Second prevalve issue delays completion of SLS Core Stage Green Run campaign February 26, 2021 A problem with another one of the eight prevalves in the Artemis 1 Core Stage for NASA’s Space Launch System (SLS) has postponed a second test-firing to wrap up the Green Run campaign. The SLS Program’s first flight article has been installed in the B-2 Test Stand at the Stennis Space Center in southern Mississippi since January 2020. After a liquid hydrogen prevalve was repaired in November, all the prevalves worked during tanking and firing tests until final preparations for a second Hot-Fire — when a liquid oxygen prevalve stopped opening correctly. Engineers are back inside the stage’s engine section to troubleshoot the failure and determine what needs to be fixed; currently, NASA doesn’t expect to be ready to test-fire the stage again until mid-March.