Live coverage: Atlas 5 countdown and launch journal

This is will be the fourth pair of O3b mPOWER satellites launched to a medium Earth orbit. Liftoff from Launch Complex 39A is set for 5:26 p.m. EST (2226 UTC).

Within days, NASA is expected to select a winner from a roster of nine eligible companies to try and become the first commercial entity to accomplish a soft landing on the moon with a robotic spacecraft. The privately-developed probe would be the vanguard in a series of unpiloted missions intended to deliver science instruments to the lunar surface and prepare for a human expedition as soon as 2024.

A United Launch Alliance Atlas 5 rocket launched at 5:02 p.m. EST (2202 GMT) Thursday from Cape Canaveral with NOAA’s GOES-S weather satellite, the second in a series of upgraded observatories destined to cover the western United States and the Pacific Ocean.