NASA’s Launch Control Center team began to fuel the shuttle Discovery early Feb. 24 in preparation for the spacecraft’s 39th and final flight, while forecasters improved an already favorable forecast for a late afternoon liftoff.

Discovery’s long-delayed 11-day assembly and supply mission to the International Space Station is scheduled to launch from NASA’s Kennedy Space Center at 4:50 p.m. EST. The shuttle’s three-hour tanking operation got under-way as scheduled at 7:25 a.m. EST.

The latest forecast called for a 90% chance of favorable conditions at the launch site, up from the previous 80%. There was a slight chance of a low cloud deck that could force a scrub.

Meanwhile, NASA’s Mission Management Team was closely following the impending rendezvous and docking of the European Space Agency’s Johannes Kepler Automated Transfer Vehicle-2. The cargo freighter, launched Feb. 16, was on a trajectory for an automated linkup with the station’s aft docking port at 10:46 a.m. EST, or about the time Discovery’s external fuel tank was to be fully loaded.

Mission commander Steve Lindsey, pilot Eric Boe and mission specialists Mike Barratt, Nicole Stott, Al Drew and Steve Bowen are to climb aboard Discovery at 1:35 p.m. EST.

The last time Discovery reached terminal count was on Nov. 5, when the launch bid was halted by a hydrogen leak. Subsequently, technicians found a long separation in the external fuel tank’s (ET) foam insulation and underlying cracks in the metal surface of the ET’s stringer region. Leak repairs and a lengthy troubleshooting followed to identify the cause of the metal cracks and develop a modification to prevent further damage.

Discovery’s astronauts will deliver and equip the station with an equipment storage module and an external spare parts platform. The shuttle is loaded with five tons of supplies and research gear, including Robonaut 2. The humanoid robot will undergo human compatibility evaluations by future space station crews.

Drew and Bowen will embark on a pair of maintenance spacewalks outside the station. The spacewalkers intend to recover and position a failed external thermal control system pump for a return to Earth later this year aboard shuttle Atlantis.