Green Run Update: NASA Investigating Valve Performance Before Second Hot Fire

The core stage for the first flight of NASA’s Space Launch System rocket is seen in the B-2 Test Stand during a scheduled eight minute duration hot fire test, Saturday, Jan. 16, 2021, at NASA’s Stennis Space Center near Bay St. Louis, Mississippi. The four RS-25 engines fired for a little more than one minute. The hot fire test is the final stage of the Green Run test series, a comprehensive assessment of the Space Launch System’s core stage prior to launching the Artemis I mission to the Moon. (Credit: NASA/Robert Markowitz)

BAY ST. LOUIS, Miss. (NASA PR) — NASA’s is reviewing the performance of a valve on the core stage of the Space Launch System rocket before proceeding with a second hot fire test at the agency’s Stennis Space Center near Bay St. Louis, Mississippi.

During checkout preparations over the weekend, engineers determined that one of eight valves (a type of valve called a prevalve) was not working properly. This valve is part of the core stage main propulsion system that supplies liquid oxygen to an RS-25 engine. During the first hot fire, all four liquid oxygen valves performed as expected as did the four liquid hydrogen valves. NASA and the core stage lead contractor Boeing will identify a path forward in the days ahead and reschedule the hot fire test that was originally scheduled for Feb. 25.

NASA is testing the new core stage on the ground to check out the operation of all systems before flight, as the agency has done with every new rocket stage ever flown. The core stage is the center core of the rocket that includes two propellant tanks and four RS-25 engines, miles of cables, all the avionics, electronics, computers – the brains of the rocket – and the plumbing that work together to launch the rocket during the first eight minutes of the mission. The Green Run test series is a comprehensive test of the core stage before it launches the Artemis missions to the Moon.

Check back at this blog for an update on the completion of the review and actions needed to resolve the issue, as well as the schedule for the hot fire test. For more information about SLS Green Run, visit