Video: Liftoff of Atlas 5 on NROL-55

The launch of a commercial Bulgarian television broadcast satellite from NASA’s Kennedy Space Center in Florida is set for Monday after SpaceX ran through a mock countdown Thursday and test-fired a previously-flown Falcon 9 rocket’s Merlin main engines.

Receiving a boost from a modified decades-old Peacekeeper missile originally built for nuclear war, a U.S. military space surveillance satellite streaked into space early Saturday from Cape Canaveral to help the Air Force track threats and debris in orbit.

Northrop Grumman is gearing up for up to four launches this year at Wallops Island, Virginia, including two launches with Cygnus cargo ships heading to the International Space Station, and a pair of Minotaur rocket flights carrying classified payloads into orbit for the U.S. government’s spy satellite agency.