsule-and-rocket system meant to take Americans back to the Moon. This deadline prompted NASA to cut back on the number of shuttle flights sent to the International Space Station. Formerly, NASA had said the minimum number of shuttle flights needed to construct the orbiting station was 28; now, that number has been reduced to 18, plus another flight to repair the aging Hubble Space Telescope. Discovery's flight and the possible May flight are considered test missions and involve no construction on the station. Crew and supplies are being ferried by Russian space vehicles.
