Live coverage: 400th Proton rocket takes off with Russian satellite

The launch of a United Launch Alliance Delta 4-Heavy rocket from Cape Canaveral was aborted three seconds before a planned liftoff at 3:28 a.m. EDT (0728 GMT). The rocket was set to loft a classified payload for the National Reconnaissance Office, the U.S. government’s spy satellite agency.

Two NASA astronauts and an Italian flight engineer took shelter in the space station’s Russian segment Wednesday as mission control analyzed a possible leak of toxic ammonia coolant aboard the complex. Initial data indicated it was likely a false alarm.

A United Launch Alliance Delta 4-Heavy rocket blasted off from Cape Canaveral at 1:51 p.m. EDT (1751 GMT) today to haul a classified satellite into space for the U.S. National Reconnaissance Office. Follow the mission in our live journal.