The Galaxy subscale module was scheduled to fly in 2008. It would be twice as large as its Genesis predecessors and represent a 50% scale model of the Sundancer manned inflatable space station. It would replace two flights of the Guardian module earlier planned.

The flight would test the operational life support system that would provide a nitrogen/oxygen atmosphere to occupants of the full-sized station. The internal structural arrangement (central hardened spine, internal longerons, solar arrays, and attitude control system) would all be more representative of the operational system.