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.

Two SpaceX rockets are standing on launch pads several miles apart on Florida’s Space Coast awaiting launch opportunities Thursday and Friday, once an oft-delayed Delta 4-Heavy rocket from rival United Launch Alliance is able to blast off from Cape Canaveral with a top secret U.S. government spy satellite.

SpaceX launched its fifth Falcon 9 rocket in 22 days on Saturday, beginning a mission to deploy 52 more Starlink internet satellites and two rideshare payloads for Capella Space and Tyvak Nano-Satellite Systems. Liftoff from pad 39A at NASA’s Kennedy Space Center in Florida occurred at 6:56 p.m. EDT (2256 GMT), and SpaceX successfully landed the first stage on a drone ship in the Atlantic Ocean.