Second prevalve issue delays completion of SLS Core Stage Green Run campaign –

An issue with one other one of many eight prevalves within the Artemis 1 Stage for NASA’s Area Launch System (SLS) has postponed a second test-firing to wrap up the Inexperienced marketing campaign. The SLS Program’s first flight article has been put in within the B-2 Check Stand on the Stennis Area Heart in southern Mississippi since January 2020.

After a liquid hydrogen prevalve was repaired in November, all of the prevalves labored throughout tanking and firing assessments till remaining preparations for a second Scorching-Hearth — when a liquid oxygen prevalve stopped opening appropriately. Engineers are again contained in the stage’s engine part to the failure and decide what must be fastened; presently, NASA doesn’t count on to be able to test-fire the stage once more till mid-March.

Second Scorching-Hearth check delayed by one other prevalve downside

The company introduced in a February 22 blog post that one of many liquid oxygen (LOX) prevalves within the SLS Core Stage for Artemis 1 not functioned correctly throughout remaining preparations carried out over the prior weekend for a second Scorching-Hearth check that was deliberate for February 25. The balky prevalve is part of the propellant feedline that delivers LOX from the stage to engine primary.

In an additional post on February 26, the company famous that the prevalve was not opening appropriately, and troubleshooting would proceed over the weekend. “After completion of troubleshooting, which can proceed over the weekend, NASA can be in a greater place to determine a possible date for the second scorching fireplace check,” the put up mentioned.

Sources indicated that an estimated goal for the second Scorching-Hearth check was no sooner than March 16.

That is the second downside with a prevalve through the Core Stage’s Inexperienced Run check marketing campaign that started in the beginning of 2020. The primary downside was with the liquid hydrogen (LH2) prevalve for engine quantity 4.

That intermittent issue with the operation of one of the LH2 prevalves interrupted the stage’s Inexperienced Run check marketing campaign in October, delaying the ultimate two of eight check instances whereas that prevalve unit was repaired in place inside the cramped quarters of the engine section. In that case, troubleshooting and fixing downside with the LH2 prevalve’s clutch mechanism delayed the Inexperienced Run schedule by a few month.

This previous week, a group that features the SLS Program, Core Stage prime contractor Boeing, RS-25 engine prime contractor Aerojet Rocketdyne, and NASA Stennis personnel have been ending preparations to start the countdown for a second Scorching-Hearth check when the brand new prevalve downside occurred.

The LOX prevalve functioned appropriately all through the Inexperienced Run check marketing campaign, together with the short, one-minute long Hot-Fire test on January 16. The early finish to the check left a number of design verification targets (DVO) incomplete, and NASA decided that a second, longer firing was necessary.

Fixing the issue with this second balky prevalve will take a while as a result of engineers wanted to get “below the hood” entry to the car, which was already closed out for the Scorching-Hearth check when the brand new downside was found. So as to get palms on the prevalve, work entry wanted to be re-established.

Credit score: Brady Kenniston for NSF.

(Photograph Caption: The flight article for Artemis 1, Core Stage-1, fires within the B-2 place of the B Check Stand at Stennis Area Heart on January 16. The Scorching-Hearth was lower quick after 67 seconds of engine runtime when the stage’s hydraulic efficiency fell beneath conservative limits simply because the engines have been being aggressively gimbaled for the primary time within the check.)

“Technicians put in platforms that permit engineers to entry the valve contained in the core stage engine part whereas the stage stays within the B-2 stand at NASA’s Stennis Area Heart close to Bay St. Louis, Mississippi,” the February 26 weblog put up famous.

There are a complete of eight prevalves on the Core Stage, 4 of which ship the liquid oxygen oxidizer through separate feedlines to every of the RS-25 engines and 4 of which ship the liquid hydrogen gas to the engines. The valves are opened simply earlier than ignition to movement gas and oxidizer from the tanks to the inlets of the 4 RS-25 engines till simply after Most important Engine Minimize-Off (MECO).

If this new situation is a recurrence of the same downside with the Core Stage Most important Propulsion System prevalves seen final October, it might produce other implications if there’s a generic situation with the prevalve {hardware} itself. The valves are important to the protected operation of the stage; they have to behave with specs, absolutely opening and shutting inside closing dates to make sure correct engine ignition and shutdown circumstances.

New test-firing date is determined by restore work

NASA mentioned the troubleshooting of the LOX prevalve would assist to determine repairs wanted. A brand new date will rely partly on how intensive and invasive the restore work is.

For the primary prevalve restore for LH2 aspect in November 2020, engineers for Boeing and prevalve vendor Vacco needed to place themselves on an erector set fashion work platform put in for entry contained in the engine part. The cryogenic propellant strains within the engine part are insulated with spray-on foam, together with the valves, so the froth needed to be eliminated throughout troubleshooting to have the ability to disassemble elements of the valve.

SLS’s flight software program steers the Stable Rocket Boosters and 4 RS-25 to take care of the correct launch trajectory and pitch profile through the preliminary part of flight of Artemis 1. (Credit score: Mack Crawford for NSF/L2)

Within the case of the LOX prevalves, they’re positioned in a distinct space of the engine part. Whereas the LH2 prevalves are on feedlines that join instantly from the LH2 tank, the LOX prevalves department off from two lengthy “downcomer” feedlines that run from the LOX tank on the of the Core Stage, down the surface of the LH2 tank, and into the engine part.

Particular tooling was designed, fabricated, and employed to carry out the primary prevalve restore and could possibly be used once more; nevertheless, work entry to the LOX prevalves could also be completely different than the LH2 prevalves. Along with the completely different location throughout the engine part, the LOX prevalve could also be in a distinct orientation than the LH2 prevalves, which might have an effect on the tempo of restore operations.

As soon as the prevalve is fastened it, will take a number of reconfigure the valve and the engine part again right into a firing configuration, together with the reapplication of froth to the prevalve in addition to uninstalling the interior platform equipment.

(Lead credit score: NASA/SSC.)


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