SpaceX has confirmed a 19 May launch date and 22 May backup from Kennedy Space Center (KSC), Florida, after cancelling 7 May and 10 May launch dates over software certification issues.
SpaceX's Falcon 9 rocket will launch a Dragon capsule with supplies to the International Space Station (ISS), and if successful will become the first commercial company to dock with the ISS.
Because of the ISS orbit, the launch window is open only once every three days. Several potential launch windows are ineligible due to a Soyuz resupply flight scheduled on 14 May.
Concerns over Dragon's software have been the cause of past delays of the flight, called commercial orbital transportation services (COTS) 2/3. The flight has been delayed from February over similar concerns.
The second COTS awardee, Orbital Sciences, is scheduled for an August launch from Wallops Island, Virginia.