Second prevalve issue delays completion of SLS Core Stage Green Run campaign - -
Feb 26, 2021 3 mins, 14 secs

December 16, 2020.

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

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

Second Hot-Fire test delayed by another prevalve problem

The agency announced in a February 22 blog post that one of the liquid oxygen (LOX) prevalves in the SLS Core Stage for Artemis 1 no longer functioned properly during final preparations conducted over the prior weekend for a second Hot-Fire test that was planned for February 25

The balky prevalve is a part of the propellant feedline that delivers LOX from the stage to engine number one

This is the second problem with a prevalve during the Core Stage’s Green Run test campaign that began at the beginning of 2020

The first problem was with the liquid hydrogen (LH2) prevalve for engine number four

That intermittent issue with the operation of one of the LH2 prevalves interrupted the stage’s Green Run test campaign in October, delaying the final two of eight test cases while that prevalve unit was repaired in place inside the cramped quarters of the engine section

This past week, a team that includes the SLS Program, Core Stage prime contractor Boeing, RS-25 engine prime contractor Aerojet Rocketdyne, and NASA Stennis personnel were finishing preparations to begin the countdown for a second Hot-Fire test when the new prevalve problem occurred

The LOX prevalve functioned correctly throughout the Green Run test campaign, including the short, one-minute long Hot-Fire test on January 16

Fixing the problem with this second balky prevalve will take some time because engineers needed to get “under the hood” access to the vehicle, which was already closed out for the Hot-Fire test when the new problem was discovered

(Photo Caption: The flight article for Artemis 1, Core Stage-1, fires in the B-2 position of the B Test Stand at Stennis Space Center on January 16. The Hot-Fire was cut short after 67 seconds of engine runtime when the stage’s hydraulic performance fell below conservative limits just as the engines were being aggressively gimbaled for the first time in the test.)

“Technicians installed platforms that allow engineers to access the valve inside the core stage engine section while the stage remains in the B-2 stand at NASA’s Stennis Space Center near Bay St

If this new issue is a recurrence of the similar problem with the Core Stage Main Propulsion System prevalves seen last October, it may have other implications if there’s a generic issue with the prevalve hardware itself

For the first prevalve repair for LH2 side in November 2020, engineers for Boeing and prevalve vendor Vacco had to position themselves on an erector set style work platform installed for access inside the engine section

The cryogenic propellant lines in the engine section are insulated with spray-on foam, including the valves, so the foam had to be removed during troubleshooting to be able to disassemble parts of the valve

In the case of the LOX prevalves, they are located in a different area of the engine section

Whereas the LH2 prevalves are on feedlines that connect directly from the LH2 tank, the LOX prevalves branch off from two long “downcomer” feedlines that run from the LOX tank at the top of the Core Stage, down the outside of the LH2 tank, and into the engine section

In addition to the different location within the engine section, the LOX prevalve may be in a different orientation than the LH2 prevalves, which could affect the pace of repair operations

Once the prevalve is fixed it, will take several days reconfigure the valve and the engine section back into a firing configuration, including the reapplication of foam to the prevalve as well as uninstalling the internal platform kit

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