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A troublesome liquid oxygen valve on the first base stage of the space launch system will prevent NASA from performing a second firing test of the rocket’s four main engines this week.
NASA had hoped to perform the second hot shot test on the center stage of the SLS on Thursday, but the agency said on Monday that the engine firing would be postponed to assess a misbehaving valve in the propulsion system. the rocket.
The space agency said on Monday that engineers identified the problem over the weekend. One of the eight “prevalent” mid-stage propulsion system was not functioning properly, NASA said.
The prevalve supplies liquid oxygen to one of the rocket’s four RS-25 main engines. The engines have remained on the Space Shuttle program and consume liquid oxygen in combination with super cold liquid oxygen. All eight prevalves functioned correctly in the first hot fire test of the main phase of the SLS on Jan. 16, officials said.
“NASA and the main contractor of the main phase, Boeing, will identify a way forward in the days to come and postpone the hot fire test originally scheduled for February 25,” NASA said Monday.
The Jan. 16 hot fire test was supposed to last over eight minutes, but all four RS-25 engines shut down just over a minute after ignition. Engineers traced the cause of the premature shutdown to a parameter in the hydraulic system that triggered a parameter that was too conservative for testing, the last phase of a “Green Run” test and verification campaign for the main SLS phase at NASA’s Stennis Space Center in Mississippi.
Center stage hydraulics drive actuators that pivot, or gimbals, the four RS-25 motors to steer the rocket after takeoff. The space launch system will fly with two solid rocket boosters mounted on either side of the 212-foot-high (64.6-meter) center stage. An upper stage and an Orion crew capsule above the main stage will bring the total height of the launcher to 98 meters (322 feet).
NASA officials have decided to redo the Green Run test firing after the early shutdown last month. Managers want to get at least four minutes of runtime on the RS-25 engines in the second hot-shot test to collect enough data to build confidence in the rocket’s performance before sending the scene to Kennedy Space Center in Florida for launch preparations.
But the goal of the second hotfire test is to burn the engines for more than eight minutes, the time during which they will fire on a real SLS flight.
Kathy Lueders, associate administrator of NASA’s human spaceflight division, said on Wednesday engineers were struggling to fully turn on liquid oxygen during checks ahead of Green Run Hotfire’s second test.
“It’s very frustrating,” Lueders said during a panel discussion at the 47th Spaceport Summit.
“On your LOX (liquid oxygen) system, if you’re trying to run your engines at the power level that we’re trying to run our engines, you’ve got to have that open predominance,” she says.
The Green Run hotfire test has been delayed by more than six months since the arrival of the SLS main stage at Stennis in January 2020. A temporary suspension of work caused by the COVID-19 pandemic initially delayed preparations for the test, and a series of hurricanes and tropical storms that hit the Gulf Coast last year have also slowed work at the Stennis Space Center.
Engineers aimed to complete the hot fire test before the end of the year, but a problem during a fuel test in December caused the engine to start in January. With the most recent delay, the first full-duration center stage test firing took place in March.
The first SLS test launch will transport an unmanned Orion crew capsule into space during NASA’s Artemis 1 mission. The Orion spacecraft will orbit the moon on a multi-week test flight before returning to Earth for a dip in the Pacific Ocean. If successful, the mission will pave the way for Artemis 2, the first SLS / Orion crewed mission, to transport four astronauts around the Moon and return to Earth as early as 2023.
The Artemis program is NASA’s initiative to bring astronauts back to the moon. NASA has been tasked by the Trump administration to land a crew near the moon’s south pole by the end of 2024. The Biden administration has expressed support for the Artemis program, but has not set a timeline for a crewed lunar landing mission.
The 2024 calendar target was already slipping away before the end of the Trump administration. Congress has approved only a fraction of the funding NASA requested in FY2021 for the development of human-value lunar landers for the Artemis program.
Lueders, a former director of NASA’s commercial crew program, said the SLS Green Run delays were “very, very difficult.”
“This is the last room we have to wait until we get down to Cape Town so we can fly,” Lueders said.
She said NASA still “hopes” to pilot the first SLS rocket by the end of this year.
“Like I said with the commercial crew program, we’ll fly when we’re ready,” Lueders said Wednesday.
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Follow Stephen Clark on Twitter: @ StephenClark1.
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