During a training exercise on Sept. 11, 2020, inside the Vehicle Assembly (VAB) at NASA’s Kennedy Space Center in Florida, a technician with the agency’s Exploration Ground Systems verifies a mock-up of the Space Launch System (SLS) aft booster segment, referred to as a pathfinder, was placed on the mobile launcher correctly. The rehearsal involved teams preparing the aft pathfinder segment in High Bay 4 of the VAB, lifting and moving it over to High Bay 3, and lowering it onto the mobile launcher in preparation for Artemis I. Stacking of the actual booster segments will occur later this year, before the SLS core stage arrives at the Florida spaceport. Artemis I is the first in a series of increasingly complex missions that will test SLS and the Orion spacecraft as an integrated system prior to crewed flights to the Moon.