Posted: Sat, Aug 22, 2009, 11:26 AM ET (1526 GMT)
Countdown clocks started Friday night for the early Tuesday launch of the space shuttle Discovery on a mission to the International Space Station. The countdown started at 11 pm EDT Friday (0300 GMT Saturday) for the launch, scheduled for 1:36 am EDT (0536 GMT) Tuesday from the Kennedy Space Center. Shuttle managers said Friday that they're tracking on technical issues and forecasts call for a 70 percent chance of acceptable weather at launch time. Discovery will bring various equipment ranks and other items to the station, including a treadmill. The mission will also swap one member of the station's six-person crew, replacing Tim Kopra with Nicole Stott.