Photos: Atlas 5 rocket aims for International Space Station

A communications satellite developed in a public-private partnership between Luxembourg government and SES is set for launch Tuesday aboard a previously-flown SpaceX Falcon 9 booster from Cape Canaveral, ready for a 15-year mission beaming encrypted, jam-resistant signals for security and military forces across Europe, Africa and the Middle East.

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.

SpaceX ran a Falcon 9 rocket through a customary preflight checkout Tuesday, filling it with super-cold propellants and firing its nine Merlin first stage engines in preparation for liftoff Friday on a resupply run to the International Space Station.