Just three weeks after the Delta 4-Heavy rocket left the launch pad on its way to a successful satellite-deployment mission for U.S. national security, a smaller booster in the family has rolled out for its August military flight.

The ocean-sailing ship that transports rocket stages from United Launch Alliance’s factory to U.S. launch sites completed its latest voyage overnight, pulling into port to deliver the Atlas 5 that will send a cargo freighter to the International Space Station in March.

Forecasters predict a 90% chance of good weather for liftoff of a United Launch Alliance Atlas 5 rocket from Cape Canaveral just after sunset Tuesday with a classified payload for the National Reconnaissance Office, the U.S. government’s spy satellite agency.