Watch conditions at Kennedy Space Center during Tropical Storm Isaias

SpaceX is set to retire its current fleet of Dragon capsules, in use since 2010, next year and begin flying supplies to the International Space Station on a new variant of the Dragon spacecraft based on the model in development to carry astronauts.

Mission managers are weighing a motley mix of weather models, safety criteria and astronaut workload considerations as they decide when SpaceX’s Crew Dragon spacecraft might have the best chance to launch from the Kennedy Space Center.

SpaceX’s Falcon 9 rocket is set for liftoff from Cape Canaveral early Thursday, heading due east over the Atlantic Ocean to deliver the Inmarsat 5 F4 communications satellite into orbit 32 minutes later.