Two NASA Space Launch System (SLS) solid rocket boosters are readied for mating to the rocket’s two aft skirts on June 16, 2020, inside Kennedy Space Center’s Rotation, Processing and Surge Facility. Together, the twin boosters provide more than 75 percent of the total SLS thrust at launch. Manufactured by Northrop Grumman in Promontory, Utah, the boosters arrived at Kennedy via train. The cross-country journey was an important milestone for the agency’s Artemis I launch. The first in a series of increasingly complex missions, Artemis I will test the Orion spacecraft and SLS as an integrated system prior to crewed missions to the Moon. Once the boosters are mated with the aft skirts, they will be moved to the Vehicle Assembly Building for stacking on the mobile launcher.