Live coverage: Kennedy Space Center to reopen Friday

SpaceX engineers ran through a customary prelaunch countdown test Saturday and fired the Falcon 9 rocket’s nine Merlin main engines at Cape Canaveral ahead of liftoff Monday with 2.2 tons of supplies and experiments for the International Space Station.

Space station commander Chris Cassidy and Robert Behnken floated back outside Tuesday for their fourth spacewalk in less than a month, completing preparations for future upgrades including the eventual installation of an airlock that will allow commercial experiments to be moved into and out of vacuum as required.

Follow the unclassified portion of the Atlas 5 rocket’s ascent to space from Cape Canaveral’s Complex 41 launch pad with the U.S. National Reconnaissance Office’s NROL-61 satellite. Launch is scheduled for Thursday at 8:37 a.m. EDT (1237 GMT).