It’s official—NASA will subject the SLS rocket to another hot fire test
February 1, 2021
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SLS Green Run Test
Enlarge / The SLS core stage at NASA’s Stennis Space Center after firing up for the Green Run test on January 16, 2021.

Trevor Mahlmann

After completing a review of data collected from a hot fire test of its Space Launch System rocket in mid-January, NASA has decided it needs to test the large vehicle again. The all-up engine firing is scheduled to occur as early as the fourth week of February.

During the January 16 test firing, when NASA intended to run the rocket’s four main engines for up to eight minutes, the test was aborted after just 67.2 seconds. NASA said the engine firing was stopped due to a stringent limit on hydraulic pressure in the thrust vector control mechanism used to gimbal, or steer, the engines.

In the days after the mid-January test firing, officials from NASA and Boeing were coy about whether they would need to test-fire the rocket a second time. While it would be useful to gain additional data, they said, there were concerns about putting the core stage, with its four space shuttle main engines and large liquid oxygen and hydrogen fuel tanks, through the stress of repeated tests. (The SLS rocket is expendable, so it is intended to be launched only a single time.)

According to the agency, the original hot fire test completed 15 of its 23 objectives. Four other objectives got most of the data sought, while three had partial data, and one no data. This last one was a test of how the liquid oxygen tank pressure would respond when liquid oxygen was largely used up and the tank emptied. Because the test objectives were not met, engineers within the agency have been pushing NASA and Boeing leadership to conduct a second test to lower the risk of a failure during launch.

On Friday, NASA made it official. “After evaluating data from the first hot fire and the prior seven Green Run tests, NASA and core stage lead contractor Boeing determined that a second, longer hot fire test should be conducted and would pose minimal risk to the Artemis I core stage while providing valuable data to help certify the core stage for flight,” the space agency said in a blog post.

NASA said that running the engines for four minutes during this second test should offer enough data to provide confidence in the core stage performance but that the main engines would fire for up to eight minutes if all goes well.

Following the second hot fire test—assuming that NASA and Boeing get the data needed—it will take about a month to refurbish the core stage and its engines. The vehicle will then be loaded onto a barge, shipped across the Gulf of Mexico and into the Atlantic, and delivered to Kennedy Space Center in Florida. This is now unlikely to happen before late March or April.

In its blog post, NASA says that once in Florida, the SLS core stage will be assembled with its solid rocket boosters and mated with the Orion spacecraft in preparation for its first launch “later this year.” However, given that a 2021 launch date was predicated on shipping the core stage from Stennis Space Center in January, a 2021 launch of the SLS rocket now seems highly unlikely.

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