Space Launch System testing. Scale model of NASA's Space Launch System (SLS) undergoing tests in a wind tunnel. SLS is a spacecraft heavy launch vehicle being designed by NASA to replace the retired Space Shuttle. It will to carry the Orion Multi-Purpose Crew Vehicle, as well as important cargo, equipment and science experiments to Earth's orbit and destinations beyond. The SLS will also serve as a back-up for commercial and international partner transportation services to the International Space Station.