This morning, NASA astronauts due to take off on STS-122 suited up and made their way to Launch Pad 39A at the Kennedy Space Center, where the shuttle Atlantis is ready to go. Liftoff is set for 2:45 EST today, but there’s only a ten-minute window during which the ship can launch—otherwise it wouldn’t effectively rendezvous with the International Space Station.

This time there aren’t any technical issues—no faulty fuel sensors, which postponed the last flight—but launch is still far from a guarantee. The problem is that the weather isn’t exactly cooperating. NASA is reporting that there’s only a 30 percent chance of good weather for liftoff, and the conditions don’t look much better for the weekend.