Live coverage: Atlas 5 countdown and launch journal

Giving every opportunity for the storm clouds to blow clear after a four-hour hold, the United Launch Alliance Delta 4-Heavy rocket counts down Thursday afternoon at Cape Canaveral until the clocks had to be halted for the day.

NASA’s Perseverance rover, set for liftoff Thursday on a journey to Mars, posed some unusual challenges for launch crews working with the robot’s plutonium-fueled power generator, but United Launch Alliance’s Atlas 5 rocket is uniquely suited for the job, the company’s CEO says.

Carrying more science research gear to the International Space Station than ever launched before by U.S. commercial logistics vehicles, the next Orbital ATK Cygnus freighter takes flight Tuesday.