By Liz White, UT staffKennedy Space Center, Florida-After more than two years of modifications and safety upgrades, particularly to the polyurethane foam insulation which covers its massive external fuel tank, the Space Shuttle Discovery arrived on the launch pad at NASA's Kennedy Space Center, Florida on 7 April. "Discovery's rollout was not without its challenges," NASA's press statement pointed out. During inspection, shortly before it moved out of the vehicle assembly building, "engineers spotted a tiny, hairline crack in the External Tank's insulating polyurethane foam." But after reviewing the data, they said that the crack, on the opposite side of the tank from the Orbiter, was not in a location where it could become hazardous. "We plan to reassess the area during and after a tanking test we have planned for next week, but based on our preliminary analysis, we don't expect to have to repair the crack," said Sandy Coleman, External Tank Project Manager.Mission will test new safety programmeLaunch of Discovery for a 12-day mission is targeted for 15 May. As well as testing new hardware and safety techniques, Commander Eileen Collins and the rest of the seven-person crew will deliver supplies to the International Space Station."Having Discovery on the pad puts us one step closer to resuming the Space Shuttle's important mission of supplying and assembling the International Space Station," said Michael Kostelnik, NASA deputy associate administrator for International Space Station and Space Shuttle Programs. Discovery underwent 41 major modifications in response to the Columbia accident two years ago, caused by damage to the shuttle wing edge from a piece of insulating foam that broke away from the tank during launch. Modifications include adding a new Orbiter Boom Sensor System; equipping the Orbiter with cameras and laser systems to inspect the Shuttle's Thermal Protection System, or heat shield, while in space; installing sensors in the leading edge of the Shuttle's wings, a new safety measure that monitors the Orbiter's wings for debris impacts; and adding a new digital camera to view the External Tank during launch. The External Tank will fly with several modifications, including two new forward bipod heaters at the forward attach fittings that connect the tank to the Orbiter.Engineers who built the external fuel tank also had access to sophisticated X-ray detectors-developed by researchers at the University of Florida-to reduce the chance of any defect in the foam insulation. A story posted on the UF website describes using these detectors as a non-destructive way of finding air-filled voids in the foam. The Columbia accident investigators believe that such a gap, especially one between the foam and the tank's surface, may have allowed the break-away of the piece of foam during Columbia's January 2003 launch. "We can do the inspection of the foam as it exists already sprayed onto the tank. We don't have to cut into it," said Warren Ussery, in the UF website article. Ussery, who is team leader for the return to flight non-destructive evaluation team at Lockheed Martin's Michoud Assembly Facility in New Orleans, added, "We're able to find critical voids." The photo shows technicians photographing the exterior of Space Shuttle Discovery on its journey to Launch Pad 39B. Images will in future be collected on each orbiter prior to every mission, and compiled into a database, as part of the new safety progamme."