Work to replace a malfunctioning computer on one of the four engines in the SLS core stage will delay its first launch to at least March, NASA announced Dec. 17. NASA/Cory Huston

WASHINGTON — A malfunctioning computer in one of the four main engines of the Space Launch System will delay that vehicle’s first launch to no earlier than March.

In a statement late Dec. 17, NASA announced that SLS engineers decided they needed to replace the controller for engine four in the core stage of the SLS. One of two redundant channels in the controller failed to power up consistently during tests of the integrated vehicle at the Kennedy Space Center.

That controller operated as expected during the core stage’s Green Run test campaign at the Stennis Space Center that concluded with a full-duration static-fire test in March. An initial investigation failed to identify the root cause of the problem.

In the statement, NASA said they will replace the engine controller, “returning the rocket to full functionality and redundancy while continuing to investigate and identify a root cause.”

NASA did not give a schedule for the work but ruled out a launch in the initial window of Feb. 12 to 27 that the agency announced in October. “NASA is developing a plan and updated schedule to replace the engine controller while continuing integrated testing and reviewing launch opportunities in March and April,” NASA said in the announcement.

In October, NASA said the next launch opportunities after the February window run from March 12 to 27 and from April 8 to 23. The windows are governed by the performance of the SLS and mission constraints, such as having the Orion spacecraft splash down in daylight conditions.

Even before this latest issue, there were doubts that SLS would be ready when the first launch opportunity opened Feb. 12. Before the launch itself, NASA will roll SLS out to Launch Complex 39B for tests, including a wet dress rehearsal where the rocket is loaded with liquid hydrogen and liquid oxygen propellants and goes through a practice countdown that stops just before engine ignition.

Industry sources said that rollout needed to take place by the end of the December to keep preparations for a February launch on schedule. However, as of Dec. 10, NASA said the program was planning a rollout in mid-January.

In a discussion about the Artemis program during the U.S. Chamber of Commerce’s Launch webinar Dec. 16, Annette Hasbrook, assistant manager for program integration for NASA’s Orion program, said rollout for the wet dress rehearsal is scheduled for “early next year.” That panel discussion did not mention the engine controller issue and said Artemis 1 was scheduled for launch in February.

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...